Microencapsulated dietary supplementation coupled with sexual inversion improves the immune and antioxidant response of Nile tilapia larvae under stressful conditions.

In tilapia aquaculture, the cultivation of single-sex animals is extremely widespread, as it allows for the standardization of lots, in addition to improving the general performance of the animals. However, it is possible that hormonal inversion interacts with other factors, such as environmental and nutritional management, and modulates the immune response and antioxidant system of animals in a distinct manner. In order to test this hypothesis, an experiment was carried out using Nile tilapia larvae six days after hatching, divided into four experimental groups: NI (non-inverted animals), I (sexual inverted animals), NI + M (non-inverted supplemented with microencapsulated products) and I + M (sexual inverted and supplemented with microencapsulated products; half of which were subjected to transportation-related stress after 28 days of the experiment. At the end, the survival rate was evaluated; the gene expression of heat shock protein (HSP70), interleukin 1 beta (IL-1ß) and cyclooxygenase-2 (COX 2) via RT-PCR; also evaluated were the activity of catalase (CAT) and superoxide dismutase (SOD) enzymes, as well as the total antioxidant capacity by 2,2-diphenyl-1-picryl-hydrazyl (DPPH). Animals from the I and I + M groups had the highest survival rate (p < 0.001) regardless of transportation stress. The highest expressions of HSP70 were found in the NI group (p < 0.001, with and without transportation). For the IL-1ß gene, there was an increase in expression for animals belonging to groups NI and NI + M (no transportation); and NI (p < 0.0001, with transportation). Increased COX 2 expression was observed for all groups after transportation (p < 0.0001). The highest SOD activities were observed in groups I and I + M (without transportation, p = 0.0004), and I (with transportation, p < 0.0001). The transportation decreased the total antioxidant capacity of DPPH in all treatments (p < 0.001). Finally, when evaluating all of the results together, we came to a conclusion that sex inversion improves the immune response and antioxidant profile of animals under stressful conditions when associated with microencapsulated dietary supplementation.

Immune response in sexual inverted and non-inverted Nile tilapia fingerlings supplemented with organic acid and essential oil.

The development and intensification of tilapia farming depends on the manipulation of some physiological functions, such as the sexual inversion of larvae using a synthetic androgen (17α-methyltestosterone). This inversion, however, may represent a potential oxidative stress factor and cause damage to animals in the short, medium, and long term. Dietary supplementation of natural antioxidant compounds is an interesting alternative to combat such damage. To test this hypothesis, an experimental trial was carried out involving sexual inverted and non-inverted Nile tilapia fingerlings, both supplemented and not supplemented with a blend of organic acids and essential oils protected by microencapsulation. Animals were divided into four experimental groups: NI (non-inverted animals), I (sexual inverted animals), NI + M (non-inverted animals supplemented with microcapsules), and I + M (sexual inverted animals supplemented with microcapsules). Blood parameters (WBC - white blood cells; LY - lymphocytes; RBC - red blood cells; HGB - hemoglobin; HCT - hematocrit number; MCH - mean corpuscular hemoglobin; MCV - mean corpuscular volume and MCHC - mean corpuscular hemoglobin concentration), as well as oxidative stress markers (enzymatic activity of superoxide dismutase - SOD and catalase - CAT; and total antioxidant capacity - 2,2-diphenyl-1-picryl-hydrazyl (DPPH)) and gene expression (heat shock protein 70 kDa - HSP70) were evaluated. The HGB (p < 0.001) and HCT (p = 0.005) parameters were reduced beyond the recommended limits for the animals in group I. The MCV varied statistically between the groups (p < 0.001). However, all values were within the recommended range for the species, jointly indicating normocytic anemia in group I fingerlings at the time of collection. The activity of CAT and SOD, as well as DPPH differed statistically between the experimental groups (p < 0.001), with the lowest SOD and CAT activity, as well as the highest DPPH registered in animals supplemented with microcapsules. The expression of HSP70 was lower in I + MI animals (p < 0.001). The synergistic evaluation of the results indicates that animals sexual inverted during the larval stage have a lower total antioxidant capacity in the fingerling stage, which reflects a worsening in hematological and enzymatic parameters related to immunity; and that dietary supplementation with blend of organic acids and essential oils protected by microencapsulation is sufficient to improve the immunological response both in sexual inverted and non-inverted fingerlings.

Expression of the PEPT1, CAT, SOD2 and GPX1 genes in the zebrafish intestine supplemented with methionine dipeptide under predation risk.

This study evaluated the effect of methionine supplementation, predation risk and their interaction on gut histology, whole-body cortisol levels, and intestinal gene expression in zebrafish. A total of 360 one-year-old animals were maintained under two environmental conditions and fed diets containing different methionine sources. Fish were fed either a control diet (CTL, without methionine supplementation), a diet supplemented with dl-methionine (DLM), or a diet supplemented with methionine dipeptide (MM) in the absence (AP) of a predator or in the presence of the predator (PP) for 48 h or 20 days. Predator-induced stress for 20 days resulted in lower body weight. Zebrafish fed methionine-supplemented diets had higher weight gain than control fish. We found no effect of predation stress or methionine supplementation on cortisol level. Predation risk and methionine supplementation showed no interaction effect on dipeptide transporter gene expression. After 48 h of predation pressure, zebrafish had higher mRNA expression of SOD2, CAT and GPX1 in the gut. After 20 days of exposure to the predator, zebrafish fed methionine-supplemented diets had lower expression of GPX1, SOD2 and CAT than those diet CTL. Methionine dipeptide and free methionine supplementation improved growth, intestinal health and survivability of zebrafish both conditions.