Plasma Components and Hepatic Insulin‐like Growth Factor Expression Indicate Nutritional Status in Yellowtail Seriola quinqueradiata

Abstract

AbstractWe examined the effect of feeding ration and refeeding time on plasma biochemical components and hepatic insulin‐like growth factor gene (IGF) mRNA expression to evaluate nutritional indicators in juvenile Yellowtail Seriola quinqueradiata (also known as Buri). Fish were fed a diet for 10 d with the following feeding rations: 80, 40, 20, and 10% satiation. Satiated feeding was 4.65% of body weight. At day 10, the plasma concentrations of albumin, calcium, inorganic phosphate, and total protein, activities of alkaline phosphatase and amylase, and hepatic IGF1 mRNA and IGF2 mRNA expression were significantly correlated with feeding ration. In the analysis of refeeding time, fish were refed after a 24‐h fasting period and plasma biochemical components and hepatic IGFs mRNA were analyzed at 0, 3, 6, and 9 h after refeeding. Plasma concentrations of total bilirubin, inorganic phosphate, creatinine, glucose, and potassium, and activities of amylase were significantly correlated with refeeding time. The correlation between refeeding time and gene expression was significant for IGF2 mRNA (r = 0.70, P < 0.05) but not for IGF1 mRNA (r = 0.67, P = 0.07). Comparing the results of the two experiments, the plasma concentrations of total protein, albumin, and calcium reflected only the feeding ration. The plasma concentration of inorganic phosphate, activities of alkaline phosphatase and amylase, and hepatic IGF1 mRNA and IGF2 mRNA reflected both the feeding ration and refeeding time. These observations suggest that these components reflected the nutritional status of Yellowtail, but sampling time should be carefully examined because of the fluctuating feature of these components.