Quantifying the contribution of zooplankton to channel catfish and hybrid catfish growth in nursery ponds

Abstract

Channel catfish fry rely heavily on zooplankton to support growth in nursery ponds. However, the extent of zooplankton use by hybrid (channel × blue) catfish fry is unknown. To improve feeding methods for channel and hybrid catfish in nursery ponds, we used stable C and N isotope ratios to quantify the fractional contribution of zooplankton and a commercial feed to fish growth. Channel and hybrid catfish fry had no differences in the timing and extent of zooplankton and feed use in ponds. Both fish types used zooplankton and feed equally to support growth (~50% from each source) from the time of pond stocking, and there were no differences in growth rates by length or weight. The fish used feed to support growth before they were visually observed accepting the feed at the surface of ponds 4 weeks after stocking. Zooplankton are clearly important to support desirable growth of channel and hybrid catfish fry in ponds. Thus, we recommend managers monitor densities of preferred zooplankton prey in ponds and use inorganic fertilization methods to enhance zooplankton production, as necessary. Although feed partially supported zooplankton production in this study, we caution against overfeeding, because this practice is expensive, inefficient, and risks hypoxia formation in ponds. Finding no differences in diets and growth rates between channel and hybrid catfish, we provisionally recommend managers practice similar pond management strategies for both fish types.