Fish don't get their food from trees, say scientists

Washington, November 25 (ANI): A new research has rejected a study which had suggested that fish get almost 50 percent of their carbon from trees and leaves.

The research from the University of Washington shows this is not likely to be true.

"Other scientists have said that up to 50 percent of the carbon was coming from this terrestrial source. We're saying that's very unlikely," said Michael Brett, a UW professor of civil and environmental engineering.

The new research shows that algae are necessary ingredients for healthy zooplankton, the animals at the base of the aquatic food web.

Brett's lab studies omega-3 fatty acids, the same ones touted in health studies.

Fish can't produce the heart-healthy lipids; they just accumulate them from their diet.

Brett's group looks at where exactly the omega-3's are coming from, largely from several groups of phytoplankton that can make these fats.

After reading the fish food study published in 2004 in the journal Nature, "we were furrowing our brows and saying 'This doesn't make sense', because the terrestrial plants aren't producing these omega-3 molecules," said Brett.

The earlier study by the Institute for Ecosystem Studies in Millbrook, New York, was a large-scale experiment on three lakes in Michigan.

Researchers fertilized these lakes with a labeled form of carbon dioxide sprinkled on the lakes' surfaces over more than a month.

They then analyzed how much of that labeled carbon showed up in animals at each position in the aquatic food web.

Even when terrestrial plant matter was only about 20 percent of the available food, they found, the animals appeared to be composed of about 50 percent land-based carbon.

The UW study took a different approach.

Brett and colleagues raised zooplankton in the lab, feeding them a diet of either pure algae, pure land-based carbon, or various mixtures of the two.

They found that zooplankton that were fed a purely land-based diet survived and reproduced, but were small and produced relatively few offspring.

Zooplankton that were fed a diet of pure algae were 10 times bigger than their tree-fed twins and produced 20 times more offspring.

Zooplankton that were fed a mixed diet, were larger and produced more offspring as the proportion of algae in their diet went up.

Even when zooplankton ate almost nothing but land-based carbon, nearly all their lipids came from algae.

"I think we were able to show that the terrestrial source is such low quality that it's inconceivable that it could be nearly as important as what that study suggested," Brett said. (ANI)