Growth and blood chemistry of juvenile Neotropical catfish (Lophiosilurus alexandri) self-feeding on diets that differ in protein-to-energy (P:E) ratio

This study evaluated the growth and blood biochemistry were examined in juvenile Lophiosilurus alexandri that were self-feeding on feeds with different protein-to-energy (P:E) ratios. Juveniles (21.10 ± 0.39 g) were stocked at a density of six fish/tank (40 L) photoperiod 12L:12D, equipped with an on-demand feeder connected to a photoelectric cell. The 50-day experiment evaluated isoenergetic diets (17.65 MJ/kg) with crude protein levels from 25 to 42% and P:E of 14.56, 17.43, 20.44, and 23.91 g protein/MJ, in four replications, in a completely randomized design. The 23.91 g protein/MJ diet had the lowest leftover food and daily intake, while the 14.56 g protein/MJ diet had the highest leftovers. Polynomial regression analysis showed that the P:E ratios affected weight, average daily consumption per fish, protein efficiency, and weight gain had their lowest estimated values at 17.80, 21.23, 19.24, and 17.77 g protein/MJ, respectively. Feed conversion ratio peaked at 15.48 g protein/MJ, while the viscerosomatic index and carcass lipid had the lowest values at 22.74 and 20.03 g protein/MJ, respectively. Glucose, cholesterol, and low-density lipoprotein (LDL) were lower for animals fed a diet containing 24.17, 22.38, and 17.25 g protein/MJ, respectively. The total protein showed a increasing linear effect as the P:E ratio increased. High-density lipoprotein (HDL) had its highest value at 22.28 g protein/MJ. Thus, diets with an P:E ratio close to 23.91 g protein/MJ provide better adaptation of L . alexandri juveniles to the self-feeding system, along with better growth rates and blood biochemistry.