Induced Spawning Using Temperature Stimulation Technique and The Embryonic Development of Razor Clam (Solen regularis) in Sarawak.

Nur Aina Syuhaida, Rusli (2020) Induced Spawning Using Temperature Stimulation Technique and The Embryonic Development of Razor Clam (Solen regularis) in Sarawak. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Razor clam is a highly prized marine bivalve that locally known as ‘ambal’ in Sarawak. There are three different species of razor clams that are commercially important and being collected in Sarawak namely Solen lamarckii (Ambal Jernang), S. regularis (Ambal Biasa) and S. sarawakensis (Ambal Riong). In order to maintain the population of razor clam in natural bed or to carry out the re-seeding activity, the information on induced spawning technique and early development of razor clams must be determined. Knowledge on embryonic development of S. regularis is important in order to obtain its planktonic and benthic larvae characteristic for future identification prior to establishing mass culture in hatcheries. This pioneer study provides some information on induce spawning technique and embryonic development stage of S. regularis. The main objectives of this study were (i) to determine induce spawning techniques of razor clams using thermal manipulation and (ii) to record the embryonic development of S. regularis in laboratory condition. In this study, sources of razor clams S. regularis were collected during their spawning season from mudflat and intertidal areas of Asajaya Laut (N 01° 36’’ E 110° 36’) and Buntal (N 01º 42’ E 110º 22’), Sarawak. The razor clams were obtained only at daytime during low tide of spring tides in March 2015 to early August 2015 and March 2016 to August 2016 with the help of local people. Induced spawning attempts were conducted in two phase, (i) Phase 1: March and April 2015 and (ii) Phase 2: May to August 2015 and March to August 2016. Dry chilling of specimens for 2 to 5 hours at 4 to 6 °C and followed by thermal shocking at temperature between 28 to 32 °C were able to provide sufficient stress toward the razor clams to release their gametes. After spawning induction trials, gametes were used in artificial fertilisation process. Larvae were reared in culture tank containing 20 L of filtered seawater at controlled temperature (25 ± 1 °C) and salinity (31 ± 1 PSU) respectively. The embryos were observed continuously for the first 24 hours. Results showed that temperature used to induce spawning of razor clams influenced the mean success rate of spawning and response time taken for the clams to release gametes. The mean success rate of induced spawning in year 2015 and 2016 showed the same trend. The highest mean success rate of spawning (83 ± 12.58%) and the largest mean of unfertilised eggs diameter (46.06 ± 9.33 µm) were recorded in May which is the peak of razor clam spawning season in natural habitat. In this study, the female clams released eggs in intermittent burst and the eggs descend to the bottom of beakers, meanwhile the male clams released sperms in thread like motion which make the water turned cloudy. It was observed that the unfertilised eggs of S. regularis had a thick vitelline membrane and no prominent jelly coat. The embryonic development started when the first polar body appeared between 15 to 30 minutes after fertilisation. A 2-cell stage completely formed within one hour post fertilisation (hpf) and followed by 4-cell stage that appeared 2 hpf. The morula started to develop at 4 to 6 hpf. Later on, blastula formation occurred at 7 to 8 hpf and this blastula started to rotate slowly because it was the first motile stage in S. regularis development. After 10 to 16 hpf, gastrula began to form with typical rotary movement and the vitelline membrane started to fade and soon disappeared. The outcomes of this study had provided scientific knowledge on induced spawning technique for S. regularis and documentation on its embryonic development that can aid in establishment of larval rearing technique in future. Keywords: Solen regularis, induced spawning techniques, thermal manipulation, embryonic development.

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