Dedicated To Tribal Aquaculture Programs
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December 1994 ~ Volume 10 | |
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Topics of Interest:
Lake Sturgeon Egg Take Procedures
Lake Sturgeon Egg Take Procedures
By: Roger Klindt
NYSDEC, 317 Washington St., Watertown, NY 13601 315-785-2261
Lake sturgeon have been collected with a variety of gear. Collections have been made using both monofilament and multifilament gill nets of mesh sizes 7-12 inch stretch measure. Gill nets are set parallel to the current in approximately 6-12 feet of water. Nets should be checked at no more than one hour intervals after setting. Captured sturgeon are then kept in holding tanks with recirculating water for several hours before surgery.
Surgical Sexing:
After a brief recovery from capture (2-4 hours) fish are ready for surgery. The surgery area should be set up before hand to expedite the procedure and reduce stress to the fish. All instruments are placed in a bath of diluted betadine solution. The scalpel should have a fresh blade. Probes should be cleaned before surgery.
Fish are taken one at a time and placed on a wet stretcher where they are measured and weighed to the nearest tenth of a kilogram. The assistant places a thumb into the mouth of the fish to act as a calming distraction. Once the fish is relaxed and not moving the surgeon cleans an area for the incision. Water and mucous are wiped from the area. Next a small amount of betadine is swabbed on the incision site. The area to be cut is located on the ventral surface approximately 5 scutes anterior of the vent. (see illustration). An incision of approximately 1-1.5 cm is made just off the ventral midline. The incision should be made carefully, only through the skin with a single stroke if possible.
Sex is determined by probing through the incision with forceps. Probing is done towards the body wall so as not to injure other tissues. Males will produce a white granular material (teste) or sperm, females will produce eggs if mature and in spawning condition. Once sex and/or maturity is determined the incision is closed. A simple interrupted pattern is used with 2/0 nylon on a swaged cutting needle. The needle should pass through the middle of the skin layer. The finished suture should be snug but not tight, to allow for swelling. Either one or two sutures will be needed, depending on the length of the incision. After sex determination is made the fish is tagged with a numbered floy tag and returned to the holding tank. Fish are then left alone for 24 hours to acclimate to the holding facility.
Hormone Injection:
Hormone injection is scheduled for egg take convenience. Fish receive their initial injection 24 hours after sex determination. Sturgeon will be ready for stripping about 30-32 hours after their first injection.
Preparation
Dry carp pituitary hormone (CCP) should be pre-weighed before hand and stored in air tight vials. Vials should contain the following amounts; 10mg, 20mg and 50mg. This will allow the proper dosage to be mixed quickly. Specific dosages for male and females are different. Using a 1 or 3cc syringe with a 23 Ga. needle, add just enough distilled water (0.3-0.5 ml) to the vial to make a solution. Shake the mixture and allow it to settle. With the syringe, remove the solution.
The injection sight is located between the dorsal and lateral scutes, at the midpoint of the body. The solution is injected into the musculature, as the syringe is withdrawn place a finger over the hole and massage the solution into the tissue.
Dosage for males
Male sturgeon receive their entire dose of hormone in one injection. Dosage for males is lmg/kg (0.4mg/lb). Because of differences in gonadal maturity, some males may be injected 12 hours after the first to insure mature sperm are available.
Dosage for females
Female sturgeon receive two separate doses of hormone. Their first injection is 10% of the total dosage. The second injection consists of the remaining 90% of hormone and takes place 12 hours later. The dosage for females is 5mg/kg (2mg/lb).
Egg Take:
Egg take operations commence about 30-32 hours after the first hormone injection. The procedure begins with taking sperm, then eggs, fertilization and packaging for transport.
Sperm:
Sperm is extracted from each male sturgeon that shows signs of being ripe. Fish are removed one at a time from the holding tank, identified, and placed in a stretcher. With an assistant restraining the fish with the "thumb in mouth" technique another individual removes the sperm. A 50-60cc syringe with a 3" piece of tygon tubing (trimmed to a point) on the end is used. The tube is inserted into the vent and is moved back and forth as the syringe plunger is withdrawn. With 40-50cc of sperm in the syringe, it is removed from the fish, capped, labeled and stored on ice. The syringe should not come in direct contact with the ice.
Egg Removal:
Egg removal requires preparation and TEAMWORK, as time is a limiting factor. Having people assigned specific tasks can be very helpful when dealing with several fish at once. Before taking eggs be certain that all fertilization equipment is set up. This equipment should include (but not limited to) the following:
Two water baths to keep materials at river temperature.
At least 3 thermometers.
Fullers Earth "mud": in 5 gallon bucket add water and enough earth so the mud will settle out 2 inch on the bottom when left alone.
Beaker for diluting sperm.
4 stainless steel bowls
2-4 extra buckets
Clear plastic bags and duct tape for transport.
Stripping is done in stages as eggs mature. Each female will be stripped normally 2 times, the 3rd will be done by opening the incision (which was previously made to sex the fish) to remove the bulk of the eggs. Females are placed in the stretcher as before. Eggs are stripped into a dry stainless steel bowl. When the first batch of eggs has been stripped, sperm is diluted into a beaker with river water. A ratio of 1:200 sperm to water is used. Sperm should come from at least 2 males, preferably 3 or 4. Eggs mature in batches within a fish. It is important to inspect the holding tank for presence of discharged eggs. If sticky eggs are present the female must be stripped immediately, presence of nonsticky eggs means the females are approaching maturity.
The following is done at river temperature by keeping pans on water baths:
After sperm is diluted it must be placed immediately on the eggs. The solution is swirled over the eggs for exactly 1-1.5 minutes. It is then decanted off and replaced with a mud solution. Fullers earth solution is added and mixed with the eggs. A swirling action is alternated with hand mixing. This solution is changed 2 times after the initial treatment. Mudding lasts for exactly 40 minutes. When mudding is complete the eggs are rinsed with clear river water until clean. Eggs are then put into clear plastic bags half filled with river water. Oxygen is injected into the bag and sealed. Eggs are then placed in coolers filled with river water at the appropriate temperature.
Conservation and Management of Lake Sturgeon In The Great Lakes
By: MTAN
The MTAN was able to participate in a lake sturgeon workshop which was held in Niagara Falls on October 26/27. The two day meeting focused on five primary topics: 1) Habitat, 2) Genetics, 3) Population Assessments, 4) Culture and Reproduction/Life History, and 5) Management and Recovery Planning. If you would like to develop additional contacts with other biologists who are working on sturgeon recovery projects, the following list of workshop presenters may be of some help.
Habitat:
Betsy Kozuchowski - USFWS, Lower Great Lakes Fishery Resources Office, Amherst, NY. Habitat management using the guild approach, (716-691-5456).
Andrew Rossiter - Univ. of Guelph, Dept. of Zoology, Guelph, Ontario, Food and foraging in juvenile lake sturgeon, (519-824-4120).
Stephan Peake - Univ. of Guelph, Dept. of Zoology, Guelph, Ontario, Swimming performance of lake sturgeon, (519-824-4120).
David Johnson - USFWS, Marquette Biological Station, Marquette, MI. Tolerance of sea lamprey larva and lake sturgeon to TFM, (906-226-6571).
Genetics:
Paul Fuerst - Ohio St. Univ., Dept. of Zoology and Molecular Genetics, Columbus, OH. Molecular genetic and biochemical studies of lake sturgeon, (614-292-6403).
Rejean Fortin - Univ. of Quebec at Montreal, Quebec, Canada, Morphology and population biology of lake sturgeon, (514-987-6113).
Harold Kincaid - NBS, Nat. Fisheries Research and Development Laboratory, Welsboro, PA. Breeding plan for small populations of lake sturgeon, (717-724-3322).
Population Assessments:
Gary Whelan - Michigan DNR, Lansing, MI. Estimates of historic lake sturgeon stocks, (517-373-1280).
Ted Cavender - Ohio St. Univ., Museum of Biological Diversity, Columbus, OH. Decline and present status of lake sturgeon in Lake Erie, (614-292-7873).
Steve LaPan - NYSDEC, Watertown, NY. Lake sturgeon field studies on the St. Lawrence River,(315-785-2261).
Culture and Reproduction/Life History:
Andrzej Ciereszko - Ohio St. Univ., School of Natural Resources, Columbus, OH. Biology of lake sturgeon semen, (614-292-7964).
Martin DiLauro - NBS, Nat. Fisheries Research and Development Laboratory, Welsboro, PA. Cryopreservation of lake sturgeon sperm, (717-724-3322).
Konrad Dabrowski - Ohio St. Univ., School of Natural Resources, Columbus, OH. Captive broodstock and diploid androgenesis, (614-292-4555).
Bill Krise - NBS, Nat. Fisheries Research and Development Laboratory, Welsboro, PA. Feeding dry diets to lake sturgeon larva as a starter diet, (717-724-3322).
Management and Recovery Planning:
Chet MacKenzie - Vermont Dept. of Fish and Wildlife, Pittsford, VT. A feasibility study of restoring lake sturgeon to Lake Champlain, (802-483-2172).
Elizabeth Hay-Chmielewski - Michigan DNR, Ann Arbor, MI. Lake sturgeon management plan for the state of Michigan, (313-663-3554).
Steve LaPan - NYSDEC, Re-establishment of lake sturgeon in tributaries of the St. Lawrence River, (315-785-2261).
Twelve Uses Of Salt On The Trout Farm
Written By Charles W. Johnson
Submitted By Mike Donofrio (Keweenaw Bay Indian Community)
Published in the September 1994 Issue of the Aquaculture Magazine
Salt (sodium chloride) is one of the safest and oldest used chemicals on fish farms. Granulated salt with no additives can be purchased in 50 or 80 pound bags at local farm supply stores. Some beneficial uses of salt include:
Parasite Control - one pound of salt for every two gallons per minute water flow in raceways or earthen systems (with good water turnover) has proven to be effective in controlling most parasites. Monthly treatments are usually adequate when water temperatures are between 50-65 F. If summer afternoon water temperatures rise to 65 F or above, weekly treatments may be needed for effective parasite control. Costia is more difficult to control with salt. If it becomes a problem, formalin treatments may be needed.
Columnaris Control - Salt flush treatments have proven effective in preventing columnaris. The frequency of treatments will vary according to conditions on each farm and the water temperature. Monthly treatments may be adequate when the water temperature is in the upper 50s. Treatments at least once a week or more may be needed when the water temperature is above 65 F. If lesions are seen on the gills of trout or other symptoms increase, salt alone may not control columnaris. Promptly begin feeding feed containing terramycin (3.5 grains active oxytetracycline per 100 pounds of fish) for 10 days.
Saprolegnia Fungus Control - Routine salt treatments on production fish usually help reduce fungal development. When fish are being moved, a 1-1.5% salt solution (8.3-12.5 pounds/100 gallons of water) either in the hauling tank or for thirty minutes prior to moving provides an effective treatment. Another recommended treatment is exposing fish to a 3% (4 ounces/gallon of water) salt solution for about four minutes or until fish show signs of distress. Weaker fish do better in the less concentrated salt solutions. Some fish culturists have noticed that when fish are weak and in water with high hardness, saprolegnia is more difficult to control.
Fish culturists who do not like using formalin may consider the use of salt on trout eggs. A treatment of 2-3% salt solution for 15 minutes every other day has been found effective in preventing growth of saprolegnia on eggs. A 2% treatment would require 2.5 pounds of salt for each gallon per minute flow for the 15 minute period. If water could be adequately aerated and recirculated for 15 minutes, a 2% treatment would only require 2.67 ounces of salt for each gallon of water. If fungus is established, treatment for a longer period of time will be needed. A treatment of 5% for up to one hour on alternate days may be required to halt an existing infection on eggs. Do not allow sac fry to be exposed to this concentration of salt.
When Using Formalin - A prior salt treatment will reduce the chances of mortality of fish and increase the effectiveness of the formalin treatment for parasite control. A salt flush immediately following the formalin treatment will help to recondition the damaged gills and reduce the chances of delayed mortality. One pound of salt for every four gallons per minute water flow should be adequate for both treatments.
Acid Rain Relief - A sudden drop in pH creates stress in trout. The fish usually act very nervous and even try to get out of the raceway or pond in order to escape the irritating effects on their gills and skin. When this condition is seen during or after a rainstorm, the immediate addition of salt will help to relieve stress. When fish have been damaged from acid rain the continuous use of white salt blocks (with no additives) at the head of the system for two or three days will assist in recovery. Salt blocks used during rainstorms when acid rain is a potential problem will be helpful in providing the fish with needed ions, as well as providing relief from some of the stress on the gills. If problems become critical, you may need to install a system at the head of your farm to add a buffer, such as hydrated lime.
Muddy Water Relief - If water becomes muddy during a heavy rain or if it is stirred up during cleaning, a salt flush treatment will aid in the removal of foreign particles on the gills. One pound of salt for every four gallons per minute should be adequate.
Grading and Inventorying For Stress Relief - A salt flush just prior to grading, inventorying, and other handling of fish will help to calm the fish and better prepare them for the handling stress. Salt relieves the gills of excess water and stimulates the release of ammonia and nitrates from the blood. It is especially beneficial to trout grown in soft water by assisting with the salt balance needed in their blood and tissues.
Hauling Stress Relief - The use of salt in transport tanks is a common practice to reduce stress. Concentrations as high as 0.8% (6.4 pounds/100 gallons of water) can be used safely for extended periods. In soft water, many biologists also recommend the addition of gypsum (3.3 ounces/100 gallons) to increase calcium hardness and baking soda (2.7 ounces/100 gallons) to help prevent the pH from dropping. After the fish are delivered to raceways or ponds, the use of salt blocks for several hours will help prevent fish health problems from hauling and handling stress.
Gill Problem Control - One of the major problems of early feeding fry in hatcheries is the accumulation of uneaten feed and fecal material on the gills. This frequently leads to environmental and bacterial gill problems. Salt treatments administered at least weekly help rid the gills and skin of excess mucus containing foreign material and organisms.
Low Oxygen Relief - When fish are gaping at the incoming water due to low oxygen, a salt flush will quickly relieve stress and reduce chances of mortality. One pound of salt for every four gallons per minute should be adequate. For extended relief, the use of salt blocks will be helpful.
Ice Control - Salt can be poured on your intake screen to help melt ice, to reduce ice problems on raceway screens and even to help keep pipes open during severe cold. It is also beneficial when sprinkled on icy work areas.
Algae Control - Salt sprinkled on filamentous algae in shallow areas around the edge of ponds will help keep the algae under control. Several applications will probably be needed during the year.
Unlike many chemicals, salt can be safely used regardless of water temperature. However, the use of salt does not replace the need for good management practices such as keeping raceways and ponds clean, starving fish before handling or hauling, maintaining proper densities, and avoiding overfeeding.
Common Salt Is Fungicidal On Trout Eggs
By: Jeffrey J. Rach, Theresa M. Schreier, and Leif L. Marking
National Fisheries Research Center, P.O. Box 818, La Crosse, WI 54601 (608) 783-6451
Malachite green, the preferred fungicide for fishery use, is no longer legal for control of fungus on fish or fish eggs. Formalin is an effective fungicide, but fishery managers are concerned about safety to the user and effects of effluent in the environment. Other antifungal agents are needed to maintain healthy fish and eggs in fish culture systems.
Salt (sodium chloride) has been widely used by the aquaculture industry as a therapeutic agent and to reduce stress to fish. Some fish farmers use salt for routine management purposes without proper knowledge of how it functions. Salt is commonly used to prevent and treat bacterial diseases, eliminate external parasites, reduce stress conditions during fish transport, and reduce toxicity of ammonia and nitrate nitrogen in fish ponds. Some reports in the literature suggest that use of seawater is effective for control of the common fungus Saprolegnia sp. on eggs of salmon. Others suggest that mixtures of sodium chloride and calcium chloride will control fungus on incubating eggs. We designed experiments to evaluate the effectiveness of sodium chloride for control of fungal infections on incubating eggs of rainbow trout.
In Vivo Procedures:
Green eggs of rainbow trout were placed in Heath incubation trays and maintained in well water with a flow rate of 1 L/minute. Groups of 500 eggs were confined within 15-cm diameter acrylic rings fastened to the screen of each incubation tray. Eggs were inoculated with fungus (Saprolegnia parasitica) actively growing on hemp seeds suspended by tea balls in the upper tray of each duplicated treatment. Infection of eggs generally occurred within 7 days. The infection rate of about 10% in each duplicate series of trays was obtained by exchanging infected eggs between the trays. Eggs infected at the 0 and 10% level were then exposed to salt solutions for 15, 30, or 60 minutes every other day for 2 weeks. Treatments ceased when the eggs began to hatch. A positive control group was inoculated with fungus, but not treated with salt; a negative control group was not inoculated with fungus nor treated with salt.
Efficacy of Common Salt:
The hatch rate for control groups of eggs was only 12% for those infected with fungus and 28% for those that were not infected, suggesting that the infection procedure was successful. These eggs were tested during August when trout eggs are generally smaller in size and lower in fertility. The 1.5% salt treatment was ineffective for control of fungus on infected eggs, but the hatch rate of uninfected eggs improved slightly. The 3% salt treatment was highly effective for controlling infection in the uninfected eggs; hatch rates were 65% in 15-min exposures, 66% in 30-minute exposures, and 72% in 60-minute exposures. These hatch rates were considerably higher than the uninfected control group (28%), confirming the therapeutic value of prophylactic treatments. Eggs that were infected with fungus at the 10% level fared much better with 3% salt treatments; infection was controlled in 30 and 60 minute exposures, and hatch rates increased over control groups to 31, 39, and 64% at the 15-, 30-, and 60 minute exposures.
Feasibility for Use of Salt:
Common salt is readily available and listed as a low regulatory priority fishery chemical. We have demonstrated that 3% salt solutions are effective for control of fungal infections and improving hatch rates of treated eggs. Lower treatment rates may be useful for preventing fungal infections through prophylactic treatments. Disadvantages of using salt are the large quantities that would need to be transported, stored, and administered to static or flow-through aquaculture systems. Perhaps the solutions could be stored in tanks or ponds and reused during the egg incubation season. We believe that salt is a viable antifungal agent where it can be used in a practical manner.
We conclude that the 3% salt treatment is the treatment of choice because it is fungicidal and yet safe for the eggs.
PUMP ALARM SYSTEM
By: Larry Wawronowicz, Fish and Game Director, Lac du Flambeau Tribal, Fish Culture Program
The Lac du Flambeau Tribal Fish Culture Program pumps water to all its facilities from two wells and Pokegama Lake. The pumped water supplies the 315 jar hatchery, the start tank facility, ten 200' raceways, 14 fish culture ponds, and the fish transport truck filling depot. Currently on station are approximately 9 tons of trout with brown, brook, and rainbow trout eggs. Walleye, muskellunge, and forage fish are reared in the spring and summer. Depending on the time of the year, 1,000 to 5,000 gallons per minute of water is being pumped.
In order for hatchery personnel to have some peace of mind, sleep nights and enjoy the weekends, it was necessary to design andinstall an alarm system for each pump. The alarm system was designed to alert hatchery personnel if power was being supplied during normal or emergency situations (i.e. power outages, switch failure).
For example, on Saturday at 7:00 pm a major snowstorm hits Lac Du Flambeau and the power lines are down. Telephone service is still available and there is no one on station. The hatchery manager is home when he receives a telephone call from Silent Knight Alarm (a private company - 715/362-7374) indicating Pump No. 1, 2 and 3 are "down". The hatchery manager hangs up, puts his pants on and heads to the hatchery. In the meantime, the emergency generators start and the transfer switches make power available to the pumps. The system used to call the hatchery manager is diagramed above.
The pump and a 110 Volt receptacle are supplied with AC power by the Delta Control Switch. An AC power sensor is connected to the 110 Volt receptacle. If the Power Sensor does not detect AC power present, it will send a signal to the Silent Knight Alarm automatic dialer and an alarm will be received by Silent Knight Security in Rhinelander, Wisconsin through the telephone line. Subsequently, a 24 hour operator at Silent Knight will call and keep on calling a list of 9 numbers until someone answers. Note since the 110 Volt receptacles and the pumps are connected on the same side of the Delta Control Switches, and if the pumps do not have power the 110 Volt receptacles do not have power. Also, because each pump has its own system the Silent Knight operator can tell the person that answers which pump is down. The Power Sensor will also activate a set of strobe lights located on the roofs of the pump houses so that in the excitement of the moment, if personnel forget which pump is down, they can see the lights flashing when driving by the rearing complex.
The major disadvantage of this system is the telephone line. If the telephone line and the power line both went down in the storm, the hatchery manager would not have been notified. The hardware as described above can be purchased for $200.00 per system and there is also a quarterly charge of $105.00 for all units. The system has worked well and has saved production on numerous occasions.
DISINFECTION OF HATCHERY FOMITES
By: Terrence Ott, La Crosse Fish Health Center, La Crosse, WI
Fish diseases are water borne microorganisms that have plagued the lives of hatchery personnel since the inception of culturing large numbers of fish in confined areas began. It can be assumed that fish are continually bathed in an aqueous suspension of microorganisms and these organisms are easily transmitted from one raceway pond to another by anything that goes into the water: brushes, nets, seines, and boots. All these "fomites" can be effectively sanitized by dipping, soaking, and rinsing in some chemical disinfectant.
Proper disinfection practices at your hatchery are an easy and inexpensive method of disease control in which destruction of a "link" in the transmission cycle of a potential fish pathogen can be broken.
Sunshine, in itself, is a fine sanitizer, and few fish pathogens can last very long under the combined assault of drying and sunshine. Hatchery tools which have come into contact with a stock of fish should always be allowed to air-dry in the sun, before contacting another stock of fish.
If time and sunshine are at a minimum, the raceway walls and bottom should be thoroughly cleaned by removing fecal material, excess food and aquatic plants, then treated with a strong solution of HTH (calcium hypochlorite) by Olin Corporation, Stamford, Connecticut. The quaternary ammonium compounds, such as Hyamine 1622, Hyamine 3500, and Roccal can be used at 600 ppm effectively as disinfecting agents. Net-Dip, distributed as Sanaqua by Aquavet, Mayward, California is a buffered chloride compound and is a good disinfectant to use in a 30-gallon tub filled with the appropriate strength and kept in a convenient location for disinfecting hatchery tools. The strength of the disinfecting solution is based on the active ingredient as purchased. Fish raceways can be disinfected by using 1 ounce (dry weight) of HTH per 25 gallons of water for 60 minutes.
Iodophors, sold under the trade names of Betadine, Wescodyne, and others, incorporate the disinfecting element of iodine, which is an oxidizing agent. Wescodyne can be purchased from West Chemical Products, New York, New York and used at a concentration of 3 ounces to 5 gallons water.
HTH is toxic to fish in very low concentrations. Do not contaminate aquatic habitats by cleaning hatchery equipment or disposing of HTH waste products into the environment. Apply this product only as specified on the label. Store HTH in a cool dry place in its original container. As with all chemicals received at your hatchery read and understand what is in the Material Safety Data sheets before handling the chemical.
Hatchery personnel entering and exiting a hatchery building can easily eliminate the spread of microorganisms by disinfecting the bottom of their boots in a footbath. This can be accomplished by placing a rubber grated mat or large sponge in the bottom of a plastic dish pan. Fill the pan with just enough disinfectant solution to cover the grated mat or saturate the sponge. This will allow wetting only of the bottom of the boot. If the entire boot requires disinfection, remove the mat or sponge from the pan and add more disinfectant to raise the level above the ankle. Change the disinfectant solution in the pan once a week to keep the solution fresh and working.
Ponds which have contained fish should receive an agricultural lime treatment of 2,000 pounds per acre, and be allowed to air-dry in the sun for several weeks before new stocks of fish are introduced.
Another method of keeping the link broken between fish and potential pathogens is to keep tools used in cleaning raceways separated from one raceway to the next. Supply each raceway on your facility with its own set of brooms, brushes, and dip nets. If this is not possible you should at least keep separate tools used for broodstock from those used for fry and fingerlings. Broodstock often carry microorganisms, which may not be harmful to them, but are easily transmitted to, and can be detrimental to, younger fish.
Keep in mind while working at your hatchery that good hygiene is one of the best ways of ensuring a good healthy stock by allowing normal physiological functioning and a proper balance between the animal and its environment, thus reducing the influence of harmful agents in that environment.
Hatching Fish Eggs Out Of Water
Commercial Fisheries Newsline, October 1994
What are you doing to invent the future? Do fish eggs really need to be incubated in water? Could small amounts of water be heated/cooled and then sprayed over eggs to speed/retard egg development?
Experiments In Hungary on white mice oocytes in an embryological laboratory have led to the development of a new form of fish egg incubator. The knowledge that pike-perch eggs can be incubated out of water in a damp spray, motivated a series of experiments. A small group of researchers, a geneticist, an electrical engineer, and a fish biologist began investigating a practical means of fish egg incubation and hatching out of water.
Their criteria were that: the new method should involve low water and energy consumption; survival should be at least equivalent to that provided by traditional incubators; sterilization should not involve malachite green, antibiotics or other banned chemicals; labor should be minimal; hatching should be at an optimal time, and the incubator should work both for freshwater and seawater fish eggs (preferably for most cultured species).
The first experiments used common carp eggs, and established that incubation did not require water, just moisturized air. The fertilized eggs were placed on a net with a mesh of about 2/3 of the eggs' diameter. Metal or plastic nets made of filamentous material proved unsuitable; hard nets were best. To increase capacity, the optimum number of eggs to be placed on the net-tray was established. In the case of carp, good results were achieved with up to 2-3 layers of eggs.
Sometimes, usually in batches with low fertilization rates, infections led to mass mortality. This was mostly when moisture was over 100% in air, and the water condensed in droplets on the eggs. With relative humidity lower than 99 percent the eggs were damaged through drying out, which meant precise temperature-humidity regulation was needed. After a year of experimentation, this was successfully refined.
The problem of sudden infections causing high egg losses remained. A further year was spent testing several chemicals and treatments to reduce the losses. A tannic acid solution was the answer, and once the treatment was perfected, even batches of eggs with less than 10% fertilization rate were free of external fungal or bacterial infections without using malachite green or antibiotics.
Later versions of the incubator have an automatic feature for separating the egg shells and larvae after hatching. The latest, and best, variant is made from material resistant to sea water corrosion. It is programmable for different species, and has even been tested for hatching the eggs of Atlantic cod. Survival was no lower than that of the control group. The fish egg incubator uses 400 liters of water per 60 hours for the incubation of 1,000,000 carp eggs.
Before marketing, the machine needs to be tested for other sea-water fish as well as salmonids, but since Hungary has no sea, this is not easy, and the company is now seeking a foundation or partner to complete the job.
More information is available from: Mr. Lajos Laslo, Biochemical Laboratory Service Ltd, H-1165 Budapest, Zselyi Aladar u. 31. Hungary. Tel: +36-1-271 2602, Fax: +36-1-271 2896.
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| Product and company names mentioned in this publication are for informational purposes only. It does not imply endorsement by the MTAN or the U.S. Government. |
