Improved P utilization of marine feed resources

Sissel Albrektsen, Kaspar Thorsen and Halvor Nygård

¹ Nofima, Kjerreidviken 16, N-5141 Fyllingsdalen, Norway

Sissel Albrektsen, Kaspar Thorsen and Halvor Nygård

Phosphorus (P) is an essential element for normal energy metabolism, skeletal development and growth in fish. The main natural source of P in commercial fish feeds are fish meals and fishery products. In fish bones, P is mainly present in a complicated crystal structure with Ca known as hydroxyapatite ((Ca- PO₄) OH₂) and as constituent of Ca₃(PO₄)₂ which must both be hydrolysed into simple phosphates for intestinal absorption. Fish have limited and variable ability to digest P from fish meal (~10 – 80 %), Cho and Bureau (2001), making it difficult to predict that adequate P is present for normal growth and health of fish. The low capacity for P digestion especially in salmonids releases about 60-80 % of dietary P through faecal and urinary excretion, which is a major environmental concern. In commercial fish farming, addition of soluble P salts in the diet is needed to avoid P deficiency. Expected limitations in rock phosphates in the near future and demand for this non-renewable resource as fertilizer element, has increased cost and the need for developing more P efficient low-pollution feed ingredients in diets for farmed fish.

Nofima Ingrediens has developed a process for alternative processing of the bone fraction of fish meal by separation and hydrolysis to make the minerals more water soluble and available. Improved digestibility (average 60%) has been demonstrated for macro minerals and trace minerals, although the variation in between elements appears to be high. Digestibility of P in fish meal produced from blue whiting has been increased by 70 – 80 % by separation and treatment of the bone fraction in strong acids. Alternative processed fish meals with improved P digestibility have further demonstrated improved growth and skeletal mineralization in salmon similar to that produced by addition of commercial soluble P salts. Selected results from a strategic institute program (NRC project 173499/130: Improved phosphorus (P) utilization of marine feed resources - Dietary impacts and optimal P nutrition in Atlantic salmon and Atlantic cod) related to technological processing of the bone fraction, and to biological performance of salmon fed the P improved feed ingredients, will be presented.