USDA lead scientist explains aquaculture's need for algae

By Luke Geiver | November 02, 2011

Aquaculture has passed the 50 percent mark, meaning it now provides more fish for human consumption than wild harvested fish, according to Rick Barrows, lead scientist for USDA’s Agricultural Research Service. “Aquaculture is growing very quickly,” he said. “It is currently a $97 billion global business, growing at 9 percent per year.” Barrows, who told a crowd at the 2011 Algae Biomass Summit that he gets calls all year long about people with fish feed products and ingredients for use in aquaculture, said we still have a limited knowledge of ingredients. And this “is where algae fits in,” he said.

For Barrows, there is a huge need for alterative ingredients and worldwide fish feed researchers are looking for every ingredient possible. “Over the last 20 years the yield of fish meal has been pretty much constant,” he said, “so we aren’t getting any more fish feed out of the ocean and we [aren’t] getting any more fish meal ingredients.” So, he asks, “What are we going to do?”

Part of the answer for Barrows is algae. “All types of species in aquaculture are interested in the essential fatty acids that can be found in algae because that is what makes fish a heart-healthy, brain-healthy food,” Barrows said. Although it is possible to use animal feed for fish meal, the cost is too expensive and certain minerals and vitamins would need to be replaced.

Using the six-step process for evaluated ingredients in fish meal, along with two separate studies that showed the effectiveness of algae-based fish meal, Barrows explained that algae can act as the next big ingredient for fish meal used in nearly every species, ranging from warm to cold water varieties.

The six-step evaluation process begins with compositional analysis of the ingredient, then the effect of the feed intake (compatibility and digestibility) is measured, followed by the absorption rate of the ingredient by the fish; then a fry screening is performed to further evaluate the first three steps. The fifth step measures the effect of the ingredient in question on the pellet forming manufacturing process, and finally, the ingredient is measured by the amount of growth it promotes in the fish.

In a recent study that used solar dried spirulina as the fish meal, “we found that the product had a significant increase in feed intake,” Barrows said. As for the functionally, they saw dramatic expansion as the meal was much more dense and easier to handle. Growth trials also showed the algae-based fish meal performed well on rainbow trout that were fed the meal.

 A white seabass study that created a total of eight different diets, four of which were based on a mixture of fish meal with algae in different doses, and four different entirely algae-based diets, also showed promising results. “The fish fed the fish meal diet with spirulina added showed no increase in growth rate, however, the fish-meal-free diet showed significant increase in growth rate,” adding that “they gained significantly more weight.”

“I had to repeat this three times before I had the courage to say we outperformed the commercial diet,” he said, “because I’m usually happy if we can match the commercial diets.”

Although the algae-meal study shows the promise of algae as a fish meal or ingredient substitute, Barrows pointed out that in some cases the algae-meal decreased the mortality rate of the fish to nearly 70 percent, a number he said can be attributed to either a missing nutrient or the increased feed intake by the fish. Neither is a breaking point he said, as diets can be adjusted to compensate for such occurrences. And in the end, regarding his talk on aquaculture and the need for algae, Barrows said, “I just wanted to show you that new ingredients are badly needed.” 


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