In 1992 at Rathbun State Fish Hatchery, experiments were conducted to evaluate the effects of stocking density on performance of larval walleyes (Stizostedion vitreum) in small (278-L) cylindrical tanks, and to compare fry performance in production-scale (6 79-L) and small tanks. Hatched fry were reared for 21 d and fed Fry Feed Kyowa B400 and B700 in all experiments. I>ensilies of 20, 30, and 40 fry/L were evaluated in two trials, and densities of 20, 50, and 60 fry/L were evaluated in another trial. Fry performance did not differ significantly among density treatments of 20, 30, or 40 fry/L. In the other trial, however, survival was significantly greater for fish stocked at 20 fry/L than for fish stocked at 50 or 60 fry/L, but the number of fry produced (yield) was 216% greater in the tanks stocked at 60 fry/L. Growth rate was not affected by density in any trial. For comparisons between 278-L and 679-L tanks, three 679-L tanks were stocked at 20 fry/L in each of the three trials. Survival and viability differences between tank sizes were inconsistent, but the highest survival was an average of 74.9% to 21 d posthatch in the three 679-L tanks in the second trial. Cannibalism and gas bladder inflation were more common in the small tanks. Incidence of cannibals was as high as 7.5% of the original number stocked in the small tanks, but did not exceed 3.5% in the large tanks. Over all three trials, from 98.5 to 100% of the survivors in the 278-L tanks, and from 88 to 96.3% in the 679-L tanks, had inflated gas bladders. The outstanding rate of gas bladder inflation is attributed to the use of a surface spray, which seems to clear the water surface of oil and debris. These experiments demonstrate the feasibility of mass culture of larval walleyes in production-scale tanks.
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