Effect of guar gum on glucose and lipid metabolism in white sea bream Diplodus sargus

Soluble non-starch polysaccharides in fish feed: implications for fish metabolism

Because of their unique glycosidic bond structure, non-starch polysaccharides (NSP) are difficult for the stomach to break down. NSP can be classified as insoluble NSP (iNSP, fiber, lignin, etc.) and soluble NSP (sNSP, oligosaccharides, β-glucan, pectin, fermentable fiber, inulin, plant-derived polysaccharides, etc.). sNSP is viscous, fermentable, and soluble. Gut microbiota may catabolize sNSP, which can then control fish lipid, glucose, and protein metabolism and impact development rates. This review examined the most recent studies on the impacts of various forms of sNSP on the nutritional metabolism of various fish in order to comprehend the effects of sNSP on fish. According to certain investigations, sNSP can enhance fish development, boost the activity of digestive enzymes, reduce blood sugar and cholesterol, enhance the colonization of good gut flora, and modify fish nutrition metabolism. In-depth research on the mechanism of action is also lacking in most studies on the effects of sNSP on fish metabolism. It is necessary to have a deeper comprehension of the underlying processes by which sNSP induce host metabolism. This is crucial to address the main issue of the sensible use of carbohydrates in fish feed.

Nutritive value of guar and copra meal after fermentation with yeast Saccharomyces cerevisiae in the diet of Nile tilapia, Oreochromis niloticus

Solid-state fermentation increases nutritional bioavailability of plant ingredients by reducing the antinutritional factors and complexity of the nutrients. The present experiment was conducted to replace fish meal (FM) with a mixture (3:1) of yeast fermented guar and copra meal (FGCM) in the diet of Nile tilapia. Five iso-nitrogenous (30% CP) and iso-lipidic (6% CL) diets were formulated replacing FM at 0% (FGCM0), 25% (FGCM 1), 50% (FGCM 2), 75% (FGCM 3), and 100% (FGCM 4) with FGCM mixture. Growth, nutrient utilisation, digestibility, digestive enzyme activity, haematological parameters, and antioxidant capacity were analysed in five treatments after a feeding trial of 75 days. Bioprocessing increased the protein and amino acid content and reduced the antinutritional factors in the guar and copra meal. The weight gain was significantly increased in 25% replaced diet. The feed conversion ratio of tilapia fed with FGCM 1 was similar to that of control and significantly lower (P < 0.05) among the treatments. The group fed with FGCM 1 exhibited significantly higher body protein and lipid content. The activity of digestive enzymes and digestibility of nutrients reduced significantly (P < 0.05) with the replacement of fishmeal beyond 25% with the FGCM mixture. Similarly, the antioxidant enzymes and blood parameters were also negatively affected when more than 25% FM was replaced with FGCM mixture. The cubic regression analysis found that 17.45% FM can be replaced with FGCM mixture for optimum weight gain in tilapia.

Adipose tissue and liver metabolic responses to different levels of dietary carbohydrates in gilthead sea bream (Sparus aurata)

This study analyzes the effects of replacing dietary lipids by carbohydrates and carbohydrates by fiber on gilthead sea bream growth, as well as lipid and glucose metabolism in adipose tissue and liver over the course of a 15-week feeding trial. Six different diets were formulated and fish were classified into two experimental groups sharing one diet. In the first group (LS), fish were fed four diets where lipids were reduced (23%-17%) by increasing carbohydrates (12%-28%) and, the second group (SF) consisted on three diets where the amount of carbohydrates (28%-11%) was exchanged at expenses of fiber (1%-18%). Differences in growth were not observed; nevertheless, the hepatosomatic index was positively related to dietary starch levels, apparently not due to enhanced hepatic lipogenesis, partly supported by unchanged G6PDH expression. In the LS group, lipogenic activity of adipose tissue was stimulated with low-lipid/high-carbohydrate diets by up-regulating G6PDH expression and a tendency to increase FAS, and promoted carbohydrate utilization versus fatty acid oxidation by modulating the transcription factors LXRα, PPARα and PPARβ expression. In the SF group, PPARs and LXRα increased parallel to fiber levels in adipose tissue. Furthermore, an adaptation of hepatic GK to dietary starch inclusion was observed in both groups; however, the lack of effects on G6Pase expression indicated that gluconeogenesis was not nutritionally regulated under the conditions examined. Overall, metabolic adaptations directed to an efficient use of dietary carbohydrates are present in gilthead sea bream, supporting the possibility of increasing carbohydrate or fiber content in diets for aquaculture sustainability.

Postprandial molecular responses in the liver of the barramundi, Lates calcarifer

The regulation of gene expression by nutrients is an important mechanism governing energy storage and growth in most animals, including fish. At present, very few genes that regulate intermediary metabolism have been identified in barramundi, nor is there any understanding of their nutritional regulation. In this study, a partial barramundi liver transcriptome was assembled from next-generation sequencing data and published barramundi EST sequences. A large number of putative metabolism genes were identified in barramundi, and the changes in the expression of 24 key metabolic regulators of nutritional pathways were investigated in barramundi liver over a time series immediately after a meal of a nutritionally optimised diet for this species. Plasma glucose and free amino acid levels showed a mild postprandial elevation which peaked 2 h after feeding, and had returned to basal levels within 4 or 8 h, respectively. Significant activation or repression of metabolic nuclear receptor regulator genes were observed, in combination with activation of glycolytic and lipogenic pathways, repression of the final step of gluconeogenesis and activation of the Akt-mTOR pathway. Strong correlations were identified between a number of different metabolic genes, and the coordinated co-regulation of these genes may underlie the ability of this fish to utilise dietary nutrients. Overall, these data clearly demonstrate a number of unique postprandial responses in barramundi compared with other fish species and provide a critical step in defining the response to different dietary nutrient sources.