Regulação do consumo de dietas com diferentes relações de energia: proteína pelo bagre neotropical Lophiosilurus alexandri

Abstract

The effect of different energy to protein ratios on voluntary feed intake was investigated in the carnivorous catfish Lophiosilurus alexandri, a species recently introduced into Brazilian aquaculture. Two experimental trials were performed. The first trial involved 16 fish distributed among 16 tanks, which were allowed to select one of two experimental encapsulated diets (24% vs 42% of crude protein or E:P of 0.068 x 0.041 MJ g - ¹ protein). The objective was to isolate sensorial influence on the choice of diet. For the second trial,six experimental groups were designed with successive increases in protein to evaluate diet selection by the self-feeding method: Group 1 - 24% of crude protein x 30% of crude protein; G2 - 24% x 36%; G3 - 24% x 42%; G4 - 30% x 36%; G5 - 30% x 42%; and G6 - 36% x 42%. These groups had the following energy to protein ratios (E:P MJ g-¹ protein): G1 – 0.068 x 0.057; G2 – 0.068 x 0.048; G3 – 0.068 x 0.041; G4 – 0.057 x 0.048; G5 – 0.057 x 0.041; and G6 – 0.048 x 0.041. Data were subjected to Levene's test for homoscedasticity and the Shapiro-Wilk test for normality. Diet selection data were arcsin (√) transformed and then subjected to the Student T test. Mean protein (g / kg of BW), energy: protein (MJ energy / g crude protein / kg BW) and energy (MJ energy / kg BW) consumption were submitted to ANOVA and Tukey test. Statistical significance was considered at P<0.05. The results of Trial 1 revealed a clear preference for diet with 42% crude protein and an energy to protein ratio of 0.041 MJ g-¹ protein (P<0.05); even with the absence of taste the fish returned to the initial pattern of selection after the contents of the capsules were changed. Trial 2 revealed that with diets containing less than 30% crude protein (G1), the fish selected diets with higher energy (P<0.05). In G2 and G6 the fish exhibited an unclear pattern of diet selection probably due to the narrow range of nutrient options or because the requirements for protein and energy were met by the diets, respectively. For the G2, G3 and G5, fish choose diets with higherprotein content (P<0.05), even after the diets were switched between feeders. The animals kept the protein intake pattern from G4 (~36-38% or 20g/BW) and energy consumption (8.42 MJ kg-1 ) for all treatments. In conclusion, levels of voluntary protein and energy intake depend on the availability or range of dietary nutrients. Based on the feeding behavior of L. alexandri in the present study, we infer that the target E:P is around 0.028 MJ g-¹ protein.