Effects of long-term feeding of fishmeal-free diet on growth parameters, bile acid status, and bile acid-related gene expression of yearling red sea bream Pagrus major (Temminck & Schlegel, 1843)

Abstract

We evaluated the effects of long-term feeding of a fishmeal-free (FMF) diet on the growth parameters and physiological status, especially the bile acid status, of red sea bream (Pagrus major) yearlings. Two isonitrogenous and isolipidic diets were prepared; a fishmeal-based diet as the control, and an FMF diet containing soybean meal, corn gluten meal, soy protein concentrate, and pea protein concentrate as plant-derived ingredients, and poultry by-product meal and feather meal as animal-derived ingredients. Six hundred red sea bream yearlings were accommodated in six net cages, and the two experimental diets were hand-fed for 36 weeks. Throughout the 36-week trial, mean body weight and feed intake were significantly lower in the FMF group than in the control group. The concentrations of serum total cholesterol and high-density lipoprotein cholesterol were also significantly lower in the FMF group than in the control group throughout the trial. The total bile acid amount per fish was significantly lower in the FMF group than in the control group between Week 32 and 36 when the water temperature was the lowest (14.3–17.2 °C). Gene expression levels of hepatic cyp7a1 and cyp8b1 tended to be lower in the FMF group than in the control group from Week 20 to the end of the trial. Expression levels of hepatic sqle were higher in the FMF group than in the control group through the trial period and were markedly high at Week 36. Expression of hmgcr was also higher in the FMF group than in the control group at Week 32 and 36. The hindgut asbt expression of fish fed the FMF diet was lower than those fed the control diet at Week 28 and 32. These results suggest that the long-term feeding of an FMF diet to red sea bream yearlings causes reduced growth due to a significant reduction in feed intake and bile acid production, and enterohepatic circulation are strongly disturbed when water temperatures are low from autumn to winter.