Optimization of fertilization practices to enhance phytoplankton communities in plastic-lined ponds for the production of red drum, sciaenops ocellatus

Date

2019-05

Authors

Gutierrez, Nathan

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Abstract

The current stock enhancement program employed by the Texas Parks and Wildlife Department (TPWD) uses pond aquaculture practices. This practice includes the fertilization of phytoplankton, stimulating zooplankton biomass forage for stocked larval fish species. Red drum (Sciaenops ocellatus) larvae are often grown-out in 1-acre (0.4 ha) plastic-lined ponds by TPWD utilizing a fixed nutrient enrichment strategy consisting of cottonseed meal additions, followed by weekly additions of nitrogen and phosphorus, and less frequent silica additions. I evaluated this practice using two alternative methods: a variable rate nutrient addition strategy of nitrogen, phosphorus, and silica based on the Redfield-Brzezinski molar ratio with and without cottonseed meal and a second method using laboratory-based nutrient enrichment bioassays (NEB) of pond water to determine nutrient limitation. In three of the four experiments, mean algal biomass was significantly less for the control (p= 2.70e-02, trial 2; p=8.61e-08, trial 3; p=7.96e-02, trial 4) than the experimental variable rate addition including cottonseed meal (pond treatment A). Overall mean estimates for diatom biomass were significantly higher for pond treatment A (p=1.15e-02) than the control. Results from NEB experiments showed when treatment was significant; ponds were most often nitrogen limited, followed by phosphorus, then silica. These results support the use of the variable rate fertilization including silica coupled with cottonseed meal in the fertilization strategy. Survival rates for pond treatments observed were 33 % for pond treatment A and B, and 5% for the control.

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Keywords

aquaculture, fertilization, fingerling, phytoplankton, red drum, variable-rate

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Attribution-NonCommercial-NoDerivatives 4.0 International

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