Optimal myo-inositol requirement for growth performance in juvenile freshwater crayfish

Abstract

Myo-inositol (MI), as a growth factor, plays a vital role in regulating the health of crustaceans. However, the optimal MI requirement of juvenile freshwater crayfish and the mechanisms that regulate growth and nutrition remain unknown. This experiment investigated the effect of MI addition on the growth, ecdysis performance, and ecdysone signaling pathway of juvenile freshwater crayfish (Procambarus clarkii). Six diets were prepared by adding 0 mg/kg (control group), 500 mg/kg, 1000 mg/kg, 2000 mg/kg, 3000 mg/kg, and 4000 mg/kg MI to the basal diet. A total of 360 juvenile freshwater crayfish were cultured for six weeks, in three parallel groups and their average body weight was (6.39 ± 0.05) g. Compared with the control group, the diet supplemented with 500 mg/kg and 1000 mg/kg MI significantly increased the weight gain rate (WGR) and specific growth rate (SGR) of freshwater crayfish (P < 0.05). Using WGR and SGR as evaluation indexes, the addition of 917–942 mg/kg MI does promote the growth of freshwater crayfish. Dietary supplementation with 1000 mg/kg inositol can significantly increase the expression of ecdysone receptor (ECR) and retinoic acid X receptor (RXR) genes in the hepatopancreas and inhibit the transcription level of ecdysis inhibitory hormone (MIH) gene (P < 0.05). Also, dietary MI enhanced digestive enzyme activity and induced the expression of genes related to the GH-IGF growth axis to promote the digestion and absorption of nutrients in freshwater crayfish. Furthermore, dietary MI reduced serum lipid molecule levels and increased serum antioxidant capacity. The results of this paper revealed the growth mechanism of juvenile freshwater crayfish in terms of digestive enzyme activities, ecdysis performance, and expression of GH-IGF axis-related genes.