COLUMBUS, Ohio - Cottonseed meal has been found to be a viable alternative food source for farm-raised trout, giving the aquaculture industry the opportunity to provide "organically grown" fish to consumers.
Ohio State University natural resource researchers found no difference in male and female rainbow trout growth over a 35-month period when cottonseed meal protein replaced fish meal protein in up to 100 percent of the trout's diet. Such findings indicate that cottonseed meal, a by-product of the cotton plant, could replace fish meal and would not affect the growth performance of the fish.
"The results presented are very unique in this particular research arena," said Konrad Dabrowski, one of the project's researchers. "Organic labeling of some fish species is a hot issue right now. If that is the way to go, it could be argued that cottonseed meal is an acceptable form of feed in organically raising fish since the main ingredient is plant-based."
The idea of organically labeling wild-caught and farm-raised fish species has been a topic of recent discussion. The U.S. Department of Agriculture's National Organic Standards Board voted in October to consider developing organic standards for some farm-raised species, but unanimously voted against creating a set of national organic standards for wild-caught fish. Fish meal is made up of marine fish, primarily wild-caught species.
Such a move, some argue, could put the aquaculture industry, already facing stiff competition from foreign imports, at a domestic economic disadvantage with the beef and poultry industries which are now eligible for organic labeling.
Dabrowski emphasizes that cottonseed meal, fed mainly to livestock, could replace fish meal as the main dietary protein source of certain fish species like trout, making them eligible for organic labeling. "There are people out there who criticize the aquaculture industry because of the fish meal being used excessively," he said.
Cottonseed meal is also much cheaper than fish meal, said the researcher.
"Fish meal costs about $550/ton, while cottonseed meal is $120/ton. Food is 50 percent of all costs in aquaculture, so it's important if we can find feed that will save the industry money," said Dabrowski, adding that some species like salmon eat up to five pounds of protein for every pound of protein gained.
"Cottonseed meal could also be beneficial for farmers if it becomes an appreciated ingredient in fish diet because they would have an additional cotton product they could sell. Cottonseed meal has relatively low value because of its limitations."
One limitation that makes cottonseed meal a challenge to incorporate in fish diets despite its advantages is the presence of gossypol. Gossypol, a natural toxin essential for the cotton plant in preventing insect damage, has been found to produce toxic effects in certain fish species, such as tilapia. Rainbow trout, however, is one of the few fish that shows resistance to the toxin.
"We followed the gossypol concentration in fish tissues throughout the study and found that the trout is not as sensitive to it as other fish are. They seem to cope with the toxin fairly well," said Dabrowski. "There is this dogma that cottonseed meal isnot good because of possible detrimental side effects. We are hoping this study will help dispel some of those concerns."
The study was funded by the National Cottonseed Products Association and the Cotton Foundation. Researchers plan to study the medicinal advantages of consuming fish meat containing gossypol. The toxin has been known to fight off breast and prostate cancer cells and is effective against the HIV virus.