Carnivorous fish are generally considered to be glucose intolerant, showing persistent hyperglycemia when ingesting carbohydrate (CHO)-rich diets. In largemouth bass (LMB), Micropt erus salmoides , excessive dietary CHO (>20%) leads to increased glycogen deposition in the hepatocytes and may lead to liver dysfunction, reduced growth, and an increase in mortality. To produce the floating feeds preferred by fish farmers, diets require CHO concentrations ≥20%. Corn flour (CF) and wheat flour (WF) are the most commonly used CHO sources in practical diets for fish, whereas dextrinized corn starch (DCS) is a purified source of hydrolyzed starch, which can be more easily digested by fish.
A 12-week feeding trial was conducted to compare the effects of different CHO sources and inclusion rates on LMB growth and feed utilization is ongoing. Nine experimental diets were formulated to be isonitrogenous and isocaloric. These diets include three CHO types (WF, CF, and DCS) at two inclusion rates (20% or 30%). Fifteen fingerling LMBs (~5.1 g) were stocked into each 76-L acrylic aquaria in a shared recirculating aquaculture system. With four replicates per diet, a total of 24 aquaria were randomly assigned to one of the diets. Fish were fed once daily to apparent satiation.
After 12 weeks, fish fed 20% DCS diet ( 37.5g) were larger (P <0.05) than fish receiving 20% WF (32.9g), 20% CF (31.7g) and 30% CF (28.7g) but not different from those receiving 30% DCS (34.1g) or 30% WF (33.8g) . Fish fed 30% DCS were larger than fish fed 30% CF but not different from other diets. Fish fed both 20% and 30% WF were larger than fish fed 30% CF. Similarly, feed efficiency was also improved in fish fed DCS (FCR , 1.0) compared to fish fed WF (1.1) or CF (1.2) . These results indicate that DCS may be a better carbohydrate source for use in diets for LMB based on improved growth and feed conversion efficiency.