Effects of feed applications with various phosphorus concentrations on the abundance of cyanobacteria and common off-flavor compounds in hybrid striped bass aquaculture ponds

Authors: Schrader, Kevin; Green, Bartholomew - Bart; Rawles, Steven - Steve; McEntire, Matthew - Matt

Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2022
Publication Date: 6/8/2022
Citation: Schrader, K., Green, B.W., Rawles, S.D., Mcentire, M.E. 2022. Effects of feed applications with various phosphorus concentrations on the abundance of cyanobacteria and common off-flavor compounds in hybrid striped bass aquaculture ponds. Journal of Applied Aquaculture. https://doi.org/10.1080/10454438.2022.2086839.
DOI: https://doi.org/10.1080/10454438.2022.2086839

Interpretive Summary: Freshwater fish grown in earthen ponds in the southern United States can acquire earthy and musty taints due to the bioaccumulation in the fish flesh of compounds produced by cyanobacteria (blue-green algae) which grow in the ponds. Nutrient inputs (e.g., phosphorous) are high in fish production ponds due to high feed application rates and result in dense phytoplankton communities. In this study, hybrid striped bass were grown for 5 months to market size in earthen ponds and fed six different types of feed formulations including feed containing phytase in order to reduce the phosphorus input to the pond from the feed. While less phosphorus was added to the ponds from the applications of feed containing phytase, the abundance of cyanobacteria and the concentrations of earthy and musty compounds in the pond water and fish fresh was not reduced.

Technical Abstract: Freshwater fish grown in earthen ponds in the southeastern United States can acquire “earthy” and “musty” taints due to the bioaccumulation of geosmin and 2-methyisoborneol (MIB), respectively, in the fish flesh and result in unpalatable and unmarketable fish. Certain species of cyanobacteria which produce geosmin and MIB are attributed as the causes of these off-flavors. Nutrient inputs (e.g., phosphorous, P) are high in fish production ponds due to high feed application rates and result in dense phytoplankton communities. In this study, hybrid striped bass (HSB; Morone chrysops x M. saxatilis) stocked in 0.1-ha earthen ponds were grown for 5 months to market size. Fish were fed one of 6 diets: 1) commercial HSB, COM; 2) fishmeal control, FM; 3) fishmeal-free, FMF; 4) FMF + phytase, FMF+PH; 5) all-plant protein, PP; and 6) PP+PH. Diets supplemented with PH were formulated with no added inorganic P and to release phytate-bound P in plant ingredients, with subsequent reduction of P input to the pond from the feed. Water samples were collected from each pond biweekly during the 5-month study and analyzed for geosmin and MIB concentrations and phytoplankton community structure. HSB fillet samples were collected at the beginning and end of the study and analyzed for geosmin and MIB concentrations. Total feed consumed did not differ significantly among diets, but significantly less total P was added to ponds receiving the PP+PH diet. Substituting phytase for inorganic P in diet formulation resulted in 33.4-45.5% less dietary P consumed by HSB fed the all-plant protein-phytase (APP+PH) diet compared to all other diets. Differences in dietary P consumption among diets did not significantly affect soluble reactive phosphorus and total phosphorus concentrations, cyanobacteria abundance, and geosmin and MIB concentrations in pond water. Significantly higher MIB concentrations in fillets were detected at harvest for fish fed the FMF+PH diet.