Fish Stories
Vol. 1 No. 3 December 20, 1994

Alabama Cooperative Extension Service
Department of Fisheries and Allied Aquacultures
Auburn University, Alabama

DRUGS APPROVED FOR USE IN AQUACULTURE---The four drugs that have been approved by the FDA for use on catfish are Terramycin, Romet-30, MS-222 and Formalin. These differ from the list of low regulatory priority (LRP) drugs for which the FDA has no current regulatory interest provided they are used according to the general criteria set forth by the FDA. The approved drugs have specific requirements and restrictions for catfish which are outlined below. "Withdrawal time" refers to the waiting period before the fish can be sold for consumption.

For more information on the regulatory status or proper usage of a
drug, call the Center for Veterinary Medicine at (301) 594-1769.

LOW REGULATORY COMPOUNDS USED IN AQUACULTURE---The following is the FDA's most recent list of low regulatory priority (LRP) drugs for aquaculture use.

     ACETIC ACID - 1000 to 2000 mg/L (ppm) dip for 1 to 10 minutes as a parasiticide for fish.

     CALCIUM CHLORIDE - Used to increase water calcium concentration to insure proper egg hardening. Dosages used would be those necessary to raise calcium chloride concentrations to 10- 20 mg/L. Up to 150 mg/L indefinitely to increase the hardness of water for holding and transporting fish in order to enable fish to maintain osmotic balance.

     CALCIUM OXIDE - Used as an external protozoacide for fingerlings to adult fish at a concentration of 2000 mg/L for 5 seconds.

     CARBON DIOXIDE GAS - For anesthetic purposes in cold, cool, and warm water fish.

     FULLER'S EARTH - Used to reduce the adhesiveness of fish eggs to improve hatching success.

     GARLIC (Whole Form) - Used for control of helminth and sea lice infestation of marine salmonids at all life stages.

     HYDROGEN PEROXIDE - Used at 250-500 mg/L to control fungi on all species and life stages of fish, including eggs.

     ICE - Used to reduce metabolic rate of fish during transport.

     MAGNESIUM SULFATE - Used to treat external monogenic trematode infestations and external crustacean infestations in fish at all life stages. Used in all freshwater species. Fish are immersed in a 30,000 mg MgSO4/L and 7,000 mg NaCl/L solution for 5 to 10 minutes.

     ONION (Whole Form) - Used to treat external crustacean parasites, and to deter sea lice from infesting external surfaces of salmonids at all life stages.

     PAPAIN - Use of a 0.2% solution in removing the gelatinous matrix of fish egg masses in order to improve hatching success and decrease the incidence of disease.

     POTASSIUM CHLORIDE - Used as an aid in osmoregulation; relieves stress and prevents shock. Dosages used would be those necessary to increase chloride ion concentration to 10-2000 mg/L.

     POVIDONE IODINE - 100 mg/L solution for 10 minutes as an egg surface disinfectant during and after water hardening.

     SODIUM BICARBONATE - 142 to 642 mg/L for 5 minutes as a means of introducing carbon dioxide into the water to anesthetize fish.

     SODIUM CHLORIDE - 0.5% to 1.0% solution for an indefinite period as an osmoregulatory aid for the relief of stress and prevention of shock; and 3% solution for 10 to 30 minutes as a parasiticide.

     SODIUM SULFITE - 15% solution for 5 to 8 minutes to treat eggs in order to improve their hatching success.

     THIAMINE HYDROCHLORIDE (Newly Added) - Used to prevent or treat thiamine deficiency in salmonids. Eggs are immersed in an aqueous solution of up to 100 mg/L for up to four hours during water hardening. Sac fry are immersed in a aqueous solution of up to 1,000 mg/L for up to one hour.

     UREA and TANNIC ACID - Used to denature the adhesive component of fish eggs at concentrations of 15 g urea and 20 g NaCl/5 liters of water for approximately 6 minutes, followed by a separate solution of 0.75 g tannic acid/5 liters of water for an additional 6 minutes. These amounts will treat approximately 400,000 eggs.

     The LRP status should not be considered an approval nor an affirmation of their safety and/or effectiveness. As information becomes available, the FDA may take a different position on the use of these substances.
     LRP compounds may be marketed for aquaculture use without drug claims. If drug claims appear on the product label, in product catalogs, or in promotional material, the product must have been manufactured according to Current Good Manufacturing Practices (CGMPs) and be drug-listed with FDA. The Agency is unlikely to object to the use of these substances provided they are:

(1) used for these indications
(2) used at the prescribed levels
(3) used according to good manufacturing practices
(4) of an appropriate grade for use in food animals
(5) not likely to adversely affect the environment.

     For the status of a drug not on this list, contact the Center for Veterinary Medicines / 7500 Standish Place / Rockville, MD 20855 or call (301) 594-1769.

SOURCE: Gary E. Stefan, Center for Veterinary Medicine.

Editor's note: The Low Regulatory Compounds of most importance to Alabama growers would probably include Calcium Chloride, Fullers Earth, Hydrogen Peroxide, Ice, Sodium Chloride, Urea and Tannic Acid.

ALABAMA FISH DISEASES---The following is a summary of the disease cases diagnosed in just one year by two Alabama fish disease laboratories. The first is the Auburn Fisheries Department (AU) and the other is the Greensboro Fish Farming Center (FCC)).
     Although the majority of fish received for diagnosis come from Alabama fish farms, the labs frequently receive fish from outside the state. These figures represent just the fish from Alabama and are provided to illustrate the multitude of diseases that are out there. This is only a partial list since other labs in the state also diagnose fish diseases.

Total diagnosis reflects the number of disease agents identified. Routine examination includes certification and other non-disease related examinations. Case load refers to the number of examinations performed.

CONTROLLING AMMONIA IN FISH PONDS---Ammonia enters a fish pond as a byproduct of fish metabolism (increasing as feeding increases) and from bacterial decomposition of organic matter such as uneaten feed or dead algae. Total ammonia nitrogen (TAN) consists of toxic ammonia and nontoxic ammonium. Only a fraction of TAN exists as the toxic ammonia but its proportion increases dramatically as the temperature and pH of the water increases. Dangerous levels of ammonia start at about 0.6 mg/L and can result in gill and kidney damage, reduction in growth, possible brain malfunctioning, and the reduction in the oxygen-carrying capacity of the fish. Several possible treatments for high ammonia levels in ponds have been suggested. Research on the potential of zeolite, formalin, bacteria, aeration, water exchange, and phosphorus to reduce ammonia concentration in pond waters was conducted at Auburn University in 1992. The results are discussed in the following paragraphs.
     Zeolite is a clay which soaks up ammonia like a sponge. Although it works well in a very small body of water like an aquarium, the amount required to reduce ammonia in a pond is economically prohibitive. Zeolite is not ammonia specific and can bind up other nutrients as well.
     Formalin (similar to formaldehyde) initially reduced high levels of ammonia in laboratory trials. Because formalin also kills aquatic plants and fish, further studies are needed before recommending its use for ammonia control.
     Certain common bacteria convert ammonia to a nontoxic form. Suspensions of these bacteria are available for application in ponds, however, additions of bacteria had no effect on ammonia conversion.
     It has been thought that aeration may somehow "blow-off" excessive ammonia but experiments with very high aeration rates (108kW/acre) caused no measurable reduction in ammonia concentrations.
     Water exchange successfully removed ammonia but this method is not usually practical or economical because it is difficult to exchange a sufficient quantity of water. However, it may provide an area of tolerable water near the water supply.
     Algae remove large amounts of nitrogen from the water but the addition of phosphorus to pond water did not stimulate ammonia uptake.
     Prevention is the best method of controlling ammonia build-up in ponds. Using quality feeds, avoiding excessively high stocking or high feeding rates, and maintaining good conditions for algal growth help prevent the initial accumulation of ammonia in the water.

HOW TO MINIMIZE THE POLLUTION POTENTIAL OF DISCHARGED WATER WHEN HARVESTING FISH PONDS ---As the aquaculture industry grows, concerns over the impact of pond effluents on the environment have also increased. The most significant release of pond effluents into the waterways occurs when ponds are drained during harvest. The act of seining has the effect of stirring up a lot of sediments which increases the pollution potential of the effluents.
     Researchers at Auburn University have found that 50% of nitrogen, phosphorus and dissolved organic matter was discharged in the last 15-20% of effluent discharge and that 50% of the settleable solids were discharged in the last 5% of effluent discharge. Researchers suggest the best way to minimize the pollution potential of aquaculture pond effluents is to harvest ponds as quickly as possible and to not drain the pond during or after seining. If the pond is drained after seining, this highly contaminated water should be discharged into a settling basin or retention pond. It also appears feasible to allow effluents to flow untreated into the environment during the preseining phase of draining, because concentrations of potential pollutants are low during this phase.

This concludes our third edition of online Fish Stories. Please direct questions and comments to:
Brandon Foster
(bfoster@acenet.auburn.edu)
202 Swingle Hall
Auburn University, Alabama 36849