Largemouth bass (LMB), Micropterus salmoides, is a high-value freshwater aquaculture species with a rapidly expanding food fish market in North America. Proper transitioning from endogenous to exogenous feeding is pivotal for early rearing success. While some species can successfully be raised on artificial (i.e., commercial) diets from first feeding, LMB require a co-feeding period of both live prey and an artificial diet. Information regarding early feeding strategies for LMB are limited. Our objective was to determine how initial yolk-sac fry stocking density, prey density, and the stocking density × prey density interaction impacts LMB growth and survival.
LMB embryos were obtained from Red Hills Fishery (Boston, GA) and transported to Auburn University. At peak hatch, fry were stocked (~27oC) in 25 L blue tanks equipped with recirculation technology at densities of 25, 50, and 100 yolk-sac fry/L. Starting at 3 days post-hatch (DPH), fry from each stocking density were factorially fed Artemia at 2, 4, and 8 Artemia/mL every 2-3 h from 07:00 to 23:00. All treatments received rotifers from 3-8 DPH and artificial diet (~0.5 to 1.0 g/tank) starting at 120 degree-days until 28 DPH. Mortalities and excess feed were removed daily. Rearing of offspring occurred under a 12-h light/12-h dark photoperiod at ~500 lux. Fish were randomly sampled weekly from 3-27 DPH for industry-relevant offspring performance traits, including notochord length, total length, eye diameter, myotome height, jaw length, yolk-sac area, body area, and fin-fold area. Daily survival and final tank biomass were recorded. To further understand phenotypic sensitivity to predator (fish) and prey density, we are currently following expression of genes associated with stress tolerance, growth, and development.
Preliminary results indicate that initial yolk-sac fry stocking density, prey density, and the stocking density × prey density interaction impacted offspring traits during this critical early life period. Highest survival (± SEM) and SGR were 90.3 ± 4.1% and 2.98 ± 0.1, respectively, when fry were initially stocked at 25 yolk-sac fry/L and fed 8 Artemia/mL. Highest biomass was 199.5 ± 5.6 g for the 100 yolk-sac fry/L and 8 Artemia/mL feeding treatment. Together, our approach will provide the global aquaculture sector with greater knowledge and technological innovation to enhance LMB hatchery production efficiency.