Fibras funcionais da linhaça e seus impactos na nutrição de jundiás

Abstract

This study aimed to evaluate the prebiotic action of functional linseed fibers with different proportions of soluble and insoluble dietary fiber and its impact on the nutrition and health of juveniles silver catfish (6.43g). For this, the soluble and insoluble fractions of linseed fiber were concentrated, using the use of physical and chemical concentration techniques. These fractions were combined in different proportions (1:0.5, 1:1, 1:2 and 1:4 soluble: insoluble fibre) to obtain functional fibers, which were added to diets and evaluated in a biological test with juveniles silver catfish. The biological assay lasted 45 days and was performed in a water recirculation system, composed of 20 tanks (290L), biofilters and water reservoir. At this time the fish were fed to apparent satiety three times a day. At the end of the period the fish were submitted to a 18 hour fast and biometry for data collection of weight, length, blood collection, tissues (liver and digestive tract), mucus and digesta for determination of performance parameters, composition and body deposition, plasma metabolites, hepatic enzymes, digestive enzymes, immunological indicators, intestinal histology and production of short chain fatty acids. After the final biometry the fish were kept in the experimental units for another five days and at the end of this period, submitted to acute stress, with subsequent collection of blood and mucus for determination of metabolites and immunological indicators. The experimental design was a completely randomized design, consisting of five treatments and four replications (600 fish). The results were submitted to the normality test, followed by analysis of variance, and the means were compared by the Tukey test at the 5% level of significance. Diets 1:2 and 1:4 provided greater weight gain, specific growth rate and crude protein deposition in fish, total circulating proteins and globulins, as well as mucoprotein content, total immunoglobulins and cutaneous mucus pH. Cortisol levels and intestinal pH were lower in these treatments. The 1:0.5 diet altered the trypsin activity in the silver catfish intestine and together with the 1:4 diet provided higher intestinal villi height. While total villus height was higher for the fish that received linseed fiber in the diet, regardless of the proportion, the inverse was observed for the thickness of the muscle layer. Regardless of dietary ratio, linseed fiber intake increased total plasma immunoglobulins and plasma alkaline phosphatase activity and cutaneous mucus. The production of intestinal acetic acid was higher in the fish fed with the 1:2 diet, whereas of the butyric acid with the 1:4 diet and propionic acid with the control diet. The control diet led to lower counts of goblet cells. After acute stress, the fish fed the diets containing soluble: insoluble fiber ratios 1:2 and 1:4 presented higher total protein, globulin and plasma alkaline phosphatase activity, as well as a higher mucoprotein content in the mucus of fish. In conclusion, the results indicate that linseed fiber has an immunostimulating prebiotic action for silver catfish juveniles, and the 1:2 and 1:4 ratios of soluble: insoluble fiber optimize the immune system and the production of short-chain fatty acids, with positive reflexes on fish performance. Moreover, in these proportions it still acts as a stress reliever.