Dietary Zinc Altered the Growth, Serum Biochemical Parameters and Immunity of Juvenile Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

Abstract

Zinc (Zn) is a kind of critical mineral element for aquaculture and play an important role in growth performance and immunity. Hence this study was aimed to assess alterations in specific growth rate (SGR), feed utilization, activities of digestive enzymes, serum biochemical indexes, the quantity and expression of immunoglobulin M (IgM) in juvenile soft-shelled turtle, Pelodiscus sinensis, response to dietary gradient Zn levels. Fish meal-based diets were supplemented with 0, 10, 20, 30, 40, and 50 mg/kg Zn, the analyzed dietary Zn contents were 35.43, 46.23, 55.38, 66.74, 75.06, and 85.24 mg/kg Zn, respectively. ZnSO₄ · 7H₂O was used as the Zn source. Turtles (weighing ~4 g) were divided into six groups and were stocked for 12 weeks. The results indicated that SGR, pepsin activity in the stomach, intestinal alpha-amylase and lipase activities, total protein content, acid phosphatase (ACP), and alkaline phosphatase (AKP)activities, the contents and mRNA of IgM and insulin-like growth factor-I (IGF-I) enhanced with dietary Zn inclusions to 55.38 or 66.74 mg/kg and then diminished with increasing Zn contents. Escalating Zn levels to 66.74 mg/kg lowered the feed conversion ratio (FCR), serum aspartate aminotransferase (AST), alanine transaminase (ALT) activities, urea nitrogen, triglyceride (TG), cholesterol, and myeloperoxidases (MPO) activity, beyond which they improved. Insufficient or extra Zn depressed the SGR, reduced the feed utilization and digestive enzyme activities, changed the biochemical indicators, and depressed the immunity. The recommended level of Zn in juvenile P. sinensis is 63.75, 61.25, and 61.20 mg/kg diet, derived from analysis of SGR, serum AST, and ALT activities.