The effect of fertilization regime on juvenile walleye growth and prey utilization in rearing ponds

Synopsis

The effect of two contrasting fertilization regimes on juvenile walleye growth, survival and harvest was tested in six identical rearing ponds treated with fermented soybean meal at either a constant (36 g m⁻³week⁻¹) or a progressively reduced (32 to 0 g m⁻³week⁻¹) rate. Walleye length, percent survival and biomass harvest in constant fertilization ponds were 32, 83 and 294% greater, respectively, than those of reduced fertilization ponds. Chironomid larvae and pupae were the dominant prey (in terms of biomass) in juvenile walleye larger than 22 mm TL. Mean chironomid biomass was significantly higher in the constant fertilization ponds (5.1 vs. 1.7 g dry wt m⁻²), particularly after peak emergence around week 4. Zooplankton were less important prey after week 2, and mean zooplankton density was not significantly different between treatments. From these data we conclude that better walleye performance in the constant fertilization ponds was due to higher chironomid density during the last half of the experiment. Our findings are reviewed in light of current knowledge of juvenile walleye feeding ecology and contemporary pond culture procedures.