Effects of Dietary Fishmeal Replacement with Soybean Meal on Growth Performance, Digestion, Hepatic Metabolism, Antioxidant Capacity, and Innate Immunity of Juvenile Large Yellow Croaker (Larimichthys crocea)

Abstract

A 70-day feeding trial was conducted to determine the effects of the replacement of fishmeal (FM) by soybean meal (SM) in diets on growth performance, digestion, hepatic metabolism, antioxidant capacity, and innate immunity of juvenile large yellow croaker (Larimichthys crocea). Four iso-lipidic and iso-nitrogenous diets replacing 0, 15, 30, and 45 FM protein by SM protein were formulated, named FM, SM15, SM30, and SM45, respectively. Results indicated that the specific growth rate (FM = 1.55, SM15 = 1.50, SM30 = 1.48, and SM45 = 1.34%) of fish showed a significant linear trend ( $P<0.05$ ). With increasing dietary SM, the activity of trypsin (262.02, 179.34, 144.41, and 123.92 U/mg·prot) significantly decreased (linear trend, $P<0.05$ ). The content of high-density lipoprotein cholesterol showed a significant linear trend and quadratic trend, and the maximum was observed in fish fed the diet with 45% protein from SM ( $P<0.05$ ). The mRNA expression of the mechanistic target of rapamycin (m-tor) and ribosomal protein S6 (rps6) showed a significant linear trend ( $P<0.05$ ). The content of malondialdehyde (81.82, 92.91, 79.64, and 126.45 nmol/mg·prot) showed a significant linear trend and quadratic trend; the minimum was observed in fish fed the diet with 30% protein from SM ( $P<0.05$ ). The activity of acid phosphatase (328.45, 300.08, 254.03, and 223.51 U/mg·prot) significantly decreased with increasing dietary SM substitution levels (linear trend, $P<0.05$ ). A significant quadratic trend was observed in the mRNA expression of interferon-γ and interleukin-1β, while the maximum was observed in fish fed the diet with 45% protein from SM ( $P<0.05$ ). In conclusion, this study demonstrated that the replacement of FM by SM in diets can decrease the growth performance, digestion, antioxidant capacity, and innate immunity and affect the hepatic metabolism of juvenile large yellow croaker. The minimum negative effect was obtained when 30% of FM was replaced by SM.