IMPACT OF DIET ON GROWTH AND HEALTH INDICATORS FOR THE LARGEMOUTH BASS (Micropterus salmoides)

The largemouth bass (Micropterus salmoides) has been cultured for decades, primarily for sport fish stocking. However, there has been increasing production of largemouth bass (LMB) for food fish, especially for live sales to Asian markets. For growout, most producers utilize diets formulated and manufactured for salmonid species, based primarily on ready availability. Health issues have occurred with LMB which are thought to be diet related. The objective of this experiment was to compare the growth, survival, and health indictors of pond raised largemouth bass fed commercial diets used for LMB production or a diet formulated at KSU specifically for LMB.

Twelve 0.04 ha ponds were each stocked with 350 feed-trained advanced fingerling largemouth bass (112 g). Ponds were randomly assigned one of four diets. Three diets were commercially available diets sold originally for either rainbow trout (40% protein/ 12% lipid: 40/12), steelhead trout (45/16) or a Classic Bass diet sold for hybrid striped bass, Barramundi, and LMB (48/18). The fourth diet was formulated at KSU and custom pelleted (Hyland Feeds, Ashland, KY). The LMB were fed to apparent satiation twice daily for 187 days.  Fish were sampled from each pond at stocking, mid-season, and harvest and submitted for parasite and bacteriological evaluations and a diagnostic profile was run on blood samples. At harvest livers were preserved for subsequent histopathological examination.

After 26 weeks survival was not significantly different among fish fed the four diets and averaged 87%, overall. Average harvest weight of fish fed the commercial trout diet (40/12) was significantly lower (525 g) than fish fed other diets, which were not significantly different and averaged 573 g. Feed conversion ratios ranged from 1.4-1.7 and did not differ significantly. Hepatosomatic Index was significantly lower in fish fed the KSU diet (0.53) compared to fish fed the three commercial diets which averaged 0.83. There were no clear trends among the four treatments in terms of bacterial or parasite evaluations and most results were normal.  Blood analyses indicted higher levels of alanine aminotransferase and total bilirubin (both indicators of liver impairment) and Creatinine (kidney function) in fish fed the Steelhead and Classic Bass diets. Results indicated no clear relationship between feeds and liver pathology or glycogen accumulation. These data indicate reduced growth in LMB fed a trout diet. Histopathological and hemeaotological results indicate potential liver and kidney dysfunction in fish fed the Steelhead and Classic Bass diets, though results could also have been related to undetected infectious agents rather than diets.