A new approach for quantifying phosphorus requirement in an Amazonian fish using CT-scanning

Phosphorus (P) is an essential mineral for fish growth, as it plays pivotal roles in skeletal development and energy transfer reactions. However, the dietary requirement of this mineral is variable among fish species and the growth stages. Thus, this study aimed to determine the digestible P (dP) requirement for tambaqui in the initial growth stage ({+/-} 17 to 150g) using growth data, mineralization of the whole body, vertebrae and scales, as well as blood chemistry as response parameters. A total of 192 tambaqui juveniles of approximately 17 {+/-} 0.85 g were stocked into a water recirculation system. Fish were assigned to 24 70L-tanks using randomized block design (two floors) with six treatments (1.3, 2.4, 4.8, 6.3, 7.8 and 8.8 g kg-1 dP) and four replicates. Fish were fed six semipurified diets with increasing levels of dP for 90 days. The dietary requirement of P was estimated using regression models (P < 0.05). Duncan and SNK multiple range tests were used when regression models were not fitted. No mortality or apparent signs of P deficiency were observed. All performance variables were improved with increasing levels of dP in the diet. Based on weight gain, the P requirement was 6.3g kg-1 diet while for increased carcass mineral deposition was 6.6g kg-1 diet and for adequate mineralization of vertebrae the requirement was 4.75 g dP kg-1 diet. The blood chemistry parameters were greatly affected by the dietary P level, except for serum calcium. Thus, the dietary dP requirement for tambaqui juveniles in the early stage was 6.3 g kg-1 diet based on growth and bone mineralization.