Role of organic fertilizers in walleye (Sander vitreus) production in plastic-lined culture ponds

This study used six 0.04 ha plastic-lined ponds to compare the effects of a fertilization regime using a one-time initial application of an organic fertilizer (alfalfa pellets) with the current regime of weekly applications of organic fertilizers on the abundance and distribution of aquatic invertebrates and walleye, Sander vitreus, fingerling production. Walleye, 3-4 days post hatch, were stocked on 1 May 2002 and harvested on 6-7 June 2002. Throughout the growing season, a ratio of 7:1 total nitrate-nitrogen to total phosphorus was maintained in all ponds regardless of the treatment. Once fry were stocked, ponds in Treatment #1 were fertilized weekly with organic fertilizer (alfalfa pellets; 112 kg ha-1 week-1) for a total of 795 kg ha-1 pond-1. Ponds in Treatment #2 only received an initial application of alfalfa pellets (112 kg ha-1). Ponds in Treatment #1 had significantly higher ammonia and nitrate levels as well as higher chironomid larvae but not zooplankton compared with the other treatment. At harvest, walleye in the Treatment #1 ponds were significantly longer and heavier; however, the survival and relative weight were not significantly different. These results suggest that weekly applications of organics are important for the benthic food base and growth of fingerling walleye reared in plastic-lined ponds.