Water quality, biofilm production and growth of fringe-lipped carp (Labeo fimbriatus) in tanks provided with two solid substrates.

The effects of two substrates, sugarcane bagasse (T(1)) and paddy straw (T(2)) on water quality and growth of Labeo fimbriatus were studied in mud-bottomed, manured cement tanks, in triplicate; a set of three tanks without substrate served as control (T(3)). Addition of manure and substrate brought about a decrease in dissolved oxygen level, but it stabilized after 15 days, when the tanks were stocked with 30 fish each, fed at 3% body weight daily and reared for 90 days. Total ammonia content in substrate based treatments was relatively lower than in the control. Significantly higher nitrite-nitrogen was recorded in the control tanks. The total plate counts (TPC) of bacteria in water did not differ significantly between treatments and control. The overall mean value of TPC with substrate was higher in T(2) than in T(1). The mean phytoplankton density in water was the highest in T(1), followed by T(3) and T(2), whereas zooplankton density was the highest in T(1) followed by T(2) and T(3). The growth of fish was significantly (P<0.05) higher in substrate-based tanks, the percentage increases over control being 30.44 (T(1)) and 28.71 (T(2)) respectively. Higher RNA, DNA and RNA:DNA ratios were recorded under T(1), followed by T(2) and T(3). Higher enzyme activity was observed in fish from substrate treatments, which was attributable to the additional nutrients derived through the biofilm. The results demonstrated that production of L. fimbriatus can be significantly increased by the introduction of biodegradable substrates into culture systems where fertilization and feeding are employed.

Growth performance of two Indian major carps, catla (Catla catla) and rohu (Labeo rohita) fed diets containing different levels of Spirulina platensis.

The influence of Spirulina platensis meal on the growth and carcass composition of two Indian major carps, catla, Catla catla and rohu, Labeo rohita was investigated in a 90-day culture trial. Four experimental diets were used and Spirulina replaced fish meal protein from the standard diet at 25%, 50%, 75% and 100% levels. There was no significant difference in the final weight attained by catla at all levels of Spirulina incorporation as compared to the fish-meal-based control diet. However, the replacement of fish meal by more than 25% Spirulina resulted in significantly superior growth of rohu. The specific growth rate and protein efficiency ratio recorded in rohu improved with higher levels of Spirulina inclusion, while in catla they did not differ significantly from the control treatment. In both the species, the digestibility of dry matter, protein and fat was found to improve marginally with increasing levels of Spirulina incorporation. The carcass composition showed an inverse relationship between protein and fat deposition. In general, fish fed with Spirulina diets had a significantly higher percentage of fat. The study demonstrated the usefulness of Spirulina for partial or complete replacement of fish meal in the diets of catla and rohu.