Channel Catfish and hybrid catfish fry have different zooplankton feeding habits

Abstract Objective The objective of this study was to compare the zooplankton feeding habits of Channel Catfish Ictalurus punctatus and hybrid catfish (male Blue Catfish I. furcatus × female Channel Catfish). Methods This study used mesh cages to evaluate the zooplankton preferences and fish growth characteristics in situ. Three small, experimental ponds were prepared and fertilized based on typical industry practices. Two cages were deployed into each pond and stocked with 500 individual Channel Catfish or hybrid catfish fry. Twenty fish from each cage were sampled weekly for 9 weeks. At each sampling, the zooplankton community of the pond was sampled using a Wisconsin-style net and compared with that collected from the stomachs of the fish fry. Before dissection, the fish were measured for total length and gape length and weighed to follow relevant growth variables. Results The results indicated no significant differences in body characteristics based on fish species. However, the prey communities varied significantly. Cladocerans composed 44.3% of the pond zooplankton community but 52.0% of Channel Catfish diets; however, only 19.2% of hybrid catfish diets were attributed to cladocerans. Meanwhile, ostracods represented only 6.9% of the pond community but contributed 34.3% to the diet of hybrid catfish fry. Both fish species selected for smaller cladocerans from the true availability. This size bias was particularly evident in Moina, the most abundantly consumed cladoceran, where Channel Catfish and hybrid catfish selected for smaller individuals (471.1 ± 12.3 µm and 463.7 ± 12.7 µm, respectively) than the average size available in the pond (617.4 ± 26.3 µm). Conclusions Although hybrid catfish are credited with higher growth rates over the course of the entire food fish production cycle, the increase does not appear to be realized during the earliest stages of life, as total length and weight were similar between the two species in the present study. The increased prevalence of ostracods and lack of cladocerans in the diets of hybrid catfish fry may also hint at differences in their vertical distribution within the water column, relative to Channel Catfish fry. This study highlights the importance of providing the preferred prey groups and size-classes in supplementing manufactured feeds with zooplankton to maximize catfish production performance.