June 26, 2009

Marine nutrients of great value to farmed fish can be better exploited in combination with plant proteins, according to scientists in Norway.

The aquaculture industry wants to use less of fishmeal, which although is a rich source of protein, it is also expensive, unsustainable and inflexible. Therefore, an increasing amount of fishmeal is being replaced with protein-rich plants.

But plants cannot completely replace marine ingredients without affecting the performance of farmed fish.

As a result, Nofima Ingrediens is attempting to increase the nutritional value of the fishmeal so that less fishmeal is required in the feed than before.

Some of the substances that make marine raw materials valuable are separated by stickwater. To exploit stickwater, it is highly concentrated and transferred back to the fishmeal. Stickwater contains substances including free amino acids, peptides, small proteins, minerals, soluble vitamins and small components such as taurine, creatinine and carnosine.

All stickwater is transferred back in the production of high quality fishmeal, but there is a surplus of stickwater in low quality fishmeal production that can be exploited in fish feed for the aquaculture industry, according to Katerina Kousoulaki of the project.

The scientists wanted to see how large the growth gain was for salmon receiving feed with different contents of stickwater, and feed in which part of the fishmeal was replaced with meal of vegetable origin.

A trial was carried out in which juvenile salmon in saltwater received eight different feeds. One of the feeds was commercial and contained 30 percent fishmeal. The remaining seven feeds contained just 10 percent fishmeal, but contained stickwater equivalent to that in the commercial feed and up to 200 percent over and above that found in commercial feed.

The results after 10 weeks' feeding showed that there was no difference in growth between fish that had received 10 percent fishmeal with an extra supply of stickwater and those that had received 30 percent fishmeal.

These results show how decisive tiny marine components are in salmon feeds containing much plant material.

Increased use of stickwater will mean that the feed producers can use more vegetable protein raw materials than previously.