Assessing body composition and dietary phosphorus retention using Dual‐energy X‐ray absorptiometry (DXA): Application on juvenile rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract

Dual-energy X-ray absorptiometry (DXA) was evaluated to estimate body composition of rainbow trout (Oncorhynchus mykiss), with an emphasis on phosphorus (P) retention. Ninety rainbow trout (36-136 g) fed with control (1.10%) or low-P (0.55%) diets were scanned using a DXA instrument, both frozen and thawed. Whole-body scans were analysed using the ‘rat whole body’ scan mode. Chemical analyses determined crude lipid and crude protein, water, ash, phosphorus (P) and calcium (Ca). Except for lipid, DXA predicted accurately body composition. The prediction capabilities of the model were assessed by comparing actual and simulated body composition using the generated equations. Results showed good agreement except for lipid and P for which adjusted equations were proposed resulting in highly improved predictions. To predict total carcass P, P retention/excretion, an equation predicting body P was developed and adjusted based on the validation (Body P [g] = −0.087 + 0.103 [BMC] + 0.00336 [lean], R2 = .91, p < .001). Retention and loading estimates for P using models from DXA are similar to those from chemical methods. Our results suggest that DXA can estimate body content of protein, moisture, ash and P; refinement is needed to predict body lipid content.