Protein to energy ratios and cost, performance, and ammonia excretion in juvenile jundiá (Rhamdia quelen), South American catfish

ABSTRACT

The determination of nutritional requirements, based on diets administered in practice, considers physiological specificities and sustainability are essential to the development of suitable aquaculture technologies for novel fish species. The growth of jundiá (Rhamdia quelen Quoy and Gaimard) juveniles (31.54 ± 4.92 g) fed five diets comprising increasing levels of digestible protein (DP 24, 29, 34, 39, and 44 %) and digestible energy (DE 12.13, 13.39, 13.81, 14.64, and 15.06 MJ kg−1) with DPDE ratios 20, 22, 25, 27, and 29 g MJ−1, respectively, was evaluated. Each diet was fed to three groups of 25 fish for 75 days. Regression analysis showed that the different DPDE ratios affected both growth and economic performance as well as excretion of total ammonia nitrogen. Fish fed diets with DPDE ratios between 22 and 27 g MJ−1 achieved a higher daily weight gain, superior apparent net protein utilization, feed conversion rates, and lower feed costs. For the economically viable and environmentally friendly farming of jundiá juveniles in the initial grow–out stage (30 to 80 g average weight), the best DPDE ratio was 25 g MJ−1 DPDE (34.05 % DP and 13.81 MJ kg−1 DE).