Sustainable production of nutritionally valuable fish and fish products

Fish are rich in protein and long chain omega -3 (n-3) fatty acids (FA) and are a good source of essential minerals and vitamins. In many countries, fish and fish products are an important protein source and with growing populations the importance of fish increases even more.

My aim is to work towards the sustainable production of fish and fish products with high nutritional value, an optimization of fish raw material use and decrease of food waste. In my lecture, I will address how to increase sustainability of aquaculture by reducing fish oil in feeds. I will also discuss possibilities to optimize the use of fish raw material during processing and to avoid waste by increasing storage stability.

A sustainability issue in aquaculture is the high use of fish oil in some feeds. Aquaculture consumes for example about 70% of the globally produced fish oil. Therefore, it is necessary to reduce the amount of fish oil in the feeds. On the other hand, it is important to keep the high nutritional value of the fish. I will give a few examples from my research how this can be reached.

Partial replacement of fish oil by plant oil has been one major strategy in the feed industry. However, this leads to a decreased proportion of the desired long chain n-3 FA in the fish, as plant oils are usually rich in omega-6 FA. Due to increased use of plant oil, in 2015 a 130 g portion of salmon from aquaculture contained only about 50% of the long chain n-3 FA compared to the same portion in 2006. One way to avoid this, is to use a so called finishing feeding technique, where the fish is fed feed with only plant oil during the growing period and then with fish oil for the final period of rearing to increase the long chain n-3 FA in the fish before marketing.

As plant oils also could be directly used for human consumption, feed sustainability would be even more increased with oil from alternative sources that do not compete with human food. Insects have been evaluated both as protein and lipid source for fish. They can be reared on for example food waste, which would contribute to a circular system and hence increased sustainability. However, insects are not a good source of n-3 and the FA composition of the up to now evaluated species can only be influenced by diet to a certain extent. Another alternative to plant oils are single cell oils produced by for example oleaginous yeasts. Yeast oils from different yeast species have successfully been tested in the feed of Arctic char. These yeasts can be grown on hydrolysates of straw and forestry by-products, which contributes to creating a circular production system. Currently high costs of insects and single cell oils compared to plant oils limit their use in fish production. Optimisation of the production is essential for successful implementation.

An example of optimized fish raw material use is the use of minced fish flesh separated from the bones of carp after filleting. This mince can be used as an n-3 rich ingredient in traditional meat products without any negative impact on sensory aspects. In another study, natural antioxidants from berries were successfully used in herring, increasing storage stability and nutritional value of the final product. In the future a combination of underutilized by-products from fish with bioactive compounds from vegetable and animal by-products can result in promising, healthy, and sustainable novel food products. Besides nutritional value and storage stability it is also important to evaluate processing effects on texture and sensory aspects. The latter are of major importance for consumer acceptance.