Fish culture waste improves growth and fatty acid composition of the polychaete Namalycastis sp. (Nereididae) and its potential use as feed for mud crabs.

Abstract

The potential use of polychaetes as feed for mud crabs and to bioremediate highly underexploited nutrient-rich aquaculture waste was evaluated in this study. Food preference of mud crabs (Scylla olivacea) given two polychaete species, namely Namalycastis sp. (Nereididae) and Eunice reticulata was first determined prior to elucidating the growth, survivorship and fatty acid composition of the selected polychaetes cultivated using fish culture waste (FCW). The effect of water temperature on the sexual maturation of selected polychaetes was also evaluated. Mud crabs fed on both polychaete species but a preference for Namalycastis was observed. Namalycastis fed FCW experienced lower survivorship (16.7–58.3%) than those in control treatments of either fish feed or no feed (41.7–100%), although statistically there were no significant differences between treatments for all three experiments. This could probably be due to mortality of FCW-grown Namalycastis after spawning. FCW-grown Namalycastis had significantly higher (p < .05) wet length than unfed polychaetes. Sexual maturation in Namalycastis was not affected by lowering ambient temperature from 28°C to 26°C. Compositions of arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid were higher in FCW-grown Namalycastis than unfed Namalycastis. Overall, Namalycastis can be cultured in captivity using FCW but further research is required to mass produce the polychaetes economically and sustainably.