Effects of supplemental dietary l-carnitine and bile acids on growth performance, antioxidant and immune ability, histopathological changes and inflammatory response in juvenile black seabream (Acanthopagrus schlegelii) fed high-fat diet

Numerous studies have demonstrated that l-carnitine (LC) and bile acids (BA) could improve growth performance, reduce fat deposition and affect the inflammatory response in fish. Hence, the main aim of the present study was to find out whether dietary LC or BA supplementation have effects on antioxidant and immune parameters, histopathological changes and inflammatory response in juvenile black seabream (Acanthopagrus schlegelii) fed high-fat diet (HFD). An 8-week feeding trial was conducted in juvenile black seabream of initial weight 2.17 ± 0.00 g. Four isonitrogenous diets (42%) were formulated, Diet1: low fat diet (11%)，Diet2: high-fat diet (17%), Diet3: high-fat diet with LC (300 mg/kg dry diet) and Diet4: high-fat diet with BA (200 mg/kg dry diet). There were no significant differences on growth performance and feed utilization among treatments. Fish fed Diet2, Diet3 and Diet4 had higher intraperitoneal fat ratio (IPF) and lipid content in muscle than Diet1 treatment. Tissue fatty acid profiles reflected the diets. The values of alkaline phosphatase (AKP) and malondialdehyde (MDA) in fish serum fed Diet2, Diet3 and Diet4 were significantly higher than Diet1 treatment. The highest lysozyme (LZM) activities in serum and liver were recorded in fish fed Diet3 and Diet4, respectively. Besides, fish fed with Diet3 and Diet4 obtained significantly higher catalase (CAT) activity when compared to Diet1 and Diet2 groups. With regards to hematological characteristics, the values of triglyceride (TG), cholesterol (CHOL) and high-density lipoprotein cholesterol (HDL-C) in fish fed diet1 were significantly higher than other treatments. However, fish fed with Diet2 showed the highest content of low-density lipoprotein cholesterol (LDL-C). The results of paraffin section of liver (400×) revealed that compared to the negative control diet (Diet 2), the shapes of some cells are regular and parts of the cell structure remained normal, some of the nucleus with nucleolus is spherical, the vacuolar fat drops are smaller and less in Diet 3 treatment, indicating that the dietary LC supplementation could be able to prevent or ameliorate the histopathological alterations induced in liver. Moreover, the hepatic triglyceride content in fish fed with Diet 3 was significantly lower than Diet2 group. The expression of pro-inflammatory cytokine including tumor necrosis factor alpha (tnfα) and interleukin 1β (il-1β) were down-regulated by LC and BA, whereas the anti-inflammatory cytokine transforming growth factor β1 (tgfβ-1) did not show any statistic differences among treatments. Besides, the hepatic fatty acid β-oxidation related genes peroxisome proliferators-activated receptor alpha (pparɑ) and carnitine palmitoyl transferase 1A (cpt1a) in fish fed with Diet 3 and Diet 4 are significantly higher than Diet 2 treatment. Overall, this study indicated that dietary LC and BA could significantly enhance antioxidant, fatty acids β-oxidation and immune ability, reduce inflammatory responses, it also had positive impacts on histopathological changes but could not improve growth performance and feed utilization of black seabream fed HFD.