Fish oil replacement in starter, grow-out, and finishing feeds for farmed aquatic animals

As aquaculture production continues to grow, there will be an increased use of lipid resources (oils and fats) alternative to fish oil for feed production. The potential for the use of these alternatives varies depending on the feeds in which they are included according to the production phase of the animals to which they are being fed. In starter feeds, where rapid growth, high survival, and normal development are critical priorities, there will remain a need for the use of lipid resources high in omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA). Fish in this starter phase have a critical requirement for the n-3 LC-PUFA docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), and fish oils remain the only cost-effective source of these nutrients in the volumes required. However, the greatest demand for lipids is in those diets for the grow-out phase. Most studies on alternative lipid use with animals in this part of the production phase show positive outcomes, in that there are few studies where all the added fish oil cannot be replaced. There are some species, however, where potential replacement levels are suggested to be more conservative, and a general substitution level in this production phase of 75% has been suggested. One of the key effects noted across the grow-out phase is that all alternatives affect the flesh fatty acid characteristics by reducing the level of n-3 LC-PUFA. This issue has provoked the concept of finisher diets, whereby a high n-3 LC-PUFA content diet is fed in order to restore the desired meat fatty acid profiles. Studies examining this concept have found that the tissue triacylglycerol fatty acids were greatly modified and responded in a simple dilution process to the added oil fatty acid composition, whereas the fatty acids of tissue phospholipids were less influenced by dietary fatty acid makeup.