Zooplankton Size and Taxonomic Selectivity of Channel Catfish Fry

Zooplankton utilization and their importance to channel catfish Ictalurus punctatus fry during pond culture is not well documented. Current fry stocking decisions are based on total zooplankton densities. We studied the feeding habits (zooplankton size and taxa selection) of channel catfish fry. Catfish fry just completing swim‐up were placed into glass aquaria or into cages in ponds and allowed to forage on natural zooplankton assemblages. The zooplankton sizes and taxa consumed by the fry were compared with the available sizes and taxa in the aquarium or pond environments. Rotifers and copepod nauplii were abundant in all environments but were never observed in the fry stomachs. Ostracods, adult copepods, and cladocerans were the only three taxa consumed. The data from both experiments indicated that ostracods were consumed in proportions equal to natural abundances, but in the field experiment larger ostracods were selected. Consumption of adult copepods and cladocerans depended on the relative proportions and sizes of each taxon present. Cladocerans, when available, appeared to be the preferred prey. When cladocerans were scarce, more copepods were eaten. We conclude that fry stocking decisions should focus on copepod, cladoceran, and ostracod densities and sizes rather than total zooplankton densities. Furthermore, the lengths of available zooplankton should be 450–700 μm for cladocerans, more than 650 μm for copepods, and more than 450 μm for ostracods.