Prey selection by larval fishes as influenced by available zooplankton andgape limitation

Feeding success during the first weeks of life is critical to determining s urvival and ultimate year-class strength of fisher. To compare the relative influence of gape limitation and available zooplankton on prey size select ion among the larvae of three species of freshwater fishes, we gathered dat a on fish gape size, prey size, and size-specific prey selection in lakes a nd reservoirs. These variables were compared among black crappies Pomoxis n igromaculatus from a lake that contained large zooplankton as prey and whit e crappies P, annularis and gizzard shad Dorosoma cepedianum (a potential c ompetitor of white crappie) from reservoirs that contained small zooplankto n. In three Ohio reservoirs (i.e., small-zooplankton systems), available zo oplankton and Larval stages of white crappies and gizzard shad were collect ed once per week during April through September 1987 and 1988. Although mea n prey size of white crappies continued to increase with Ash size, mean pre y size of smaller-gaped gizzard shad did not. However, as documented for bl ack crappies in north-temperate lakes, white crappies in reservoirs continu ed to consume prey that were smaller than other available prey, even when t hey were no longer gape limited. Thus, although the potential for gape limi tation differed between large- and small-zooplankton assemblages, prey sele ction did not differ as expected. Given between-species prey size selection , gizzard shad (that prefer small zooplankton) should be relatively more su ccessful in reservoirs with small zooplankton,whereas white and black crapp ies (that prefer large zooplankton) should have better success in lakes wit h large zooplankton.