A push is on to replace at least a portion of the diets of farm-raised fish with plant sources such as soybeans. One key reason why: growing pressure on the world’s wild fish and seafood stocks.

Demand for fish oil and fishmeal has skyrocketed over the past decade due to the growing popularity of Omega-3 fatty acids that many species contain, says Stanford University professor Rosamond Naylor in the September 8 Proceedings of the National Academy of Sciences.

Tighter regulations needed 
Naylor, an environmental professor of Earth system science, says that it takes as much as 5 lbs. of wild fish to produce 1 lb. of farm-raised salmon. “Our thirst for long-chain Omega-3 oils will continue to put a strain on marine ecosystems, unless we develop commercially viable alternatives soon,” she says.

Naylor calls for tighter regulations to reduce the use of fishmeal and fish oil in feeds. The scientist says that a 4% reduction in fish oil would cut the amount of wild fish needed to produce 1 lb. of salmon from 5 lbs. to 3.9 lbs.

This would be a far more efficient strategy than reducing use of fishmeal, she continues, as a 5% cut in fish meal use would have little environmental impact. Naylor says that “with appropriate economic and regulatory incentives, the transition toward alternative feedstuffs could accelerate.”

That search is well underway, J. T. Winkler, a London Metropolitan University, says in a Nutra Ingredients article.

Alternative feedstuffs 
Algae is one potential source, others are genetically modified (GM) soy and rapeseed (canola). The article says that genes with high levels of Omega-3 could be added to the crops to make them possible replacements for fish oil and fish meal, although research is continuing on both sides of the Atlantic.

In the United States, aquaculture production continues to expand at a rate of 15% and the largest cost component in aquaculture is feed, accounting for about 50% of production costs in the grow-out phase.

Fish meal (FM) is a major feed component and replacement of it with plant products provides two primary benefits, namely cost reduction and elimination of mercury contaminant problems associated with fish meal, according to a study conducted at the University of Rhode Island.

Fish showed maximum growth on a 40% soybean meal replacement diet plus taurine, significantly greater than all other diets except 40% plus amino acids and 40% plus taurine and phytase, while the FM diet was not significantly different from 40% plus amino acids, 40% plus phytase, or 40% plus taurine and phytase. Fish growth on all 70% replacement diets was significantly less than on all of the FM or 40% replacement diets, but no significant differences existed within the suite of 70% replacement diets.

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