Replacement of live-food with refrigerated-plankton food for Cyprinus carpio (L.) larvae cultured with three different types of biological filters

Common carp, Cyprinus carpio (L,) larvae were cultured with either live-foo d or refrigerated-plankton food in the recirculating system. Three types of biological filters: (i) pebbles, foam and weed (Lemna major) filter system (PFWS), (ii) pebbles and foam filter system (PFS), and (iii) only weed (Le mna major) filter system (WS) were used for each feeding scheme. After 40 d ays of culture, a significantly higher (P < 0.01) rate of survival was obta ined with the lire-food system (LFS) than the refrigerated-plankton food sy stem (RPFS) regardless of filtration type. The final average weight was inf luenced by both filtration unit and food. Significantly higher (P < 0.05) v alues for average weight (130 +/- 1.5 mg), specific growth rate (4.69 +/- 0 .01), and RNA/DNA ratio (5.60 +/- 0.13) were obtained in the PFWS of live-f ood treatment. Food was more efficiently utilized in the LFS as indicated b y the significantly lower (P < 0.05) values of food conversion ratio (0.93 to 1.60) compared to the RPFS (3.87 to 4,91), Amylase (0.09-0.162 mg maltos e/mg protein/h) and proteolytic enzyme (2,52-4,70 mg tyrosine/mg protein/h) activities were significantly higher in the LFS than the RPFS. Significant ly higher values for ammonia (0.014 +/- 0.031 mg/l), phosphate (0.150-0.157 mg/l) and COD (197-207 mg/l) were? observed in the PFS than for the other two filter systems. Results indicate that use of Lemna major alone or in co njugation with pebbles and foam helped in the maintenance of improved water quality in the culture system which resulted in the better performance of carp larvae.