A comparative laboratory trial on the effect of Sargassum wightii incorporated formulated feed on growth performance and immunity development of Asian sea bass Lates calcarifer (Bloch 1790): can it be an alternative to commercial feed?

Asian sea bass (Lates calcarifer) is a high valued seafood throughout the world. Bacterial infections can cause huge losses in Asian sea bass culture and among them Aeromonas hydrophila is ubiquitous. Inclusion of bioactive compounds present in seaweeds into fish diets can enhance the fish growth and immunity combating the bacterial diseases. This study was conducted to determine whether feeding with Sargassum wightii incorporated feed could enhance immunity of the fish to bacterial infections. A feed trial was conducted using four treatments comprising a commercial feed, two formulated feeds incorporated with 20 g/kg and 40g/kg of S. wightii in each feed and a formulated feed without seaweed as the control diet. Three replicate tanks stocked with 15 advanced fingerlings were used for the each treatment and reared 40 days under the optimum conditions. Growth parameters were tested and effect of different feeds on growth performance was evaluated. Fish survival rate and cost of formulated feed were calculated. At the end of feed trial, nine fishes from each treatment were artificially challenged with 1.50 ppm dose of A. hydrophila and observed for 7 days. There was a significant difference in weight gain in commercial feed compared to other three treatments (P0.05). The challenge with A. hydrophila showed 11.1% disease prevalence in L. calcarifer fed with 20g/kg of seaweed incorporated feed. Highest disease prevalence of 100% was recorded in fish that had been fed with the seaweed free formulation. The highest level of immunity enhancement was reported using the feed that contained 20g/kg seaweed. Production cost of formulated feed was lower than the commercial feed.