EFFECTS OF SURFACE-WATER SPRAY, DIET, AND PHASE FEEDING ON SWIM BLADDER INFLATION, SURVIVAL, AND COST OF PRODUCTION OF INTENSIVELY REARED LARVAL WALLEYES

Three experiments were conducted to determine the effects of a surface water spray and diet on survival and swim bladder inflation of intens ively reared larval walleyes. Survival and swim bladder inflation were determined at 30 d posthatch. In each experiment, 275-L cylindrical t anks were stocked with 20 fry/L. In experiment 1, a spray of water was applied to the surface of three tanks, and three additional tanks rec eived no surface spray. BioKyowa FFK-B diet was fed to fish in all tan ks. Survival of fish with the spray (11.8%) and without the spray (9.1 %) was not significantly different, but the incidence of swim bladder inflation was higher with (98.4%) than without the spray (51.7%). In e xperiment 2, larval walleyes were fed one of three commercially availa ble larval feeds-FFX-B, San Francisco Bay Brand EPAC, and Zeigler Larv al AP200-and all tanks received a surface spray. Only the fish fed FFK -B had reasonable 30-d survival (33.1%) and swim bladder inflation rat es (95.6%). In experiment 3, phase feeding was tested in conjunction w ith a surface spray. The fish were fed FFK-B until 11 d posthatch and then either FFK-B, FFK-C, or WS9112 (our experimental formulation) for the remainder of the 30-d trial. Survival (30.2-33.1%) and swim bladd er inflation rates (95.3-95.6%) were similar among diet treatments. Fi sh fed WS9112 did not gain as much weight and had a higher body fat co ntent than the fish fed the other two secondary diets. Feeding FFK-C i nstead of FFK-B during the second phase reduced feed costs by 76% with out a reduction in survival or swim bladder inflation.