Cobia, Rachycentron canadum has emerged as a global species

for aquaculture in the recent past. Eventhough seed production

of cobia is being practiced at many tropical countries, there is

very little information on the embryonic development of the

species. The details of fertilized eggs, cleavage, embryonic

phases and newly hatched larva are documented with

photographs. The experiments were carried out at a temperature

range of 28.5-30°C. The average diameter of the freshly

spawned eggs ranged from 1.1 to 1.2 mm. The time of different

stages of development after fertilization is provided. The larva

hatched out after 22 hours of fertilization. The total length of

the larvae ranged from 2.2 to 2.7 mm. The newly hatched larva

was without mouth opening and with a prominent oil globule.

The description given in the paper can be made use of in the

larval production of cobia in hatcheries

Gopakumar, G

Kalidas, C

Maharshi, V Ashok

Nazar, A K A

Ramamoorthy, N

Rao, K Srinivasa

Sakthivel, M

Tamilmani, G

CMFRI Digital Repository

J. Mar. Biol. Ass. India, 54 (2), 29-32,  July-December 2012Embryonic development of cobia, Rachycentron canadum  (Linnaeus,1766) in controlled conditionsOriginal ArticleM. Sakthivel, A. K . Abdul Nazar,  G. Tamilmani, C. Kalidas, N. Ramamoorthy, V. Ashok Maharshi, K. Srinivasa Rao and G. Gopakumar*Mandapam Regional Centre of Central Marine Fisheries Research Institute, Marine Fisheries post, Mandapam, Tamil Nadu, India-623520.*Correspondence e-mail: drggopakumar@gmail.comReceived: 31 May 2011, Accepted: 25 July 2012, Published: 8 Oct 2012AbstractCobia, Rachycentron canadum has emerged as a global species for aquaculture in the recent past. Eventhough seed production of cobia is being practiced at many tropical countries, there is very little information on the embryonic development of the species. The details of fertilized eggs, cleavage, embryonic phases and newly hatched larva are documented with photographs. The experiments were carried out at a temperature range of 28.5-30°C. The average diameter of the freshly spawned eggs ranged from 1.1 to 1.2 mm. The time of different stages of development after fertilization is provided. The larva hatched out after 22 hours of fertilization. The total length of the larvae ranged from 2.2 to 2.7 mm. The newly hatched larva was without mouth opening and with a prominent oil globule. The description given in the paper can be made use of in the larval production of cobia in hatcheries.Keywords: Cobia, Rachycentron canadum, embryonic development, newly hatched larva.Available online at: www.mbai.org.in doi: 10.6024/jmbai.2012.54.2.01685-05IntroductionCobia aquaculture has been expanding in many tropical countries during the recent past mainly due to its fast growth rates and good meat quality. The success of cobia farming in Taiwan (Yeh, 2000; Su et al., 2000; Liao and Leano, 2005) has led to the rapid expansion of cobia farming throughout Southeast Asia, the Americas and Carribian regions (Benetti and Orhun, 2002; Kaiser and Holt, 2004; Schawrz et al., 2006,2007; Benetti et al., 2008; Nhu et al., 2010;2011). Realising the potential of cobia farming in India, the Central Marine Fisheries Research Institute (CMFRI) focused research attention on the broodstock development of cobia and the ﬁrst successful spawning was obtained in March 2010 (Gopakumar et al., 2011). Literature on the embryonic development of cobia is rather scanty and hence a stage by stage description of the same along with photographs is presented in the paper.Material and methodsInduced spawning was carried out in the selected broodstock ﬁshes of cobia which were reared in sea cages at Mandapam, Tamil Nadu, India. The female showing intra-ovarian egg diameter of 700μ size with a migratory nucleolus stage were selected and administered with human chorionic gonadotropin (hCG – FERTIGYN, Unimed Technologies Ltd., Gujarat, India) Journal of the Marine Biological Association of India Vol. 54, No.2, Jul-Dec 2012M. Sakthivel et.al.30for induced spawning experiments at a dosage of 500 IU per kg body weight and at the rate of 250 IU per kg body weight for male. Human chorionic gonadotropin (hCG) was used for induction because it acts much faster, via direct stimulation of the gonad, in inducing FOM, spermiation and spawning.  The spawning occurred at 39 hours after hormonal induction. The ﬂoating eggs were collected using 500 μ mesh and introduced in the incubation tanks of 5 tonne capacity each. The water temperature recorded in the incubation tank ranged from 27 - 29°C, pH: 8.2, and salinity 32-35 ppt. The fertilized eggs were regularly examined under the microscope for recording all the embryonic developmental stages. The microphotographs were taken using a trinocular microscope attached with a digital camera.Results and discussionThe developmental stages of the embryo are presented in Fig. 1a–1p. The time of different embryonic stages after fertilization is given in Table 1. Fertilized eggEggs were perfectly spherical, translucent, buoyant and non-adhesive. The diameter ranged from1.0 to 1.1 mm. Each egg had one conspicuous oil globule (Fig. 1a).CleavageThe ﬁrst cleavage began at approximate 20 minutes after fertilization which resulted in two cells / blastomeres of equal size (Fig. 1b). The second cleavage was observed at about Fig.1: Embryonic developmental stages of cobiaa b c de f g hi j k lm n o p© Marine Biological Association of IndiaEmbryonic development of cobia in controlled conditions31Table 1  Time of different embryonic stages after fertilization in cobiaFig.No.1 Stage of development Time after fertilizationa. Fertilized egg 0:00 hb. 2-cell stage 0:20 hc. 4-cell stage 0:40 hd. 8-cell stage 1:00 he. 16-cell stage 1:20 hf. 32-cell stage 1:40 hg. 64-cell stage (Morula) 2:30 hh. Blastula 3:15 hi. High-dome (high mound of cells before gastrulation)4:30 hj. Early gastrula 7:00 hk. Late gastrula 13:00 hl. Bud 16:00 hm. Segmentation 18:00 hn. High-pec (dechorionated embryo) 20:00 ho. Hatching 21:00 hp. Newly hatched larva 22:00 hTable 2: Timing and temperature of hatching in other marine fishesSpecies of fish Time until hatching (h) Hatching temperature ReferenceHalichoeres poecilopterus 19 23.4 °C Kimura and Kiriyama, 1993Dentex gibbosus 35 20.0 °C Palacios et al., 1994Epinephelus marginatus 30 23.0 °C Glamuzina et al., 1998Epinephelus costae 24 25.5 °C Glamuzina et al., 2000Sparus aurata 53 18.5 °C Kamaci et al., 2005Gadus morhua 330 6.5 °C Avery et al., 2009Liza ramada 48 21.0 °C Mousa, 2010Labrus viridis 127 14.5 °C Kozul et al., 2011Rachycentron canadum 22 28.0 °C Present study40 minutes after fertilization resulting in 4 cell stage (Fig. 1c). Subsequent cleavage occurred approximately after one hour which resulted in 8 cells (Fig. 1d). The 16-cell and 32 cell stages were observed at 1 hour 20 minutes and 1hour 40 minutes, respectively (Fig. 1e and f). The ﬁrst 4 cleavages were synchronous resulting in the formation of 16 cells. At 5th cleavage, the ﬁrst horizontal orientation of cleavage plane occurred and resulted in 2 tiers of cells (Fig. 1f). Cleavages after 32 cell stage were meta-synchronous resulted in a multi-tiered mount of cells and resulted in morula stage at about 2 hours 30 minutes after fertilization (Fig. 1g). The blastula stage reached after 3 hours 15 minutes after fertilization (Fig. 1h). GastrulaGastrulation started with a high dome of blastoderm cells sitting on top of the yolk sphere (Fig. 1i). The high blastula stage was observed at 4 hours 30 minutes after fertilization. The blastoderm thins as it moves down the yolk until the eggs looks spherical (Fig. 1j). The gastrulation movements started 7 hours after fertilization and it continued up to 13 hours to reach late gastrula stage and the embryonic area was well marked (Fig. 1k).Embryonic body formationOrganogenesis of the embryo became clearly distinguishable at about 16 hours after fertilization with the appearance of head and tail buds. The brain region began to form anteriorly while the tail bud at the posterior end.  The pigmentation on the embryonic body was prominent at this stage (Fig. 1l). The cephalic vesicle, optic vesicles and eye rudiment could be identiﬁed at about 18 hours after fertilization (Fig. 1m).  At about 20 hours after fertilization embryo started detaching from the chorion (Fig. 1n) and the hatching process started at 21 hours after fertilization (Fig. 1o).   Newly hatched larvaeAt about 22 hours after fertilization, the larvae hatched out. The newly hatched larvae measured 2.2-2.7 mm TL (Fig. 1p). Larvae had large oval shaped yolk with an oil droplet at the posterior end. The mouth opening was not yet formed. The present description of embryonic development of cobia is similar to those described for labrid ﬁsh, Halichoeres poecilopterus (Kimura and Kiriyama, 1993), Dentex gibbosus, (Palacios et al., 1994), dusky grouper, Epinephelus marginatus (Glamuzina et al., 1998), goldblotch grouper, Epinephelus costae (Glamuzina et al., 2000), gilthead sea bream, Sparus Journal of the Marine Biological Association of India Vol. 54, No.2, Jul-Dec 2012M. Sakthivel et.al.32aurata (Kamaci et al., 2005), Atlantic cod, Gadus morhua (Avery et al., 2009), thin lipped grey mullet, Liza ramada (Mousa, 2010) and green wrasse, Labrus viridis (Kozul et al., 2011). The timing and temperature of hatching in other marine ﬁshes are given in Table 2. However, variations in time of different developmental stages after fertilization were noted. This may be due to the difference in the incubation temperatures. The detailed description of embryonic development of cobia in this communication will be of applied value in cobia hatcheries due to its aquaculture importance. AcknowledgementsThe authors thank Dr. G. Syda Rao, Director, Central Marine Fisheries Research Institute (CMFRI), for his constant support and encouragement rendered throughout this study.References Avery, T.S., S.S. Killen and T.R. Hollinger. 2009.  The relationship of embryonic development, mortality, hatching success, and larval quality to normal or abnormal early embryonic cleavage in Atlantic cod, Gadus morhua.  Aquaculture., 289: 265-273. Benetti, D.D. and M.R. Orhun.  2002.  Aquaculture of pelagic fish: IV.  Cobia (Rachycentron canadum). Global Aquacult. Alliance Advocate., 5: 61-62. Benetti, D.D., M.R. Orhun, B. Sardenberg, B.O. Hanlon, A. Welch, R. Hoenig, I. Zink, J.A. Rivera, B. Denlinger, D. Bacoat, K. Palmer and F. Cavalin.  2008.  Advances in hatchery and grow-out technology of cobia Rachycentron canadum (Linnaeus).  Aquacult.Res., 39: 701-711.  Glamuzina, B., B. Skaramuca, N. Glavic, V. Kozul, J. Dulcic and M. Kraljevic. 1998.  Egg and early larval development of laboratory reared dusky grouper, Epinephelus marginatus (Lowe, 1834) (Pisces, Serranidae).  Sci. Mar., 62(4): 373-378.  Glamuzina, B., N. Glavic, P. Tutman, V. Kozul and B. Skaramuca.  2000. Egg and early larval development of laboratory reared goldblotch grouper, Epinephelus costae (Steindachner, 1878) (Pisces, Serranidae).  Sci. Mar., 64(3): 341-345.  Gopakumar, G., A. K. Abdul Nazar,  G. Tamilmani,  M. Sakthivel, C, Kalidas,  N, Ramamoorthy, S. Palanichamy,  V. Ashok Maharshi, K. SrinivasaRao,  and  G. Syda Rao, 2011. Broodstock Development and Controlled Breeding of Cobia Rachycentron canadum Linnaeus 1766) from Indian Seas. Indian J. Fish. 58(4): 27-32.Kaiser, J.B. and G.J. Holt. 2004. Cobia: A new species for aquaculture in the US. World Aquacult., 35: 12-14. Kamaci, H.O., S. Saka and K. Firat.  2005.  The cleavage and embryonic phase of Gilthead Sea Bream (Sparus aurata Linnaeus, 1758) eggs. E.U. J. Fish. Aquat. Sci., 22(1-2): 205-209.  Kimura, S. and T. Kiriyama. 1993.  Development of eggs, larvae and juveniles of the Labrid fish, Halichoeres poecilopterus, reared in the laboratory. Jap. J. Ichthyol., 39(4): 371-377. Kozul, V., N. Glavic, P. Tutman, J. Bolotin and V. Onofri. 2011.  The spawning, embryonic and early larval development of the green wrasse, Labrus viridis (Linnaeus, 1758) (Labridae) in controlled conditions.  Anim.  Reprod. Sci., 125: 196-203.  Liao, I.C. and E.M. Leano. 2005.  Cobia aquaculture in Taiwan. World Aquacult., 36: 31-36.Mousa, M.A.  2010. Induced spawning and embryonic development of Liza ramada reared in freshwater ponds. Anim. Reprod. Sci., 119: 115-122.  Nhu, V.C., Nguyen, H.Q., Le, T.L., Tran, M.T., Sorgeloos, P., Dierckens, K., Reinertsen, H, Kjorsvik, E and Svennevig, N. 2011. Cobia Rachycentron canadum aquaculture in Vietnam: Recent developments and prospects. Aquaculture. 315: 20-25.Palacious, H.F., D. Montero, J. Socorro, M.S. Izquierdo and J.M. Vergara. 1994. First studies on spawning, embryonic and larval development of Dentex gibbosus (Rafinesque, 1810) (Osteichthyes, Sparidae) under controlled conditions.  Aquaculture, 122: 63-73. Schwarz, M.H., Craig, S. and McLean, E. 2006. Cobia Update: Fast- growing species first focus of international aquaculture initiative. Global Aquacult. Alliance Advocate, 9: 50-52.Schwarz, M.H., McLean, E. and Craig, S.R. 2007. Research experience with cobia: Larval rearing, Juvenile nutrition and General physiology. In: I.C. Liao and E.M.Leano, (Eds.), Cobia Aquaculture: Research, Development, and Commercial Production. Asian Fisheries Society, Manilla, Philippines, World Aquaculture Society, Louisiana, USA, The Fisheries Society of Taiwan, Keelung, Taiwan, and National Taiwan Ocean University, Keelung, Taiwan, p. 1-17.Su, M.S., Y.H. Chen and I.C. Liao. 2000.  Potential of marine cage aquaculture in Taiwan: Cobia culture. In: I.C. Liao and C.K. Lin (Eds.) Cage Aquaculture in Asia, Asian Fisheries Society, Manila, and World Aquaculture Society, Southeast Asian Chapter, Bangkok, p. 97-106.  Yeh, S.P. 2000. Cobia culture in Taiwan (Rachycentron canadum).Global  Aquacult. Alliance Advocate, 3: 67-68.

Embryonic development of cobia,

Rachycentron canadum (Linnaeus,1766) in

controlled conditions

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Embryonic development of cobia, Rachycentron canadum (Linnaeus,1766) in controlled conditions

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