Dedicated To Tribal Aquaculture Programs March 2001 ~ Volume 35 Coordinator: Frank G. Stone  (715-682-6185) Ext. 12 U.S. Fish and Wildlife Service Email: Frank_Stone@fws.gov

Topics of Interest:

Dissolved Oxygen and The Venturi Aeration Process for Conditioning Water for Aquaculture

Treatment of Fish Diseases

Guide to Drug, Vaccine, and Pesticide Use in Aquaculture

Dissolved Oxygen...Critical inAquaculture and Fish Farming
by: Gail Karet, R&D Magazine

Controlling dissolved oxygen--the volume of oxygen contained inwater--is critical in aquaculture. While fish grow and thrive with 5-12 mg/Ldissolved oxygen (DO) levels, they stop feeding at levels of 3-4 mg/L and die atlevels below 1 mg/L of DO.

Oxygen depletion usually occurs in the summer because warm water holds lessdissolved oxygen than cool water. For example, 32C water can hold up to 7.3mg/L of oxygen, while 7C water can hold 12.1 mg/L. Higher temperatures putfish in special danger because their metabolic rates are higher and as a resultthey need more oxygen.

In summer months lakes also become stratified because of differences in waterdensity with temperature. Cool water sinks, warm water rises, and the water atthe top of the lake is heated more rapidly through radiation by the sun.Although the lakes cool bottom layers hold more dissolved oxygen when summerstarts, microbial decomposition of organic materials may deplete the oxygen at alake bottom before the summer ends.

Fish farmers use oxygen sensors to monitor dissolved oxygen and preventoxygen depletion. If levels drop too low, turning on an aeration systemincreases dissolved oxygen. Dissolved oxygen control systems can be preset to dothis automatically.

The Venturi Aeration Process for Conditioning Water for Aquaculture and FishFarming
By: John Solonich, Pelham, NH, 603-635-8239, http://www.venturi-aeration.com

One of the best mechanical aeration technologies that can satisfy the demand forincreased levels of DO is the Venturi Aeration Oxygenator. The Venturi AerationOxygenator is a unique mechanical aeration device that is ideally suited foraquaculture and fish farming because not only does it induce high levels ofdissolved oxygen into a liquid but it also simultaneously strips carbon dioxide(CO₂) from the water as it is being treated. Increased CO₂levels resulting from the metabolic activity of fish can lower pH to acidiclevels, however, stripping CO₂ with the Venturi Aerator raises pHnon-chemically to neutral levels that are beneficial for growth and development.In this manner the Venturi aeration process "conditions" the water.Additionally, the Venturi Aerator can be configured to aid in cooling the waterstemperature to make the water more favorable for growth of the various aquaticspecies and increased levels of DO through increased solubility.

The Venturi Aerator is configured to bring the most anoxic (oxygen-deficient)water into the aerator. This is where the Venturi can achieve higher transferrates of dissolved oxygen because there is less resistance at the air/liquidinterface. It works differently from other diffuser-type aeration devices thatuse a buoyancy transfer model for dissolved oxygen. In the buoyancy model, anair bubble is "bubbled" through the liquid and the size of the bubble,rate of rise in the liquid and available surface area predict oxygen transferperformance. Other mechanical aerators try to "beat" air into theliquid by reducing the resistance at the air/liquid interface and use turbulenceto effect the transfer.

The Venturi Aerator uses a kinetic oxygen transfer model wherein the liquidis converted into a macro-droplet of water and it is imploded with 2.2 volumesof ambient air to one equivalent volume of liquid. Transfer takes placepredominantly within the "mixing and oxidizing" zone of the aerator.Up to 20% of the aspirated ambient air is transferred; typically, the aeratorwill induce up to 7.5 mg/L of DO into the liquid being treated. However, variousconfigurations have been developed wherein it can induce up to 10-11 mg/L of DO,depending on variables of temperature and elevation. However, at 7.5 mg/L DOthere are sufficient enough levels of DO to allow aquatic species to flourishand grow.

The Venturi Aerator can be easily configured for retrofit into existingtanks, lagoons or lakes, and requires only a pump with sufficient pressure (21psi) at the nozzle to activate the unit for treating the water. Flow rates rangefrom 50 gpm for a small unit up to 1,300 gpm for the largest units.

The following benefits for aquaculture and fish farming can be obtained usingthe Venturi Aeration process:

1. Dissolved Oxygen: The liquid being processed through the Venturi Aeratorunit is saturated with dissolved oxygen. The discharged liquid is highlyoxygenated with DO levels ranging between 5.0 mg/L and 7.5 mg/L, and thedischarged liquids can be configured to reach levels of 10.0-12.0 mg/L in astilling well if mixing and equalization for diffusion and dispersion are notrequired.

2. Mixing and Equalization: The kinetic energy of the discharged liquids fromthe aerator unit mixes and equalizes liquids and provides for good diffusion anddispersion of the aerated waters into anoxic or hypoxic waters in streams orponds.

3. Odor Control: Imbedded malodorous and corrosive hydrogen sulfide (pHlowering) from decaying organic material is readily oxidized into soluble SO₄,a non-odorous form of sulfur, by keeping the processes aerobic instead ofanaerobic.

4. BOD Reduction: Aeration induces large amount of dissolved oxygen into thestream or lagoon to effect BOD₅ reduction and reduce the competitionfor dissolved oxygen.

5. Nitrification: With excess amounts of dissolved oxygen available in thestream, nitrification begins at pH levels greater than 6.8 reducing nitritetoxicity.

6. Temperature: The Venturi Aeration Oxygenator has the ability to reduce thetemperature of the influent water. In field tests with municipal sewage, temperature reductions have beendocumented to range between 2 and 6 C in summer months. Reducing elevatedtemperatures of stagnant waters increases the solubility of dissolved oxygen,thus allowing for greater amounts of DO for aquatic growth and sustainedmetabolic activity.

7. Non chemical pH Control: As fish become more active they produce greateramounts of carbon dioxide as a digestive byproduct. The increase in carbondioxide lowers the pH. This acidity may stress aquaculture inhibiting growth.Since carbon dioxide is readily strippable using the Venturi Aerator, a morebalance pH level can be maintained.

8. Hydraulic Shear: Organic solids in the pond or lagoon are conditioned bythe shear generated by the Venturi aeration device thus increasing their surfacearea to enhance digestion and degradation.

9. Strips VOCs: The Venturi aeration strips certain weak Henrys Constantsubstances (CO₂).

10. Adding Enzymes: Adding enzymes to the tank, pond or lagoon aids inclarification while aiding in the breakdown of organic solids reducing sludgevolumes. The enzymes catalyze natural biological reductions from the nascentmicroorganisms in the pond or lagoon.

Imprinting

Both natural habitat spawning and hatchery release areas will have healthierstocks when they are exposed to higher levels of dissolved oxygen. Further, whenDO "trails" are added to streams and rivers there is an increase inreturn of various migratory species to headwaters for spawning. High dissolvedoxygen levels have a very beneficial effect on imprinting. When DO, generated bythe Venturi Aerators, is added to a channel it may provide a DO trail for fishto follow, even in the presence of high levels of turbidity. Certain specieswill not swim through turbid conditions, but they will make the attempt if theyare following a DO "trail."

Treatmentof Fish Diseases
Reprinted From: Introduction To Fish Health Management, U.S. Fish and WildlifeService

Prophylaxis and chemotherapy aretwo methods used to treat diseases of fish. Prophylactic treatments arepreventative and protect against the occurrence of an epizootic. Such treatmentsare used primarily for ectoparasites and stress-mediated bacterial diseases.Chemotherapeutic treatments are initiated after clinical signs of the diseaseappear in a population of fish.

Seventeen and Rules of Chemical Treatment:

1. Fish should be examined to diagnose the disease or problem to betreated. Seek professional assistance if in doubt of the cause. A shotguntreatment is poor policy and can lead to drug resistant microorganisms.

2. Determine general condition of fish. Fish may not be able towithstand standard treatments. In this case, it is advisable to give serialtreatments with progressively higher concentrations of the chemical.

3. Clean holding unit before chemical treatment. Many chemicals areinactivated by organic materials. A holding unit which is not clean oftenprovides a sanctuary for the organism under attack.

4. Remove fish from feeding schedule 24-48 hours prior to treatment.Oxygen consumption is reduced when fish are taken off feed and fish are more aptto withstand the treatment.

5. All leaks in the holding unit should be repaired prior totreatment. This rule is important in order to maintain a constant chemicalconcentration.

6. Auxiliary aeration devices should be on hand and operative. Thisrule applies more to bath treatments where oxygen depletion is more likely.

7. Determine proper dosage, amount or concentration of chemical to beused. Always double check your calculations. Determine the correct method, routeof application and accurately determine withdrawal time of the chemical.

8. Compare economic value of fish with cost of treatment. If cost ofdesired treatment is greater than the value of the fish, it may be worthchanging your choice of chemicals or even abandoning the treatment.

9. Always check the route of chemical discharge at the facility. It ispossible that the chemical in use may cause environmental damage after it leavesthe unit being treated.

10. Before beginning treatment, check the condition of chemical beingused. Some chemicals are altered when improperly stored. This alteration couldyield an ineffective or a toxic chemical.

11. Check concentration of the stock chemical. Many treatmentrecommendations are based on active ingredients.

12. Dilute chemical before applying to the holding unit.

13. Ensure proper mixing and distribution of the chemical in the watercolumn of the holding unit.

14. NEVER leave the holding unit while treatment is in progress.

15. Observe fish closely during treatment. If distress is observed,the treatment should be terminated, or if low dissolved oxygen is the problem,additional aeration should be provided.

16. Periodically examine fish to determine efficacy of treatment.

17. Do not stress (by handling, crowding) treated fish for 24-48 hoursafter treatment.

17. Make every effort to determine the predisposing factor orfactors for the condition being treated and correct for them if possible. If thepredisposing factor is not removed, it is likely that the condition willreappear.

Guide to Drug, Vaccine, and Pesticide Use in Aquaculture
Texas Agricultural Extension Service, The Texas A&M University System,Publication No.: B-5085, June 1994
Prepared by the Federal Joint Subcommittee on Aquaculture, http://ag.ansc.purdue.edu/aquanic/publicat/govagen/usda/gdvp.htm

The Guide to Drug, Vaccine, and Pesticide Use inAquaculture is available in printed form from the Aquaculture InformationCenter, National Agricultural Library, U.S. Department of Agriculture, 10301Baltimore Blvd., Rm. 304, Beltsville, MD 20705; 301/504-5558. The guide is alsoavailable from state Cooperative Extension Services, state Sea Grant MarineAdvisory Services, and national aquaculture associations.

Introduction

The aquaculture industry in the United States has grown considerably inrecent years and is now recognized as a significant supplier of food productsfor U.S. consumers. Aquaculture also provides aquatic stocks for recreationalfishing, the restoration of threatened and endangered species, and wild stockenhancement, as well as for the bait, aquarium, and ornamental fish trades. Toensure the safety of aquatic food products, the integrity of the environment,the safety of target animals, and the safety of persons who administer variouscompounds, it is critical that all regulated products be used correctly andresponsibly.

At present, no drugs used in aquaculture are considered by FDA to begenerally recognized as safe (GRAS) or effective (GRAE) for their proposed uses.For a compound to be classified as GRAS or GRAE, general recognition by expertsmust be supported by published scientific studies that meet strict FDAstandards.

Drugs in Aquaculture Feed

New animal drugs that are added to aquaculture feed are subject to FDAapproval and must be specifically approved for use in aquaculture feed. Drugsapproved for use in feed, like the drugs approved for administration in otherforms, must be safe and effective.  Approved new animal drugs may be mixedin feed only for uses and at levels that are specified in FDA medicated-feedregulations. It is unlawful to add drugs to feed unless the drugs are approvedfor feed use. For example, producers may not top-dress feed with awater-soluble, over-the-counter antibiotic product.

Some medicated feeds, such as Romet 30, may be manufactured only after FDAhas approved a medicated-feed application (Form FDA 1900) submitted by the feedmanufacturer. This requirement applies whether the producer or a commercialcompany makes the medicated feed. Neither an approved 1900 Form nor FDAregistration is required for the manufacture of certain other medicated feeds,such as those containing Terramycin. However, those who manufacture such feedsare subject to the regulations covering current good manufacturing practices anddrug usage.

Water Treatments

Many of the chemicals used in aquaculture are applied directly to water. Thefederal agency (either FDA or EPA) with jurisdiction over chemicals applied tothe water is determined by the intended use of the product.  Fish and otheraquatic species are exposed to any compound present in the water. An off-flavoris an example of a condition that can develop when fish are exposed to certaincompounds--even those found naturally in water.

Although some products may be beneficial when applied to aquaculture systemsat low concentrations, they may also act as irritants or even become toxic athigher concentrations. The improper use or application of water treatments cancause severe stress, which can lead to an animal disease outbreak or even death.Some compounds can accumulate in the animal and may cause illegal chemicalresidues in tissues intended for human consumption. Illegal residues can alsoresult from the improper use of products to control weeds or unwanted fish or toalter water quality. To prevent possible fish losses and illegal chemicalresidues from excessive treatment levels, always read and strictly followproduct label directions.

Record Keeping

Record keeping is essential for any aquaculture business and is a criticalelement of quality assurance programs. A good record keeping system helpsproducers keep track of specific treatments and their results with identifiable,known populations or stocks of aquatic animals, as well as the specific waterand land areas involved.  Good records provide a basis for sound,cost-effective management decisions. The treatment status of animals, ponds, andother areas is known at all times. Records are needed to determine dosage ratesand certify withdrawal times. Processors may require records to demonstrate thatall drugs and chemicals have been used properly. Federal seafood processinginspection regulations may also require such record keeping. Records providevaluable evidence and protection in liability cases.

Calculating Withdrawal Times

Product withdrawal times must be observed to ensure that any product used inan aquatic site or on animals does not exceed legal tolerance levels in theanimal tissue. Using proper withdrawal times helps to ensure that productsreaching consumers are safe and wholesome. All federally approved products listany specific required withdrawal times. Withdrawal information is found on theproduct label, package insert, or feed tag.

Storage, Handling, Mixing, and Disposal

Always follow label directions for storing, handling, mixing, diluting,reconstituting, and disposing of regulated products and their containers. Thispreserves the activity and quality of the product and helps prevent misuse,damaging effects on plants and animals, human injury, and environmentalcontamination.

The use of any pesticide (and some other regulated products) requiresadequate protection from exposure. Users should always read the product labelfor information on recommended personal protective equipment. Common-senseprecautions should be followed, such as wearing gloves, long-sleeved shirts andlong pants, socks, shoes or boots, a hat and goggles, protective glasses, and/ora face shield.

It is important that unused portions of a regulated product and emptycontainers be disposed of properly. The best approach is to purchase only theamount of material that will be used within a reasonable time period and to useall of the product for its intended purpose.

Pesticide Applicator Certification

Restricted use pesticides can be purchased and applied only by a CertifiedPesticide Applicator or under a Certified Applicator's direct supervision.Certification includes both "private" (mostly farmers) and"commercial" applicators. Pesticide certification programs are offeredthrough state Departments of Agriculture and state Cooperative ExtensionServices and through EPA regional offices.

Importation of Regulated Products

To be imported, a new animal drug must either be approved by FDA or beintended for investigational use under an INAD exemption. Without approval orproper identification as an investigational new animal drug, a compound can berefused entry into the United States. If the drug is imported under falsepretenses, the responsible person's involved are subject to enforcement actionby FDA as well as the U.S. Customs Service.

FDA-regulated Drugs for Aquaculture

The drugs listed in this section include FDA-approved new animal drugs aswell as unapproved drugs of low regulatory priority (LRP). Federal approval ofnew animal drugs applies only to specific products that are the subject ofapproved new animal drug applications.

Active ingredients from sources other than the listed sponsors are notconsidered approved new animal drugs. Such products cannot legally be marketedor used. States may impose additional regulatory requirements and restrictionson FDA-regulated drugs for aquaculture.

Table 1. FDA-Approved New Animal Drugs

Table 2. Unapproved Drugs of Low Regulatory Priority for FDA (see note atbottom of table).

NOTE: The FDA is unlikely to object atpresent to the use of these low regulatory priority substances if the followingconditions are met:

* The drugs are used for the prescribed indications,including species and life stage where specified.

* The drugs are used at the prescribed dosages.

* The drugs are used according to good managementpractices.

* The product is of an appropriate grade for use in foodanimals.

* An adverse effect on the environment is unlikely.