The Biology of ACETES (Crustacea; Sergestidae) and 

Identification Guide

John Rheo P. Dela CruzMSF ‐ Fish. Bio. I

1

Introduction

species of the genus Acetes are small planktonicshrimp living mainly in the estuaries and coastalwaters of the tropical and subtropical regions.

genus has been established by H. MilneEdwards in 1830 based on material collected atGanges Riverg

14 species and 5 subspecies are recognized, ofwhich 2 species, Acetes Intermedius and A.

imarinus are new.

10 species are distributed in the Indo‐WestPacific and the Indo‐Malayan region is particularlyy g p yrich in species

Acetes affords a major source of protein to someof the people in Asia and East Africaof the people in Asia and East Africa.

the largest zooplankton‐based fisheries in theworld.world.

2

Introduction

they account for at least 13.5% of the world’scrustacean fisheries production (Xiao andGreenwood, 1993)

form an important component of coastalzooplankton communities (Grabe & Lees, 1992)

play important role in the dynamics of coastalecosystems, especially in lagoons, sea‐grass bedsand mangrove swamps by linking vegetaland mangrove swamps, by linking vegetalmaterials, phytoplankton, zooplantonkton andanimals of higher trophic levels (Rao et al., 1980)

acetes range from 10‐40 mm in total length andwidely distributed (Omori, 1975; Holthuis, 1980)

resilient under laboraty conditions (Ball andCowan, 1977)

3

Introduction

school and swarm of acetes in coastal asia, arethe bases of important commercial fisheries forpconsumption by humans and domestic animals(Omori 1975)

potential food organism in aquaculture industry (Ung & Itoh, 1989)

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Adult External Morphology

knowledge of acetes morphology is limited

h d d i i f l

elongated and laterally compresseddecapods, with a well developed abdomenadapted for swimming there are good descriptions of external,

but muscular, circulatory, endocrine andnervous systems are basically unknown.

adapted for swimming

somite is enclosed with a dorsal tergum, aventral sternum and two lateral pleura.

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(Omori M. 1975)

Distinctive features of AcetesDistinctive features of Acetes

1.  rostrum  5. Periopods

2. compound eye are stalked and mobile

3. Antennule and Antennae 

4 Mouthparts: Labium mandibles

6. Pleopods

7. Uropods and Telson4. Mouthparts: Labium, mandibles, Maxillae and Maxillipeds

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(Omori M. 1975)

Larval External Morphology

larval morphology of acetes is generally known from the work of Brooks (1882)

Brooks (1882) the first to follow larval development of acetes and describe Brooks (1882) the first to follow larval development of acetes and describemorphology (Acetes americanus)

The first detailed and reliable account was given by Soejima (1962) for A japonicas

how did they determine the stage of acetes

The first detailed and reliable account was given by Soejima (1962) for A. japonicas.

1 use of larval rearing 2 .using specimen from series of phytoplankton samples.

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Larval Stages in Acetes

1. Nauplius(4)  2. Zoea (Protozoea)(2)

pyriform larger anteriorly thoracic somites are formed

formation of sessile compound eyes (appear 3 pairs of natatory cephalic appendages

uniramous antennules

bi t d dibl

formation of sessile compound eyes (appearanteriorly beneath the carapace)

antennules and antennae are now segmented biramous antennae and mandible

red, conspicuous, median naupliareye present in the anterior end

gand still used for locomotion

eye present in the anterior end

8(Liu & Zhang, 1951, 1981) (Liu & Zhang, 1951, 1981)

Larval Stages in Acetes

3. Mysis (2) 4. Postlarvaelarge exopod appear on all thoracic appendages larvae swim backwards

uniramous pleopods become large

antennae lost locomotory function

three pairs of maxillipeds are functional

postlarvae swim forwards with rhythmic beating of the pleopods chelae on the first three pairs of pereiopods

gill rudiment appear on the thoracic appendages

chelae on the first three pairs of pereiopodsare now functional

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(Liu & Zhang, 1951, 1981) (Liu & Zhang, 1951, 1981)

Feeding Habits:

In the study of Ephrime B. Metillo entitled Feeding Ecology of Acetes intermediusOmori 1975 (Crustacea Decapoda Sergestidae) in Iligan Bay Philippines (2011) – foundOmori 1975 (Crustacea, Decapoda, Sergestidae) in Iligan Bay, Philippines (2011) foundout that A. intermedius is an omnivorous zooplanktivore with copepods, ostracods,decapod crustacean larvae, gastropod and bivalve veligers, and amorphous materials asdominant food itemsdominant food items

Amin et al entitled Diet Composition of Sergestid Shrimp Acetes serrulatus from Amin et. al., entitled Diet Composition of Sergestid Shrimp Acetes serrulatus fromthe Coastal Waters of Kukup, Johor, Malaysia (2011) found out that the food items inthe gut of A. serrulatus were comprised of phytoplankton, zooplankton, plant matter,appendages of decapods, debris and unidentified fragments and concluded that A.appendages of decapods, debris and unidentified fragments and concluded that A.serrulatus is omnivorous and feed on phytoplankton, zooplankton andmicrocrustacean.

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Maturity:

Acetes japonicasmatures at body length of > 12 mm in the Ariake Sea

Wu & Cheng (1571) identified four ovarian stages in A chinensis

Acetes japonicas matures at body length of > 12 mm in the Ariake Sea A. chinensismatures at a body size of 18‐43 mm

Wu & Cheng (1571) identified four ovarian stages in A. chinensis1.  Immature ovaries‐ eggs are small in size (0.0230‐0.0828 mm in diameter)‐mixture of small and large eggs.mixture of small and large eggs.‐ ovary is ribbon like‐ no spermatophore are implanted in the thelycum.2. Mature ovaries ‐ egg size varies considerably, most being 0.0640‐0.1610 mm in diameter, but some small eggs as above are present‐ spermatophore are implanted in the thelycum.3. Near spawning ovaries ‐ the eggs are all of 0.0828‐0.2070 mm in diameter, and regularly arranged.‐ general colour of the ovary is green or brown at or near spawning4. Spent ovary ‐ there are no mature eggs in the protruding parts of the margins of the ovary‐ in some cases, the ovary may be completely empty, or with only a few eggs.

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Maturity:

Amin et. al., (2010). Reproductive seasonality and maturation of the sergestid shrimp,Acetes japonicus (Decapoda: Sergestidae) in coastal waters of Malacca, PeninsularMalaysia They found out that female attained sexual maturity at a minimum size of 17 5Malaysia. They found out that female attained sexual maturity at a minimum size of 17.5mm total length and inferred that A. japonicus breeds continuously throughout the yearin thecoastal waters of Malacca Peninsular Malaysiacoastal waters of Malacca, Peninsular Malaysia.

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Reproductive system and reproduction: acetes posses secondary sexual acetes posses secondary sexualstructures

male possess petasma

copulation where male deposits a pairof spermatophores into the thelycum ofthe female

female possess thelycum

petasma thelycum

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Spawning

Omori (1974) asserted A. japonicus spawns generally a few days after copulation

Wu (1991) speculated that A. chinensis spawns 10‐15 days after copulating and when the ovaries maturewhen the ovaries mature.

A. chinensis spawns at night 

Female acetes spawn their eggs directly into the water.

14(J. Marin  ‐ FISHERIES AND AQUACULTURE – Vol. II ‐ Shrimps and Krill )

The eggs:

the eggs of Acetes are round and relatively small(<0.4 mm)

Acetes eggs are either pelagic , semipelagic or demersal

A. chinensis produce demersal eggs, but nearly buoyant (Liu & Zhang, 1981) or 

A. japonicus (Soejima, 1926) and A. indicus (Pillai, 1973) have pelagic eggs

semipelagic (Wu, 1991) eggs.

Fecundity:

fecundity of acetes is positively related to body size fecundity of acetes is positively related to body size

Ikematsu (1953, 1963) 13 A. japonicusmeasuring 12‐29 mm body size have eggs ranged from 680 to 6800 Zhang (1992) 87 A. chinensis with body range 26‐38 mm have eggs ranged from 1013 to 9863.

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Eggs Colour 

Acetes eggs may show regional differences in colour

Ariake Sea (Soejima, 1926) – green

Korea (Yoshida, 1949) – orange (A. chinensis)

Okayama (Yasuda et. al., 1953) – colorless

Puhai (Wu, 1991) – colourless and transparent

Pillai (1973) – golden brown (A. indicus)

Moulting

general descriptions of the moulting process in Acetes have been made, but on intermoult data periods and increment in body and carapace length.

l d f d l d ( A. japonicus intermoult period of < 5 days in nauplius, zoea and mysis stages (Soejima, 1926).

Ikematsu (1953) noted that of the 22 A japonicusmeasured 50% moulted

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Ikematsu (1953) noted that, of the 22 A. japonicusmeasured, 50% moulted within 3 days of capture and 94% within 7 days.

Longevity

longevity of Acetes, as in other crustaceans, is difficult to estimate accuratelybecause of the obvious difficulties in ageing these animals, and hence estimates areavailable for both natural and laboratory populations.available for both natural and laboratory populations.

Ikematsu (1953) estimated from fields samples that life span of A. japonicus is 9‐10months for the winter generation and 2.5‐3.0 months for the summer generation.

Acetes longevity is less than that of penaieds.

Yoshida (1949) suggested that A chinensis has a lipe span of about one year inYoshida (1949) suggested that A. chinensis has a lipe span of about one year inwestern Korea.

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Findings

‐ Some problems and approach that needs to tackle in the study of Acetes

f h li l b di d (l k f b i bi l i l d ) anatomy of acetes has little been studied (lack of basic biological data)

extensive data on spatiotemporal distribution of acetes (but no reliable extensive data on spatiotemporal distribution of acetes (but no reliable estimates of age are available)

no studies have been made on the age structures of acetes populations.

despite good documentation of swarming little is known about the causes of this behaviour in acetes.

fisheries for acetes is largely unknown for the western world

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Morphological Guide in Identifying Acetes

Diagram of a male Acetes:Am.‐ appendix masculina; antfl. – antennal flagellum; antrpd. – antennular peduncle;antsc. ‐ antennal scale; ch. ‐ chela; crn. ‐ cornea; end. ‐ endopod; eyst. ‐ eyestalk; exp. ‐exopod; gc. ‐ genital coxa; hs. ‐ hepatic spine; lf. –l ower flagellum;mxpd. ‐maxillipied; pt. ‐p g g p p g p p pprocurved tooth; r. ‐ rostrum; uf. ‐ upper flagellum; rps. ‐ red pigment spot on uropod areindicated by dark dots.

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Characteristics used for identification of adult Acetes

1 Body length in mm

CharacterNumber Description

y g2 Number of denticles on the rostrum behind the terminal point3  Ratio of cornea width to length of cornea and eye stalk, X:1004 Ratio of length of second to first segment of antennular penduncle, X:1005 R ti f thi d t fi t t f t l d l X 1005 Ratio of third to first segment  of antennular penduncle, X:1006* Number of clasping spines on lower antennular flagellum7 Number of segments of lower antennular flagellum8 Details of basis of third pereiopod : 0.‐projection absent; 1.‐projection present on distal  inner p p p j ; p j p

margin; 2.‐projection present on distal inner margin a little before end9 Details of coxa of third periopod: 0.‐tooth rudimentary or absent; 1.‐tooth present on  distal inner 

margin10 Details of third thoracic sternite 0 protuberances rudimentary or absent 1 a pair of conspicuous10 Details of third thoracic sternite: 0.‐protuberances rudimentary or absent; 1.‐a pair of conspicuous 

proturberances present11* Anterior margin of genital coxa: 1.‐round; 2.‐pointed12* Details of petasma: 0.‐pars astringers absent; 1.‐ pars astringers presentp p g p g p13 Procurved tooth between first pleopod: 0.‐absent; 1.‐present14 Ratio of length of telson to exopod of uropod, X:10015 Details of apex of telson: 1.‐round; 2.‐truncate; 3.‐triangular16 Ratio of length of non ciliated part of outer margin of exopod of uropod to entire margin (non16 Ratio of length of non‐ciliated part of outer margin of exopod of uropod to entire margin (non 

ciliated part plus ciliated part), X:100* ‐ characters seen in male only

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Acetes japonicus

Descriptive remarks: In male individual, lower antennular flagellum bears 2clsping spines with 10‐12 segments. In the petasma, the distal part of thep g p g p , pcapitulum is expanded like a bulb and has numerous hooks. The appendixmasculine has 2 hooks. The third thoracic sternite is produced backwards orposteriorly in females. The endopods of the uropod has one red spot on the

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proximal part in both females and males. The tip of the telson is broadly rounded.Amin et. Al., (2011). Update on the Species Composition and Distribution of Sergestid Shrimps (Acetes spp.) in Malaysian Waters

Acetes intermedius

Descritive remarks: In the males lower antenular flagellum is 13 or 14 with 1 clasping spine.The petasma pars astringens and capitulum of petasma with 4 subsequently large hooksalong outer margin The coxa of the third periopod lacks a tooth on the distal inner marginalong outer margin. The coxa of the third periopod lacks a tooth on the distal inner margin.Appendix masculine hold 3 hooks. In females, first segment of antennular penduncle at mostas long as second and third segments combined. The lower antennular flagellum is 12‐15segmented There is a small procurved tooth between the bases of the first period in both

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segmented. There is a small procurved tooth between the bases of the first period in bothfemales and males. The apex of telson in male is sharply pointed and triangular

Amin et. Al., (2011). Update on the Species Composition and Distribution of Sergestid Shrimps (Acetes spp.) in Malaysian Waters

lower examples of the antennularflagellumof a male

petasma

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Thank YouThank You……..

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