Researchers at Texas Sea Grant study changes to aquaculture diet for greater sustainability

by Cindie Powell, Texas Sea Grant

A discovery by a Texas Sea Grant-funded researcher may help decrease demand on the world’s fish stocks for use as feed in marine aquaculture.

Dr. Lee Fuiman, professor and director of the Fisheries and Mariculture Laboratory at The University of Texas Marine Science Institute in Port Aransas, is leading a study on the influence of diet on the fatty acid composition of the eggs of red drum, Sciaenops ocellatus. He found that while a feeding regimen high in fatty acids is necessary to produce high-quality eggs and offspring in marine aquaculture, the length of time at least one of these nutrients is needed in feed is much briefer than the industry’s current practice.

“If you look at the feeding practices of red drum producers, they typically feed a really rich diet for many months to fatten their fish up to produce good eggs, which suggests that they believe the female has to store rich nutrients in its body months before spawning,” Fuiman says.

All of the nutrients in eggs — fatty acids, amino acids and vitamins — come from the mother, but some of them come from stores in her body and others from her diet. It is not well known how far in advance in a pre-spawning regimen  female fish needs to be fed a diet rich in fatty acids so the optimal amount are passed to the eggs.

Essential fatty acids are needed for biological processes, but they are not produced by the body and therefore must be ingested in the diet. The composition of fatty acids in marine fish eggs has been shown to affect the growth and development of the embryos and fish larvae. Fuiman and others have demonstrated its importance in the ecological performance of the young fish, commonly known as fingerlings, including their ability to evade predators.

“Producing high-quality eggs produces better quality fingerlings. They grow faster if you can pack all the right nutrients into the egg,” Fuiman says.

The fatty acids in marine aquaculture feed come primarily from the ocean harvest of small, oily fish like anchovies and menhaden. With finite supply and growing demand, fishmeal is an increasingly expensive and possibly unsustainable component of aquaculture feed.

The researchers found that changes to the fatty acid content of female fish, specifically concerning the fatty acid arachidonic acid (ARA), were reflected in the fatty acid content of the eggs. These changes were recorded within two to 16 days of the mother’s diet having changed.

“With ARA, we’ve found it’s what the female eats in the few weeks before spawning that really matters,” Fuiman says. “This means we can make egg production much more efficient, less expensive and more sustainable.”

Their studies are ongoing for a second fatty acid, docosohexaenoic acid (DHA), and many others.

Red drum, also known as redfish, is a significant commercial aquaculture species in Texas with harvests valued at about $9 million a year. It is also one of the two most popular species for saltwater recreational fishing in the state, with an economic impact of more than $560 million a year, and is the focus of a major long-term restocking program run by the Texas Parks and Wildlife Department. The agency breeds fish in aquaculture facilities and releases the fingerlings into the bays and estuaries; how well those fish survive in the wild is an important factor in the success of the program, and egg quality may contribute to that success.