Methodology for Environmental Toxicology: Assessing Feeding and Rearing Strategies in Largemouth Bass (Micropterus nigricans) Larvae

Poly- and perfluoroalkyl substances (PFAS) are an anthropogenic group of chemicals known for their persistence in the environment and their potential to bioaccumulate. PFAS can bioaccumulate in largemouth bass (Micropterus nigricans), yet the effects of exposure on bass larvae are unknown. While largemouth bass are commonly raised for aquaculture, techniques for rearing bass which enable controlled experiments at known densities, a necessity for toxicity studies, are poorly understood. Furthermore, the live prey typically used in existing approaches are not suitable for PFAS studies due to high background concentrations. The objective of this project was to assess different venues (indoors vs. outdoors) and feeding regimes to determine how to raise healthy larvae conducive to PFAS exposure studies. Four treatment groups were used to determine the success of different combinations of venue and food: (1) indoor tanks with live zooplankton only, (2) indoor tanks with zooplankton and powdered Otohime A fish food, (3) outdoor tanks with a single zooplankton addition, and (4) outdoor tanks with zooplankton replenished daily. Live zooplankton samples were collected from the treatment groups and analyzed under a microscope to assess community composition, relative abundance, and to classify them by size. Larval survival, growth, and body condition were assessed with respect to observed densities of zooplankton across treatments. Analysis did not detect statistical differences between indoor and outdoor rearing (p = 0.2398), food density (p = 0.2233), or an interaction of rearing and food density (p = 0.7392). However, density dependent growth with statistically significant relationships between outdoor treatment survival and length (p < 2.2e-16), weight (p = 1.613e-9), and body condition factor (p = 0.04048) suggest food may have been a limiting factor. Increasing densities of edible zooplankton and conducting exposure studies outdoors appear to be the best approach for exposure studies with early-stage largemouth bass.