Liver structure and function in yellowtail kingfish, Seriola lalandi, in response to alternative oils in feed

The inclusion of low cholesterol alternatives to fish oil (FO) in aquaculture diets could result in alterations to the biosynthesis and availability of bile acids for the digestions and absorption of dietary lipids. In this study the effects of graded substitution of FO with poultry oil (PO) and the replacement of PO with canola oil (CO) in formulated feeds on Yellowtail Kingfish (1.45 ± 0.12 kg; n = 342) liver function was investigated over 84 days. Dietary FO was replaced with PO at 100%, 75% and 50% inclusion levels (Diets 1, 2 and 3, respectively). The lipid source (PO) was further replaced with CO at 0%, 33.3%, 66.7% and 100% (Diets 2, 4, 5 and 6, respectively). The liver vacuole volume as a proportion of the liver cell volume (VPLC%) was significantly increased (P = 0.008) in fish fed the 100% PO diet (Diet 1) compared to that of fish fed diets with greater levels of FO inclusion (Diets 2 and 3). Regression analyses showed that: 1) liver VPLC% increased as FO decreased (r² = 0.588; P = 0.016), 2) total bile acid concentration in liver tissue decreased with increasing CO and decreasing PO (r² = 0.402; P = 0.027), and 3) liver CYP7A1 concentration increased with increasing PO and decreasing FO (r² = 0.506; P = 0.032). No statistically significant differences were observed in any of the blood biochemistry parameters measured from fish fed diets with decreasing FO and increasing PO nor from fish fed diets formulated with FO and a graded PO and CO blend. Yellowtail Kingfish may be able to be fed a formulated diet containing: 1) ∼25% dietary lipid level (2.12 g 100 g⁻¹ of ƩLC n-3 PUFA) with up to 100% of the FO component replaced by PO; and 2) ∼25% dietary lipid level (2.12 g 100 g⁻¹ of ƩLC n-3 PUFA) with up to 100% of the commercially used alternative lipid source (PO) replaced with CO without an apparent negative impact on any of the parameters measured in this study.