Influence of dietary carbohydrate level on endocrine status and hepatic carbohydrate metabolism in the marine fish Sparus sarba

Abstract

Silver sea bream, Sparus sarba, were fed two diets of different carbohydrate levels (2 and 20% dextrin) for 4 weeks, and the effects on organ indices, liver composition, serum metabolite and hormone levels and gene expression profile of key enzymes of carbohydrate metabolism in the liver were investigated. By using real-time PCR, mRNA expression levels of carbohydrate metabolic enzymes including glucokinase (GK, glycolysis), glucose-6-phosphatase (G6Pase, gluconeogenesis), glycogen synthase (GS, glycogenesis), glycogen phosphorylase (GP, glycogenolysis) and glucose-6-phosphate dehydrogenase (G6PDH, pentose phosphate pathway) in liver of sea bream have been examined, and it was found that high dietary carbohydrate level increased mRNA level of GK but decreased mRNA levels of G6Pase and GP. However, mRNA levels of GS and G6PDH were not significantly influenced by dietary carbohydrate. Silver sea bream fed high dietary carbohydrate had higher hepatosomatic index (HSI), liver glycogen and protein, but there were no significant changes in gonadosomatic index (GSI), serum glucose and protein level, as well as liver lipid and moisture level. Pituitary growth hormone (GH) and hepatic insulin-like growth factor I (IGF-I) transcript abundance were assayed by real-time PCR, and it was found that both parameters remained unchanged in fish fed different dietary carbohydrate levels. Serum triiodothyronine (T(3)) and thyroxine (T(4)) were not significantly affected by dietary carbohydrate levels, but lower serum cortisol level was found in fish fed high dietary carbohydrate level. These results suggest that silver sea bream is able to adapt to a diet with high carbohydrate content (up to 20% dextrin), the consumption of which would lead to fundamental re-organization of carbohydrate metabolism resulting in hepatic glycogen deposition.

Growth and metabolic responses in Nile tilapia (Oreochromis niloticus) subjected to varied starch and protein levels of diets

“…In our study, liver GK activity improved with increasing dietary starch levels, which was similar to previous studies (Leung & Woo 2012). In addition, plasma glucose level was higher in fish fed the carbohydrate-rich diets, indicating more energy intake.…”

Molecular adaptations of glucose and lipid metabolism to different levels of dietary carbohydrates in juvenile Japanese flounderParalichthys olivaceus

“…The present study showed that the increase in glycogen in the liver was correlated with the increase in dietary carbohydrate levels, which could be mediated via increased glycogenic gys2 mRNA levels and reduced glycogenolytic pygl mRNA levels. This is consistent with previously reported studies in silver sea bream (Sparus sarba), rainbow trout (Oncorhynchus mykiss) and Wuchang bream (Megalobrama amblycephala) (Leung & Woo, 2012;Zhou et al, 2013). In the present study, intake of 120 g/kg dietary carbohydrates induced higher hepatic mRNA levels of gck and pfkl and HK activity, which are the rate-limiting genes in glycolysis (Massa, Gagliardino, & Francini, 2011;Song, Marandel, Skiba-Cassy, et al, 2018).…”

Dietary carbohydrate/lipid ratios affect stress, oxidative status and non-specific immune responses of fingerling blunt snout bream, Megalobrama amblycephala

“…This indicated that high dietary lipid might cause metabolic stress of fingerling blunt snout bream since cortisol is generally released when an organism undergoes stressful conditions [45]. In addition, cortisol levels increased first then decreased as dietary CHO:L ratio [21], rohu (Labeo rohita) [16] and silver sea bream (Sparus sarba) [46]. Secondly, high dietary carbohydrate might cause stress response of this species.…”