Effect of muscle growth dynamics on nutritional requirements of Nile tilapia

Nile tilapia is an African freshwater fish species, which has become one of the main farmed fish species worldwide in the past decades. This rapid increase in tilapia production was made possible by an intensification of farming practices. Among other factors, the use of formulated feeds largely contributes to improving the growth rate of farmed fish. The efficiency at which formulated feeds are utilised by fish to grow has a large influence on the environmental footprint and economical performance of tilapia production. In this regard, the retention of dietary protein into muscle tissue (i.e., fillet) is of particular importance. Protein deposition into white muscle tissue is an energy-demanding process. This makes the balance between dietary protein and non-protein energy content an important aspect of overall feed efficiency. In Nile tilapia, most proteins are retained in the white muscle tissue. Unlike in other farmed animals (e.g., mammals and birds), post-embryonic white muscle growth results from both the recruitment of new fibres (hyperplasia) and the enlargement of existing ones (hypertrophy) in fish. However, both processes are limited in the sense that hyperplasia decreases with age and that hypertrophy is limited by a maximal functional fibre size. Whether such limitations affect the protein gain capacity of fast-growing fish is not clear yet. This PhD project has the following objectives: - test if Nile tilapia growth and feed efficiency can be optimized through changes in the balance between dietary protein and non-protein energy content. In other words: is there an optimal dietary P/E ratio for Nile tilapia feeds? - describe the evolution of white muscle fibre hyperplasia and hypertrophy with increasing fish age and size. In other words: are there time and size limitations to the recruitment and enlargmeent of white muscle fibres in Nile tilapia? - test if contrasts in the rates of white muscle fibre hyperplasia and hypertrophy induced during early life affect the protein gain capacity of Nile tilapia at later life stages. These questions will be answered through analysis of existing data and in vivo experiments.