We determined the effect of four concentrations of dietary crude protein, 30.7, 37.2, 41.8 and 46.8% on growth rate, survival and body composition of the juvenile cauque river prawn (Macrobrachium americanum). The prawns were hatched in the laboratory from the spawn of one wild ovigerous female. Prawns consuming 37.2% crude protein reached a final weight of 0.58 g (feed conversion ratio of 2.15), which was significantly better than the other treatments. Survival was 100% in all treatments. Protein content in the diets had no significant effect on whole body proximate composition and amino acid profile. Juveniles consuming the 37.2% crude protein diet grew faster than those fed the other diets. Specific growth rate was adjusted to the two-slope broken-line regression analysis model to estimate the optimal protein requirement. In conclusion, these results demonstrated that the 37.2% protein level diet is optimal for juvenile cauque river prawn M. americanum in the experimental conditions of this study.

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The use of biostimulants in fish diets is a promising strategy to reduce the use of antibiotics, enhance the biochemical and immune response, which contributes to improving productive yields and reducing economic losses. The biochemical and immune response was evaluated in juvenile red tilapia (Oreochromis mossambicus × O. niloticus), with different levels: 0 (control), 1, 2, 3, 4 and 5% chitosan in diet. 270 animals (7.53 ± 0.50 g of initial weight), distributed in a completely randomized design of 6 treatments with 3 replicates and 45 tilapia.treatment-1, were sown in 18 tanks with 90 L of water in a closed system. The juveniles were fed for 55 days with the experimental diets and at the end of the bioassay the tissue and blood plasma samples were taken. Differences were found (p<0.05) in the variables evaluated responses, where the content of lipids, triglycerides, cholesterol, carbohydrates and glucose showed higher levels (p<0.05) at lower chitosan concentrations. However, for protein content, a better response (p<0.05) was found at higher levels of chitosan in the diet. Regarding dry matter and ash, no differences were found (p˃0.05). While superoxide dismutase and leukocytes were found in higher concentration (p<0.05) when supplemented with chitosan by 3 and 4%. It was concluded that the juvenile biochemical and immune response of red tilapia was favored with dietary chitosan supplementation.

Administration of immunostimulants in fish is a preventive method to combat infections. A wide variety of these biological molecules exist, among which one of the yeast wall compounds stands out for its different biological activities. The β-glucan that forms the structural part of yeast is capable of generating immune activity in fish by cell receptor recognition. The most frequently used β-glucans for the study of mechanisms of action are those of commercial origin, with doses recommended by the manufacturer. Nevertheless, their immune activity is inefficient in some fish species, and increasing the dose may show adverse effects, including immunosuppression. Conversely, experimental β-glucans from other yeast species show different activities, such as antibacterial, antioxidant, healing, and stress tolerance properties. Therefore, this review analyses the most recent scientific reports on the use of yeast β-glucans in freshwater and marine fish.

The effect of the habitat and sex on biological indicators and blood biochemistry of Andinoacara rivulatus in the province of Los Ríos - Ecuador was evaluated. Were captured 60 specimens for each zone (180 total), the eight of the animals, length, thickness of the head, tail and the factor were evaluated. Blood glucose, cholesterol and triglyceride indicators were determined. A completely randomized design was used with factorial arrangement (three x two), three habitats and two sexes. A double classification analysis of variance was applied considering the habitat and sex as sources of variation. The results showed the highest morphometric values for males and varied with the habitat, except in the body indices, what were the females. The functional relationship between length and weight was established using quadratic regression equations, with greater significance for males with r2 greater than 0.70. No interaction between zones and sex was shown for the blood indicators studied. The results showed interaction between the habitat locations and sex for the different morphometric indicators evaluated. The biochemical indicators of the blood were conditioned by the habitat.

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