Ecological effects of chemicals used in pond culture of catfish and percid fishes
We performed a series of experiments to evaluate the efficacy and effects of fertilizers, herbicides and algaecides used in percid and catfish ponds of the State Fish Hatcheries of Ohio. First, we conducted fertilization experiments comparing the original phosphorus fertilization rate of 30 ?g P/L with lowered fertilization rates of 20 ?g P/L and 10 ?g P/L and a constant inorganic nitrogen fertilization rate of 600 ?g N/L. Our results showed that lowering of phosphorus fertilization rate from 30 to 10 µg P/L neither affected the larval saugeye production nor the maintenance of adequate zooplankton forage base throughout the culture duration. Lowering the phosphorus fertilization rate in percid ponds may reduce the potential risks of deteriorated water quality conditions and the discharge of nutrient-rich effluent into surrounding waters. Second, we evaluated the efficacy and ecological effects of the herbicide fluridone and the algaecide copper sulfate, in catfish ponds. The combined application of fluridone and copper sulfate resulted in substantially less macrophyte biomass than did the fluridone-only treatment. The phytoplankton community composition shifted towards species tolerant to copper which in turn affected zooplankton community composition along with direct toxic effects of copper on sensitive zooplankton species. Fluridone treatments reduced total phytoplankton and Cyanophyta biomass, which suggests its algaecidal potential. Catfish survival and yield were not significantly different among treatments. Third, we evaluated the extent and effects of carry-over copper on percid culture in double-cropped aquaculture ponds. We found relatively higher copper concentration in the pond sediments at Senecaville State Fish Hatchery. Pond waters during percid culture had higher total and dissolved copper concentrations than did the source water, which suggests the remobilization of copper from the sediment into the water column. The laboratory experiment conducted to assess the chronic toxic effect of copper on a native cladoceran species showed that the low dissolved copper concentrations (6-9 ?g/L) and low free copper ion activities (10-10M-10-11M) encountered in Senecaville waters can negatively affect the reproductive output of cladocerans. Further manipulative experiments need to be conducted to establish the direct and indirect effects of low concentrations of copper on plankton biomass and percid production.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:percid catfish plankton fluridone copper
Date of Publication:01/01/2008