Larval rearing of orange mud crab, Scylla olivacea: improving survival rate and shortening metamorphosis period

Abstract

Orange mud crab (Scylla olivacea) is an important aquaculture species in Southeast Asian countries, especially in the Southwest costal region of Bangladesh. Due to unavailability of hatchery produced seeds the farming of S. olivacea in exclusively depends on the wild for small juveniles resulting in exploitation of this species in Bangladesh. The development of proper hatchery techniques considering better understandings related to larval development are needed to increase the survival and growth rate of S. olivacea in hatchery conditions. Therefore, this study aimed to optimize the water treatment strategy for the upgrading of water quality, minimizing mortality and shortening the metamorphosis duration during larval rearing of mud crab. Newly hatched larvae were reared in three different rearing conditions where the water was treated with both prebiotic (Super-TCT-Biotic, 5 ppm) and probiotics (Fish probiotic, 0.5 ppm) in treatment-1 (T1) but only prophylaxis (mixure of 0.025 ppm Teflan and 0.3 ppm Furazolidone) in treatment-2 (T2). In treatment-3 (T3), prebiotic (5 ppm) and probiotics (0.5 ppm) were combinedly used during first 10 days and prophylaxis (0.3 ppm) was also used from day 14 to day 25. The stocking density was maintained as 50 zoea.L^-1 and rotifer, liquid rotifer, enriched Artemia and liquid Artemia were used as feed for the larval growth. The findings revealed that hydrological parameters viz., temperature, salinity, pH, dissolved oxygen and ammonia in all the treatments were similar and found within the acceptable ranges for mud crab larvae rearing. The value of larval stage index (LSI) was found significantly higher (p<0.05) on 21^st day of rearing in T3 (6.87±0.06) than T1 (6.74±0.04) and T2 (6.61±0.07). Between, zoea1 and crablet phase, the significantly higher survival rate was observed in T3 (7.00±1.00) than T1 (5.00±0.00) and T2 (4.00±1.00). The result of the present study suggested that combined water treatment with prebiotic, probiotic and prophylaxis can shorten the metamorphosis period and enhance the survival rate of S. olivacea.