Importance of diet type, food particle size, and tank circulation for culture of Lake Hallwil whitefish larvae

A commercial dry diet and both live and frozen zooplankton were compared as food for cultured larvae of Lake Hallwil whitefish Coregonus suidteri duri ng the first 3 weeks after hatching. Whitefish larvae fed live zooplankton grew considerably larger (16.4 mm final length) than those fed frozen zoopl ankton (14.4 mm), but mortality did not differ significantly (0% versus 3%) . Larvae fed the dry diet reached nearly the same length (13.6 mm) as the f ish fed frozen zooplankton. However, mortality of fish fed the dry diet was significantly higher (34%) than that of fish fed live or frozen zooplankto n. We conclude that diet acceptance is a key factor for whitefish larvae, a ccounting for the highest growth rates by larvae fed live zooplankton. We a lso tested the effect of two additional factors on larval mortality: food p article size and water circulation in the rearing tanks. The size of food p ellets was reduced from 200-400 mum to 100-200 mum. The water inflow to the tanks was placed below the water surface to increase the time the dry diet was afloat. Our results showed that neither particle size nor inflow place ment affected mortality when fish were fed ad libitum. Nevertheless, feed f loating times were prolonged significantly when the inflow was placed below the water surface, making it possible to decrease the feeding frequency, r educe food losses, and, thus decrease the amount of daily ration fed.