484625. than from PVC (54±55% of DM) or bagasse (51± 58% of DM). It is concluded that substrate type has a strong effect on periphyton productivity and composition, and on ®sh productivity. Good ®sh production was achieved without feed inputs. More research is needed to study the economic viability of periphyton-based systems in the context of Indian aquaculture.

The effect of feeding Spirulina platensis on the growth, carcass composition, organoleptic quality, digestive enzyme activity and digestibility of common carp, Cyprinus carpio L., was studied through a culture trial lasting 120 days. Four experimental diets were employed by replacing fish meal protein from the standard diet at 25%, 50%, 75% and 100% through the incorporation of Spirulina. Another diet with Spirulina as the sole source of protein was also used. The final weight gain, specific growth rate, food conversion ratio and protein efficiency ratio of common carp were not affected by Spirulina supplementation. However, the diet with Spirulina as the sole source of protein resulted in better net protein retention. The muscle RNA:DNA ratio of fish fed Spirulina diets was higher than that of fish fed control diet. There was no significant difference in carcass moisture and protein content in the fish fed Spirulina diets as compared to fish‐meal‐based control diet. The carcass ash and fat contents were positively and negatively correlated with dietary Spirulina level, respectively. Organoleptic evaluation revealed no effect of Spirulina feeding on the quality of both raw and cooked fish. The gut digestive enzyme activity did not show any definite trend with respect to Spirulina supplementation. Spirulina improved the protein digestibility of the diets.

The effect of feeding Spirulina platensis on the growth, carcass composition, organoleptic quality, digestive enzyme activity and digestibility of common carp, Cyprinus carpio L., was studied through a culture trial lasting 120 days. Four experimental diets were employed by replacing fish meal protein from the standard diet at 25%, 50%, 75% and 100% through the incorporation of Spirulina. Another diet with Spirulina as the sole source of protein was also used. The final weight gain, specific growth rate, food conversion ratio and protein efficiency ratio of common carp were not affected by Spirulina supplementation. However, the diet with Spirulina as the sole source of protein resulted in better net protein retention. The muscle RNA:DNA ratio of fish fed Spirulina diets was higher than that of fish fed control diet. There was no significant difference in carcass moisture and protein content in the fish fed Spirulina diets as compared to fish-meal-based control diet. The carcass ash and fat contents were positively and negatively correlated with dietary Spirulina level, respectively. Organoleptic evaluation revealed no effect of Spirulina feeding on the quality of both raw and cooked fish. The gut digestive enzyme activity did not show any definite trend with respect to Spirulina supplementation. Spirulina improved the protein digestibility of the diets.

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