Optimum dietary fiber level could improve growth, plasma biochemical indexes and liver function of largemouth bass, Micropterus salmoides

An 8 week feeding trial was conducted to evaluate the effects of dietary fiber levels on growth, plasma biochemical parameters and liver function of juvenile largemouth bass. Five isonitrogenous (49% crude protein) and isolipidic (11% crude lipid) diets were formulated to contain 1.24%, 3.43%, 5.12%, 6.95% and 8.50% fiber levels, respectively. Four groups of largemouth bass were randomly assigned to each diet. The results indicated that largemouth bass fed the diets containing 8.5% fiber had significantly lower weight gain (WG) and protein efficiency ratio (PER) than those fed the other fiber diet. The whole-body lipid and liver lipid contents and hepatosomatic index (HSI) decreased with increasing dietary fiber levels, while whole-body protein content rose. Meanwhile, plasma triglyceride (TG) and total cholesterol (TC) contents and aspartate transaminase (AST) activity significantly decreased as dietary fiber levels increased, whereas plasma alkaline phosphatase (ALP) activity significantly rose. The carnitine palmitoyltransferase I (CPT-1), adenosine 5'-monophosphate (AMP)activated protein kinase (AMPK) activities and peroxisome proliferator-activated receptor (PPAR-alpha) content in liver significantly increased with increasing dietary fiber levels. Furthermore, the activities of superoxide dismutase (SOD), catalase (CAT) and oxide synthase (NOS) increased and the malondialdehyde (MDA) content in liver decreased significantly as dietary fiber levels increased. In addition, the liver histological investigation showed an improvement in liver histostructure at high fiber levels. These findings indicated that dietary fiber levels could improve liver function and antioxidant ability of M.salmoides; also, higher dietary fiber levels have a positive impact and decrease the potential risk of disease in M. salmoides. Based on WG, a dietary fiber level of 4.07% was optimal for growth performance of juvenile largemouth bass.