It's one of the great environmental ironies of aquaculture – although the fish themselves come from farms, the food that they're raised on still contains wild-caught fish. A few years ago, however, a study showed that prawns could be fed microbes instead of fish byproducts. Now, a more recent study has concluded the same thing about tilapia, one of the most farmed fish in the world.

Ordinarily, fish meal and fish oil are included in commercial feeds in order to help fish grow large, and to do so quickly. When it comes to the oil, though, scientists from Dartmouth College have found that the marine microalgae Schizochytrium works even better.

In lab tests, juvenile Nile tilapia were given a food containing dried Schizochytrium in place of the usual fish oil. When compared to a control group being raised on regular food, they were found to exhibit higher weight gain and better food-to-growth conversion, plus their flesh was higher in healthy omega-3 fatty acids. Vegetable oils have previously been put forward as a fish oil alternative, although they don't result in such high omega-3 levels.

The scientists are now looking at replacing the fish meal as well, and are exploring cost-effective methods of raising microalgae for use in the aquaculture industry.

"Researchers have to find the ways to cut the high production cost of microalgae in order for such nutritionally enhanced tilapia to succeed in the market," says Prof. Anne Kapuscinski. "Towards this end, we are exploring ways to reduce production costs and the environmental footprint of microalgae production by using organic waste streams as a partial replacement for expensive inputs of inorganic fertilizer normally used to grow microalgae."

A paper on the research was recently published in the journal PLOS ONE.