... The following material is based upon work supported by the Cooperative State Research Service and Extension Service, U.S. Department of Agriculture, under Special Project No. 87-EXCA-3-0836.

When a Tribal fish hatchery program is first conceived and construction begins, the initial cost of the program can be substantial. This problem is compounded by the monthly operation and maintenance cost that are needed to keep the facility operating properly. Perhaps one solution to help offset these expenses is to build into your program a means of maximizing your initial investment. One method of accomplishing this is to diversify your aquaculture facility to also include a baitfish production program. Part 2 of this article will appear in the next issue of the MTAN.

Baitfish production provides an attractive alternative to traditional fish farming in many parts of the United States. Baitfish are used by sportfish enthusiasts who prefer live bait over artificial lures or attractants. Baitfish are also used as feeder fish.

Although the baitfish industry has not always been profitable, previous successes and increasing demand for baitfishes present an optimistic future for new producers. Species preference in selected regions of the United States indicates golden shiners are most popular in the Southeast, Southwest and West. Fathead minnows are the dominant species in the Midwest and Northeast. White suckers and golden shiners are also important species. Feeder fish markets are developing in the mid-Atlantic and Southeastern states for use in striped bass and hybrid striped bass culture.

PRODUCTION METHODS

Quality, disease-free fish from a cultured line are the best broodfish. These fish can be obtained from established, reputable farms. Select ungraded yearling broodfish and have them evaluated by a diagnostician. Avoid fish which display any kind of bacterial or parasitic infection of any kind.

Wild Spawn is an extensive method of production. Stock 20-40 pounds of broodfish per acre. Fish should weigh 3 to 12 pounds/1000 or be from 333 to 83 fish per pound. Golden shiners are vegetative spawners. Plant a band of rye grass around the pond to serve as spawning material. Fish start spawning when water temperatures reach 70F and stop at water temperatures above 85F. Eggs are deposited on the rye grass and hatch in 7 to 10 days. Fertilize each pond within a week after hatching. Apply 100 pounds of fertilizer (0-46-0, 18-46-0 or equivalents) per surface acre. Start feeding minnow fry 4 days after hatching. Feed a high protein meal, 38% crude protein or higher. Overfeed initially to insure all fish have the opportunity to feed. When fish are one month old, change to a 32% crude protein meal or crumbled pellet. Begin feeding 2 pounds per acre and gradually increase to 10-20 pounds per acre.

Using the wild spawn method, egg laying, hatching, and grow-out occur in the same pond. Harvest the adults shortly after spawning stops. This prevents spread of disease from the adults to the young. Production using this method ranges from 200-350 pounds per acre.

INTENSIVE CULTURE

Two methods are used: (1) egg transfer and (2) fry transfer. For either method, stock broodfish at 300-500 pounds per acre. Place spawning mats, 21 x 30 inches, made of Spawntex (material similar to heating and air conditioning filters) sandwiched between 6" x 6" concrete reinforcement wire in the pond. Keep the pond free of vegetation to prevent uncontrolled egg deposition.

Egg Transfer Broodfish start "running" (swimming parallel) to the pond bank prior to spawning. Place spawning mats in shallow water about 1" below the surface when fish begin running. Stake the pond side of the mat to hold it parallel to the bank. Place mats in an end-to-end arrangement. There is no recommended number of mats for brood ponds, but it is not uncommon to use 500 or more in a ten acre brood pond.

Mats are ready to transfer to fry rearing ponds when they are uniformly covered with eggs. Egg covered mats appear as if dusted by a fine powder or snow. Mats are usually covered with eggs in 12-24 hours after placement. Never leave a mat in a brood pond more than 24 hours regardless of egg coverage. As spawning slows down, decrease the number of mats in the pond. Mats are picked up, stacked on a trailer or pickup truck bed, and covered by a tarp or burlap-like material. Mats can stay out of water up to one hour if they are kept moist and out of direct sunlight. For rearing ponds, stock 50-75 egg-covered mats per acre. Place the mats in shallow water 6-12 inches deep to allow eggs to hatch. Leave mats in the rearing pond for one week after hatching. This provides a protective area for fry. Use the same fertilization and feeding schedule as with the wild spawn method.

Fry Transfer Place 100-200 egg-covered mats per acre in ponds. The objective is to produce as many fry as possible, grow them to about " then transfer them to grow-out ponds. Fry are harvested using lift traps and fine mesh fry seines. Stocking densities for golden shiners depend on when fish are to be sold, size of fish desired and length of growing season. Most ponds are stocked with 50,000 to 200,000 fry per acre. Fry numbers may be determined by a volumetric displacement method. Count the number of fry in 1 ounce. Multiply that number by the number of ounces of fry transferred.

FATHEAD MINNOWS

Select broodfish at least 2" long. Males grow faster than females, so selection based on large size leads to mostly male populations. Fathead minnows have fewer parasite problems than other baitfishes. However, potential broodfish should be examined by a diagnostician. Fathead minnows are fractional spawners, releasing only a few eggs at each spawn. Culture of fathead minnows is restricted to wild spawn and fry transfer methods.

Wild Spawn Stock broodfish at 500 to 2,000 (2 to 10 pounds) per acre. Fish should be 2 inches long and weigh 5 pounds per 1000 (200 fish per pound). Sex ratios should be five females per male. There is a size difference between adult male and female fathead minnows, and the sexes can be separated using a 15/64 or 16/64-inch bar grader. Most females swim through the grader while males are trapped. Take samples of each sex to estimate numbers.

Fathead minnows spawn on the underside of objects in the pond. Use spawning boards, 12 x 4 x 1 inches stapled to wire stretched parallel to the pond bank. Space boards about 1 foot apart. Some producers use oak pallets tied to posts driven into the ground (placing four to six pallets per acre). The broodfish spawn over several months. Ponds are fertilized and fed at the same rate as with golden shiners.

Fry Transfer Stock broodfish, five females per each male, at 20,000 to 25,000 fish per acre (100 to 125 pounds per acre). This method can produce up to three million fry per acre. Stock fry at 100,000 to 300,000 per acre. Estimate numbers using the same method as with golden shiners.

GOLDFISH

Broodstock selection depends on the market. Fish are produced for the aquarium, landscape pond, feeder or bait market. Pay attention to color and shape of the adult fish. Slim-bodied varieties are preferred for bait. Cull heavy, thick-bodied fish. Plumper fish, trilobed tail, and "bug-eyed" condition are desirable traits for the aquarium market. Feeder goldfish are smaller (3-5 pounds/1000 fish), so use the same criteria used for selecting broodfish for bait.

The same spawning methods are used in goldfish production as with golden shiners. For wild spawn, stock 10-20 pounds of broodfish per acre. Fish should weigh 17-50 per pound (3-5 inches in length). Avoid using broodfish over pound. These fish may have parasites such as: Trichodina, Gyrodactylus and Dactylogyrus. Avoid using broodfish infected with "ulcer disease." This disease can kill 100% of the broodfish.

For the egg and fry transfer methods, stock broodfish at 800-1000 pounds per acre. Rearing ponds are stocked at 50-150 mats per acre. Fry are stocked from 25,000-1,000,000 per acre. Rearing ponds are fertilized and fed at the same rates as golden shiners. Many producers fertilize ponds based on light penetration into the pond water. Ponds are fertilized when a shiny object is visible at water depths greater than 16 inches.

WHITE SUCKERS

This species is more common in northern states. Broodfish are harvested from the wild. Broodfish collection may require special permits or be subject to regulation.

Collection of Eggs Sucker spawning dates are regulated by water temperature and may range from mid-April to late May. Suckers "run" when water temperatures are between 45F and 59F. Fish are trapped or seined below dams or waterfalls. Brooders are sorted by sex and put in tanks for transportation to the hatchery. Before releasing the fry, let the plastic bag float along the pond's edge. This lets the temperatures equalize and prevents temperature shock.

Sucker fry settle to the bottom of the hatching jar when the water is shut off. Numbers of fry can be estimated at this time. Pour the fry into a graduated container and allow them to settle. Determine the volume of fry in ounces. There are about 2,720, 5-day-old fry per ounce. A pond stocked at 40,000 fry would need 14.7 ounces of fry. Fry can be transported from the hatchery to rearing ponds in oxygenated plastic bags.

Stocking Rearing Ponds Sucker ponds are stocked at 40,000 fry per acre. Some growers adjust stocking rates to influence fish size. Suckers require no special feed. They grow on plankton, insects and invertebrates in the pond.

Overwintering Suckers Suckers too small for sale the first year can be overwintered in ponds. It is essential to keep snow off ice-covered ponds. Snow cover prevents light penetration and limits oxygen production. Some producers use large aerators to prevent formation of ice cover.

FEEDING AND NUTRITIONAL REQUIREMENTS

Most baitfish ponds need to be fertilized and supplemental feeding increases production. Fry need a nutritionally complete diet high in protein. Starter feeds should be fine. Fry feed should be made into a slurry and fed on all sides of the pond. This ensures all fish have the opportunity to feed. Feeding rates are determined by species and stocking rates. Golden shiners, goldfish and fathead minnows are fed 10-20 pounds per acre per day during the growing season.

HARVESTING, HANDLING, HOLDING AND TRANSPORTING

Baitfish species may be harvested by baiting and seining a pond corner, seining a whole pond or draining the pond. Traps are sometimes used for goldfish and fathead minnows.

Seining Seines and dip nets should be made from knotless, woven nylon. The most common mesh size is 3/16 inch. Smaller mesh seines collect debris and are more difficult to handle. Large mesh seines catch fish behind the gills (gilling). Seine length should be 50% longer than the width of the pond. Seine depth should be twice the average pond depth. For ponds 1-2 acres in size, stretch the seine across the end of the pond. One or two people are needed on each end of the seine. Walk slowly when pulling the seine so the lead line drags across the pond bottom. Angle the brail at 45 to 60 to pull the lead line ahead of the float line. Beaching the seine is the most critical step in seining. The lead line must not be raised off of the bottom, but it should not dig into the mud. Pull the float line in faster than the lead line. The float line "rolls over" to form a bag when the lead line is pulled into the shore forming a box type trap. "Stake" the corners with concrete reinforcement bars or electric fence posts. Fish are dipped out of the seine into 5 gallon buckets. A bucket holds 15-20 pounds of water and 25 pounds of fish. The buckets are carried to a transport truck and emptied into aerated tanks. Many fish mortalities are caused by improper harvesting, handling and transporting.

Lift Nets and Traps Lift nets and traps can be used for harvesting fathead minnows and goldfish. To use a lift net, lower the net in a shallow area. Place a ball of moistened fish food in the center of the net. Wait 15-30 minutes, approach the net cautiously, and lift the net rapidly by means of a lever. Dip the fish out of the net and reset.

Several traps can be used simultaneously. For traps, wrap the fish food in burlap or cheesecloth. Lower the trap to the pond bottom. Wait 15-30 minutes, grab the float line, lift the trap, empty the fish into a bucket, and reset the trap.

Holding Holding vats are made from concrete blocks or poured cement. Sizes vary depending on the operation. Vats 5 feet x 30 feet x 18 inches deep are most common. Holding facilities need an adequate water supply. Aeration for vats is usually provided by electric agitators or blowers.

Transportation Long distance hauling trucks have liquid or compressed oxygen tanks and insulated holding compartments. Hauling tanks may be constructed from marine plywood, styrofoam insulated sheet metal or insulated fiberglass. Tanks need a drain at least six inches in diameter. Hauling tank aeration systems include 12 volt agitators, blowers and oxygen systems. Two to four agitators are needed per compartment. One blower can serve four, 75-gallon compartments. Oxygen systems require a oxygen cylinder, regulator, one flow meter per compartment and an oxygen dispersion hose. The regulator is set at 20 pounds per square inch. Flow meters are set at 3-5 liters per minute. Both can be adjusted depending on the fish load and the number of compartments.

PROBLEMS OR CONSTRAINTS

Anticipation of problems and knowing how to solve them are essential to the successful operation of a fish farm. In the baitfish industry, some common problems include parasites, diseases, water quality deterioration, predators, weed infestation and legal or regulatory constraints. The severity, frequency and duration of disease outbreaks can be reduced by controlling fish stress.

... The next issue of the MTAN will contain additional information regarding baitfish production. The focus of which will cover water quality, weed and predator control and marketing techniques.

Best Management Practices For Baitfish Production

... Reprinted from the May/June 1995 issue of Aquaculture Magazine.

The baitfish industry is currently facing several concerns including increased regulations and the fear of spreading zebra mussels. To address these concerns a Best Management Practice (BMP) program should be initiated. A well conceived BMP program will identify critical areas in the baitfish production cycle. Proper care and practices at each of the critical areas will improve quality of the final product. Critical areas and practices include site selection, water source, broodfish screening, animal husbandry practices, maintaining good water quality, not sharing equipment between 'wild water' and pond water and education at the final sales point.

Regulatory agencies are concerned with chemicals that reside in non-food as well as food fish. Therefore, producers should be concerned about pond site selection including land use history.

Wetlands are another consideration. Before any pond construction begins, the site's wetland status must be determined.

The baitfish producer's BMP program should include careful selection of the water source. Groundwater is the ideal source for fish farming. The water must be free of chemical contaminants. Spring water is also a good source but must be available during the drought season. Streams can be used as a water source but must be free of zebra mussels and contain pathogen free (wild) fish. Stream water must be also be screened to prohibit the entry of predatory fish into your pond facility.

Healthy broodfish produce larger eggs, which result in improved fry survivability. A good screening program should eliminate the presence of such diseases as "goldfish ulcer disease," milk scale, various grub species and the anchor worm. Reject any fish that are unusually thin or has abnormalities such as curved spine, misshaped head or lacks the body conformation the fish culturist desire.

Good animal husbandry should be part of the producer's BMP program. Cultured fish need a quality diet. The fish must be reared under the least stressful conditions possible. Rough handling during harvest and transport should be avoided as well as unneeded chemical treatments. Good quality water in ponds and tanks is essential for fish survival. Another important practice is to not share equipment between "wild water" and pond water.

To eliminate stress, adequate aeration is needed in ponds, during transport and at the grading facility. Proper tempering is also a must when changing fish from one body of water to another.

Wildfish can introduce unwanted disease organisms into ponds and the water can also be a source of zebra mussels. It is imperative to avoid using equipment utilized in harvest of wildfish in commercial aquaculture ponds. This includes the use of nets and seines, dipnets, waders, buckets and boats.

Another concern involves genetics. Baitfish from cultured ponds may have a different genetic make-up than the baitfish in the native body of water. If these fish happen to cross, the native batifish can loose some of its genetic identity. Baitshop owners should urge fishermen to avoid releasing unused baitfish into the water. Fishermen should be urged to destroy the unused bait when finished fishing.

A final BMP practice involves educating people at the final sales point of the baitfish. People are becoming very concerned over the impact fishermen have on the aquatic environment caused by the release of baitfish into a receiving body of water. Many people are concerned that non-indigenous species may upset the balance of nature in these areas.

Although these suggestions will not solve all the baitfish industry's problems they make good sense and are also easy and inexpensive to implement.


A BIBLIOGRAPHY ON THE CULTURE OF BAITFISH

Ball,R.C., and E.H. Bacon. 1954. Use of pituitary material in the propagation of minnows. Prog. Fish-Cult. 108-113.

Bauman, A. C. 1946. Bait minnow production in ponds. Mo. Cons. 7(6)3-5.

Bell, R. C. 1960. Propagation of bait minnows in California.

Calif. Dept. Fish Game Inland, Fish. Admin. Rept. No.56-1 1.

Benoit, D. A., and R. W. Carlson. 1977. Spawning success of fathead minnows on selected artificial substrates. Prog. Fish Cult. 39(2):67-69.

Branch of Fish Hatcheries. 1965. Fish baits: Their collection, care, preparation and propagation. U.S.F.W.S. Leaflet FL-28.

Clark, C. F. 1943. Creek chub minnow propagation. Ohio Cons. Bull.7(6):12-13.

Cook, F. A. 1954. Baitminnows - their propagation is a necessity. Miss. Game Fish 18(2):3-5.

Cooper, G. P. 1935. Some results of forage fish investigations in Michigan. Trans. Amer. Fish. Soc. 65:132-142.

Davis, H. S. 1953. Culture and diseases of game fish. Univ of Calif. Press, Berkley, Calif. 332 p

Davis, J. T. 1986. Baitfish. In: R.R. Stickney Culture of Nonsalmonid Freshwater Fishes. CRC Press, Boca Raton, Florida.

Doble, J. 1948. Minnow propagation. Minn.Dept.Cons.Bull.No. 13.

Doble, J. 1972. Rearing suckers for bait in Minnesota. Minn. Dept. Nat. Res. Invest. Rep. No. 256.

Dobie, J. R., 0. L. Meehean, S. F. Snieszko, and G. N. Washburn. 1956. Raising bait fishes. U.S.F.W.S. Cir. 35.

Flickinger, S. A. 1969. Pond culture of bait fishes. Colo. State Univ. Coop. Ext. Ser. Bull. 478A. 39 pp.

Flickinger, S. A. 1973. Investigation of pond spawning methods for fathead minnows. Proc. Annu. Conf. S.E. Assoc. Game Fish Comm. 26:376-391.

Fomey,J.L. 1957. Bait fish production in New York ponds. N.Y. Fish Game J. 4:150-194.

Fomey, J. L. 1975. Raising baitfish and crayfish in New York ponds. Cornell Univ. Coop. Ext. Ser. Bull. No. 986, Ithaca.

Gast, M. M., and W. A. Brungs. 1973. A procedure for separating eggs of the fathead minnow. Prog. Fish-Cult. 35:54.

Giudice, J. J., D. L. Gray, and J. M. Martin. 1981. Manual for bait fish culture in the south. Univ. of Arkansas Coop. Ext. Ser. EC-550, Little Rock.

Guest, W. C. 1977. Technique for collecting and incubating eggs of the fathead minnow. Prog. Fish-Cult. 39(4):188.

Hasler, A. D., H. P. Thomsen, and J. Neiss. 1946. Facts and comments on raising two common bait minnows. Wis. Cons. Dept. Bull. No. 210.

Hedges, S. B., and R. C. Ball. 1953. Production and harvest of bait fishes in Michigan. Mich. Dept. Cons. Misc. Publ. No.16. 30pp.

Hickman, G. D., and R. V. Kilambi. 1974. Growth and production of golden shiner under different stocking densities and feeding rates. Proc. Ark. Acad. Sci. 28:28-31.

Hubbs, C. L. 1934. Some experiences and suggestions on forage fish culture. Trans. Amer. Fish. Soc. 63:53-63.

Huner, J. V., and H. K. Dupree. 1984. Third Report to the Fish Farmers. U.S. Fish and Wildlife Service.

Hutchens, L. H. 1946. Bait minnow and their propagation. L11. Cons. II:14-15.

Jensen, J. W. 1983. Home fish bait production. Auburn Univ. Coop. Ext. Ser. Cir. ANR 329, Auburn.

Johnson, S. K. 1978. Maintaining minnows - A guide for retailers. Texas A&M Univ. Coop. Ext. Ser. Bull. MP-1320, College Station.

Johnson, S. K., and J. T. Davis. 1978. Raising minnows. Texas A&M Univ. Coop. Ext. Ser. Bull. NIP-783, College Station.

Langlois, T. H. 1937. Bait culturists guide. Ohio Dept. Ag. Bull. No. 137.

Markus,H.C. 1939. Propagation of bait and forage fish. U.S.Bur. Fish. Cir. No.28.

Martin, M. 1954. Minnow culture in Kentucky. Div. Fish., Ky. Dept. Fish Wildl. Res. 28pp.

Mayer, F. L. 1976. 2,4-D reduces Saprolegnia on fathead minnow eggs. Prog. Fish-Cult. 38(l):19.

Mural, T., and J. W. Andrews. 1977. Effects of salinity on the eggs and fry of the golden shiner and goldfish. Prog. Fish. Cult. 39:121.

Nagel, R. 1976. Techniques for collecting newly hatched fathead minnow fry. Prog. Fish. Cult. 38(3):137.

Prather, E. E. 1956. Experiments on the commercial production of golden shiners. Proc. Annu. Conf. S.E. Assoc. Game Fish Comm. 10:150-155.

Prather, E. E. 1957. Preliminary experiments on winter feeding small fathead minnows. Proc. Annu. Conf. S.E. Assoc. Game Fish Comm. 11:249-253.

Radcliffe, L. 193 1. Propagation of minnows. Tran. Amer. Fish. Soc.61:131-138.

Raney, E. C. 1941. Propagation of the silvery minnow in ponds. Trans. Amer. Fish. Soc. 71:215-218.

Rosenberg, R. B., and R. V. Kilambi. 1975. Growth and production of golden shiner under different stocking densities and protein levels. Proc. Annu. Conf. S.E. Assoc. Game Fish Comm. 28:385-392.

Saylor, M. L. 1973. Effect of harvesting methods on production of fingerling fathead minnows. Prog. Fish-Cult. 35(2):110-114.

Wascko, H., and C. F. Clark. 1948. Pond propagation of bluntnose and blackhead minnows. Ohio Div. Cons. Nat. Res., Wildl. Cons. Bull. No. 4.16 pp.

Washburn, G. N. 1945. Propagation of the creek chub in ponds with artificial raceways. Trans. Amer. Fish. Soc. 75:336-350.

COMMON DISEASE PROBLEMS IN BAITFISH CULTURE

By: Terrence Ott, La Crosse Fish Health Center, La Crosse, WI

Commercial warmwater fish farming was begun in the late 1920's and early 1930's by a few persons who raised minnows to supply the growing demand for baitfish for sport fishing. Shortly after World War II, the demand for minnows increased as the result of the boom in farm pond and reservoir construction and the many water conservation projects inspired by the dust-bowl years of the 1930's.

The baitfish industry blossomed during the 1960's producing over 20 species of fish for bait in North America with golden shiner Notemigonus crysoleucas, fathead minnow Pimephales promelas and white sucker Catostomus commersoni becoming the three most popular species cultured in the Upper Midwest.

Parasites and diseases pose a serious threat to the intensive production of baitfish and loss of income can be substantial. Many producers have learned that some parasites and diseases can spread rapidly and kill an entire fish population in a short time.

It is essential that a baitfish producer observe the fish daily and be able to recognize the clinical signs of fish diseases when they first appear. Good health management practices is the key to successful production of healthy baitfish.

Bacterial diseases occur in baitfish as primary or secondary invaders. Columnaris disease is caused by the bacterium Flexibacter columnaris and is a primary invader of baitfish. The disease begins externally on the body surface producing lesions. As the disease progresses, these lesions spread over the rest of the body causing necrosis of the underlying muscle fibers. Virulent strains of F. columnaris may attack gill tissue and cause a "gill rot" condition. Systemic infections due to less virulent strains may occur with no apparent external signs. However, cutaneous infections seem to be more prevalent in most baitfish. Water temperature is a major influence on the occurrence of columnaris.

Outbreaks seldom occur below 13C, but may be explosive above 18C. Summer is the season with the highest incidence of columnaris outbreaks. Crowding, handling, and other stressors are also predisposing factors to columnaris outbreaks.

A. hydrophila is a secondary invader closely associated with handling injuries and stress. This motile aeromonad is among the most common bacteria in freshwater habitats throughout the world. These bacteria can be opportunistic and develop increased virulence under ideal conditions. Stress caused by high water temperatures, low oxygen levels, accumulations of waste products, and overcrowding are predisposing factors which can lead to disease outbreaks. Nutritionally deficient fishes are especially susceptible to secondary infections, as are fishes with injuries or damaged skin or gills.

The organisms are usually transmitted orally except in those instances when fish have skin or gill abrasions and the organism may enter through these routes. External parasites which abrade skin and gills have been implicated in the transmission of A. hydrophila. The bacteria multiply in the intestine or at the site of invasion and are spread throughout the body by the blood stream.

Saprolegnia is the major fungal disease encountered at baitfish farms. This fungus is thread-like in appearance, and possesses profusely branched non-septate hyphae that appear as white to gray tufts in the water. There are no primary causes of saprolegnia among baitfishes; rather infection may be secondary to other infections or injuries. Bacterial disease, external parasites, and physical or environmental stressors may predispose a fish to fungal infection. Saprolegniais more detrimental to fish eggs than to fish.

A microsporidean, Plistophora ovarie, parasitizes the developing ovaries of adult golden shiners. This parasite reduces fecundity and may produce sterility in older females. P. ovarie is an intracellular parasite with a tremendous reproductive capacity. Microsporiasis is characterized as a chronic condition in which masses of developing spores form within the ovaries of the shiner. Disintegration of the tissue in which the spore is present releases spores. Ingestion of infected fishes by other fishes also releases spores from the infected fish. Those released to the environment must be ingested by the new host, either directly or as contaminants on food. Golden shiners with microsporiasis at an advanced stage of development may become lethargic, emaciated, may become solitary or may have different body colors.

Golden shiner virus is another pathogen infecting golden shiners. This disease causes low-grade chronic mortalities in ponds and has been reported to cause high mortality in shiners held in tanks. Visible signs of the disease include a red-back or red-head condition caused by expanded blood vessels beneath the surface of the skin, and intestinal hemorrhage and hyperemia on the ventral surface of the fish.

Ichthyophthirius multifilis a protozoan parasite is a ciliated, motile protozoan with a horseshoe-shaped nucleus. "Ich", as this parasite is commonly called, thrives at temperatures around 15C. The adult form becomes attached and forms a visible cyst that appears as white pustules on the fins and body. Slight to moderate infections will not cause behavioral changes in the fish. Marked or extreme infections may be accompanied by lethargy, listlessness, rubbing on the sides or bottom of the pond and difficulty in obtaining oxygen if the gills are badly damaged.

Another common parasite of baitfish is the monogenetic trematode, Gyrodactylus elegans. This trematode can be identified by the developing embryo inside the adult along with the lack of eye spots. The posterior end has a haptor with a single pair of large hooks. Under optimum conditions these worms can be seen by the naked eye. G. elegans occurs in epizootic levels during late winter and early spring. Usually little or no harm is done to the fish, but on occasion this fluke contributes to disease of the fish if it becomes too numerous at any one time.

Another consideration in a baitfish culture operation is the control of predators and competitive organisms. Predators must be controlled in and around baitfish production ponds. A few predators can often capture and eat enough baitfish to make the production system unprofitable. Control of these predators often depends on the ingenuity of the farmer. Since a special license or permit is often required before some nuisance animal can be killed or removed, the baitfish farmer should consult with appropriate State and Federal conservation authorities before beginning a control program.

Keeping levees and dikes clean of debris and mowed helps control small borrowing mammals like muskrats.

Snakes of various species can be quite abundant around baitfish ponds. Sometimes snakes will lie on spawning mats or boards waiting to prey on brood fish.

Tadpoles and crayfish are a nuisance in harvesting, and are also a competitor with baitfish. In addition, there is evidence that tadpoles and frogs carry certain fish parasites and diseases.

A successful baitfish culture is the result of an effective health protection program, and can be as challenging and complex as the actual control of existing diseases. Key components of disease prevention include the reliable detection of disease carriers, knowledge of how pathogens are transmitted, development of effective methods to limit the entry of pathogens or carriers into clean baitfish cultural facilities, and the capacity to provide environmental conditions conducive to good fish health.

Flow Rates Control Fungal Infections Of Rainbow Trout Eggs

By: Jeff Rach, Jennifer Marks and Verdel Dawson, National Fisheries Research Center, La Crosse, WI 54602

Hatchery personnel have used many chemicals to control disease outbreaks on fish eggs. The number of chemicals presently permitted for use with eggs has dwindled to three: hydrogen peroxide, salt, and formalin. Chemical treatments can be expensive to apply and toxic to sensitive fish species.

Elevated flow rates to roll eggs in hatching-jar systems seems to reduce the incidence of fungal infections. Green eggs can be highly sensitive, however, and vigorous rolling may induce death. We tested various flow rates for controlling fungal infections and improving egg survival in a hatching jar system by using both uninfected rainbow trout egg's and eggs artificially infected with fungus (Saprolegnia parasitica).

EGG HATCHING JARS WERE USED To EVALUATE TREATMENTS

Green eggs were obtained from Trout Lodge (Sumner, Washington) and shipped to the National Fisheries Research Center, La Crosse, Wisconsin. Eggs were received within 36 h of spawning, acclimated to 12 1C, and 30 ml (about 300 eggs) of eggs were transferred into each miniature egg hatching jar (5 cm in diameter; 15 cm long).

The egg hatching system was composed of a headbox, miniature egg hatching jars, and glass aquaria.

Continuously flowing well water at 12 1C entered the headbox and flowed by gravity to the egg jars. The effluent from the egg jars then flowed into glass aquaria that collected hatched fry from the jars.

Two separate trials were conducted. Uninfected eggs (trial 1) were compared with eggs artificially infected (inoculated) with fungus (trial 2) in tests that exposed eggs to variable flow rates of 300, 600, 1,200, and 1,800 ml/min. Each flow rate was tested in triplicate. Comparisons (P < 0.05) of percent hatch at different flowrates were made by analysis of variance.

ROLLING OF EGGS INHIBITED FUNGUS

The four flow rates were selected to achieve a range of egg movement. Eggs cultured in the 300-ml/minute flow showed no movement, whereas eggs in the 600-ml/minute flow displayed slight movement but did not roll. Eggs in the 1,200-ml,/minute flow were raised in the water column and exhibited a slight to moderate rolling action. Eggs in the 1,800-ml/minute flow were elevated higher in the water column and rolled vigorously.

In trial 1, the egg hatching success in the three lower flows (300, 600, and 1,200 ml/minute) were not significantly different and average hatches were 85.4, 83.1, and 82.2%. Because the incidence of naturally occurring fungus is generally low in eggs cultured in the Center's well water supply, fungal infections did not develop at any of the flow rates. However, only 20.2% of the eggs hatched at the 1,800-ml/minute flow, presumably because of the excess agitation.

The procedure used to infect eggs with fungus (trial 2) resulted in the infection of eggs at the 300 and 600-ml,/minute flows and the hatch rates in these flows were less than 10%. At the 1,800-ml/minute flow rate, the hatch rate was only 25%. Although most of the eggs at this flow were dead within the first week of testing, there was no observed fungal infection. The 1,200-ml,/minute flow was the optimum flow with a mean hatch rate of 78%, which was significantly (P < 0.05) higher than the hatch rates at the other flows. This flow was high enough to control the fungus without causing death of eggs.

MANAGEMENT IMPLICATIONS

... The rolling of fish eggs is useful in controlling fungus on eggs. Its effectiveness for hatchery use is dependent on the ability of culturists to observe egg movement and adjust flows to generate the appropriate movement of the eggs.

Physical manipulation of eggs does not eliminate the need for chemical treatments. Raising salmonids in stacks of Heath incubators requires chemical treatments for fungal control. Hatcheries that use surface water for culturing eggs usually have a higher incidence of fungal infestations. Eggs being shipped between hatcheries are vulnerable to stress and rapidly spreading fungal infections. A combination of chemical treatment and physical manipulation would probably be needed in most hatcheries.

Hatchery Tip

By: MTAN

The MTAN and the Bureau of Indian Affairs (Minneapolis Area Office) have been successful in scheduling a one day workshop regarding "Rearing Fish At High Densities In Water Reuse Systems". This workshop will be held during the September 19-21 meeting of the Native American Fish and Wildlife Society. The fee for this course will be paid by the Minneapolis Area Office. The workshop will be given by Gene Hanson who began investigating in aquaculture in 1984. Intrigued by its potential, he continued he's research which lead him in the development of Aurora-Aqua Inc.. Since then he has developed several commercial water reuse systems. Currently Mr. Hanson is President of Aurora-Aqua, Vice President and newsletter editor of the Minnesota Aquaculture Association and an active member of the Minnesota Aquaculture Commission.

Keep that water cool! The MTAN recently heard of a South Dakota hatchery that lost 400,000 walleye fingerlings while in transport to the release site. The heat and stress of the move were assumed to cause the death of the fish. South Dakota officials said the incident may cause the hatchery division to review fingerling transportation procedures. The department's fish transport vehicles are equipped with aerators and oxygen for the fish, but that may not be enough. They're now considering air and water temperatures more carefully and may decide to wait for cool weather or transport the fish during cooler times of the day. They may also consider adding ice to the water to reduce the heat stress on the fish.

Greg Fischer (Red Cliff Tribal hatchery biologist) recently received several fiberglass rearing tanks from the Hyperdyne Corporation, which is located in Bemidji, MN. According to Greg he is very pleased with the new tanks. He said they were strong and still priced very competitively. If you're in the market for rearing tanks, you may want to contact Greg or Paul Shough of Hyperdyne (218-751-9310) for more information.

The MTAN reviewed a video from Aurora-Aqua that very nicely describes the application of water reuse systems. If you would like to view this tape please call Frank Stone at the Ashland FRO (715-682-6185).

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