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Use of Medicated Feed in Channel Catfish

by University of Florida    

Use of Medicated Feed in Channel Catfish ¹

Pond-raised channel catfish are the most popular species of food fish grown in the southeastern United States. Because of crowding and associated stressors encountered in modern aquaculture, they are more susceptible to disease than free-ranging animals. Bacterial disease is frequently the cause of death of catfish, though often secondary to other problems such as poor water quality or excessive parasitism . Medicated feeds can be used to control bacterial disease . However, the results of treatment may only be temporary unless underlying problems are also corrected.

WHAT IS BACTERIAL DISEASE?

A few bacteria are considered opportunistic pathogens. These bacteria are always present and usually cause no problem. However, under certain conditions they can cause disease in fish. Common examples of opportunistic pathogens which can cause disease and death of catfish include Aeromonas sp., Pseudomonas sp., and Flexibacter sp.

A few bacteria are considered obligate pathogens , which means they are likely to be the sole cause of disease rather than a secondary problem. There is some speculation that Edwardsiella ictaluri may be an obligate pathogen.

Separate fact sheets on the bacterial diseases mentioned above are available. Aeromonas and Pseudomonas cause very similar diseases often characterized by large ulcers on the side of the fish, distended abdomen (dropsy), and exopthalmia (popeye) . Flexibacter columnaris causes a disease called "columnaris disease" or "saddleback disease." It is usually an external problem which begins by loss of color (paleness) along the back of the fish . As the disease progresses, large ulcers may develop . Mixed infections with Aeromonas and Pseudomonas are common in advanced cases.

Poor management practices are often the cause of these infections. For example, rough handling damages the skin and mucus of the fish and can result in secondary bacterial infections. Control of these infections often requires the use of medicated feed . Because these infections are usually opportunistic, it is sometimes possible to control the spread of the bacterial infections by correcting management problems that preceded disease outbreak (e.g., excessive parasitism or poor water quality).

Edwardsiella ictaluri is a bacterium considered by some to be an obligate pathogen . This may not be precisely true, but this organism without doubt causes the most significant bacterial disease of channel catfish - enteric septicemia of catfish, or ESC . Some producers refer to ESC as "hole-in-the-head disease." It frequently causes ulcers in the middle of the skull of fingerlings, just above the eyes.

Medicated feed is almost always recommended to control ESC outbreaks. Catfish which are becoming sick with ESC often stop eating so early diagnosis and treatment is essential to minimize losses.

What is Medicated Feed?

Terramycin

Terramycin must be fed for 10 days, and the fish must be held an additional 21 days before they can be marketed to allow complete elimination of the drug from the fish . This 21-day withdrawal period assures that the drug will be absent from fish intended for human consumption . Slaughter of fish before the end of the withdrawal period is a violation of federal law . Consider market plans before treating fish with Terramycin. Once treatment begins, the fish are non-saleable for 31 days (10-day treatment period + 21-day withdrawal period).

A final consideration when feeding Terramycin is that it is only available as a sinking feed . This drug is broken down by the high temperatures needed to make a pellet of fish feed "puff up" so it will float . Feeding a sinking fish food to sick fish is a disadvantage because it is very difficult to determine if fish have eaten the medicated food.

Romet

The withdrawal period for Romet in channel catfish is only 3 days . This is considerably less than the withdrawal period for Terramycin . With only 5 days required for treatment and a 3-day withdrawal period, catfish treated with Romet can be slaughtered 9 days after the drug treatment is started.

Another advantage of Romet is its availability as a floating feed . This allows direct observation of the fish eating the medicated pellets. Again, early diagnosis and treatment are necessary because once fish are sick they are unlikely to eat.

Homemade Medicated Feeds

Once a bacterial disease is in progress, medicated feed should be used immediately . It is possible under emergency circumstances to mix your own feed in small quantities if the commercially prepared diet is not available . Terramycin premix may be purchased as a soluble powder, which is available at many stockman supply stores. A 6.4 ounce packet should contain 10 grams of oxytetracycline, but check the label to be sure. One 6.4 ounce packet contains 50 level teaspoons of premix. Each teaspoon, therefore, should contain 200 mg of active oxytetracycline. If fish eat 3 percent of their body weight per day, each pound of feed should contain one gram of drug (5 teaspoons). Vegetable oil or fish oil work well as binders. The oil, feed and powdered premix should be thoroughly mixed to assure even distribution of the drug to all pellets. To coat the pellets properly, mix the powdered premix with the oil, then add this mixture to the feed. This mixture should be made daily immediately before feeding. This is an expensive, time-consuming and laborious process and is practical only in emergency situations.

Romet is available in a form called Romet-B. This product has easy-to-follow directions for mixing the premix with the feed. Again, binding agents like fish oil or vegetable oil can be used. A disadvantage of Romet-B is that it is only sold in 10 lb. canisters which are too expensive to be practical for use by small farmers.

Storage of Medicated Feed

How to Know Which Medicated Feed to Use

Figure 1 .

A fish health professional can perform a sensitivity test for you and recommend which antibiotic to use. Remember there are some circumstances when treatment with an antibiotic may not be necessary.

SUMMARY

Only two antibiotics are available in medicated feeds for channel catfish . Terramycin contains the drug oxytetracycline. It is effective against all the organisms listed above, but is only approved for use against Aeromonas and Pseudomonas infections . Feed against Aeromonas and Pseudomonas infections . Feed Terramycin for 10 days followed by a 21-day withdrawal period. It is only available in a sinking feed.

Romet is a potentiated sulfonamide which contains two drugs, sulfadimethoxine and ormetoprim. It is approved for use against Edwardsiella ictaluri infections and against Aeromonas infections which are not sensitive to Terramycin. Romet does not appear to be effective against F. columnaris disease, therefore, is not recommended for use during F. columnaris outbreaks . Feed Romet for 5 days followed by a 3-day withdrawal period . It is available as a floating feed.

The final choice for an antibiotic should be based on a laboratory test called a sensitivity test . The test determines which antibiotic will work best to control the bacteria isolated from your fish. A fish health professional can complete this test and recommend the best control of a bacterial disease outbreak on your facility . Keep in mind that bacterial diseases are usually a consequence of poor water quality, excessive parasitism or improper handling . These management problems must be corrected for successful, long-term control of infections.

Tables

Footnotes

2. Ruth Francis-Floyd, D.V.M., M.S., associate professor; Peggy Reed, biological scientist; Department of Large Animal Clinical Sciences, College of Veteriary Medicine, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.

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