Location: Aquatic Animal Health Research
Project Number: 6010-32000-027-022-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jun 1, 2023
End Date: May 30, 2028
Fish farmers often encounter dense algal blooms in ponds due to the high concentrations of nutrients in aquaculture pond water. As water temperature increases as a result of global warming, algal blooms occur more frequently. Depending on the type of algae, the certain blooms can result in the fish having an “off-flavor,” which delays marketing, or an oxygen depletion can occur in the ponds, threatening the survival and health of the fish. Various chemicals have been used to control algal blooms, such as copper (Cu) compounds (e.g., copper sulfate), diuron, potassium permanganate, and chlorine. These chemicals could have additive and non-additive effects on algae. It is vitally important to understand the mixture effects of these chemicals to develop an application strategy that maximizes the effectiveness and avoids overuse of chemicals that could cause harmful effects on fish and other aquatic species in aquaculture production systems. In addition, chemical bioavailability and toxicity to aquatic organisms are dependent on their chemical forms (species). For example, research has shown that ionic metals (free metals, especially Cu) are the most bioavailable metal species and are responsible for toxic effects on aquatic organisms. Water chemistry has been shown to affect metal speciation in aquatic environments. The pH, alkalinity, organic carbon, and hardness are the most important factors that affect metal speciation and, therefore, bioavailability and toxicity to aquatic organisms. In addition, metal toxicity is dependent on the species of organisms. Consequently, it is essential to understand the sensitivity of fish produced via aquaculture to chemicals before applying to control algae to minimize negative chemical impacts on fish. A recently developed general biotic ligand model (BLM) that considers chemical and biological factors when determining protective metal concentrations for aquatic organisms has been used for setting Cu water quality criteria for aquatic organisms in the U.S. and Europe. This BLM may help manage chemical additions to aquaculture ponds. This proposed study will support the development of a chemical mixture application strategy that can effectively control algal blooms in pond aquaculture.
To determine chemical treatment method that efficiently treats harmful algal bloom and protect aquaculture fish from chemical effects, toxicological experiments to determine the toxicity of chemicals to algae, fish, and pathogenic carrying species (i.e., horn snails) will be conducted under different environmental conditions that cover the range of water quality of aquaculture ponds. The chemicals to be considered are those applied by producers, including copper sulfate, flumioxazin, sodium carbonate peroxyhydrate, etc. Water quality to be considered is hardness, pH, alkalinity, and dissolved organic carbon. The experiments will be conducted with both individuals and mixtures of chemicals. Bioavailability models will be developed to predict the toxicity of chemicals to the organisms of concern based on water quality parameters. The models can be used to determine chemical application methods to control algal bloom and protect fish.