Fishmeal-free salmon feeds says Skretting scientist20 November, 2009 –
A GROWING list of functional feed ingredients is delivering potential for productivity, health promotion and sustainability in aquaculture.
Skrettings Aquaculture Research Centre (ARC) is giving increasing attention to feed ingredients that perform special functions.
Wolfgang Koppe, leader of the ARC Fish Nutrition team explains: As we developed a deeper understanding of fish nutrition over the past 20 years we realised there are some minor ingredients that have an important effect in addition to, or even without contributing to, conventional nutrition for growth. We refer to these compounds as functional ingredients.
Probably the first and best known group are the beta-glucans, which stimulate the immune system of the fish, he continues. However, research in recent years has revealed a much longer list of ingredients with a wide range of functions. These functional ingredients contribute to feed conversion and growth rate, fish health and welfare and, importantly for the future of aquaculture, to reducing dependence on high levels of fishmeal in the feeds.
The arrival of beta-glucans in the early 1990s and their ability to boost immune systems provided an important tool in efforts to combat the effects of bacterial diseases such as furunculosis that had become an increasing problem. However, it was a few years before the full significance of such functional ingredients was explored.
Dr Koppe adds: In the 1990s our attention was focused on analysing the nutrient content of fish meal as a package of nutrients: fatty acids, amino acids, minerals and vitamins. Using this knowledge, we were able to bring fishmeal levels down to 25% while still delivering diets to support fast growing, robustly healthy fish. However, 25% seemed to be the limit. Then we turned our approach around and began to explore whether some nutrients had functionalities that we had not observed and that might depend on the form in which the nutrient is provided.
For example, we have known for some time that the fatty acids EPA and DHA are essential nutrients for fish. But in fishmeal both are present as phospholipids whereas they are bound as triglycerides in fish oil. Triglycerides are absorbed and used mainly for energy generation and fat deposition. Phospholipids are known to influence digestive processes. Other functional ingredients we have identified support, for example, gut health and hepatic function. Others act as immuno stimulants and as antioxidants performing important functions within the fish body down to cellular level. The presence of antioxidants in the right form also improves uptake of pigmentation.
These functional ingredients deliver benefits in terms of performance and health and many are present as part of the nutritional package provided by fishmeal. This led us to ask whether added functional ingredients in the right form could help us take fishmeal contents in diets below the 25% that seemed to be the lower limit. We ran a series of low fishmeal feed trials with combinations of functional ingredients in a variety of forms. These led to the advances first announced in 2008 where we have entirely successful fish performance from feeds with fishmeal contents of 15%. It is clear that when replacing fishmeal it is essential to be accurate in terms of the form of functional ingredients and in covering the full range. If you only address the limiting factor, you will not progress far before finding the next limit.
We have recently made further progress with feeds containing significantly less fishmeal close to 0%. In parallel, we are investigating the potential of other raw material sources, for example the by-products of other industries, to provide functional ingredients in the form required. There is another aspect of functional ingredients opening up as we explore and that is known as nutrigenomics. Nutrigenomics is the effect certain feed ingredients have on gene expression, switching the gene function on or off.
The original functional ingredients, beta-glucans, continue to provide health benefits and are now supported by other ingredients that our research has identified. We use various combinations in our health promoting diets such as the Protec diets being used for salmonids and marine species. In Protec diets, for example, the beta-glucans combine with a unique blend of organic acids and plant extracts that stimulate gut health and optimise gut micro-flora while antioxidants work on an intra-cellular level to mop up the free radicals generated by an immune system fighting an infection.
Dr Koppe concludes: There is no doubt that an understanding of functional ingredients has helped us make substantial progress in fish nutrition and in the supply of feeds that deliver performance and health benefits. Equally, there is no doubt that continuing exploration of functional ingredients will bring further advances in feed performance and will enable us to contribute to the sustainable expansion of aquaculture.