Topics to be covered• Reproduction• Life cycles• Growth

Reproduction, Early Life Stages, Growth(Chapter 6 and additional material)

Reproduction – hormones of the reproductive system

• Brain-hypothalamic hormones (note error in textbook) Gonadotropin-releasing hormone (GnRH) Gonadotropin release-inhibitory factors (GnRIF; such as

dopamine)• Pituitary hormones: gonadotropins

FSH: controls gonadal growth LH: controls gamete maturation and release

• Gonadal hormones (steroids) 11-ketotestosterone (androgen) 17β-estradiol (estrogen) Progesterone or its derivatives (progestins, they induce

gamete maturation and ovulation; Maturation-Inducing Hormone = MIH)

Reproduction, Early Life Stages, Growth

Reproduction – general environmental regulation

brain

gonad

Fish

pituitary

steroid hormones

Environment

seasonal photoperiod profileseasonal temperature profile

food availabilitycontaminants

other liver

LHFSH

•androgens•estrogens

Vg

gonadaldevelopment

•progestins

Reproduction, Early Life Stages, Growth

Brain

Pit

Gonad

dopamine

-LHRH

+

LH

Gametes

Reproduction – hormones that control release of gametes

Reproduction, Early Life Stages, Growth

Reproduction – captive spawning

• Captive spawning is preferred over collection of natural seed because,

Greater control over timing of seed availability Greater control over number of available seeds

• Many of the current aquacultural species do not spawn naturally in captivity

• Often, problem is with the spawning of captive female, not male, fishes

• Methods for natural and hormonally induced spawning of captive fishes and other aquacultural organisms have been developed based on knowledge of their reproductive physiology

Reproduction, Early Life Stages, Growth

Reproduction – captive natural spawning

Zebrafish spawning

• photoperiod - 14L:10D• temperature - 28~29 °C• spawning container overnight

spawning containers

fish in spawning containers

Reproduction, Early Life Stages, Growth

Reproduction – captive induced spawning

MIH

MIH

R.W. Rottmann et al. 1991

LHRH = GnRH

Reproduction, Early Life Stages, Growth

Reproduction – captive induced spawning

R.W. Rottmann et al. 1991

MIH

hCG = human chorionic gonadotropin

Reproduction, Early Life Stages, Growth

Reproduction – shellfish

• Decapod crustaceans X-organ/sinus gland system of eyestalk produces gonad-

inhibiting hormone Eyestalk ablation removes gonad-inhibiting hormone and

causes completion of gametogenesis in male and female decapod crustaceans (in some species, eyestalk can regenerate)

• Bivalves Spawning cues include change in water temperature,

change in salinity, lunar cycles, pheromones

Reproduction, Early Life Stages, Growth

Reproduction, Early Life Stages, GrowthEarly life stages

• Fertilization leads to Zygote• Depending on species, embryogenesis occurs over period of hours

to weeks• Following hatching, several stages of development can be described:

Embryo-larval transition (endogenous feeding) Larval development Larva-juvenile transition (metamorphosis) Juvenile (prepubertal) growth

Embryo-larva transition

Reproduction, Early Life Stages, GrowthEarly life stages

• Embryo development (endogenous nutrition) Days to weeks

Need to clean egg mass following fertilization Use clean water for incubation (filtered water) Keep good levels of oxygen Appropriate temperature

• Embryo-larva transition (fishes – endogenous nutrition) Days to weeks

Culture techniques similar to embryo• Larval development

Days to weeks Onset of exogenous feeding; providing appropriate food

becomes major aspect of rearing (microalgae for molluscs and shrimps; rotifers and brine shrimp nauplii for fish and older shrimp larvae)

Nitrogenous waste can become problem; need close monitoring of general water quality - rearing often occurs in large tanks to help with water quality

Density of larvae reduced as they grow

Reproduction, Early Life Stages, GrowthEarly life stages (continued)

• Larval development is abbreviated or non-existent in some species (direct development)

Embryos hatch already bearing juvenile form• Larva-juvenile transition: metamorphosis

Slight to marked changes in morphology, physiology and behavior, depending on species

• Juvenile development Postmetamorphic juvenile fishes are progressively weaned

off live feeds on to artificial diets Initial culture is in hatchery tanks

• Grow out Final phase of culture when juveniles are grown until

harvested

Reproduction, Early Life Stages, GrowthGrowth

• Bioenergetics Energy equations (note: specifics here are different from text

but overall meaning is same) Simple equation: p x F = M + G

p = proportion of food consumed that is assimilatedF = amount of food consumedM = catabolism (energy release)G = growth (anabolism)

Expanded equation: C = (Mr + Ma + SDA) + (F + U) + (Gs + Gr)C = rate of energy consumptionMr = standard metabolic rate (rate of energy use by a fasting animal at rest)Ma = metabolic rate increase (over standard) due to activitySDA = metabolic rate increase (over standard) due to digestion and assimilation of

foodF = waste due to egestion (feces)U = waste due to excretion (urine)Gs = somatic growth rateGr = reproductive or gonadal growth rate

Reproduction, Early Life Stages, GrowthGrowth

• Patterns of growth of an organism can be described in several ways: Absolute growth: increase in size (length or weight), equal

Y2-Y1

Absolute growth rate: increase in size per unit time, equal (Y2-Y1)/(t2-t1) Initially small, but as animal grows in size, there is

increased capacity to take in and assimilate food Relative growth: increase in size relative to initial size,

equal (Y2-Y1)/Y1

Relative growth rate: increase in size per unit body size per unit time, equal (Y2-Y1)/[Y1(t2-t1)] Initially rapid, but slows down with development

Infle

xion

poi

nt

Reproduction, Early Life Stages, GrowthGrowth

• Measuring growth: Growth measurements are needed to monitor health and

predict harvest time Measures

Length: linear dimension using calipers or ruler - quick and easy Wet weight: most common assessment of whole body growth of

fishes - quick and easy Dry weight: wet weight minus water (in oven at ≤100°C). Can

usually be applied only on dead organism; it is most accurate method for assessing animal tissue growth, since changes in tissue water content may occur due to stress etc.

Condition factor: weight/(length)3

Ash-free dry weight: dry weight – inorganic ash (up to 24 h at 500°C). It is the dry weight of organic matter in the animal. Useful for animals with large inorganic components (e.g., bivalves) where it is relatively difficult to measure organic tissue content. Sometimes simply expressed as ash weight.

Proximate composition: determination of different categories of compounds in tissues. Most commonly measured categories include carbohydrates, proteins, lipids.

Reproduction, Early Life Stages, GrowthGrowth

• Measuring growth in fishes: Length measurements

Total length (TL): tip of snout to tip of longest caudal fin rays. Difficult to measure accurately if caudal fin is damaged

Fork length (FL): tip of snout to fork (median caudal fin rays). Used in fishes with clear forks

Standard length (SL): tip of snout to base of caudal fin (or tip of notochord in larval fish)

Notes on Chapter 6 reading material

• Subsections 6.3.1, 6.3.2, and 6.3.3, 6.4.2: general knowledge of topic covered in these subsections is necessary, but no need for details

• Formulas in subsection 6.4.1 are not required reading (you must instead know formulas covered in class)

• Under subsection 6.4.4, discussion of bivalves and decapod crustaceans is not required reading

• Table 6.2 is not required reading

Reproduction, Early Life Stages, Growth