Comparison of Experimental Growth Rates of Pond-Raised Largemouth Bass, Micropterus salmoides, Fed Natural and Artificial Foods William R. Leopold email: billatjonesfish@hotmail.com

Bill Leopold (right) and Adam Hater exhibiting several adult Largemouth Bass collected during a population survey on a northern Ohio lake, Summer 2000

The production, rearing and stocking of largemouth bass (Micropterus salmoides) represents a large economic asset in the aquaculture industry of the midwestern U.S., requiring extensive information on the biology of this species. Very little research has compared the effectiveness and results of raising fingerling bass on two different food items, as opposed to differing formulations of prepared food pellets. This study attempted to: (1) assess and compare growth of second year largemouth bass being fed a natural diet to those fed an artificial diet; and (2) assess and compare precision and accuracy of scale-estimated and otolith-estimated ages of cultured largemouth bass. First year largemouth bass fingerlings (8.1 g ± 0.5 g) were pellet trained, then stocked at a density of 0.923 fish/m² into six earthen ponds at Jones Fish Hatchery, Newtown, OH in June 1996. Bass in three ponds were fed a commercially available prepared fish food containing 42% crude protein dry-weight, while fish in the three remaining ponds were fed a live natural food source, the fathead minnow (Pimephales promelus) having 12.9% crude protein wet-weight. Feeding rates were calculated on estimated body weight of bass per pond, with the two food sources standardized to equal protein levels per gram of body weight. Monthly samples tracked average growth, with all fish harvested August 1997, representing 12 months growth utilizing the two different food sources. Final analyses indicate fish had a higher average length (19.6 cm) and weight (95.9 g) when fed a natural food source over commercial fish food (17.3 cm and 72.0 g, respectively; p=0.000). Otolith ageing analysis indicated that annuli (one pair of opaque and translucent bands) formed between November and May. Accuracy of otolith and scale age readings may decrease slightly with age, with otoliths having higher accuracy (maximum R-squared=0.54) than scales (maximum R-squared=0.46) for estimating known age. Precision analyses indicate no significant difference between reader age estimates for otoliths (p=0.428), but with significant difference for scales (p=0.000). Cost/benefit analysis indicates greater net profit for fish fed commercial food than for minnow-fed fish. Largemouth bass that retain pellet food feeding behavior appear to grow more quickly and economically on a prepared diet than on live food, and give a greater return on investment. Otoliths were preferred over scales for ageing bass to 3 years.