Location: Warmwater Aquaculture Research UnitTitle: Water quality and plankton communities in hybrid catfish (female channel catfish, Ictalurus punctatus x male blue catfish, I. furcatus) ponds after partial fish harvest
|MISCHKE, CHARLES - Mississippi State University|
Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2016
Publication Date: 8/6/2016
Citation: Tucker, C.S., Mischke, C.C., Brown, T.W., Torrans, E.L. 2016. Water quality and plankton communities in hybrid catfish (female channel catfish, Ictalurus punctatus x male blue catfish, I. furcatus) ponds after partial fish harvest. Journal of the World Aquaculture Society. 48:46-56.
Interpretive Summary: Catfish aquaculture in the United States is changing rapidly as farmers use fast-growing hybrid catfish and provide higher levels of aeration. These practices allow farmers feed fish more feed than previously, which can degrade pond water quality. This study was conducted to determine whether reducing fish biomass in midsummer would improve water quality by decreasing the amount of feed fed to fish. Contrary to expectations, mid-summer removal of about 25% of fish had no meaningful effects on water quality. Lack of water quality improvement is caused by accumulation and recycling of large amounts of nitrogen, phosphorus, and other substances added to the pond in fish wastes before partial harvest. Decisions to use partial fish harvest to manage single-cropped catfish ponds should therefore be based on economics and risk reduction rather than the expectation that biomass reduction will improve water quality.
Technical Abstract: Twelve, 0.4-ha ponds were stocked with 10,000 hybrid catfish fingerlings in March 2015. Six ponds were partially harvested in August to remove fish larger than ~ 0.57 kg. All remaining fish were removed in October and November. Partial harvest of faster-growing fish removed ~26% of fish initially stocked; feeding rate (and therefore external nutrient loading) was reduced by about the same amount. However, reduced nutrient loading after partial fish harvest had no meaningful effects on water quality, phytoplankton biomass, phytoplankton and zooplankton community structure, or need for supplemental aeration. Lack of ecosystem change is the result of hysteresis caused by high nutrient loading before partial harvest and persistent, high rates of internal nutrient recycling after partial harvest. Decisions to use partial fish harvest to manage single-cropped hybrid catfish ponds should be based on economic considerations and risk reduction rather than the expectation that fish biomass reduction will improve water quality.