Catfish may survive oxygen concentrations under 1.0 ppm, but research shows that when dissolved oxygen is maintained above 3.0 ppm, catfish eat more than twice as much feed and grow twice as fast as fish exposed to lower levels of oxygen.
By Anne Florence Brown
Ordering catfish at any roadside, chain or even a posh restaurant is simple enough, but the process behind the growing, harvesting and shipping that filet has a bevy of science and an entire industry behind it, whether the plating is fried with hushpuppies on the side or elegant with rice pilaf and asparagus.
Catfish farming is said to have been born, casually, in Yazoo County in 1959. In any event, Mississippi has been at the center of this form of aquaculture with ongoing research into the breeding, raising and harvesting healthy fish in manmade ponds dotting, for the most part, the flat and fertile Mississippi Delta.
From the start, the industry has been buffeted by challenges including the marketing of a species once widely viewed as undesirable, cheaper imports and rising production costs, especially for the corn-based feed that must be blasted daily over impoundments. In more recent years, heat and flooding – both associated with climate change – have entered the picture as obstacles to profit.
Aquaculture – the growing of wild fresh and saltwater food animals under controlled conditions – takes place around the world. Freshwater aquaculture typically takes place in ponds or manmade water systems, but systems can also include cages, raceways, and recirculating systems. The biggest freshwater aquaculture product in Mississippi is the farming of catfish, and it’s also the biggest freshwater product in the nation with farms mainly in the South due to the favorable weather.
A driving force was when restaurants serving catfish grew wildly popular in the 1960s. Some of this was, no doubt, due to the influence of Craig Claiborne, respected food editor of The New York Times and a Mississippi Delta native, whose columns “civilized” a freshwater species that had previously had little respect.
All of a sudden, fishermen could not catch as many catfish from natural waters as the public demanded. Catfish pond-farming became the norm, with marketing emphasis that the “bottom-feeders” had instead been raised in clean containments and on nothing but pure foods.
Scientists, many of them based at Mississippi State University and the Mississippi Cooperative Extension Service based there, conducted research into gaining efficiencies and keeping impounded fish healthy. That work continues, although the industry has been facing hard times.
In the early days, harvesting catfish was done by draining the catfish ponds (usually smaller than one acre), taking bathtubs into the drained ponds, and loading the fish into the tubs. Next, the fish would be weighed on cotton scales to decide if they were ready for harvest. Today, the process is much more precise. Farmers harvest catfish year-round by using seine nets to capture the fish, attach the nets to a crane equipped with a scale and drop them off directly on the harvesting trucks. Water quality is tested daily against standards developed by aquaculture scientists and flesh of the fish is monitored and tested for disease or parasites.
Catfish farming is the leading aquaculture industry in the United States. According to a report at mshistorynow.com, commercial catfish production generates over 27 percent of the value of aquaculture. The report tallied annual sales of 319 million pounds in 2016.
Early in the boom, Belzoni, a small town in the heart of the Delta, was dubbed the “Catfish Capital of the World.” At the industry’s peak, Belzoni claimed had more millionaires than any other city in Mississippi in a direct correlation to catfish production. The town in Humphreys County and in 1976 had more than 6,000 acres of catfish farmland, more than any other county in the nation. It was around this time when the first World Catfish Festival was held, attracting 3,000 attendees and tourists and, in turn, boosting. Belzoni still holds an annual catfish festival each spring, which includes a Miss Catfish pageant and a catfish-eating contest, but the size of the down has declined from nearly 3,000 in 2000 to about 1,918 in 2018.
At a peak, Humphrey County’s aquaculture increased to 20,600 acres of the state’s 100,000 acres.Mississippi still led the U.S. in production in 2017 with 350 million pounds or 55 percent of all U.S. catfish production, but any Google search will reveal dozens catfish farms for sale. Jimmy Avery, aquaculture expert for the Missississippi Cooperative Extension Service, said there was about a 50 percent drop in catfish farms from 64,000 acres in 2010 to 35,300 in 2020.
Analysts, farmers and experts have noted a variety of causes for the nosedive in the industry.
They sum the factors as higher feed prices, cheaper foreign imports and stagnant live fish prices. Climate change looms as a factor, too.
The import situation is largely political, and intense marketing of the U.S. brand has been the response. Far more than 20 years, Vietnam and other Asian nations have been selling similar species to restaurants and grocery stores at significantly lower prices. Complaints that other nations were illegally subsidizing their farmers in order to penetrate the lucrative American market have been raised, and lobbying by catfish and other trade associations has resulted in some improved labeling requirements. There have also been marketing campaigns stroking patriotism and encouraging consumers to insist on only U.S. farm-raised catfish. Regardless of the efforts against imports, the American catfish industry has not come away unscathed.
Compounding the import challenge has been a surge in the price of corn, the main ingredient in catfish feed. That surge was driven by the surge in ethanol producers who distill the corn into fuel. Avery said the feed cost challenge has been met, at least in part by research that started at Mississippi State back in 1986. Costs rose to $780 per ton, but has been reduced to $360. “If we had not done that research and found other options, prices would still be at $780.”
It’s at this point that climate change enters as a contributor making catfish farming even more risky. The main obstacles in terms of climate change are flooding and rising temperatures, which results in decreased water oxygenation and a rising risk of disease.
Science says the climate is changing because the earth is warming in response to increased carbon dioxide in the air — up as much as a 40 percent since the late 1700s. Other heat-trapping greenhouse gases are also increasing. These gases have warmed the surface and lower atmosphere of the planet about one degree Fahrenheit during the last 50 years. One degree may not sound like much, but evaporation increases as the atmosphere warms, which increases humidity, average rainfall, and the frequency of heavy rainstorms in many places while contributing to drought in others. There are other indicators. While most of the Earth warmed, natural cycles and sulfates in the air cooled Mississippi. Sulfates are air pollutants that reflect sunlight back into space. Now sulfate emissions are declining, and the factors that once prevented the state from warming are unlikely to persist.
A separate threat is when rainfall or overland flooding overtops rims of catfish ponds. “In the coming decades, Mississippi will become warmer, and both floods and droughts may be more severe… Annual rainfall has increased, more rain arrives in heavy downpours, and sea level is rising about one inch every seven years,” according to the U.S. Environmental Protection Agency.
The impact of backwater flooding that inundated most of the Mississippi Delta for almost half of 2019 had well-documented results. Harvests were down by a third in some locations.
The issue of flooding in the Mississippi Delta does not seem to halt any time soon. “As global warming continues to exacerbate sea level rise and extreme weather, our nation’s floodplains are expected to grow by approximately 45 percent by century’s end,” according to the Climate Science Special Report issued as part of the Fourth National Climate Assessment, which reports on climate change in America. More is occurring in the Mississippi River Valley while U.S. coastal flooding has doubled in a matter of decades,” the report says.
Water temperature is a factor in managing algae and disease. Warmer water is more challenging to keep “clean” than cooler water.
Hypoxia or decreased water oxygenation is a second heat-related factor, and one that specifically drives up costs. When the carbon dioxide levels increase, much of this heat is absorbed by the waters. As the water heats, the oxygen levels decrease in the water.
Oxygenation makes a big difference
As time goes on, more aeration will be needed to satisfy the catfish need for oxygen. Aeration is provided by pumps or wheels that spin in the water to create bubbles. Powering aerators is done by electric, gasoline or diesel motors, and that becomes a significant expense on top of other expenses that have contributed to catfish farmers going out of business.
Studies show catfish may survive oxygen concentrations under 1.0 ppm, but the research results showed that when dissolved oxygen is maintained above 3.0 ppm, catfish eat more than twice as much feed and grow twice as fast as fish exposed to lower levels of oxygen. Careful management and analysis can show whether growing fish faster but more expensively is wiser than growing fish slower at a lesser cost. The farmers who have remained in business and profited, have done so largely through the understanding and application of oxygen management. Avery said much of the industry has consolidated. Large farm that own a processing plant are the biggest acreages that remain,” he said.
There’s very little simple about this industry. People worldwide delight in the products of aquaculture, but viability of the industry rests on effective management of an number of variables, including those brought on by climate change.
By far the most frequent cause of fish kills in farm ponds is low oxygen. Low oxygen can be the result of two separate phenomena in ponds. The first is simple oxygen depletion, which usually occurs from July through September during the time of the highest water temperature. Die-offs caused by low dissolved oxygen levels result from natural biological processes, and preventive measures are rarely efficient except for running a very expensive aerator every night.” Factors that can contribute to low water oxygen levels:
- Dense plankton blooms or dense stands of pond weeds.
- Several days of cloudy weather that reduce plant oxygen production.
- High temperatures, which decrease the solubility of oxygen in the water and increase oxygen consumption by plants and animals.
- A sudden die-off of plants or algae, especially associated with herbicide use.
- Unusual weather patterns, such as storm fronts and heavy, cold rain.
- Overstocking fish, excessive fertilization, or high feeding rates.
- The input of organic matter, such as hay, straw, or cottonseed meal for turbidity or algae control, and materials such as animal manure or sewage.- http://extension.msstate.edu/content/fish-kills