Quantitative description of body composition and rates of nutrient deposition in rainbow trout (Oncorhynchus mykiss)

Current animal growth models rely on accurate quantitative description of body composition and nutrient deposition. The objectives of the study were to: (1) describe mathematically the chemical and physical composition of rainbow trout across life stages based on an extensive survey of the literature, and (2) examine rates of nutrient deposition. Data on chemical (proximate analysis, i.e. water, protein, lipid, ash) and physical (dressed carcass, viscera, etc.) composition of rainbow trout were obtained from 83 studies encompassing a wide variety of strains, life stages, and rearing conditions. The relationships between body weight (BW) and composition and rates of nutrient deposition were analyzed using linear regressions. Body protein stood out as the key predictor of BW across life stages. Body water mass was predicted most accurately from absolute contents of body protein and body lipid. Theoretical rates of nutrient deposition (Objective 2) were computed from a simulated growth curve using regression equations obtained under Objective 1. Theoretical rates of nutrient deposition were compared with observations from the literature. Theoretical and observed protein deposition (PD, [g (°C * d)− 1]) were similar across life stages of rainbow trout and increased until 370 to 500 g BW before levelling off, inducing presumably a change in growth trajectory. Lipid deposition rates [g (°C * d)− 1] were variable and continued to increase albeit at a slower rate after fish reached ∼ 400 g. Our results suggest that body weight gain (g/d) could be accurately predicted by the following equation: 1.86 + [6.09 × PD (g/d)]. This study is, to our knowledge, the first to examine rates of protein and lipid deposition in rainbow trout as a function of body weight. This type of information is crucial for developing a better comprehension of growth processes in fish.