EFFECT OF LARVAL WALLEYE (STIZOSTEDION-VITREUM) AND FERTILIZATION ON THE PLANKTON COMMUNITY - IMPLICATIONS FOR LARVAL FISH CULTURE

Plankton abundance which greatly affects larval fish growth and surviv al can be regulated by fish predation and nutrient input. In this stud y, we examined community effects of larval walleye and fertilizer type on plankton in ponds involving three densities (0, 250 000, and 500 0 00 fish/ha) of larval walleye (Stizostedion vitreum) and two fertilize r types (inorganic or organic). Walleye survival was not affected by f ish density or fertilizer type, and more fish yield was gained in high fish density ponds. The best fish growth was obtained in ponds with l ow fish density and inorganic fertilizer. As fish density increased, t he abundances of Daphnia, Diaptomus and nauplii, Secchi depth, NH3-N, NO3-N and chironomids were reduced, whereas primary productivity, Scen edesmus, flagellates, colonial algae, Anabaena, rotifers and pH were e nhanced. Compared to organic fertilizer, inorganic fertilizer increase d the levels of primary productivity, algal abundance, dissolved oxyge n, pH and total phosphorus. Inorganic liquid fertilizer with N:P ratio at 20:1 and a stocking density of 250 000-500 000 fry/ha is recommend ed for larval walleye culture. The stocking and fertilization protocol for larval walleye culture could be applied to the larval culture of other planktivorous fish species.