Hybrid striped bass: culture and use in Midwestern waters

In response to increased demand from fisheries managers, the Iowa Department of Natural Resources and Iowa State University worked to produce standard operating procedures for pond culture of hybrid striped bass Morone saxatilis × M. chrysops in Iowa. In 2011 we evaluated an organic fertilization regime in nutrient rich earthen ponds. In addition to pond fertilization, the role of offering a supplemental commercial feed during phase I culture was also investigated within plastic-lined ponds. With greater utilization and stocking of hybrid striped bass fingerlings in local waters, we also sought to evaluate the effects that introductions have on the trophic dynamics of an established reservoir fishery. Within our earthen ponds, the addition of an organic fertilizer (alfalfa meal) had minimal benefits to fish growth. However, final mean (±SE) fish biomass was significantly greater within the fertilized ponds (66 kg/ha ±6.6) than in the non-fertilized (38 kg/ha ±12.4) ponds. Results suggest minimal benefits of organic fertilizers in earthen culture ponds with existing high nutrient levels. Further research should focus on the possible benefits of nutrient ratio manipulations to foster the development of desirable zooplankton for larval hybrid striped bass. Although there were no significant differences in overall zooplankton population densities in both experiments, fertilizer and feed application did affect preferred zooplankton prey. Mean final fish length was significantly greater within the ponds that were offered feed; fish weight, survival, growth, and biomass were not significantly different between treatments (P \u3c 0.1). We found a significant enrichment in both delta 15 N and delta 13 C values of fish, zooplankton, and Chironomidae larvae within fed ponds (P \u3c 0.10). Using a three-source mixing model, the mean (±SE) percent composition of feed in the fish\u27s isotopic signature increased from 5% ±2 to 20% ±6 within 16 days. Although fish production was not greatly impacted through the addition of a commercial fish feed, enriched delta 15 N and delta 13 C values of fish tissue indicated that palmetto bass fingerlings did utilize prepared diets. However, natural pond biota continued to account for ≥ 80% of the fish\u27s isotopic signature, based on tissue analysis. Using the current knowledge of carbon and nitrogen stable isotope ecology, along with multivariate techniques for constructing isotopic niche spaces, we attempted to describe dietary overlap among the top predators in Three Mile Lake, Iowa. From our analysis, we concluded that the hybrid striped bass predominately preyed on prey located in littoral habitats and did not selectively consume the pelagic yellow bass. Niche overlap between hybrid striped bass and largemouth bass also appeared to be greater than that with walleye. Although competition or detrimental effects due to this overlap in resources could not be determined, continued monitoring of the sport fish population dynamics is highly recommended