At the turn of this century the production of farmed largemouth bass (LMB) stood at 178 tonnes. By 2019, worldwide production was above 480,000 tonnes, with most being farmed in China. The massive increase in LMB cultivation has been attributed to technological innovation in the hatchery combined with farmers switching from tilapia due to the higher market price of LMB. As with other aquaculture ventures several issues obstruct future growth of LMB farming. Major impediments include emergence of various diseases, lack of genetically selected strains, and poor quality, production, and distribution of seed. LMB has a high dietary protein requirement, and this is generally supplied in the form of fishmeal (FM). Demand for FM remains elevated, and the future promises higher raw material costs for aquafeed manufacturers. Already feed represents 60% of LMB farming operational costs and, unless cheaper, more sustainable alternative protein-based diets emerge, this too will represent an obstruction to sector growth. To demonstrate the potential for excluding FM from LMB aquafeeds we compared the performance of an open-source, FM and fish oil (FO) free diet (F3) against two commercial, closed formulation LMB feeds (Xinxin or Alltech-Coppens [A-C]).
A 10-week feeding trial was undertaken in a RAS using 3 randomly designated tanks per diet. Fish (15 g, n=20/tank) were fed twice daily to satiation over 5 min. Groups were weighed every 3 weeks and at trial end to monitor feed conversion ratio (FCR) protein efficiency ratio (PER) and weight gain. There were no differences in FCR or PER between diets (P > 0.05; Table 1). However, weight gain and survival were lower in fish fed the A-C feed.
Whole body proximate composition of fish at trial end differed (P < 0.01; Table 2) reflecting the composition of feeds. There were no differences between feeds for percent apparent digestibility coefficients or phosphorus availability. This study demonstrates that total replacement of dietary FM/FO in LMB feeds is a realistic and economically viable proposition.