This study aimed to evaluate the effect of oregano oil on the intestinal and liver morphometry of yellow tail tetra, Astyanax altiparanae. Fish (1.46 ± 0.09 g) were kept in a 60-L aquaria, at a stocking density of 0.5 fi sh L -1 . Six diets containing varying amounts of oregano oil were evaluated (0.0; 0.5; 1.0; 1.5; 2.0 and 2.5 g of oregano oil kg -1 ). At the end of 90 days, the fi sh were euthanised. Four intestines and four livers were collected per treatment, which were fi xed in Bouin and embedded in resin. For height and width folds, the absorption surface area and thickness of the muscular layer a positive linear effect of oregano oil was observed. A decrescent linear effect on the total number of goblet cells was also observed. For the cytoplasmic percentage of hepatocytes and liver glycogen, a positive linear effect of oregano oil was observed. There was a decreasing linear effect on the percentage of nuclei in the hepatocytes and capillaries. Thus, the oregano essential oil promotes increased absorption areas, modulates the amount of goblet cells involved in protecting the intestinal mucosa and promotes cytoplasmic increase with greater deposition of liver glycogen in yellow tail tetra.

We aimed to evaluate the effect of poultry liver protein hydrolysate (PLPH) as feed additive on the productive performance of Nile tilapia reared in a water recirculation system and investigate stress responses and redox status after an air exposure challenge. Nile tilapia juveniles were distributed in 24 aquariums and fed plant-based diets supplemented with increasing levels of PLPH (0, 10, 20, and 40 g/kg) for 45 days. At the end of the experimental period, we did not observe a significant effect of PLPH on productive performance variables or body indices. Air exposure triggered stress responses in fish, as evidenced by an increase in blood glucose; PLPH supplementation, however, did not mitigate this effect. There was a quadratic effect of PLPH supplementation on malondialdehyde level and superoxide dismutase, catalase, and glutathione S-transferase activities, with optimum PLPH values estimated at 25.14, 25.91, 22.57, and 18.83 g/kg, respectively. Increasing PLPH levels reduced carbonylated protein contents and increased hydrogen peroxide levels in gills. Although PLPH supplementation increased antioxidant enzyme activity and attenuated protein damage, it also enhanced reactive oxygen species production and lipid peroxidation. Further studies are needed to better understand the mechanisms of action of protein hydrolysates on the redox status of fish subjected to intensive management.

With this study, we aimed to assess the safety of using Curcuma longa in fish feed. Juvenile Astyanax aff. bimaculatus (0.83 AE 0.04 g) were kept in 24 80-L aquaria, at a density of 0.5 fish L À1 for 60 days. Six diets supplemented with 0.0, 20.0, 40.0, 60.0, 80.0 and 100.0 g kg À1 were evaluated. Histopathological analysis of the gills showed that there was an increasing linear effect of turmeric on the frequency of lamellar aneurysm, hypertrophy of mucous cells, oedema and necrosis. There was a quadratic effect of turmeric supplementation on the frequency of fusion and disruption of secondary lamellae, vacuolation and hypertrophy of the epithelial cells, and the estimated values to minimize these variables were 4.63, 25.93 and 24.46 g kg À1 respectively. There was a quadratic effect of turmeric on the gills index (I BRA ), and the estimated value to minimize this index was 30.23 g kg À1 . No effect of turmeric on the frequency of histopathological changes and organ index in fish liver was observed. Thus, we conclude that turmeric is not hepatotoxic for A. aff. bimaculatus; however, its use is safe at concentrations up to 30.23 g kg À1 diet as a function of its gill toxic effect at higher doses.