2. SUMMARY REPORT OF THE TECHNICAL SESSIONS

2.1 Session 1. Energy

One review paper and four experience papers were presented, mainly dealing with a critique of the different methods employed for the determination of energy requirements in salmonid fish, including energy balance methods, comparative carcass analysis methods, direct and indirect calorimetry, factorial analysis, and apparent digestibility indicator methods. Particular emphasis was placed on the importance of nutritional energetics in diet formulation and development of dietary feeding standards, and the need of studying the energy balance of fish on a whole animal basis.

2.2 Session 2. Proteins and amino acids

One review paper and ten experience papers were presented, mainly concerning methodological approaches for the determination of dietary protein and amino acid requirements, including dose-response methods based on long term growth studies, direct and indirect amino acid oxidation methods, plasma and whole body tissue amino acid concentrations, and methods based on carcass nitrogen retention or deposition. Particular importance was given to the need to determine dietary protein and amino acid requirements within rapidly growing fish using nonrestrictive feeding regimes. In general it was felt that the essential amino acid (EAA) requirements of fish were not too different from higher vertebrates and that the differences observed in EAA requirements between fish species were probably due to methodological differences between laboratories rather than to real species differences. In addition, it was generally felt that the whole body EAA pattern of fish served as a good reference standard for the formulation of test diets or rations for new fish species.

2.3 Session 3. Digestion, utilization of protein and energy

Nine experience papers were presented, mainly concerning methodological approaches for the estimation of nutrient utilization and digestibility in fish, including starvation and carcass analysis methods, nitrogen excretion methods, oxygen uptake methods, and in-vivo and in-vitro methods for the estimation of nutrient digestibility. In general it was felt that in-vivo digestibility measurements using dietary markers were extremely useful for ascertaining the utilization of dietary nutrients and performance of diets and as such should be routinely estimated within nutritional growth trials.

2.4 Session 4. Lipids and essential fatty acids

One review paper and four experience papers were presented, mainly dealing with methodological approaches and criteria for estimating the essential fatty acid (EFA) requirement of fish, including dose-response methods based on long-term growth studies, analyses of liver phospholipids, and methods based on the use of radioactive polyunsaturated fatty acid (PUFA) precursors and cell culture techniques. In general it was felt that still relatively little was known regarding the metabolic function of EFA or concerning their exact quantitative dietary requirements in fish. Particular emphasis was placed on the importance of dietary EFA balance, and in particular the ratio between ω3 and ω6 fatty acids, and effect of dietary lipids and EFA on tissue histology and carcass fish quality.

2.5 Session 5. Carbohydrates

One review paper and two experience papers were presented concerning the digestibility and utilization of dietary carbohydrates in fish. Particular emphasis was placed on the profound effect of heat processing, dietary carbohydrate inclusion level and dietary feeding regime on carbohydrate digestibility. In addition, evidence was presented which suggested that glucose utilization in fish may be influenced by the dietary concentration of chromic oxide used for measuring nutrient digestibility.

2.6 Session 6. Minerals and trace elements

One review paper and four experience papers were presented, mainly dealing with methodological approaches for determining the dietary mineral requirements of fish, including mineral balance studies and dose-response methods based on fish growth and indicators such as tissue mineral retention or storage. Particular attention was given to the factors influencing the mineral requirements of fish such as fish size and growth rate, diet composition, mineral chemical form and availability, and mineral interactions with other dietary or water borne elements.

2.7 Session 7. Vitamins

One review paper, six experience papers and seven poster papers were presented, mainly concerning methodological approaches and criteria for determining the dietary vitamin requirements of fish, including dose-response methods based on fish growth, vitamin tissue storage levels, specific vitamin-dependent enzyme activities, and stress or immune responses. Particular importance was given to the need of determining dietary vitamin requirements within rapidly growing fish under environmental conditions similar to the intended practical farming system. It was clearly shown that the reported dietary vitamin requirements of fish was dependent upon the criteria used by researchers to estimate the requirement, ranging from low requirement levels for optimal growth to high requirement levels for maximum tissue storage or optimum disease resistance.

2.8 Session 8. Feed additives

One review paper and two experience papers were presented, mainly dealing with methodologies for the evaluation of feed additives within fish feeds, including technical tests, short and long-term biological tests, tests concerning the health of the fish, tests on the sensory aspects of the product, and environmental tests. Particular emphasis was placed on the importance and need for good experimental design and standardization of environmental conditions when testing feed additives so as to minimize variations between treatments.

2.9 Session 9. Application of nutrient requirement data

One review paper, six experience papers and four poster papers were presented concerning the application of nutrient requirement data under practical farming conditions. Particular attention was placed on the need to design nutrient requirement studies in such a manner that the ensuing results can be directly applied to practical semi-intensive or intensive farming conditions. The need to determine the dietary nutrient requirements of warmwater freshwater fish species within semi-intensive pond farming systems was emphasized. In addition, it was generally felt that experimental methodologies should ensure that non-restricted dietary feeding regimes are employed and that an analysis of fish quality and tissue histology be undertaken on a routine basis during nutritional feeding trials whenever possible.