The relationship between prey selectivity and growth and survival in a larval fish

We examined prey preference, growth, and survival of small larval (8-10 mm total length (TL)), large larval (11-17 mm TL), and early juvenile (>18 mm TL) walleye (Stizostedion vitreum) in laboratory aquaria and field mesocosms using multiple prey assemblages that included cladoceran, copepod, and rotifer prey of varied sizes, Both prey taxa and size affected prey preference during the larval period. All sizes of walleye avoided rotifer and nauplii prey. Small and large larvae selected for intermediate-sized (0.4-0.9 mm) cladoceran prey and selected against large prey (>0.9 mn) of both taxa, Although neither capture efficiency nor handling time differed between prey taxa, larvae oriented more frequently towards cladoceran prey suggesting that they were more visible than copepods to these small fish. Larval walleye that were fed exclusively cladoceran prey survived better than fish that were fed other prey. Early juveniles selected primarily on the basis of prey size, choosing large copepods and cladocerans. Prey taxa did not affect early juvenile growth or survival. Prey taxa and prey size interacted with predator size to influence selectivity and its effect on growth and survival. Consequently, these factors must be considered in combination when examining the importance of foraging decisions in young fish.