Terramycin:
Terramycin® has been used for treatment of food fish for many years. It contains the drug oxytetracycline. This drug is usually effective against many bacteria which cause disease in food fish.
The FDA specifically approved Terramycin® for control of Aeromonas hydrophila (A. liquefaciens) and Pseudomonas sp. infections in catfish and Aeromonas salmonicida, A. salmonicida achromogens (Haemophilus piscium), A. hydrophila (A. liquefaciens) and Pseudomonas sp. in trout. A. hydrophila causes motile aeromonas septicemia, A. salmonicida causes furunculosis, and A. salmonicida achromogens causes ulcerative disease in trout and goldfish.
Terramycin® is incorporated into the feed by commercial mills and fed at a rate of 3.75 grams (g) of the drug per 100 pounds of fish per day.
Terramycin® must be fed for 10 days to control the infection. The fish must be held for an additional 21 days before they can be marketed for food to allow complete elimination of the drug from the fish.
Marketing fish for human consumption before the end of the 21-day withdrawal period is a violation of federal law. As a result, marketing plans must be considered before treating fish with Terramycin® . Once treated, fish cannot be sold for at least 31 days (10-day treatment period plus 21-day withdrawal period).
An additional consideration when feeding Terramycin® is that it is only available from commercial mills as a sinking feed. The drug is broken down by the higher temperatures needed to make an extruded (floating) pellet. Feeding a sinking food is a major disadvantage for sick pond fish because it is difficult to determine if they are eating the medicated feed.
Romet:
Romet® (Romet-30® , Romet-B® ) is also approved for use in both trout and catfish as well as in salmon. This product contains two drugs, sulfadimethoxine and ormetoprim. These drugs in combination are more effective than either drug used alone.
Romet® is specifically approved for treatment of Edwardsiella ictaluri infections in catfish and Aeromonas salmonicida infections in trout and salmon. E. ictaluri causes enteric septicemia of catfish.
Romet® medicated feed is produced by commercial feed mills and should be fed at a dosage of 23 milligrams (mg) of drug per pound of fish (50 mg of drug per kilogram of fish) per day for 5 days.
If the feed contains 33.3 pounds of Romet-30® premix per ton, then the fish need to consume at least 1 percent of their body weight to achieve a therapeutic dose of the drug. At varying Romet® concentrations, the proper feeding rate can easily be calculated.
For example, feed mixed with 11.1 pounds of Romet-30® per ton of feed should be fed at 3 percent of body weight. The withdrawal period for Romet® is only 3 days for channel catfish. This is considerably less than for Terramycin® .
With a 5- day treatment period and a 3-day withdrawal period, catfish treated with Romet® can be slaughtered only eight days after the drug treatment is initiated. Trout, however, are required to have a 42-day withdrawal period from Romet® before being slaughtered.
Another advantage of Romet® is its availability from commercial mills in a floating pellet. This allows direct pond observation of the fish eating the medicated feed.
Selecting the proper medication:
To optimize the response to antibiotics provided in feed, producers should correct other problems which may have predisposed fish to the bacterial infection. This should include checking water quality parameters and submitting proper fish and water samples to a diagnostic laboratory.
If the fish have a bacterial disease and the causative agent has been identified, a sensitivity test should be performed to ensure that the correct medication is used. A sensitivity test (Figure 1) shows the resistance of the disease-causing bacteria to various antibiotics.
If bacteria are unable to grow in the presence of a particular antibiotic, a zone of inhibition or clear area is present surrounding the area treated with that drug. If the drug has no effect on the bacteria, they will grow up to or over the top of the disc.
A fish health professional or disease diagnostic laboratory can perform the sensitivity test for you and recommend an antibiotic to be used. Remember, there are circumstances when treatment with an antibiotic is unnecessary or ineffective. Some bacterial diseases cannot be controlled with medicated feed. For example, there is currently no antibiotic available that is truly effective against Renibacterium salmoninarum which causes bacterial kidney disease in salmonids.
Economics and other factors also help to determine the appropriateness of using medicated feed. A farmer with a 1-acre pond stocked with 1,000 1/2-pound fish, for example, would probably be wise to spend an extra $50 to $85 on medicated feed (cost will depend on the type of antibiotic and source of feed) if he were losing $10-worth of fish each day.
On the other hand, if he were only losing $2-worth of fish a day and a qualified fish health professional does not think that the mortalities will continue for a month, then spending $70 for a medicated feed treatment may not be economically wise.
Treatment strategies:
The basic objective of treating fish is to save money for the producer. One must make sure, for example, that the cost of treatment does not exceed the value of the fish in the pond! If possible, expensive treatments should be avoided unless they are likely to save money for the fish farmer in the long run.
A good example is the treatment strategy for ESC caused by Edwardsiella ictaluri. This disease occurs when temperatures are between 68 and 82o F when the bacteria is in its optimum growth range. Fish dying from ESC will usually stop dying as temperatures rise above or fall below this temperature range.
Starting affected fish on a medicated feed treatment just before temperatures are forecast to be in the 90s, for example, is often not advised, because the disease stops on its own due to the high temperatures. Using this strategy will save a significant amount of money by not spending for the medicated feed.
Homemade medicated feeds:
If commercial medicated feed is not readily available in your area, it is possible under emergency circumstances to mix your own feed in small quantities. Both Terramycin® and Romet® can be used in this manner. FDA approval and/or an extra-label prescription by a veterinarian are necessary before using this treatment.
The powdered premix is combined with the binder and then added to the feed. A 5 percent gelatin solution as well as vegetable or fish oil work well as binders.
The feed and antibiotic must be mixed thoroughly to assure even distribution of the drug to all the pellets. The coated feed should then be spread out to air dry. After several hours of drying, the feed can be re-bagged and stored under proper conditions.
This is an expensive and time consuming process that is practical only if commercial medicated feed is unavailable and relatively small quantities of medicated feed are required.
In addition, a significant quantity of the antibiotic may leach out of the homemade medicated feeds before being consumed by the sick fish. Many producers feel, however, that the homemade treatment is better than none when formulated medicated feeds are not available.
Terramycin® premix may be purchased as a soluble Terramycin powder at many agricultural supply stores. A. 6.4-ounce packet usually contains 10 grams of oxytetracycline, but check the label to be sure.
Two packets of Terramycin® can be added to a 5-gallon bucket full of feed (approximately 17 pounds of feed). If the fish consume the feed at 3 percent of their body weight, they will receive the needed therapeutic dose of antibiotic.
If the fish are eating less than 3 percent of their body weight, then more than 2 packets of Terramycin® will be needed. A qualified fish health professional or veterinarian can be contacted for help in calculating the appropriate quantity of medication needed.
Romet® is available in powdered premix called Romet-B® . A disadvantage of Romet-B® is that it is only available in 25-pound canisters, which may be too expensive to be practical for small farmers.
The amount of feed that will fill a 5 gallon bucket (about 17 pounds of feed) should be mixed with Romet-B® powder using the number of grams from the table below depending on the amount of feed that the fish will consume (based on % of the fish’s body weight).
Authors:
Robert M. Durborow and Ruth Francis-Floyd
