Culture of Brachionus calyciflorus as fish food organisms: an approach to improve larval survival of freshwater fish.

Abstract

Live food organisms move in the water column and serve as a source of all the nutrients such as essentialproteins, lipids, carbohydrates, vitamins, minerals, amino acids and fatty acids for larval stages of fish. Hence, they arecommonly known as “living capsules of nutrition”. Most of the fish and shellfish larvae in nature feed on these smallphytoplanktonic and zooplanktonic organisms. Zooplankton is required as the first food for much-cultured fish; for others, itcontributes to faster growth and higher survival. Among zooplankton, rotifers (Phylum: Rotifera) popularly called as wheelanimalcules forms an important group of live food organisms for use in aqua hatcheries. Rotifera includes three classes, theMonogononta, the Bdelloidea, and the marine Seisonidea. Most of the rotifer species vary between 200 to 500 micrometers insize, and are primarily omnivorous, but few species have been known to be cannibalistic. The diet of rotifers is decomposed ordead organic materials, unicellular algae and other phytoplankton. Such feeding habits make rotifers primary consumers.Rotifers in turn act as prey to carnivorous secondary consumers, including shrimp and crabs. Though rotifers are representedby about 2,500 species, the monogonont genus Brachionus is the most known form of all rotifers, and widely distributed inmarine and freshwaters worldwide. They serve as an ideal starter diet for early larval stages of many fish and prawn species inmarine as well as in freshwater, due to its smaller size as compared to Cladocerans. Among Brachionus, B. calyciflorus is themost commonly cultured freshwater rotifer for both freshwater and marine water fish species and shrimps, because of itsnumerous characteristics like small size, slow mobility and easy catchability. Moreover, B. calyciflorus has been found toconserve energy when food is scarce by decreasing its respiration rate, while other species of rotifers show no change in therespiration rate. Generally in laboratory their culture is maintained on algal concentrate with sufficient light, aeration at pHranged between 6-8 and temperature at 25oC. However, there is need to conduct in-depth study to standardize the abioticconditions like light, pH, and hardness for mass-scale production of rotifer to meet the nutritional requirements of young larvaeof fishes that encounter huge mortality during their larval stages. Successful mass scale production of rotifers will hold thekey to higher efficiency in the seed production of important species like Clarias magur, Anabas testudeneus, etc