Effects of simple management techniques on microbial community dynamics within biofloc-based culture systems and the relationship to shrimp (Litopenaeus vannamei) production
Ray, Andrew J.
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Biofloc-based aquaculture is an environmentally friendly approach to growing shrimp (Litopenaeus vannamei) that is reliant on dense microbial communities for nutrient cycling and system stability. This study examined the impact of three management techniques on microbial community structure and the resultant effect on shrimp production. Each management technique had two variations; high and low protein feeds, high and low shrimp stocking density, and suspended solids removal (cropping) versus no solids removal. The combination of management variations led to eight unique treatments that were each replicated four times and randomly assigned to 32, 6.3m3 tanks. The changes in microbial dynamics were documented using light microscopy with relative quantification assessments, differential epifluorescence imaging with image analysis quantification, and fatty acid biomarker profiling. Overall shrimp performance was measured by individual mean weight, total biomass, feed conversion ratio (FCR), and survival. Changes in system dynamics caused differences in water quality parameters among treatments. Protein level (carbon/nitrogen ratio of nutrient inputs) did not detectably alter microbial abundance. Increased shrimp density (overall nutrient input) led to increased bacteria and zooplankton abundance while cyanobacteria were reduced. Cropping (light availability and selective organismal removal) caused a decrease in bacteria, zooplankton, and cyanobacteria. Low density treatments had increased growth, increased survival, and lower FCRs, but less end biomass. Low protein treatments had slightly better growth but reduced survival and there was a trend towards improved shrimp performance in cropped treatments. This project demonstrated the direct impact that changes in management protocols have on the function of aquaculture systems as a whole and the implications this may have for commercial applications.