Aquaculture Reports (Aug 2023)
Effects of digestible carbohydrate levels on growth performance, feed utilization, body composition, and biochemical indices of juvenile spotted knifejaw, Oplegnathus punctatus
Abstract
The effects of digestible carbohydrate levels (0–25 %) on growth, body composition, feed efficiency, and biochemical parameters of juvenile Oplegnathus punctatus (IBW, 12.51 ± 0.02 g) were studied. By adjusting the ratio of corn starch to cellulose, six iso-nitrogenous and iso-lipid diets were formulated. Each diet was divided into three groups (18 fish per replication) for 8 weeks. The results showed that specific growth rate (SGR) and weight gain (WG) were significantly improved (P < 0.05) as digestible carbohydrate levels increased from 0 % to 20 %, but this trend was reversed when the level exceeded 20 %. Correspondingly, feed conversion rate (FCR), protein efficiency ratio (PER), and nitrogen retention (NR) values tended to improved. As digestible carbohydrate levels increased from 0 % to 25 %, daily energy intake (DEI) increased while energy retention (ER) decreased (P < 0.05). Additionally, whole-body crude protein and crude lipid content tended to increase with rising digestible carbohydrate levels. The glycogen content in the liver and muscle increased as digestible carbohydrate levels rose from 0 % to 15 %, while plasma triacylglycerol (TG) concentration decreased as digestible carbohydrate levels increased from 0 % to 20 % (P < 0.05). Compared with other groups, fish fed the C25 diet displayed lower (P < 0.05) amylase activity. Based on the quadratic regression analysis of SGR and WG, dietary digestible carbohydrate levels of 18.31–19.00 % can provide maximum growth for juvenile O. punctatus.
