RESUMO
This study aimed to evaluate the effect of the biofloc technology (BFT) system and the replacement of fish meal with Spirulina biomass on productive performance, intestinal histomorphometry, plasma biochemistry, and oxidative stress of Nile tilapia juveniles (Oreochromis niloticus) fed suboptimal levels of protein. Two factors were evaluated: production systems (clear water × BFT) and replacement of fish meal with Spirulina (0, 33, 66 e 100%). The design was in a 2 × 4 randomized factorial scheme with four replications, and the fish were evaluated for 48 days. Four isoproteic (28% crude protein) diets were formulated with gross energy values close to 4300 kcal kg-1. Nile tilapia juveniles (0.23 ± 0.01 g) were distributed in 16 circular tanks (70 L) at seven fish/tank. The diets were formulated with protein levels approximately 20% below that required for the species and life stage. No interaction was observed between the factors evaluated (production systems × Spirulina inclusion). Rearing the fish in the BFT system avoided the adverse effects of diets with suboptimal protein levels on performance, intestinal histomorphometry, and protein metabolism. Lower values lower lipid peroxidation and higher antioxidant capacity were observed in fish reared in the BFT system, showing evidence of improvements in antioxidant responses and lower levels of physiological oxidative stress. Spirulina completely replaced fish meal in the diets of Nile tilapia juveniles without adverse effects on intestinal morphometry, protein metabolism, and antioxidant response. Replacing 66% of fish meal with Spirulina improved the productive performance, regardless of the rearing system.
Assuntos
Ração Animal , Ciclídeos , Dieta , Intestinos , Spirulina , Animais , Ciclídeos/metabolismo , Ciclídeos/crescimento & desenvolvimento , Ração Animal/análise , Intestinos/efeitos dos fármacos , Dieta/veterinária , Proteínas Alimentares/administração & dosagem , Estresse Oxidativo/efeitos dos fármacos , Fenômenos Fisiológicos da Nutrição Animal , Aquicultura/métodosRESUMO
The objective of this study was to evaluate the toxicity of the antiparasitic agent eprinomectin in two subtropical soils, using ecotoxicological lethality, reproduction and avoidance behavior tests with springtails (Folsomia candida). Eprinomectin concentrations were 0 (control), 0.5, 1, 2, 4, 8, 12, 16 and 20â¯mgâ¯kg-1 of dry soil combined with either Entisol or Oxisol soils. Statistically significant toxic effects of eprinomectin on springtails were observed in both soils. Eprinomectin was lethal starting at 8â¯mgâ¯kg-1 of dry soil in Entisol, and 20â¯mgâ¯kg-1 of dry soil in Oxisol, with effects less than 50% at lethal concentrations. Reductions in the reproduction rate of the springtails were also observed starting at 8â¯mgâ¯kg-1 of dry soil in Entisol, and 0.5â¯mgâ¯kg-1 of dry soil in Oxisol. ECrepr50 value calculated for Entisol was 4.38⯱â¯0.62â¯mgâ¯kg-1 of dry soil; for Oxisol the ECrepr50 was above the highest tested concentration. For avoidance behavior, the effect occurred from 0.5â¯mgâ¯kg-1 of dry soil for both soils. In Entisol, all concentrations caused avoidance of more than 95%, and in Oxisol the ECavoi50 value was 1.33⯱â¯0.83â¯mgâ¯kg-1 of dry soil. We conclude that eprinomectin affected survival, reproduction and caused avoidance behavior of F. candida in both soils. The toxic effects were greater as the concentration in the soils increased. The effects in Oxisol were less intense than those in Entisol with respect to the affected springtails. This discrepancy may be attributed to the different physicochemical characteristics of the soils that determine the retention capacity for eprinomectin; in particular, there are greater contents of clay, organic matter and cation exchange capacity in Oxisol.