The effect of dietary protein level on pond water quality and feed utilization efficiency of pacu Piaractus mesopotamicus (Holmberg, 1887)

The effect of supplemental feeds with different levels of crude protein on pond water quality and food utilization efficiency by pacu (Piaractus mesopotamicus) was evaluated in a semi-intensive culture system. Fish were stocked at a density of one individual per m(2), raised for 299 days, and fed isocaloric diets containing soybean meal, blood and bone meal, and yellow maize. Dietary treatments consisted of diets containing 25%, 35%, and 45% crude protein. Ponds receiving the two highest protein levels showed significantly higher values of alkalinity, conductivity and nitrites. High dietary protein diets resulted in no significant improvements in final weight (336.4 +/- 77.2, 308.2 +/- 92.6 and 368.4 +/- 82.2 g, mean +/- standard deviation, for 25%, 35% and 45% protein levels respectively). Moreover, fish carcass composition was not significantly different among treatments. Instead, significant augmentations in feed conversion ratio (1.36, 1.54 and 1.73 respectively) and reductions in protein retention (35.7%, 33.5% and 29.0% respectively) occurred as protein levels increased. Results indicate that at the lowest protein level, pacu growth rates and carcass composition were similar to the other experimental treatments, with a significant improvement in pond water quality and feed utilization efficiency.