Salinity effects on the development of embryos and larvae of a high-valued sea urchin, Tripneustes gratilla (Linnaeus, 1758)

Abstract

Aim: To investigate the standard salinity levels on the embryonic and larval development thatwill be helpful for the optimum growth and larval development in the seed production of Tripneustes gratilla for aquaculture and conservation. Methodology: Gametes were collected by injecting 0.5 M KCl into coelomic cavity of the adult sea urchin, T gratilla and insemination was done using 10'5'dry'sperm dilution from where around 500 fertilized eggs were transferred into eight transparent plastic tubes containing 50 ml artificial seawater each with different salinities (19%o, 22%o, 25°% 28%o, 31%o, 34%o, 37°% and 40°%). To set up this experiment, 31%o salinity was considered as a control treatment containing normal sea water. Hatching rate with required time at each salinity level were studied. Each treatment of this experiment was conducted with three replications at 26.0 ± 1.0°C. All the developmental stages of embryos and larvae were observed at time intervals after insemination until attaining the metamorphic competent stage, and the duration of different development stageswas also estimated. Results: Fertilization rate was highest at 28%, followed by those obtained at 28%, 34%, 25%, 37%, 22%, and 40%, while the lowest rate was achieved at 19% salinity level, decreased with increasing and decreasing salinities (p < 0.05). The development times of 16-cell and morula stages were significantly different at 31% and 28% salinity than those at 34% and 37% salinity, whereas, in blastula, there was no significant difference (p > 0.05) among 31%, 28% and 34%. The developmental times in the early prism, 2arm and 4-arm pluteus stages showed significant differences at the salinity levels of 31% and 37%. There were no significant differences (p > 0.05) recognized on the length and width of prism larva in these salinity levels at all. However, the differences were found to be significant (p < 0.05) in all the morphological characteristics of the 2and 4-armed pluteus larvae of T gratilla. Interpretation: To date, this is the first effort to study the influence of salinity on embryonic and larval morphometric development, and survival and growth in tropical sea urchin, T gratilla in Malaysia. The results obtained from this study would be helpful towards the development of induced breeding, larval rearing and seed production of this high-valued sea urchins for commercial aquaculture and biodiversity conservation.