Largemouth bass (LMB), Micropterus salmoides is the most popular sportfish in the US, with a rapidly expanding global food fish market. Farmers traditionally raise LMB in earthen ponds, however, they are often plagued with high mortality at the larval stage. Thus, circumventing these initial pond stages to complete indoor intensive culture would streamline production and minimize risks. Therefore, our objectives were to (i) identify the optimal thermal regime for rearing LMB in an indoor recirculation aquaculture system (RAS); (ii) assess the performance of Florida vs. Northern LMB for RAS culture; and (iii) elucidate thermally induced phenotypic changes and inter-linked expression of targeted genes involved in early development.
Florida and Northern LMB were reared at 21oC, 24oC, and 27oC using RAS technology. Fish were randomly sampled at 2 to 28 days post-hatch (DPH) for total length (TL), body area (BA), myotome height (MH), eye diameter (ED), jaw length (JL), yolk area (YA), and oil droplet area (ODA). Yolk utilization efficiency (YUE) and yolk utilization rate (YUR) were calculated. Weight was also determined at 29 DPH along with survival and expression of targeted genes.
There was a significant temperature effect for all morphometric traits, where both sub-species increased in size over the temperature gradient, with the largest traits (TL, BA, MH, ED, JL) detected at 27oC (Fig. 1AB). Northern LMB larvae were typically larger with respect to morphometric traits and weighed more after 29 DPH (Fig. 1C). LMB reared at 21oC had higher survival than those reared at 24 or 27oC, and Northern (17%) had higher survival than Florida bass (11%). Gene expression and yolk results are ongoing. These results suggest that 1) rearing larval LMB at 27oC improves growth performance during early ontogeny, and 2) there is supporting evidence that Northern LMB is selected for faster growth when reared in an indoor RAS.