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Water Quality and Fish Water Quality and Fish

HealthHealth

Dr. Dr. SubhenduSubhendu DattaDatta

Sr. ScientistSr. Scientist

Kolkata, IndiaKolkata, India

IntroductionIntroduction

Health condition of any animal deteriorates when the environmentHealth condition of any animal deteriorates when the environmental condition al condition is not congenial. is not congenial.

A simple example may be when the temperature started dropping duA simple example may be when the temperature started dropping during the ring the onset of winter season, we face all the symptoms associated withonset of winter season, we face all the symptoms associated with cold and cold and cough (e.g. sneezing, running nose occurs).cough (e.g. sneezing, running nose occurs).

Good water quality is the key to successful fish/prawn productioGood water quality is the key to successful fish/prawn production. n. Fish and Fish and prawn under normal condition is in a state of equilibrium with iprawn under normal condition is in a state of equilibrium with its environment ts environment and diseaseand disease--producing organisms. producing organisms.

Any alteration in the environment disturbs this equilibrium resuAny alteration in the environment disturbs this equilibrium resulting in stress to lting in stress to the fish/prawn and they become more vulnerable to disease producthe fish/prawn and they become more vulnerable to disease producing ing organismsorganisms. .

The presence of harmful impurities in water is mainly due to natThe presence of harmful impurities in water is mainly due to natural ural contamination or as a result of human activities polluting watercontamination or as a result of human activities polluting water may cause may cause health problems to fish/prawn. health problems to fish/prawn.

A number of A number of abioticabiotic factors beyond optimum levels are responsible for poor factors beyond optimum levels are responsible for poor health of fish/prawn. health of fish/prawn.

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TemperatureTemperature

Fish/prawn respond to an increase in environmental temperature Fish/prawn respond to an increase in environmental temperature particularly in summer season by particularly in summer season by increasing the respiration rateincreasing the respiration rate as as well as well as cardiac ratecardiac rate and cardiac output. and cardiac output.

Fish/prawn eventually dies from abnormally high temperatures Fish/prawn eventually dies from abnormally high temperatures because of because of lack of oxygenlack of oxygen and malfunction of enzyme systems.and malfunction of enzyme systems.

Most of the tropical species may die when temperatures drop beloMost of the tropical species may die when temperatures drop below w 66°°C. Exotic carps and Indian major carps cannot survive at C. Exotic carps and Indian major carps cannot survive at temperature above 50temperature above 5000C. C.

Optimum water temperature range for major carps is 20Optimum water temperature range for major carps is 20°°--3838°°C. C.

Fish/prawn can tolerate upward changes in temperature better thaFish/prawn can tolerate upward changes in temperature better than n downward changes. downward changes.

It is always advisable to It is always advisable to gradually acclimatize fish/prawn to water gradually acclimatize fish/prawn to water temperature changetemperature change of 3of 3°°C in either direction. C in either direction.

Temperature Temperature ((contdcontd……))

During extreme summer due to high temperature fishes/prawns During extreme summer due to high temperature fishes/prawns refuse feeding or become easily prone to intestinal inflammationrefuse feeding or become easily prone to intestinal inflammation. .

When temperature exceeds tolerance capacity, When temperature exceeds tolerance capacity, excitability and excitability and convulsive movement of fishesconvulsive movement of fishes are observed with are observed with dark dark colourationcolourationthroughout the gillsthroughout the gills followed by collapse and death. followed by collapse and death.

Low temperature affected by Low temperature affected by cold shockscold shocks (3(3--55°°C) with the symptom C) with the symptom of disturbances in fish equilibrium causing damage of skin, of disturbances in fish equilibrium causing damage of skin, oedemaoedema, , intestinal damages, intestinal damages, haemolysishaemolysis and death due to paralysis of and death due to paralysis of respiratory centres. respiratory centres.

Sudden drop of water temperature causes pathological changes in Sudden drop of water temperature causes pathological changes in gills resulting impaired respiration and abnormally copious mucugills resulting impaired respiration and abnormally copious mucus s production, production, gills turn whitegills turn white indicating circulatory disorders and it also indicating circulatory disorders and it also causes disarray in the embryonic development in fishes. causes disarray in the embryonic development in fishes.

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OxygenOxygenIt is the most important environmental factor influencing the heIt is the most important environmental factor influencing the health alth condition of fish/prawn in a water body and thus being the limitcondition of fish/prawn in a water body and thus being the limiting factor ing factor in fish production. in fish production.

Dissolved oxygen value of Dissolved oxygen value of 55--10 10 ppmppm is optimum for normal growthis optimum for normal growth and and reproduction in tropical waters. reproduction in tropical waters.

At levels At levels below 3 below 3 ppmppm fish/prawn may live but will not feed or growfish/prawn may live but will not feed or grow but but the concentration the concentration < 1 < 1 ppmppm is lethalis lethal to many species if sustained for a to many species if sustained for a long period.long period.

Low oxygen levels are frequently a problem during the summer dueLow oxygen levels are frequently a problem during the summer due to to high temperature with heavy algal and or phytoplankton bloom. high temperature with heavy algal and or phytoplankton bloom.

As a result of photosynthesis during bloom period the dissolved As a result of photosynthesis during bloom period the dissolved oxygen oxygen values fluctuate during the day with maximum values during late values fluctuate during the day with maximum values during late afternoon (2afternoon (2--3 PM) and minimum values in early morning because 3 PM) and minimum values in early morning because during night dissolved oxygen in water is utilized for respiratiduring night dissolved oxygen in water is utilized for respiration but no on but no production of oxygen due to lack of photosynthesis.production of oxygen due to lack of photosynthesis.

Oxygen Oxygen ((contdcontd……))

On the other hand, during day time both production and On the other hand, during day time both production and utilization of oxygen takes place by photosynthesis and utilization of oxygen takes place by photosynthesis and respiration respectively. respiration respectively.

Typically, the Typically, the fish/prawn will be found dead or in severe stress fish/prawn will be found dead or in severe stress at dawn when oxygen levels may approach zeroat dawn when oxygen levels may approach zero. Typically . Typically larger fish die first and water often changes in smell and coloularger fish die first and water often changes in smell and colour. r.

Inadequate supply of oxygen leads to embryonic mortality. Inadequate supply of oxygen leads to embryonic mortality.

Sudden death of vegetation and blooms further complicate the Sudden death of vegetation and blooms further complicate the problem by increasing the biological oxygen demand (BOD)problem by increasing the biological oxygen demand (BOD) in in the decay/decomposition/oxidation process. the decay/decomposition/oxidation process.

Algae growth is restricted in the winter that is why Algae growth is restricted in the winter that is why low oxygen is low oxygen is not a problem during colder monthsnot a problem during colder months. .

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OxygenOxygen ((contdcontd……))

The basic problem during summer months is generally overcrowdingThe basic problem during summer months is generally overcrowding with an with an abundance of water nutrients (nitrates, phosphates) resulting frabundance of water nutrients (nitrates, phosphates) resulting from fish/prawn om fish/prawn wastes, decaying of artificial fertilizers, sewage, feeds, and owastes, decaying of artificial fertilizers, sewage, feeds, and organic manures. rganic manures.

This decaying process also reduces the available dissolved oxygeThis decaying process also reduces the available dissolved oxygen from the n from the water due to oxidation process. water due to oxidation process.

High salinity, low atmospheric pressure, shortened day length, aHigh salinity, low atmospheric pressure, shortened day length, and cloudy nd cloudy weather also decline the dissolved oxygenweather also decline the dissolved oxygen levels from the water body. levels from the water body.

The basic requirement of dissolved oxygen for fish/prawn varies The basic requirement of dissolved oxygen for fish/prawn varies between between species. species.

Besides, younger fish/prawn requires more oxygen than adult, actBesides, younger fish/prawn requires more oxygen than adult, active fish/prawn ive fish/prawn requires more oxygen than resting fish, fish normally requires mrequires more oxygen than resting fish, fish normally requires more oxygen as ore oxygen as temperature rises, oxygen requirement increases after feeding betemperature rises, oxygen requirement increases after feeding because oxygen cause oxygen is required to digest the food, stressed fish/prawn requires moris required to digest the food, stressed fish/prawn requires more oxygen and e oxygen and when fishes are transferred suddenly from cold to warm water andwhen fishes are transferred suddenly from cold to warm water and vice versa. vice versa.

In deficiency of oxygen the defensive mechanism of fishes/prawnsIn deficiency of oxygen the defensive mechanism of fishes/prawns is no longer is no longer maintained at optimum level, hence the possibility of infestatiomaintained at optimum level, hence the possibility of infestation with various n with various pathogens is maximumpathogens is maximum. .

OxygenOxygen ((contdcontd……))

When water is having lower concentration of oxygen, fish begin tWhen water is having lower concentration of oxygen, fish begin to rise to water o rise to water surface or crowd near inlets particularly surface or crowd near inlets particularly in the early morning hours gulping air in the early morning hours gulping air with the mouth wide openwith the mouth wide open and the and the gills of stressed fish become palegills of stressed fish become pale. .

If the low dissolved oxygen condition persists for a long periodIf the low dissolved oxygen condition persists for a long period in a pond it may in a pond it may produce significant sub lethal and lethal effect in fish. produce significant sub lethal and lethal effect in fish.

In extreme depletion of dissolved oxygen level, In extreme depletion of dissolved oxygen level, fish may die due to asphyxiafish may die due to asphyxia. . The oxygen can be elevated manually by The oxygen can be elevated manually by splashing the water with bamboo splashing the water with bamboo stickssticks, which helps in dissolving atmospheric oxygen in water or by us, which helps in dissolving atmospheric oxygen in water or by use of e of commercial commercial aeratorsaerators or by or by pumping the waterpumping the water and spraying over the surface and spraying over the surface simultaneously. simultaneously.

Low levels of potassium permanganate (2Low levels of potassium permanganate (2--4 4 ppmppm) have been used as ) have been used as algaecides as well as to quickly raise the oxygen; however, the algaecides as well as to quickly raise the oxygen; however, the increased BOD increased BOD resulting from decaying algae will further complicate the probleresulting from decaying algae will further complicate the problem. m.

Surface agitation, increased inflow of aerated water, and thinniSurface agitation, increased inflow of aerated water, and thinning the population ng the population of fish are effective methodsof fish are effective methods used singly or in combination to remedy the used singly or in combination to remedy the problem. problem.

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Following precautionary measures may be taken Following precautionary measures may be taken

to minimize the oxygen depletion in the pond:to minimize the oxygen depletion in the pond:

Feed should be given in the afternoon or evening not in early Feed should be given in the afternoon or evening not in early morningmorning as oxygen requirement in fish after feeding increases as oxygen requirement in fish after feeding increases and dissolved oxygen is minimum in pond during early and dissolved oxygen is minimum in pond during early morning. morning.

During application of organic manure in the pond, by During application of organic manure in the pond, by determining the BOD value of the manure from dry matter determining the BOD value of the manure from dry matter content of it the maximum amount of oxygen that would be content of it the maximum amount of oxygen that would be consumed for stabilization of a given quantity of manure at a consumed for stabilization of a given quantity of manure at a particular temperature can be predicted. particular temperature can be predicted.

Thus, the quantity of manure to be applied daily without the Thus, the quantity of manure to be applied daily without the hazard of oxygen depletion can be calculated taking into hazard of oxygen depletion can be calculated taking into consideration the availability of dissolved oxygen during 24 consideration the availability of dissolved oxygen during 24 hours in the pond water.hours in the pond water.

OxygenOxygen ((contdcontd……))

Proper care has to be taken during death of Proper care has to be taken during death of

phytoplankton and/or algal blooms to phytoplankton and/or algal blooms to

compensate the oxygen used for decomposition compensate the oxygen used for decomposition

of dead blooms by microorganisms. of dead blooms by microorganisms.

During summer season as the oxygen declines During summer season as the oxygen declines

due to higher temperature and increased due to higher temperature and increased

respiration of bacteria, proper oxygenation respiration of bacteria, proper oxygenation

methods should be appliedmethods should be applied. .

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AmmoniaAmmonia

The total ammonia concentration in water comprises two forms, The total ammonia concentration in water comprises two forms, viz., viz., NHNH33 (unionized ammonia) and NH(unionized ammonia) and NH44 (ionized ammonia). They (ionized ammonia). They maintain equilibriummaintain equilibrium as per the equationas per the equation--

NHNH33 + H+ H22O NHO NH44 + OH+ OH--

The The unionized ammonia fraction is more toxic to fishunionized ammonia fraction is more toxic to fish and the amount and the amount of the total ammonia in this form of the total ammonia in this form depends on the pH and depends on the pH and temperaturetemperature of the water. of the water.

As a general rule, As a general rule, higher the pH and temperature,higher the pH and temperature, the the higher thehigher thepercentage of the total ammonia is present in the percentage of the total ammonia is present in the toxic unionized toxic unionized formform. .

In aquatic systems ammonia accumulates as a result of the normalIn aquatic systems ammonia accumulates as a result of the normalmetabolism of the fish where it is excreted by kidneys as well ametabolism of the fish where it is excreted by kidneys as well as by s by the gill tissue. the gill tissue.

AmmoniaAmmonia ((contdcontd……))

Ammonia is also formed by the normal decomposition processes of Ammonia is also formed by the normal decomposition processes of protein protein (uneaten/excess artificial fish or prawn feed), organic manure, (uneaten/excess artificial fish or prawn feed), organic manure, inorganic inorganic ammonia based fertilizers and dead ammonia based fertilizers and dead phytophyto or zooplankton. or zooplankton.

Industrial and domestic wastes released in the water areas produIndustrial and domestic wastes released in the water areas produce ce ammonia. In ponds, high ammonia levels are result of insufficienammonia. In ponds, high ammonia levels are result of insufficient water flow t water flow for the amount of fish/prawn stocked. for the amount of fish/prawn stocked.

Fate of ammonia in the water body depends on oxygenation of the Fate of ammonia in the water body depends on oxygenation of the water. water. Such as Such as in oxygenated water; ammonia produced is oxidized to nitrite andin oxygenated water; ammonia produced is oxidized to nitrite andharmless nitrate (nitrification process) whereas in deoxygenatedharmless nitrate (nitrification process) whereas in deoxygenated waters waters nitrate is converted to harmful nitrite and ammonia (nitrate is converted to harmful nitrite and ammonia (denitrificationdenitrification processprocess).).

Two types of bacteria facilitate the oxidation of ammonia: Two types of bacteria facilitate the oxidation of ammonia: NitrosomonasNitrosomonas sp. sp. converts ammonia to nitrite and converts ammonia to nitrite and NitrobacterNitrobacter sp. sp. converts nitrite to nitrateconverts nitrite to nitrate..

Nitrates are utilized by plant and bacteria or denitrified to gaNitrates are utilized by plant and bacteria or denitrified to gaseous nitrogen seous nitrogen and eventually fixed into plants by specific bacteria. and eventually fixed into plants by specific bacteria.

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AmmoniaAmmonia ((contdcontd……))

Generally Generally closed systems do not have enough plant life to remove nitrates,closed systems do not have enough plant life to remove nitrates,leading to the necessity of clearing nitrates by water replacemeleading to the necessity of clearing nitrates by water replacement.nt.

Nitrates are not toxic but they act as growth promoting substancNitrates are not toxic but they act as growth promoting substances for many es for many bacteria, which are undesirable in closed system of fish/prawn cbacteria, which are undesirable in closed system of fish/prawn culture. ulture.

0.020.02--0.04 0.04 ppmppm ammonia is considered as safe concentration for many tropical ammonia is considered as safe concentration for many tropical fish and prawn species whereas 0.05fish and prawn species whereas 0.05--0.39 0.39 ppmppm and 0.40and 0.40--2.5 2.5 ppmppm produce subproduce sub--lethal and lethal effects on the many fish/prawn specieslethal and lethal effects on the many fish/prawn species respectively depending respectively depending on the oxygen, pH, and temperature of the water.on the oxygen, pH, and temperature of the water.

Ammonia stress in fishes/prawns causes gill hyperplasia, reducedAmmonia stress in fishes/prawns causes gill hyperplasia, reduced activity, and activity, and growth. growth.

Liver, kidney and brain damage also occur. In prawn surfacing ocLiver, kidney and brain damage also occur. In prawn surfacing occurs. curs. Ammonia Ammonia in water is a predisposing factor to bacterial gill disease. in water is a predisposing factor to bacterial gill disease.

High level of ammonia probably interferes with respiration resulHigh level of ammonia probably interferes with respiration resulting in ting in physiological oxygen depletionphysiological oxygen depletion. .

High levels of nitrite produced from High levels of nitrite produced from denitrificationdenitrification process also cause mortality to process also cause mortality to fishes/prawns. fishes/prawns.

Measures to reduce the effects of ammoniaMeasures to reduce the effects of ammonia

Appropriate measures should be taken for maintaining Appropriate measures should be taken for maintaining safe ammonia concentration in water for successful safe ammonia concentration in water for successful aquaculture to produce healthy fish/prawn. aquaculture to produce healthy fish/prawn.

Normally Normally at high salinity, low dissolved oxygen, and high at high salinity, low dissolved oxygen, and high carbon dioxide concentration, the toxicity of ammonia to carbon dioxide concentration, the toxicity of ammonia to fish/prawn is increasedfish/prawn is increased. .

Aeration will increase the dissolved oxygen concentration Aeration will increase the dissolved oxygen concentration and decrease the pH thereby reducing toxicityand decrease the pH thereby reducing toxicity. .

Aeration will bubble out some of the gaseous unionized Aeration will bubble out some of the gaseous unionized ammonia from water. Ammonia will get oxidized to water ammonia from water. Ammonia will get oxidized to water and gaseous nitrogen (4 NHand gaseous nitrogen (4 NH33 + 3O+ 3O22 = 2 N= 2 N2 2 + 6H+ 6H22O). O).

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Measures to reduce the effects of Measures to reduce the effects of

ammonia (ammonia (contdcontd……))

Healthy phytoplankton population removes ammonia Healthy phytoplankton population removes ammonia from high ammonia content. from high ammonia content. The manure should be The manure should be dried to allow ammonia gas to escape and then dried to allow ammonia gas to escape and then applied in the pond. applied in the pond.

Sodium chloride is used to reduce the toxicity of Sodium chloride is used to reduce the toxicity of ammoniaammonia in water. For example in in water. For example in ClariasClarias farming, farming, sodium chloride is used at the rate of 200sodium chloride is used at the rate of 200--300/ 300/ kg/1600 mkg/1600 m22 to reduce toxicity of ammonia. to reduce toxicity of ammonia.

Biological filters may be used to treat water for Biological filters may be used to treat water for converting ammonia to nitrite and then to harmless converting ammonia to nitrite and then to harmless nitrate through nitrification process. nitrate through nitrification process.

NitriteNitrite

Nitrite is an intermediate product in the biological oxidation oNitrite is an intermediate product in the biological oxidation of ammonia f ammonia to nitrate called the nitrification process. to nitrate called the nitrification process.

In most natural water bodies and in In most natural water bodies and in wellwell--maintainedmaintained ponds nitrite ponds nitrite concentration is low. In water bodies with high organic pollutioconcentration is low. In water bodies with high organic pollution and/or n and/or low oxygen concentration nitrite concentration may increase. low oxygen concentration nitrite concentration may increase.

Less than 0.02 Less than 0.02 ppmppm nitrite concentration in water is considered to be safe nitrite concentration in water is considered to be safe to the fish/prawn life, whereas, 0.02to the fish/prawn life, whereas, 0.02--0.90 0.90 ppmppm and 1.0and 1.0--10 10 ppmppm are sub are sub lethal and lethal levels for many warm water fish species respeclethal and lethal levels for many warm water fish species respectively. tively.

Nitrite is highly toxic to fish. When fish absorbs nitrite it reNitrite is highly toxic to fish. When fish absorbs nitrite it reacts with acts with haemoglobinhaemoglobin to form to form methaemoglobinmethaemoglobin. This . This methaemoglobinmethaemoglobin gives brick gives brick red colour to fish gills and it also unable to carry oxygen leadred colour to fish gills and it also unable to carry oxygen leads to death of s to death of fish. fish.

To maintain safe nitrite level in water, correct stocking, feediTo maintain safe nitrite level in water, correct stocking, feeding, and ng, and fertilization practices should be maintained. The pond should befertilization practices should be maintained. The pond should be kept well kept well oxygenated. oxygenated. BiofiltrationBiofiltration is done through special filters by which is done through special filters by which biological conversion of nitrite to harmless nitrate occur. biological conversion of nitrite to harmless nitrate occur.

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pH pH (Hydrogen Ion Concentration)(Hydrogen Ion Concentration)

Fish can tolerate wide range of pH and the Fish can tolerate wide range of pH and the optimum pH range for most fish and prawn optimum pH range for most fish and prawn species is from 7 to 8.5.species is from 7 to 8.5.

Too acidic and alkaline pH is detrimental to fish.Too acidic and alkaline pH is detrimental to fish. pH 9.0 produces sub lethal effects on pH 9.0 produces sub lethal effects on many fish species, pH 10many fish species, pH 10--10.9 is lethal to many fish/prawn species if exposed over a 10.9 is lethal to many fish/prawn species if exposed over a prolonged period otherwise in short duration sub lethal effects prolonged period otherwise in short duration sub lethal effects occur, pH 11 is lethal to occur, pH 11 is lethal to all fish/prawn species. all fish/prawn species.

At pH 5At pH 5--6, poor pond productivity and reduced fish/prawn growth occurs, 6, poor pond productivity and reduced fish/prawn growth occurs, pH 4.1pH 4.1--4.9 4.9 produces sub lethal effects, and at pH 4, direct mortality occurproduces sub lethal effects, and at pH 4, direct mortality occurs in many fishes. s in many fishes.

There are several factors that influence the acidity of waters. There are several factors that influence the acidity of waters. As mentioned earlier that As mentioned earlier that high level of free carbon dioxide increases the toxicity of acidhigh level of free carbon dioxide increases the toxicity of acids. s.

The primary effect of acidity is to disrupt the ionic balance ofThe primary effect of acidity is to disrupt the ionic balance of fish/prawn. Thus, an fish/prawn. Thus, an increase in the concentration of calcium, magnesium, sodium and increase in the concentration of calcium, magnesium, sodium and chloride cations will chloride cations will help to protect fish from the harmful effects of acids. help to protect fish from the harmful effects of acids.

The fry stage or hatchlings of fish are normally most vulnerableThe fry stage or hatchlings of fish are normally most vulnerable to acidsto acids. Some acid . Some acid ponds can be successfully used for fish farming if fingerlings rponds can be successfully used for fish farming if fingerlings rather than fry are ather than fry are stocked.stocked.

Several measures can be taken for rectifying Several measures can be taken for rectifying

alkaline and acidic water bodiesalkaline and acidic water bodies

For alkaline waters For alkaline waters

Ensuring good water management may rectify rapid fluctuations inEnsuring good water management may rectify rapid fluctuations in pH caused by pH caused by excessive phytoplankton populations. Water body should have an aexcessive phytoplankton populations. Water body should have an alkalinity of more than lkalinity of more than 50 50 ppmppm as calcium carbonate. as calcium carbonate.

By application of acid forming fertilizers. By application of acid forming fertilizers.

By application of gypsum (5By application of gypsum (5--6 tons/ha) or raw cow dung 20 tons/ha.6 tons/ha) or raw cow dung 20 tons/ha.

Apply Dolomite in saline water Apply Dolomite in saline water

For acidic waters For acidic waters

By application of lime: Limestone CaCOBy application of lime: Limestone CaCO33, slaked lime Ca(OH), slaked lime Ca(OH)22, quick lime , quick lime CaOCaO or or dolomite are used to rectify the acidic water bodies depending udolomite are used to rectify the acidic water bodies depending upon the pH. pon the pH.

Salt water like seawater may be flushed through water bodies of Salt water like seawater may be flushed through water bodies of coastal farms to coastal farms to neutralize acidity. neutralize acidity.

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AlkalinityAlkalinity

Alkalinity refers to the concentration of bases in waterAlkalinity refers to the concentration of bases in water and the capacity of water and the capacity of water to accept acidity i.e. the buffering capacity. to accept acidity i.e. the buffering capacity.

If the water contains various dissolved salts or bases such as If the water contains various dissolved salts or bases such as carbonates, carbonates, bicarbonatesbicarbonates etc., not only will the pH be naturally higher than neutral butetc., not only will the pH be naturally higher than neutral but these these negatively charged ions will combine with hydrogen ions which esnegatively charged ions will combine with hydrogen ions which essentially sentially avoids a pH drop. avoids a pH drop.

Proper alkalinity in ponds is important for successful fish prodProper alkalinity in ponds is important for successful fish production. Waters uction. Waters with a low alkalinity i.e. with a low alkalinity i.e. total alkalinity less than 20 total alkalinity less than 20 ppmppm as CaCOas CaCO33, have a very , have a very low buffering capacitylow buffering capacity and consequently are very vulnerable to fluctuations in and consequently are very vulnerable to fluctuations in pH, for example, during rainfall and phytoplankton blooms.pH, for example, during rainfall and phytoplankton blooms.

Such fluctuations may be directly harmful to fish populations. Such fluctuations may be directly harmful to fish populations. Ponds with low Ponds with low alkalinity also tend to be much less productive than high alkalialkalinity also tend to be much less productive than high alkalinity ponds,nity ponds,although ponds with alkalinity greater than 500 although ponds with alkalinity greater than 500 ppmppm may also be unproductive may also be unproductive because of limitations carbon dioxide availability at such high because of limitations carbon dioxide availability at such high concentrations.concentrations.

Alkalinity value ranging between 100Alkalinity value ranging between 100--250 250 ppmppm is ideal for fish/prawnis ideal for fish/prawn, whereas , whereas the value less than 20 the value less than 20 ppmppm creates stress in fish/prawn, Low alkalinity ponds creates stress in fish/prawn, Low alkalinity ponds can be treated with lime to rectify it. can be treated with lime to rectify it.

Total HardnessTotal Hardness

Cations of alkali earth metals; mainly calcium and magnesium conCations of alkali earth metals; mainly calcium and magnesium constitute the stitute the total hardness of a water bodytotal hardness of a water body. .

The total hardness concentration in majority of the water areas The total hardness concentration in majority of the water areas should be should be similar to the total alkalinity. This is because the calcium andsimilar to the total alkalinity. This is because the calcium and magnesium ions magnesium ions are commonly bound to the main alkalinity bases, carbonate and bare commonly bound to the main alkalinity bases, carbonate and bicarbonate. icarbonate.

There are several factors that influence hardness in water areasThere are several factors that influence hardness in water areas. . In water In water bodies where the total hardness concentration is more than totalbodies where the total hardness concentration is more than total alkalinity the alkalinity the calcium and magnesium cations are bound to anions other than carcalcium and magnesium cations are bound to anions other than carbonate bonate and bicarbonate and bicarbonate viz., viz., sulphatesulphate and chloride. and chloride.

Total hardness value of more than 50 Total hardness value of more than 50 ppmppm is satisfactory for pond productivityis satisfactory for pond productivityand should help to protect fish/prawn against harmful effects ofand should help to protect fish/prawn against harmful effects of pH fluctuations pH fluctuations and metal ions but total hardness value of less than 20 and metal ions but total hardness value of less than 20 ppmppm creates stress in creates stress in fish/prawn. fish/prawn.

Ponds with low hardness can be treated with lime for rectificatiPonds with low hardness can be treated with lime for rectification. on.

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Carbon dioxideCarbon dioxide

Carbon dioxide is present in the atmosphere in very Carbon dioxide is present in the atmosphere in very small quantity. For this reason, in spite of its high small quantity. For this reason, in spite of its high solubility in water, its concentration in most water bodies solubility in water, its concentration in most water bodies is low is low «« 6 6 ppmppm. .

It occurs in waters in three closely related forms It occurs in waters in three closely related forms viz., viz., i) i) Free carbon dioxide ii) bicarbonate ion (HCOFree carbon dioxide ii) bicarbonate ion (HCO33

--) iii) ) iii) carbonate ion (COcarbonate ion (CO33

--22). ).

The amount of each forms present; depend on the pH of The amount of each forms present; depend on the pH of water.water. For example, in neutral or acidic waters high For example, in neutral or acidic waters high concentration of free carbon dioxide i.e. the toxic form is concentration of free carbon dioxide i.e. the toxic form is frequently found. frequently found.

The concentration of free carbon dioxide may rise The concentration of free carbon dioxide may rise

under following circumstances:under following circumstances:

If it is an acidic ground water.If it is an acidic ground water.

In water areas with large phytoplankton bloom, carbon In water areas with large phytoplankton bloom, carbon dioxide may reach high levels due to dioxide may reach high levels due to

a) respiration of phytoplankton at nighttime a) respiration of phytoplankton at nighttime

b) during cloudy weather b) during cloudy weather

c) decay of dead phytoplankton. c) decay of dead phytoplankton.

In water area is heavily loaded with organic manure In water area is heavily loaded with organic manure and feed. and feed.

In natural waters high concentration may occur after In natural waters high concentration may occur after herbicide treatment. herbicide treatment.

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High external concentration of carbon dioxide interfere High external concentration of carbon dioxide interfere the uptake of dissolved oxygen from waterthe uptake of dissolved oxygen from water causing causing respiratory problems and stress. respiratory problems and stress.

Thus the effects of high carbon dioxide are acute at low Thus the effects of high carbon dioxide are acute at low dissolved oxygen concentration. dissolved oxygen concentration.

Up to 11.9 Up to 11.9 ppmppm of carbon dioxide is tolerable to fishof carbon dioxide is tolerable to fish at at low oxygen concentration. low oxygen concentration.

1212--49.9 49.9 ppmppm produces sub lethal effectsproduces sub lethal effects may include may include respiratory stress and the development of kidney stones respiratory stress and the development of kidney stones ((nephrocalcinosisnephrocalcinosis))

5050--60 60 ppmppm is lethalis lethal to many fish species with prolonged to many fish species with prolonged exposure.exposure.

Several measures can be taken for controlling high carbon diSeveral measures can be taken for controlling high carbon dioxide oxide concentration. Such as, concentration. Such as,

Repeated aeration of water Repeated aeration of water

Increasing the pH of water by Increasing the pH of water by adding hydrated lime adding hydrated lime (calcium (calcium hydroxide). It acts according to the reaction: hydroxide). It acts according to the reaction:

Ca(OH)Ca(OH)22 + 2 CO+ 2 CO22 Ca(HCOCa(HCO33))22

Experiments have shown that approximately 1 Experiments have shown that approximately 1 ppmppm of hydrated lime of hydrated lime can remove1.68 can remove1.68 ppmppm of free carbon dioxide. Therefore in water of free carbon dioxide. Therefore in water bodies with low alkalinity care must be taken not to apply excesbodies with low alkalinity care must be taken not to apply excessive sive lime because it may cause the pH to rise, creating stress to fislime because it may cause the pH to rise, creating stress to fish. h.

The phytoplankton population and the organic loading in a water The phytoplankton population and the organic loading in a water body should be regulated by correct stocking, feeding, and body should be regulated by correct stocking, feeding, and fertilization. fertilization.

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Hydrogen sulfideHydrogen sulfide

Hydrogen sulfide above optimum level in water can cause stress tHydrogen sulfide above optimum level in water can cause stress to fish and o fish and prawn. prawn.

Hydrogen sulfide is the product of the anaerobic action of bacteHydrogen sulfide is the product of the anaerobic action of bacteria during ria during organic matter degradation,organic matter degradation, which accumulates and forms a thick layer of which accumulates and forms a thick layer of organic deposit at the bottom. organic deposit at the bottom.

The bottom soil turns black and a rotten smell is discharged wheThe bottom soil turns black and a rotten smell is discharged when it is n it is disturbed.disturbed. Unionized hydrogen sulfide is toxic to fish,Unionized hydrogen sulfide is toxic to fish, but the ions resulting but the ions resulting from its dissociation are not very toxic from its dissociation are not very toxic

(H(H22S = HS + HS = HS + H++, HS = S, HS = S+2+2 + H+ H++). ).

Hydrogen sulfide concentration of 0.01Hydrogen sulfide concentration of 0.01--0.5 0.5 ppmppm is lethal to fishis lethal to fish and any and any detectable concentration in water creates stress to fish. detectable concentration in water creates stress to fish.

At a concentration of 0.1At a concentration of 0.1--0.2 0.2 ppmppm, prawn loses their equilibrium, creates sub , prawn loses their equilibrium, creates sub lethal stress,lethal stress, and at a concentration of 3.0 and at a concentration of 3.0 ppmppm prawns die instantly. prawns die instantly.

Some measure can be taken to rectify Some measure can be taken to rectify increase in hydrogen sulfide. Such as increase in hydrogen sulfide. Such as

frequent exchange of waterfrequent exchange of water to prevent to prevent building up of hydrogen sulfide in the building up of hydrogen sulfide in the water body water body

if if pH of water is increased by limingpH of water is increased by liming the the toxicity of hydrogen sulfide decreases. toxicity of hydrogen sulfide decreases.

14

Suspended solidsSuspended solids

Lots of solid materials are present in the water body, which areLots of solid materials are present in the water body, which are retained when retained when the water is filtered through a 0.45 the water is filtered through a 0.45 µµm mesh size filter paper. m mesh size filter paper.

Natural weathering of the rocks, land erosion, or pollution is tNatural weathering of the rocks, land erosion, or pollution is the factors he factors responsible for origin of the suspended solids in the large wateresponsible for origin of the suspended solids in the large water body. r body.

But in the small culture area suspended solids in water is constBut in the small culture area suspended solids in water is constituted by ituted by phytoplankton bloom, uneaten feed particles, and phytoplankton bloom, uneaten feed particles, and faecesfaeces. .

The effects of suspended solids depend on the nature of the soliThe effects of suspended solids depend on the nature of the solid. d.

Abrasive particles such wastes from coal washing or long Abrasive particles such wastes from coal washing or long spinedspined diatoms or diatoms or sometimes, sometimes, copepodiccopepodic zooplankton is harmful to various stages of fishes than zooplankton is harmful to various stages of fishes than soft materials. Gill tissue is the most susceptible. soft materials. Gill tissue is the most susceptible.

Gill damage through excessive mucus production or clogging.Gill damage through excessive mucus production or clogging. Bacterial gill Bacterial gill disease is common to high levels of suspended solid load in watedisease is common to high levels of suspended solid load in water.r.

Suspended solids and turbidity are important in reducing the penSuspended solids and turbidity are important in reducing the penetration of light etration of light in the ponds, reducing the productivity, and increasing the riskin the ponds, reducing the productivity, and increasing the risk of of deoxygenationdeoxygenation. .

Adequate water depth is needed not only for optimum growth of fiAdequate water depth is needed not only for optimum growth of fishes shes and prawns but also to provide enough space and oxygen to them. and prawns but also to provide enough space and oxygen to them.

The ponds where water source is monsoon rain, after the end of tThe ponds where water source is monsoon rain, after the end of the he season season water levels starts decreasing gradually and shortage of water iwater levels starts decreasing gradually and shortage of water is s quite common duringquite common during summer season, which is the most crucial time for summer season, which is the most crucial time for fish culture since the fish growth rate is faster in this periodfish culture since the fish growth rate is faster in this period. .

In fact, In fact, during the time of lowest water level the ponds contain the during the time of lowest water level the ponds contain the maximum biomass. maximum biomass.

In shallow and seasonal ponds sufficient phytoplankton populatioIn shallow and seasonal ponds sufficient phytoplankton population fails n fails to appear and soft sediment layer is vigorously stirred up by fito appear and soft sediment layer is vigorously stirred up by fish, making sh, making the water more turbid, thereby reducing the photosynthetic procethe water more turbid, thereby reducing the photosynthetic process by ss by limiting light penetration. limiting light penetration.

Eventually total amount of dissolved oxygen may not be at time sEventually total amount of dissolved oxygen may not be at time sufficient ufficient to meet the demand for respiration of total community and the chto meet the demand for respiration of total community and the chemical emical oxygen demand of the sediment, resulting sometimes in mass mortaoxygen demand of the sediment, resulting sometimes in mass mortality lity of fish and of fish and planktonicplanktonic collapse. collapse.

15

On the other hand in the dipper perennial ponds where On the other hand in the dipper perennial ponds where the water column is more than 3 m, fish life is again the water column is more than 3 m, fish life is again adversely affected.adversely affected.

In such ponds, the photosynthetic or oxygen producing In such ponds, the photosynthetic or oxygen producing zone is less in comparison with oxygen consuming zone, zone is less in comparison with oxygen consuming zone, which leads to negative oxygen balance and create to which leads to negative oxygen balance and create to stress to fish health. stress to fish health.

Suspended solid concentration of up to 10,000 Suspended solid concentration of up to 10,000 ppmppm (up (up to 4% by volume) to 4% by volume) is tolerable to freshwater carpsis tolerable to freshwater carps, , Tilapia Tilapia sp. and catfishes, although effect will depend upon the sp. and catfishes, although effect will depend upon the nature of the suspended particles. nature of the suspended particles.

Persistent turbidity problems in water if caused by Persistent turbidity problems in water if caused by fine fine clay mineral particles can be treated with alum @ 25clay mineral particles can be treated with alum @ 25--45 45 kg/ha or lime. kg/ha or lime.

MetalsMetals

Originally the natural weathering process determines the backgroOriginally the natural weathering process determines the background level und level of metals in a particular water body. of metals in a particular water body.

Though it is a natural process, the rate of weathering is influeThough it is a natural process, the rate of weathering is influenced by man nced by man made changes in land use pattern and by acid rain. made changes in land use pattern and by acid rain.

Effluents from mining, industry, and domestic use are also the sEffluents from mining, industry, and domestic use are also the source of ource of metals (Zn, Cu, Hg, Ni, metals (Zn, Cu, Hg, Ni, PbPb, , CdCd, Cr, AI, Fe etc.) in the water body. If the , Cr, AI, Fe etc.) in the water body. If the water is hard (300 water is hard (300 ppmppm as CaCOas CaCO33) with a pH of 8, heavy metals will ) with a pH of 8, heavy metals will precipitate as carbonates or sulphates. precipitate as carbonates or sulphates.

In softer, low pH water (less than 100 In softer, low pH water (less than 100 ppmppm as CaCOas CaCO33) the metals are in ) the metals are in their ionic form and are more toxic to fish. their ionic form and are more toxic to fish.

In acid waters high levels of metals with low pH are recorded duIn acid waters high levels of metals with low pH are recorded during period ring period of high rainfall. Most metals dissolve more easily in acid waterof high rainfall. Most metals dissolve more easily in acid water of pH < 7 and of pH < 7 and therefore acid water usually contain higher concentrations of metherefore acid water usually contain higher concentrations of metals than tals than neutral or alkaline waters. neutral or alkaline waters.

16

Following factors influence toxicity of metals to fish/prawnFollowing factors influence toxicity of metals to fish/prawn

The The presence of organic substancespresence of organic substances like sewage effluents, organic manure, like sewage effluents, organic manure, humichumic acids acids have all been shown to reduce the toxicity of metals, because orhave all been shown to reduce the toxicity of metals, because organic substances complex ganic substances complex the free ions, i. e. the toxic component of metal and render thethe free ions, i. e. the toxic component of metal and render them harmless. m harmless.

CalciumCalcium is one of the most important inorganic substances affecting metis one of the most important inorganic substances affecting metal toxicity. High al toxicity. High levels of calcium in water protect the gills from metal damage blevels of calcium in water protect the gills from metal damage by slowing down the y slowing down the diffusion in of metal ions. diffusion in of metal ions.

Acidity and low alkalinityAcidity and low alkalinity make many metals more toxic because they change the metal make many metals more toxic because they change the metal into the more harmful soluble form. into the more harmful soluble form.

Increased temperature and low oxygen levelIncreased temperature and low oxygen level usually increase toxicity of metals because usually increase toxicity of metals because at low oxygen concentration fish pumps more water hence more toxat low oxygen concentration fish pumps more water hence more toxic metals over their ic metals over their gills. Moreover at higher temperature, water contains less oxygegills. Moreover at higher temperature, water contains less oxygen making the problem n making the problem worse. worse.

More than one metal can act together to produce more pronounced More than one metal can act together to produce more pronounced toxicity than a single toxicity than a single one. one.

Fish acclimated relatively high concentration of metal in water Fish acclimated relatively high concentration of metal in water are better able to are better able to withstand a potentially toxic concentration than nonwithstand a potentially toxic concentration than non--acclimated fish. acclimated fish.

In general In general small fry are more vulnerable than older fish. small fry are more vulnerable than older fish.

The toxic effects of most metals are nonThe toxic effects of most metals are non--specific. specific. Acute Acute responsesresponses exhibit exhibit gill damage in the form of swelling of gill damage in the form of swelling of epithelial cells, separation of gill epithelium, severe epithelial cells, separation of gill epithelium, severe osmoregulationosmoregulation problems, and mucus productionproblems, and mucus production. .

This results in loss of body salts, poor oxygen exchange, This results in loss of body salts, poor oxygen exchange, and eventual death. and eventual death.

Chronic effectsChronic effects range from range from proliferation of epithelial cells, proliferation of epithelial cells, fusion of secondary lamellae, clubbing at the end of gill fusion of secondary lamellae, clubbing at the end of gill filaments and changes in the blood chemistryfilaments and changes in the blood chemistry. .

The response of fish to some metals is more specific e.g. The response of fish to some metals is more specific e.g. the the neurotoxicneurotoxic effects of lead. effects of lead.

However, since most effects are nonHowever, since most effects are non--specific it is essential specific it is essential in many suspected case of heavy metal poisoning to carry in many suspected case of heavy metal poisoning to carry out analysis of heavy metal content of water and fish tissues out analysis of heavy metal content of water and fish tissues together with measurements of oxygen, alkalinity, hardness together with measurements of oxygen, alkalinity, hardness and pH to establish the cause of death. and pH to establish the cause of death.

17

Recommended safe level of metals suggested by EPARecommended safe level of metals suggested by EPA

i) 0.01

ppm in

water

having

10 ppm

of

CaCO3

Ii) 0.05

ppm in

water

having

more

than 50

ppm of

CaCO3

i) 0.01

ppm

at 20 ppm

hardness

of water

ii) 0.04

ppm at

320 ppm

hardness

of water

i) 0.0002

ppm in

water

ii) 0.0005

ppm in

tissues

(wet

weight

basis)

i) 0.005 ppm

in water

having 10

ppm of

CaCO3

ii) 0.03 ppm

in other

types of

water

iii) 0.05 ppm

produces

sublethal

effects, toxic

to nervous

systems in

fishes, black

tails are

diagnostic of

lead

poisoning

1.0 ppm is

safe but 1.2-

10.5 ppm is

lethal to

common

carp, death

attributed

to the

precipitation

of ferric

ydroxide

on gills

forming

brown

deposit on it

i) 0.005 ppm

in water

having 10

ppm of

CaCO3

ii) 0.02 ppm

in water

having 50

ppm of

CaCO3

iii) 0.04 ppm

in water

having 100

ppm of

CaCO3

i) 0.004

ppm in

hard

water

i.e.400

ppm of

CaCO3

ii)

0.0004

ppm in

soft

waters

i.e. 40

ppm of

CaCO3

0.1

ppm

at pH

5.2-

5.4

Zn NiHg PbFe Cu CdAI

PesticidesPesticides

The widespread use of pesticides in pest control of crops and foThe widespread use of pesticides in pest control of crops and forestry has restry has threatened the fishery waters. threatened the fishery waters.

Although many pesticides are useful in fishery management there Although many pesticides are useful in fishery management there are many are many others, which are dangerous for fish life and can produce severaothers, which are dangerous for fish life and can produce several types of l types of deleterious effects. deleterious effects.

Three types of pesticides such as Three types of pesticides such as organochlorinesorganochlorines, organophosphate, and , organophosphate, and carbamatescarbamates are of importance causing pollution in waters. are of importance causing pollution in waters.

These pesticides may come into the water bodies accidentally or These pesticides may come into the water bodies accidentally or by by deliberate application. deliberate application.

Accidental entry may happen due to i) run off from sprayed agricAccidental entry may happen due to i) run off from sprayed agricultural field ultural field ii) washing of sprayed equipments, plants crops in water etc. deii) washing of sprayed equipments, plants crops in water etc. deliberate liberate application occurs during i) control of aquatic weeds ii) controapplication occurs during i) control of aquatic weeds ii) control of mosquito l of mosquito larvae iii) elimination of unwanted fish from the pond iv) contrlarvae iii) elimination of unwanted fish from the pond iv) control of insects ol of insects

v) control of parasite. v) control of parasite.

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Formulation and chemical stability of pesticides Formulation and chemical stability of pesticides are two important are two important factors, which can influence the toxicity of pesticide in water.factors, which can influence the toxicity of pesticide in water.

The active ingredients of any pesticide are the main toxic The active ingredients of any pesticide are the main toxic components and its formulation in oil emulsion, components and its formulation in oil emulsion, wettablewettable powders, or powders, or granules very often determines the toxicity to fish. granules very often determines the toxicity to fish.

For example, it is reported that DDT is more toxic to fish in anFor example, it is reported that DDT is more toxic to fish in an oil oil base emulsion than in water. base emulsion than in water.

Water based pesticides are more easily washed away than oil Water based pesticides are more easily washed away than oil based emulsion, which tend to be more persistent.based emulsion, which tend to be more persistent. Granule Granule formulation releases the toxic component of the pesticide over aformulation releases the toxic component of the pesticide over alonger period of time thereby reducing the toxicity to fish due longer period of time thereby reducing the toxicity to fish due to to dilution. dilution.

As per as stability is concerned As per as stability is concerned organochlorinesorganochlorines are very stableare very stable and and are recorded to persist in the environment for a longer durationare recorded to persist in the environment for a longer duration. .

Other pesticides e.g. organophosphates are known to be less stabOther pesticides e.g. organophosphates are known to be less stable le and easily degradable becoming less toxic to fish. and easily degradable becoming less toxic to fish.

Following factors can influence the toxicity of pesticides to fiFollowing factors can influence the toxicity of pesticides to fishsh

The joint action of mixture of pesticides can often be lethal toThe joint action of mixture of pesticides can often be lethal to fish fish than effect of a single pesticide. than effect of a single pesticide.

The toxicity of pesticides to fish varies with fish species and The toxicity of pesticides to fish varies with fish species and the size the size of fish. For example, fish fry are most susceptible than adult fof fish. For example, fish fry are most susceptible than adult fish. ish.

Fish is more susceptible to pesticide poisoning if the water quaFish is more susceptible to pesticide poisoning if the water quality is lity is bad. For example, at a bad. For example, at a higher temperature and low dissolved higher temperature and low dissolved oxygen condition in water most fishes pump in more water and oxygen condition in water most fishes pump in more water and hence more pesticides over their gillshence more pesticides over their gills. .

In water bodies with In water bodies with high turbidityhigh turbidity the effect of pesticide pollution is the effect of pesticide pollution is diminished. diminished.

Most pesticides are easily bound to the large amount of organic Most pesticides are easily bound to the large amount of organic matter present in such water bodies and are consequently renderematter present in such water bodies and are consequently rendered d less toxic. less toxic.

19

Recommended Recommended safe safe levels levels of of different pesticides in different pesticides in

water water and tissue suggested by EPAand tissue suggested by EPA

-< 0.0015 EkalusQuinalphos

-0.001 FuradanCarbofuran

-< 0.006 SevinCarbaryl

Carbamates

-<0.003 Metacid-50

-< 0.003 FolidolParathion

-0.008 CvthionMalathion

-< 0.003 HinosanEdifenphos

-0.11 RogarDimethoate

-< 0.010 Zineb

-< 0.005 Captan

-< 0.003 NuvanDichlorvos

Organophosphates

0.1 0.002 TafdrinEndrin

0.1 0.003 ThiodanEndosulfan

0.1 0.005 OctaloxDieldrin

-< 0.18 -BHC

-0.002 Gesarol NeocidDDT

Organochlorine

Tissue Water

Safe Level (ppm) Trade Name Common Name

Other environmental mediated diseasesOther environmental mediated diseases

Gas bubble diseaseGas bubble disease::

Gas bubble disease can occur in fish under condition in which Gas bubble disease can occur in fish under condition in which there is an excess of gasesthere is an excess of gases (CO(CO22, N, N22, O, O22 and Hand H22S) in the water and S) in the water and normally happens due to high organic load at pond bottomnormally happens due to high organic load at pond bottom. .

During decomposition of fertilizers and manures gases are During decomposition of fertilizers and manures gases are released in the form of bubblesreleased in the form of bubbles. .

The fingerlings of fish try to ingest them mistaking it for The fingerlings of fish try to ingest them mistaking it for planktonicplanktonic food and accumulate in the intestinefood and accumulate in the intestine. .

Sometimes gas bubbles may enter into the blood circulation and Sometimes gas bubbles may enter into the blood circulation and transported to brain or heart, fish can die suddenly with no othtransported to brain or heart, fish can die suddenly with no other er signs. signs.

Bubbles just under the surface of the skin may be seen. Bubbles just under the surface of the skin may be seen.

20

The young fishes show The young fishes show erratic movementerratic movement and gradually die and gradually die exhibiting the whirling movement. exhibiting the whirling movement.

The abdomen is swollen and the balance of fish is lostThe abdomen is swollen and the balance of fish is lost due to due to accumulation of large gas bubbles in the intestine. accumulation of large gas bubbles in the intestine.

HaemorrhagingHaemorrhaging of the fins is common due to the occlusion of of the fins is common due to the occlusion of small blood vessels by gas bubbles. small blood vessels by gas bubbles.

With stopping application of unfermented fertilizers and With stopping application of unfermented fertilizers and addition of fresh water in the ponds, the condition can be addition of fresh water in the ponds, the condition can be checked. checked.

Algal Algal toxicosistoxicosis

The pea soup The pea soup colouredcoloured bloom of algaebloom of algae ((MicrocystisMicrocystis sp. and sp. and Anabaena Anabaena sp.) may occur in the ponds sp.) may occur in the ponds due to excessive use of due to excessive use of fertilizers and feedsfertilizers and feeds. .

Overcrowding of algae causes its mass mortality because of lack Overcrowding of algae causes its mass mortality because of lack of nutrients or lack of carbon dioxide. of nutrients or lack of carbon dioxide.

The dead and decomposing cells release enough breakdown The dead and decomposing cells release enough breakdown products or toxins called algal toxins, which are harmful to products or toxins called algal toxins, which are harmful to fish/prawn and produce serious loses in pond culture. fish/prawn and produce serious loses in pond culture.

There is There is clogging of gills by the algae causing respiratory clogging of gills by the algae causing respiratory distressdistress. .

Small fishes die first after erratic swimming movement and Small fishes die first after erratic swimming movement and convulsions occur with acute kidney inflammation in severe convulsions occur with acute kidney inflammation in severe cases followed by death. cases followed by death.

21

For controlling the condition following For controlling the condition following

measures can be takenmeasures can be taken

Copper Copper sulphatesulphate is applied in the pond @0.5 is applied in the pond @0.5 ppmppm..

(Suspended particles may be settled by application of lime)(Suspended particles may be settled by application of lime)

Algal bloom can be restricted by application of Algal bloom can be restricted by application of TakazineTakazine –– 50 50 ((CymazineCymazine)) @@ 22--4 kg / acre4 kg / acre. .

If the pond water is covered by floating weeds, If the pond water is covered by floating weeds, WolfiaWolfia. sp (. sp (microweedsmicroweeds) ) or or LemnaLemna minor, minor, LemnaLemna major, major, SpirodellaSpirodella for one week then also the for one week then also the algal growth is checked due to lack of penetration of sunlight.algal growth is checked due to lack of penetration of sunlight.

Dry Cow dung cakes @ 200 kg/ha is sprinkled over the surface of water. These process blocks the sunlight penetration in water.

Some surface area of pond is covered with water hyacinth therebySome surface area of pond is covered with water hyacinth therebyblocking sunlight penetration in water.blocking sunlight penetration in water.

ConclusionConclusion

In aquatic environment fishes continually adjust In aquatic environment fishes continually adjust themselves to the change of themselves to the change of physicophysico--chemical parameters chemical parameters which impose a great stress on their limited homeostatic which impose a great stress on their limited homeostatic mechanism. mechanism.

Such stress causes totally upsetting the defensive Such stress causes totally upsetting the defensive mechanism or immune system resulting in susceptibility of mechanism or immune system resulting in susceptibility of various diseases. various diseases.

Besides abnormal environmental quality also causes direct Besides abnormal environmental quality also causes direct adverse effect on fish. adverse effect on fish.

Proper monitoring and management of culture system can Proper monitoring and management of culture system can only help in healthy fish/prawn production and make the only help in healthy fish/prawn production and make the culture operation profitable. culture operation profitable.