Note Embryonic development of the spiny eel, Mastacembelus aculeatus (Bloch, 1786)

Transcription

1 Indian J. Fish., 54(3) : , Note Embryonic development of the spiny eel, Mastacembelus aculeatus (Bloch, 1786) S. K. SAHOO, S. S. GIRI, A. SAHA, S. CHANDRA, A. K. SAHU AND N. SARANGI Central Institute of Freshwater Aquaculture, Kausalyaganga Bhubaneswar , Orissa, India ABSTRACT Induced spawning of the freshwater spiny eel, Mastacembelus aculeatus was undertaken to obtain fertilized eggs for studying the embryonic development. The fertilized eggs were sticky, demersal and green in colour. The perivitelline space of fertilized eggs was unequal. Several oil globules were visible on the yolk and sizes varied from mm in diameter. First cleavage appeared at 50 min, producing two equal blastomeres. The size of blastomeres gets reduced as development proceeds. The fertilized egg took 4 h 10 min to reach morula stage. The hatching of egg started at 31 h 30 min and all the eggs hatched within h at C. The newly hatched yolksac larvae were 4-5 mm in length. Mastacembelus aculeatus, popularly known as spiny eel is regarded as one of the important species among the family Mastacembelidae. It grows to a size of 20-25cm. The mastacembelids are seen in tropical countries of Africa and Asia and is mostly collected during post-monsoon from the canals, swamps, beels, paddy fields and water bodies adjacent to paddy fields (Travers 1984 a, b). Due to the absence of intra-muscular spines, there is great market demand for this species in Asian countries. The natural population of mastacembelids is gradually declining due to over exploitation. Therefore, developing captive breeding, seed production as well as viable culture technologies would solve this problem. Studies on embryonic development of the fertilized eggs of species helps in identifying a specific stage of development during a particular time. The embryonic development for some economically important eel fishes viz. Anguilla japonica (Yamamoto et al., 1975), A. dieffenbachii (Lokman and Young, 2000), A. anguilla (Pedersen, 2004) and M. mastacembelus (Sahinoz et al., 2006) have been reported. However, studies on the embryonic development of M. aculeatus have not been reported so far and hence the present work is taken up. M. aculeatus of cm in length and g in weight were procured from the wild and transported to the hatchery. They were released in a 16m 2 (4 4m) cement tank with 2 cm soil at the bottom. The volume of water in the tank was maintained at l. Thirty numbers of brood fish were maintained acclimatized for one month prior to breeding operations. The fishes were fed once daily with pelleted feed containing 30% protein. During the spawning season (July - August), perspective brood fishes having an average weight of 23 ± 4.37 g were selected. Ovaprim (sgnrha + Domperidone) was used for induced breeding and a ratio of one female and 2 males was used. The females and males were injected ml and 0.025ml Ovaprim, respectively. The broods were released in a

2 S. K. Sahoo et al. 334 round ferro-cement tank (1.5 m dia) with 500 l of water and provided with continuous aeration. After h, the female released eggs which were collected immediately by siphoning. Around fertilized eggs were randomly collected from the spawning pool in a petriplate and embryonic development was observed under the microscope having photographic facility. The embryonic development of M. aculeatus are presented in Table 1 and Figs. (1-13). The diameter of fertilized eggs ranged from mm (mean 1.35mm ± 0.02), which were sticky and demersal in nature (Fig. 1). The perivitelline space was unequal around the yolk and the yolk was green in colour. Oil globules from mm in size were visible in the yolk. As the development proceeded, the oil globules were found to aggregate and TABLE 1: Different events during early development of Mastacembelus aculeatus Developmental stages of egg Age (h) Fertilization 0.00 Blastodisc 0.30 Two cell 0.50 Four cell 1.30 Eight cell 2.05 Sixteen cell 2.50 Thirtytwo cell 2.20 Sixtyfour cell 3.30 Morula 4.10 Blastula 6.40 Gastrula Complete embryo twitching Hatching coalesce thereby reducing their numbers. Similar presence of oil globules was reported in the fertilized egg of New Zealand freshwater eel, A. dieffenbachii (Lokman and Young, 2000) and Mesopotamian spiny eel, M. mastacembelus (Sahinoz et al., 2006). The single cell stage became clear with the accumulation of cytoplasm over the animal pole as a protrusion at 30 min representing early blastodisc or germinal disc stage (Fig. 2). Fig. 1. Fertilised egg Fig. 2. Blastodisc stage Cytoplasmic disc became thick and the first cleavage occured at right angle forming two identical blastomeres at 50 min post fertilization (Fig. 3). Four (Fig. 4) and eight-cell (Fig. 5) stages appeared at 1 h 30 min and 2 h 05 min respectively. The blastomeres were unequal in size and remained in two rows. Sixteen (Fig. 6), thirtytwo (Fig. 7) and sixtyfour (Fig. 8) cell stages appeared at 2 h 50 min, 3 h 30 min and 4 h 10 min respectively. The blastomeres at these stages were still reduced in size as compared to 2-8 cell stages. This reduction in size of blastomeres could be due to addition of more compact blastomeres which is a common feature during embryonic development in many teleosts (Thakur, 1980; Rahman et al., 2004; Gonzalez-Doncel et al., 2005). During the morula stage (6 h 40 min), the blastomeres were further reduced in size and accumulated around the animal pole, which gave a flowery appearance (Fig. 9). The central

3 Embryonic development of spiny eel, Mastacembelus aculeatus 335 Fig. 3. Two-cell stage Fig. 6. Sixteen-cell stage Fig. 4. Four-cell stage Fig. 7. Thirtytwo-cell stage Fig. 5. Eight-cell stage blastomeres were very small, compact and darker. Blastula stage was observed at 10 h 45 min. The marginal blastomeres lost their boundaries and were compressed, as the individual blastomeres were not recognized Fig. 8. Sixtyfour-cell stage properly (Fig. 10). Gastrula stage appeared at 15 h 15 min, where sheet of cells migrated from animal pole on both sides towards the vegetal pole (Fig. 11). The cell migration continued and covered 40-50% over the yolk. It appeared like a cord which was slightly broader at one end

4 S. K. Sahoo et al. 336 Fig. 9. Morula stage Fig. 11. Gastrula stage and narrow at the other end (25 h 30 min) indicating future head and tail. Body axis completely encircled the vitelline sphere with attached head and tail end over the yolk (Fig. 12). The tail appeared at h after fertilization, which was 6 h shorter as compared to A. dieffenbachii (Lokman and Young, 2000). This variability might be due to the difference in the rate of development among the species at different water temperatures. Fig. 12. Complete embryo 1.0 mm respectively, which might be responsible for difference in larval length of both the species. It was observed that each stage of development after morula stage took much more time compared to initial stages in the present study. Fig. 10. Blastula stage Twitching movement was observed at 31h and first hatching was observed at 31 h 45 min. However, the hatching time reported for other eel species ranged from h (Yamamoto and Yamauchi, 1974; Prokhorchik, 1986). The larvae measured 4-5mm (mean 4.48 ± 0.15) in length (Fig. 13). The total length of newly hatched A. anguilla larvae was reported to be 2.35 mm (Pedersen, 2004). The egg size of M. aculeatus and A. anguilla was 1.35 and Fig. 13. Hatched larva

5 Embryonic development of spiny eel, Mastacembelus aculeatus 337 Acknowledgement The authors are thankful to the Director, C.I.F.A, Kausalyaganga, Bhubaneswar for his encouragement during the study. References Gonzalez-Doncel, M., M. S. Okihiro, S. A. Villalobos, D. E. Hinton and J. V. Tarazona A quick reference guide to the normal development of Oryzias latipes (Teleostei, Adrianichthyidae). J. Appl. Ichthyol., 21: Lokman, P. M. and G. Young Induced spawning and early ontogeny of New Zealand freshwater eels (Anguilla dieffenbachii and A. australis). New Zealand J. Mar. Fresh. Res., 34: Ochi, Y., Y. Sato and Y. Yanagisawa Obligate feeding of cichlid eggs by Caecomastacembelus zebratus in lake Tanganyika. J. Fish Biol., 54: Pedersen, B. H Fertilisation of eggs, rate of embryonic development and hatching following induced maturation of the European eel, Anguilla anguilla. Aquaculture, 237: Prokhorchik, G. A Postembryonic development of European eel, Anguilla anguilla, under experimental conditions. J. Ichthyol., 26: Rahman, M. R., M. A. Rahman, M. N. Khan and M. G. Hussain Observation on the embryonic and larval development of Silurid catfish, Gulsha (Mystus cavasius Ham.). Pak. J. Biol. Sci., 7: Sahinoz, E., Z. Dogu and F. Aral Development of embryos in Mastacembelus mastacembelus (Bank & Solender, 1794) (Mesopotamian spiny eel) (Mastacembelidae). Aquacult. Res., 37: Thakur, N. K Notes on the embryonic and larval development of an air breathing catfish Clarias batrachus (Linn.). J. Inland Fish. Soc. India, 12: Travers, R. A. 1984a. A revision of the Mastacembeloidei, a sub-order of synbranchiform teleost fishes. Part I. Bul. Brasil. Nat. His. (Zool.), 46: Travers, R. A. 1984b. A review of the Mastacembeloidei, a sub-order of synbranchiform teleost fishes. Part II. Phylogenetic analysis. Bul. Brasil. Nat. His. (Zool.), 47: Yamamoto, K. and K. Yamauchi Sexual maturation of Japanese eel and production of eel larvae in the aquarium. Nature, 251; Yamamoto, K., K. Yamauchi and S. Kasuga On the development of the Japanese eel, Anguilla Japonica. Bul. Jap. Soc. Fish., 41: Date of Receipt : Date of Acceptance :