Balancing protein and energy in Nile tilapia feeds: A meta-analysis

Farmed fish are increasingly grown in intensive and semi-intensive systems where most nutrients are provided by formulated feeds. These are formulated to minimise costs and optimise growth, notably the rate of muscle protein synthesis (i.e., fillet). Protein synthesis depends on the availability of amino acids (i.e., protein) and energy. Thus, fish feeds are often formulated to provide a balanced ratio of protein to energy (P:E). Above and below the optimal dietary P:E, absorbed protein and energy are expected to be under-utilised for body protein synthesis, respectively. Estimates of the optimal dietary P:E vary largely for Nile tilapia (Oreochromis niloticus (L., 1758)). Published values range from 13 to 26 g of dietary protein per MJ of energy. Here, we challenge the idea that growth, protein utilisation efficiency and body composition can all be simultaneously optimised, when Nile tilapia are fed an optimal dietary P:E. Through linear and non-linear regression meta-analyses, we quantitatively describe the effects of protein and energy intake on nutrient partitioning, feed efficiency and growth. We find linear relationships between the dietary P:E and protein retention efficiency. The lack of an inflection contradicts the existence of an optimal P:E. Our regressions of protein and energy intake versus protein gain, indicate that protein gain is often simultaneously limited by both protein and energy intake, and may be limited by other factors than protein and energy intake, such as a maximal protein deposition capacity (PDmax). We conclude that there is no physiological basis for an optimal P:E in Nile tilapia feeds.

Automated summary

This study challenges the idea of an optimal P:E ratio in Nile tilapia feeds, and quantitatively describes the effects of protein and energy intake on nutrient partitioning, feed efficiency, and growth. The results suggest that there is no physiological basis for an optimal P:E, contradicting previous beliefs.