The science behind fish nutrition

The science behind fish nutrition

Yvette Converse

Did you know that most recovery plans for threatened and endangered fish species identify captive propagation as necessary to achieve recovery? That’s really no different than for, say, condors or ferrets. Captive spawning and rearing programs for fishes are necessary to maintain genetic safety nets and allow managers to supplement wild populations until long-term threats like habitat loss can be addressed. Without captive propagation programs, many fish would go extinct in the wild.

But spawning and rearing wild fish in captivity is not as easy as it may sound. It requires scientists to retain in captive fish the attributes and natural adaptive potential of wild stocks. Every aspect of the fish’s ecology must be considered to accomplish this, including what and how to feed captive fish to keep them suitable for the wild.

The science behind fish nutrition is complex. Managers must address such factors as the physiological capabilities of each species, nutrient balance and availability of formulated diets, and the feeding ecology and physical mechanics of how a particular species feeds. Feed characteristics also change as fish develop from larvae to adults. Understanding the interaction among these variables and the species requires sophisticated research and knowledge of the science of fish nutrition.

At the Fish and Wildlife Service’s Bozeman Fish Technology Center in Montana, researchers have successfully developed specialized diets for several imperiled fish species. A focus on endangered fish began in the 1990s with a call from the Colorado River Fishes Recovery Program. Fish culturists were experiencing difficulties raising the endangered razorback sucker (Xyrauchen texanus). Although the fish spawned successfully, offspring were experiencing up to an 80 percent rate of spinal deformities and poor growth and survival. After a specialized diet was created, spinal deformities in razorback suckers decreased to as low as five percent and survival is greatly improved.

In recent years, biologists at the Service’s Dexter National Fish Hatchery and Technology Center in New Mexico and at New Mexico State University observed low survival and uncharacteristic “whirling” behavior in captive stock of the endangered Rio Grande silvery minnow (Hybognathus amarus). Their facilities were in a fight against time to establish captive refugia for the small, short-lived species as the wild population neared extinction during extreme drought conditions. The problem turned out to be a deficiency of the vitamin pyridoxine. Within days after a new flake feed was developed, whirling ceased and fish stopped dying. Other species for which specialized diets have or are being developed to prevent deformities include Gila trout (Oncorhynchus gilae), pallid sturgeon (Scaphirhynchus albus), and June sucker (Chasmistes liorus).

Much work remains to be done and nutritional and economical feeds are needed all over the country. The Bozeman Fish Technology Center continues to get calls for help. In June of 2006, it was contacted about an especially rare and vulnerable species, the endangered Devils Hole pupfish (Cyprinodon diabolis). Endemic to a single natural spring in Death Valley, California, it is vulnerable to a drop in water levels from local irrigation. After more than 30 years of carefully monitoring the wild population, biologists are scrambling to establish a refugium for this small fish. With a historically low number of individuals remaining, this short-lived species may be nearing extinction. The species has never been successfully raised in captivity and initial attempts have been tenuous. Service biologists at the Bozeman Technology Center are developing and testing diets to improve survival of captive Devils Hole pupfish, and the preliminary results are promising.

The current fish nutrition program at Bozeman works closely with a co-located U.S. Department of Agriculture fish nutrition program. Dr. Rick Barrows, a fish nutritionist with the Agricultural Research Service, coordinates with the Technology Center’s senior researcher and fish culturist, Greg Kindschi, to develop species-specific diets and design studies that detect the subtle effects of various ingredients, qualities, or nutrients. Matt Toner, manager of the Bozeman Hatchery, oversees feeding trials and maintains controlled rearing conditions, usually involving several diets so that comparisons can be made. Some studies may involve an evaluation of the physiological or immunological response of fish to different diets. In these situations, Technology Center biochemists Eli Cureton and Mariah Talbott conduct laboratory analyses, bio-assays, and histological preparation. In addition, Dr. Molly Webb, fish reproductive physiologist, Linda Beck, micro-biologist and fish immunologist, and Cal Fraser, water quality specialist–all staff of the Technology Center–work as a team to evaluate spawning, survival, immune conditions, and behavior. The program benefits from a one-of-a-kind Fish Feed Nutrition Laboratory with a variety of equipment capable of producing feeds under commercial conditions or with new experimental processing technologies. No other laboratory in North America has this diversity of scientific and technological capabilities.

With so many fish, mussel, and amphibian species facing conservation challenges, the Service is fortunate to have nutritional research facilities like the Bozeman Fish Technology Center and the salmonid nutrition program at the Abernathy Fish Technology Center in Washington State to assist in recovery.

Yvette Converse is the Assistant Director at the Bozeman Fish Technology Center.

COPYRIGHT 2007 U.S. Fish & Wildlife Service

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