Historical developments and current issues in fish nutrition

For many decades, the yearly growth rate of cultured fish is above 7%. Currently, more than 50% of human fish consumption comes from aquaculture. This presentation addresses the historical developments in terms of nutrition. It includes: changes in nutrient levels and energy content of fish feeds; changes in feed processing; progress in knowledge on requirements; alteration in ingredients used in fish feeds (fishmeal & –oil replacement). Comparisons are made to show similarities and differences to land animals. Aquaculture is characterized by a large variability in many aspects. This variability is a challenge for fish nutritionist to formulate/develop optimal fish feeds. More than 100 species are commercially farmed and their number is still increasing. Differences in feeding ecology, trophic levels, anatomical differences (e.g., gastric vs agastric species), differences in aquatic environment (fresh water, brackish or marine; cold, temperate or tropical), all can have implications on meeting nutrient requirements. Next to species diversity, culture/husbandry conditions exhibit large diversity (pond, race way, cages; water quality management/water refreshment). Examples are given on impacts of husbandry conditions on meeting nutrient/energy requirements. In culture systems with minimal water exchange, the diet can indirectly influence fish by its impact on water quality (feed waste/spillage, faeces and metabolite excretion). In other words, feed ration size and composition are important factors, which determine the quality of the environment in which the fish live. This presentation addresses the implications of the biotic and abiotic factors as well as husbandry conditions in relation to nutrition such as: nutrient requirements; impact of physical condition feed/food type consumed (e.g. size & water content); interaction between nutrition and water quality; impacts of fishmeal/oil replacement.