Off-flavor in farm-raised catfish is a very important problem to producers. Off-flavor is the presence of objectionable flavors in the fish's flesh. The off-flavor may be so intense that it makes the fish unmarketable.
During the fall, more than 50 percent of production ponds may have off-flavor fish. This means that ponds cannot be harvested, and harvest and processing schedules are disrupted. Producers are left feeding and maintaining these fish, which increases production costs, disrupts cash flow, and extends risks.
Off-flavor is a complicated problem and requires that producers understand the probable causes, possible cures, and, most important, how to check the fish before they are marketed.
Off-flavor is cause by chemical compounds which enter the fish from the water. Research has shown that some of these compounds are produced by certain pond bacteria and algae.
The bacteria belong to a group of filamentous bacteria called the actinomycetes. These bacteria are found in the water column, but they are most abundant in the bottom mud. Actinomycetes thrive in ponds during warm weather, using nutrients from fish wastes and uneaten feed.
Algae commonly associated with off-flavors belong to the blue-green group. Blue-green algae, though always present in ponds, are most abundant in the summer and fall. Blue-green algae also thrive in nutrient-rich ponds and can dominate other types of algae. Blue-green algae often float and form paint-like scums or a "soupy" layer near the surface.
Off-flavors can be described in many ways. Possible descriptions include: earthy, musty, rancid, woody, nutty, stale, moldy, metallic, painty, weedy, putrid, sewage, petroleum, and lagoon-like. Obviously, many compounds and causes are involved. The causes of some off-flavors are still to be identified.
Two specific compounds have definitely been identified as producers off-flavors: geosmin and 2-methylisoborneal (MIB). These compounds are produced by both blue-green algae and actinomycetes. Geosmin causes a musty or woody off-flavor, and MIB causes a musty or weedy off-flavor. Both produce off-flavor in minute concentration of 2 to 3 parts per billion (ppb) in pond water.
Off-flavor compounds are eliminated from the flesh of the fish in time, if the compounds are no longer in the pond. Depending on temperature and other weather conditions, it can take from a few days to more than a month for the sources of off-flavor and the off-flavor itself to dissipate.
A producer can do very little about off-flavor except wait for it go away. It is nearly impossible to control the bacteria or algae in the pond. The use of herbicides to control the algae is not effective. Research in Arkansas has found that stocking catfish ponds with tilapia reduced the occurrence of off-flavor. Problems of obtaining tilapia fingerlings, controlling reproduction, and finding a market for them are still to be solved, however.
Placing fish in clean water is another option. This method works well, but it is costly in terms of facilities, labor, energy, time, and weight loss of the fish being held.
Processors check fish for off-flavor before scheduling harvests. Producers should check fish for off-flavor also. Start checking the fish at least 2 weeks before the planned harvest, again 3 days before harvest, and finally the day of harvest. Fish can go off-flavor within a few hours and even during harvest operations. If off-flavor is found, continue testing weekly. The future of the catfish industry depends on a quality product, so every producer must make sure that the fish are not off-flavor.
Use the following procedure to test catfish for off-flavor:
Learn to check your fish. Know when an off-flavor problem exists. And remember, a first-time catfish consumer who eats an off-flavor fish may be a one-time customer.