ENERGY-REQUIREMENTS, UTILIZATION AND DIETARY SUPPLY TO SALMONIDS

Energy needs of fasting salmonids are about 30-80 kJ/kg body weight/da y, depending mainly on water temperature. Maintenance energy requireme nts are estimated as 75-100 kJ/kg/day, about 10- to 20-fold lower than those of terrestrial vertebrates. Under negative N-balance or mainten ance conditions, body protein oxidation accounts for a greater part of the energy supply in fish than in higher animals. Energy requirements for body growth and tissue deposition have been studied to some exten t and current estimates vary between 15 and 18 MJ of DE/kg of live wei ght gain, being affected by water temperature, genotype, body size and growth rate. While the apparent digestibility coefficients of protein and fat from most commonly used feed ingredients are high, those of c arbohydrates vary widely. The additive nature of DE values appears to make the use of DE values reliable in feed formulation and feeding and the use of metabolizable energy (ME) values, especially those drawn f rom poultry nutrition, bears little practical significance. Due to the relatively high contribution of protein and amino acids as preferenti al energy substrates in fish, much attention is paid to the digestible protein to digestible energy (DP/DE) ratios, but precise, optimal val ues are not available for all species. Heat increment of feeding appea rs to be mainly related to protein intake. Few attempts have been made in the recent past to draw feeding tables based on DE requirements fo r maintenance and growth, the validity of which needs confirmation und er practical farming conditions.