Lupins in fish feed

Janne Karin Brodin

Fish feed can contain semi bitter lupin varieties as well as larger quantities of seeds from the lupin plant family without impairing the health and growth of the fish

Through using not only the sweet but also the semi bitter and more resistant lupin varieties in fish feed, the need for pesticides will be reduced.

Edison Serrano Photo: Janne Brodin

This is the conclusion in Chilean PhD student Edison Rodrigo Serrano Gutierrez, who defended his PhD thesis on April 27th 2011 at Norwegian University of Life Sciences. These results entail that plant growers in Chile can cultivate the more bitter varieties of lupin for feed production.

Even though lupin seeds are rich in protein, its use in fish feed has been limited. The reason for this is among other things the bitter taste, and a lack of knowledge about the level of lupin the fish will tolerate.

Lupins – a bitter protein source
In Chile, fish farming is an important production, and as in Norway it is necessary to find alternative feed ingredients to fish meal.

South America has a wide variety of lupins. The plant is well adapted to the climate, and there is serious interest in this production. Lupins are legumes, and lupin seeds contain more protein than both peas and soy beans. Salmon needs protein rich feed, so lupins are interesting as a protein source.

The problem is that lupins also contain the alkaloids lupinine and sparteine. Alkaloid is a common appellative for a large group of nitrogenous, harmful or poisonous compounds. Many of these are found in plants.

These substances often taste bitter. This is why lupins are left alone by grazing animals, says Serrano.

Found the tolerance limit for lupin seeds and alkaloids
In order to find how much lupin rainbow trout is willing to consume, and the limit for how much alkaloids the fish can take, Serrano conducted a series of feed experiments where he mixed varying levels of white lupin and the two alkaloids lupinine and sparteine into the feed.

The results show that the fish tolerated a high level (up to 50%) of white lupin without either reduced growth or any effect on internal organs or organ weights. However, the fatty acid profile in the fish fillet changed slightly when lupin content in the feed exceeded 30%.

When the alkaloid level exceeded 100 mg per kg feed, the bitter taste of the alkaloids led to reduced feed intake, and consequently to reduced growth.

Can use half bitter lupins
Even so, up to 100 mg of alkaloids per kg feed is a level way higher than what has been used till now. These results means that plant growers in Chile can produce half bitter lupin varieties containing 10 times more alkaloids than the sweet lupin varieties they grow today, says Serrano.

Lupins Photo: Edison Serrano

Alkaloids are the plant’s self defence
Wanting to increase the use of lupins for feeds, plant growers have tried to reduce the alkaloid content.

Lupins with a high alkaloid content are easier to grow, because these substances are the plant’s self defence against grazing, insects, pests and fungi. Low alkaloid content in the plants means increased need for pesticides in the plant production, Serrano explains.

No short term health risk from high doses
Many types of harmful effects of high doses of certain alkaloids have been reported. Therefore, Serrano wanted to examine whether alkaloids were harmful to fish health. Diets with up to 5000 mg per kg feed were tested.

The results showed that the high doses of lupinine and sparteine had clearly negative effects on taste and therefore on feed intake. Still, alkaloids in these high doses did not entail any demonstrable short term risk for the health of the fish, says Serrano.

Edison Serrano dissecting fish Photo: Liv Torunn Mydland

Norway-Chile project co-operation
This doctoral project is a co-operation between Aquaculture Protein Centre, a Centre for Excellence hosted by the Norwegian University of Life Sciences, and Universidad Católica de Temuco, Chile.

Updated: 16.05.11
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