Effects of different lipid sources on growth performance, body composition and lipid metabolism of bullfrog Lithobates catesbeiana

• To investigate effects of different lipid sources on growth performance, feed digestibility and lipid metabolism of bullfrog
• FO can be totally replaced by SO or PO in bullfrog diets without negatively affecting growth performance.
• Lipid sources could affect hepatic lipid metabolism of bullfrog.

Fish oil is the most important lipid source, but its limited supply and high cost has forced the feed industry to investigate alternative lipid sources. The goal of this study was therefore to investigate effects of different lipid sources on growth performance, feed digestibility, body composition and lipid metabolism of bullfrog Lithobates catesbeiana. Bullfrogs were fed five diets containing 5.2% of either fish oil (FO), poultry fat (PF), pork lard (PL), soybean oil (SO) or palm oil (PO) for 8 weeks. Growth and feed utilization were significantly (P < 0.05) affected by different lipid sources. Weight gain and feed intake of bullfrogs fed diets with FO, SO and PO showed no significant difference. Body composition, feed conversion ratio and protein efficiency ratio of bullfrog were not affected by lipid sources. Apparent digestibility coefficients (ADC) of diets and test lipid ingredients were significantly (P < 0.05) different among all treatments; the highest ADC for lipid was observed in FO and SO, and the lowest value was found in PF. Fatty acid profiles of muscle reflected the fatty acid composition of dietary lipid source. The activities of hepatic enzymes related to lipid metabolism were significantly affected (P < 0.05) by lipid sources; the PF and PL groups had lower activities, compared to other groups. In conclusion, this study shows that fish oil can be totally replaced by SO or PO in bullfrog diets for a period of 8 weeks without negatively affecting growth performance. These alternative lipid sources have no effect on the body composition of bullfrog, while the fatty acid composition of muscle could be modified by lipid sources. Moreover, lipid sources could affect hepatic lipid metabolism of bullfrog.