Comparison and optimization of a novel larval rearing method for bighead carp Hypophthalmichthys nobilis

Bighead carp Hypophthalmichthys nobilis is a species that is widely cultured throughout Asia, currently ranking 5th in overall global fish production. Despite the prevalence of this species culture it is considered invasive in North America and a threat to local fish communities. Investigations into the early life environmental requirements and optimization of intensive larval rearing have been limited. The present study attempts to establish most desired larval rearing conditions of bighead carp by investigating a novel static rearing method utilizing continuous light, salinity (2 parts per thousand; ppt), algal turbidity, and continuous food availability as compared to traditional recirculating culture system methods. Increased levels of salinity (3 and 5 ppt) were also examined in the novel rearing environment. A 2x2x3 full factorial ANOVA design was implemented to compare the main effects of larval rearing system, feeding regime, and stocking density (12.5, 25, and 50 fish L-1) and the interactions between the main effects on survival, biomass, length, weight, proportion of large fish (measure of heterogeneity), and specific growth rate over twenty days of feeding. A desirability function was then constructed to maximize survival (%), biomass (g L-1) and proportion of large fish to optimize larval rearing for diet nutritional requirement studies. Mortalities recorded in the experiment primarily occurred within the first ten days of feeding and leveled off during the second ten days of feeding. The desirability function identified the novel static rearing method, at high initial stocking density (50 fish L-1), and feeding with Artemia nauplii from inception as having the maximum desirability (0.733) for the selected variables. The predictions for biomass, survival and proportion of large fish from the desirability function were 2.38 g L-1 (95% CI, 2.14-2.62), 70.3% (95% CI, 60.1-80.6), and 0.768 (95% CI, 0.696-0.841) respectively. Elevated salinity, 3 and 5 ppt, was found to increase survival (51.3 +/- 3.5 and 64.3 +/- 10.1%, respectively) and proportion of large fish (0.76 +/- 0.08 and 0.82 +/- 0.02, respectively) i.e. decreased heterogeneity, as compared to 2 ppt (33 +/- 3% and 0.63 +/- 0.03) in the novel static rearing environment. This indicates that current results may further be improved if bighead carp are reared at higher salinities (3-5 ppt). The optimization methodology which was utilized in the current study could potentially be applied to any larval rearing program to select for treatments which meet specific desired outcomes.