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New "fishless" feeds could make aquaculture more sustainable

When it comes to commercial aquaculture, a lot of people have some legitimate concerns – fish farms can introduce antibiotics, anti-algal chemicals and concentrated fish waste into the ocean; escaped fish can upset the local ecological balance; and wild fish still need to be caught in large numbers, as a food source for some species of farmed fish. While there have been recent efforts to address the first two concerns, the fish-in-the-fish-food problem is now being taken on in two different research projects. These are aimed at replacing the fish content in fish feed with more sustainable ingredients.

A diet of microbes for prawns

Traditionally, farmed prawns (or shrimp, depending on where you’re from) have been fed pellets that contain some fish meal and fish oil. These are included mainly to help the animals grow large, and to do so quickly. Scientists at Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO), however, have spent the past 10 years developing a feed additive that does away with those fishy ingredients. The result, known as Novacq, was officially announced at the end of last month.

Novacq contains marine microorganisms that have been bred in captivity, and which have been shown to play a crucial role in prawns’ growth process. In a large-scale field test, the product was mixed with an existing commercial feed (taking the place of the usual fish meal and oil), then used in ponds at an Australian prawn farm. According to CSIRO, the Novacq-consuming black tiger prawns grew an average of 30 percent faster than their regular-food-eating counterparts, plus they were healthier.

Turning meat-eating fish into vegetarians

Fish meal and oil are also used in the pellets eaten by carnivorous fish, such as sea bream and striped bass. Scientists at the University of Maryland Center for Environmental Science, however, have developed an alternative feed that consists entirely of plant-based ingredients.

Instead of fish meal, the experimental new feed includes corn, wheat, and soy. Taking the place of fish oil is a combination of lipids (fatty acids) from algae, amino acid supplements, and soybean or canola oil.

Not only have test fish apparently thrived on the feed, but their flesh reportedly has PCB and mercury levels that are 100-fold lower than those found in fish consuming regular pellets containing wild-caught fish. According to co-creator of the feed Dr. Allen Place, this would allow consumers to eat striped bass twice a week, as opposed to the once every two weeks that’s currently recommended.

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