SLUDGE-GROWN ALGAE FOR CULTURING AQUATIC ORGANISMS .2. SLUDGE-GROWN ALGAE AS FEEDS FOR AQUATIC ORGANISMS

This project investigated the feasibility of using sewage sludge to cu lture microalgae (Chlorella-HKBU) and their subsequent usage as feeds for rearing different organisms. Pari II of the project evaluated the results of applying the sludge-grown algae to feed Oreochromis mossamb icus (fish), Macrobrachium hainenese (shrimp), and Moina macrocopa (cl adocera). In general, the yields of the cultivated organisms were unsa tisfactory when they were fed the sludge-grown algae directly. The bod y weights of O. mossambicus and M, macrocopa dropped 21% and 37%, resp ectively, although there was a slight increase (4.4%) in M. hainenese. However, when feeding the algal-fed cladocerans to fish and shrimp, t he body weights of the fish and shrimp were increased 7% and 11% accor dingly. Protein contents of the cultivated organisms were comparable t o the control diet, although they contained a rather high amount of he avy metals. When comparing absolute heavy metal contents in the cultiv ated organisms, the following order was observed: alga > cladocera > s hrimp, fish > sludge extracts. Bioelimination of heavy metals may acco unt for the decreasing heavy metal concentrations in higher trophic or ganisms.