The growth of fish is a consequence of two events, namely hyperplasia (increase in muscle fibre number) and hypertrophy (increase in muscle fibre size). In our previous study, we identified four phases of growth based on the muscle fibre recruitment pattern in rainbow trout. These phases are- hyperplasia (2.2 - 15 g), hypertrophy (15 - 50 g), hyperplasia (50 - 150 g), and hypertrophy (150 - 350 g). Based on these growth phases, the aim of this study was to determine the least cost feeding strategy for the nutritional programming of rainbow trout to maximize growth, feed utilization, and fillet quality.
In a six -month feeding trial, 1400 fish (5.8 g) were distributed into seven treatments in triplicates (70 fish/tank), fed isonitrogenous (42% crude protein) and isolipidic (20% lipid) diets according to the feeding protocol depicted in Figure 1. Briefly, T1, T4, and T7 fed fish meal (FM), plant protein (PP), and additive mixture ( AF, krill meal, taurine, and organic selenium) supplemented diets throughout the feeding trial, respectively, whereas the other four treatments were subjected to diet switching during the end of each growth phase.
Both FM (T1) and AF (T7) individually or in any combinations (T5 and T6) showed higher (p<0.05) weight gain than other groups in the last phase (PHASE 4) (Figure 1). The feed conversion ratio (FCR) of T2 and T4 was higher than other groups; however, no difference in FCR was found among other groups. Muscle fibre recruitment pattern, the expression of myogenic genes, and fillet quality are being analyzed. Conclusively, during hyperplasia, the high-quality protein-demanding phase, AF performs better than FM. The application of targeted nutrition to different growth phases shows promising results to maximize growth and reduce the feed cost. Overall, this novel feeding strategy will reduce the cost of fish production .