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At a time when imported seafood has been found with illegal residues of pesticides and antibiotics, salmon farms are polluting coastal waters, and wild fish are not as plentiful, fish from inland aquaculture operations in the United States could be a more attractive meal option. However, the consumer health record of inland fish farms is mixed, depending on what type of fish is being produced and the intensity of the operation.

Catfish

More than 1,000 aquaculture businesses, the majority of them small operations in Alabama, Arkansas, Louisiana, and Mississippi, raise enough catfish to make it the number one farmed fish in the country.^1,2

Fish farmers usually raise catfish in 17.5-acre artificial ponds that they drain infrequently––every six to 10 years––so that they can re-use the water.³

After harvesting the catfish, operators typically use rotenone, antimycin A or some other piscicide (the aquatic synonym for pesticide) to kill other fish so that they do not compete with the next batch of catfish. Then they restock the ponds. If inhaled, rotenone can cause respiratory paralysis. It has also been found to cause characteristics of Parkinson’s Disease in laboratory rats.⁴ The human health effects of antimycin A have never been studied.⁵

Bacterial diseases, such as Enteretic septicemia, commonly infect farmed catfish. Aquaculturists use the antibiotics oxytetracycline, sulfadimethoxine ormetoprim, and florfenicol to deal with such diseases, raising concerns about antibiotic resistance.⁶ oxytetracycline and a close relative of sulfadimethoxine ormetoprim are both important drugs in human medicine, so their overuse in fish farming and animal production in general could render them ineffective against bacteria that infect humans.

While most commercial catfish feed contains 5 to 10 percent wild fish, fish farmers can raise catfish on a vegetarian diet of soybean meal and distillers grain.⁷ Although freshwater fish often lack the high levels of omega-3 fatty acids present in marine fish, catfish can be fed diets with supplements to increase the omega-3s in their flesh.^8,9

Rainbow Trout

Among Idaho’s mountains and rivers, trout farmers grow mass quantities of fish in concrete canals and troughs. The heart of a concentrated industry, Idaho hosts more than 75 percent of U.S. rainbow trout farming.¹⁰

However, production of the second leading species of farmed fish raises environmental concerns. Water flushes through concrete raceways at a rate of 500 to 2,000 gallons per minute before discharging into a collecting pond.¹¹ Like other in-tensive food production systems, trout farming uses chemicals to increase output. To prevent fungus from growing on trout eggs operators use a formaldehyde solution, called formalin, which is potentially carcinogenic to humans.^2,12 Additionally, trout farmers commonly use the antibiotics oxytetracycline, sulfadimethoxine ormetoprim, and florfenicol to treat bacterial diseases, raising concerns about antibiotic resistance.⁶

Trout aquaculture relies heavily on wild fish to use as feed. A close relative of salmon, trout need high levels of fishmeal, produced from ground wild fish, in their diet. It takes about 3 pounds of wild fish to produce one pound of farmed trout.¹³

Tilapia

Ponds and tanks raising this white, mild-tasting African fish can be found across the country. To keep the non-native tilapia from escaping into the wild where they might harm native species and the local ecosystem, producers use physical barriers to isolate their facilities.

Most tilapia are farmed in ponds or indoor tanks, although a few producers use cages in lakes.² Each system must manage temperature requirements, water use, and pollution. Tilapia are warm-water fish that require temperatures above 65 degrees Fahrenheit, so pond and cage production can only take place year-round in southern states. Indoor facilities heat tank water to the mid 80s.²

In order to harvest tilapia, operators must drain the ponds because the fish jump over or burrow under seine nets used to catch them.¹⁴ In tanks, 90 to 99 percent of the water is treated and re-circulates through the system every day.¹⁵ In cage culture, uneaten feed and feces accumulate directly in the surrounding lake.

Aquaculturists also find different ways to prevent the tilapia from reproducing so that they can grow larger without having to compete with baby fish for food. In pond production, tilapia farmers treat young fish with the hormone methyl testosterone to try to turn females into males.² They then discard the remaining females. In tanks, however, tilapia are so densely packed that they are unable to mate. Likewise, in cage culture, fish eggs often fall through the bottom of the cage, and even if fertilized, they do not survive.¹⁶

Largely herbivorous, tilapia eat algae and decaying matter in the wild. Although some feed contains fishmeal, tilapia can thrive on diets of soybean meal or corn gluten meal and soy flour, if these proteins are supplemented with vitamins and minerals.^16,17,18

Hybrid Striped Bass (aka Sunshine Bass)

Along the southeastern U.S. coast, aquaculture operators produce hybrid striped bass by catching wild white bass and breeding them with wild striped bass.^2,19 More than 60 percent of hybrid striped bass operations are ponds; the others are tanks, raceways, or cages.²

Hybrid striped bass are raised in a series of two ponds, each of which is drained to collect the fish and then pass them on to the next step. After harvest, operators either allow the pond bottom to dry, or they apply a pesticide such as rotenone to kill remaining fish and insects.² If inhaled, rotenone can cause respiratory paralysis. It has also been found to cause characteristics of Parkinson’s Disease in laboratory rats.⁴

Like trout producers, bass farmers regularly use formalin, which is potentially carcinogenic, to prevent fungal infections in bass eggs and fish.^2,13 However, although hybrid striped bass are highly susceptible to infections, the Food and Drug Administration has not approved antibiotic use for adult bass.²

While hybrid striped bass farmers often use salmon or trout feed, the fish can thrive on feed in which up to three-quarters of the feed contain soybean meal and amino acid supplements.²⁰ However, even with this significant replacement of fish-meal, it still takes more than two pounds of wild fish to produce one pound of farmed bass.²¹

Malaysian Prawns (aka Freshwater Shrimp)

A small industry with fewer than 100 operations in the United States, Malaysian prawn could become an alternative to the intensive farming of marine shrimp.¹ Most artificial ponds are one to five acres.² Prawns have dietary requirements similar to catfish, and do not require wild fish in their diet. Young prawns feed on naturally available pond organisms, but after reaching a weight of five grams, they can thrive on a vegetarian diet of soybean meal and distiller’s by-products.²² Thus far, disease has not been a problem, but it could become an issue if operators densely stock the prawns.²

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