Dedicated To The Tribal Aquaculture Program

 

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Topics Of Interest:

Dome Technology

Methods of Controlling Growth Rate of Rainbow Trout

Walleye Spawning in Michigan

Examination of External Signs and Behavior Patterns

Tribal Hatchery Updates

Hatchery Tip

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Dome Technology an Economic Solution to Scaling Down Costs in Aquaculture

By: Lane Roberts, Dome Technology, Marketing Management Team, Idaho Falls, ID 83401, 208-529-0833, Fax -0854

Throughout history, the dome has been the architectural form of choice wherever efficiency and strength are required of a structure. From the simple igloo that shelters the Arctic hunter throughout the ravages of a blinding storm, to the awe-inspiring magnificence of the Sistine Chapel, the dome has been used in every culture, on every continent, as one of man's most versatile buildings.

Today, the modern construction techniques and materials reinforce the dome's position as the most classically versatile of all structures. The insulated concrete dome is the ideal solution wherever strength combined with low construction and maintenance costs are called for. Compared to other types of structures, the dome encloses more volume with the greatest floor area, and the least amount of surface area and perimeter. Superbly energy-efficient, firesafe, and with an inherent strength that enables it to withstand whatever nature throws at it--hurricanes, earthquakes, even tornadoes. It is no wonder that the modern concrete dome is experiencing a surge of popularity throughout the world.

Dealing with the unpredictability of weather is rarely a factor in dome construction. Since most of the construction process takes place under the sheltering umbrella of an inflated form, work goes on regardless of the weather. Dome construction is rapid and cost-efficient compared to other construction techniques. Modern insulated concrete dome construction combines several materials to create a strong, efficient, weather-proof structure. Compared to other types of structures for the same application, the insulated concrete dome is 50-75% more energy-efficient.

CONSTRUCTION PROCESS

Insulated concrete dome construction consists of four main phases. Refinements to the design are dictated by application which will determine the work required after the construction of the basic dome.

Phase One-Pour Ring Beam Footing. Continuous reinforcing bars are embedded in the ring beam foundation. These rebar dowels securely connect the dome to its footing.

Phase Two-Attach and inflate Airform. The airform is attached to the ring beam footing, and inflated with dual inflator fans, each powered by an independent power source. An airlock entrance allows free access to the interior. The airform is a thin, tough membrane that becomes the dome's outer covering when construction is complete.

Phase Three-Apply Polyurethane Foam. Polyurethane foam is spray-applied from the interior to stiffen the air from and provide a secure surface to which reinforcement bar is affixed. The foam hardens and creates a superior insulating layer in the final structure.

Phase Four-Reinforced Concrete. After the polyurethane foam is applied and allowed to harden, a framework of reinforcement bar is place and attached to the interior surface of the foam. This will serve as a skeleton to which concrete is applied. Application of shotcrete to the reinforcement bar framework comprises the final step in construction of the dome. The rebar framework is embedded by the shotcrete, creating an extremely strong, fire resistant and energy efficient structure.

Let's briefly explore the reason why this innovative method of construction is so energy efficient by taking a page from the California Energy Commission Passive Solar Handbook, paragraph 1.4, Optimal Use of Mass and Insulation.

"A heavy wall must have two qualities in order to dampen diurnal changes in the exterior environment and thus keep the internal temperature of a room relatively constant: heat capacity--the ability to store heat, and low heat conductivity--the ability to resist, or to insulate against heat flow. If one intermittently exposes an adobe brick first to a blow torch and then to cold water (and if each exposure time is relatively short) the temperature of the brick never reaches either extreme, but oscillates somewhere in between. The heat capacity of the brick keeps its temperature from rising rapidly with the small heat addition, or dropping rapidly with the small heat extraction. The brick's insulating quality prevents heat from entering or leaving very rapidly.

"Adobe, however, doesn't happen to have the optimum combination of eat capacity and insulation. This problem can be resolved by the way the material is used which is an important as what material is used. The most effective way of maximizing the two qualities--the capacity and insulation--in a building wall is to use two separate materials. Ideally, one would choose a material with little heat capacity but high resistance to heat flow, and a material with high heat capacity having little resistance to heat flow. By placing the insulating material next to the external environment, little heat is allowed into or out of the building and with the high heat capacity material next to the inside environment, what heat does enter or leave (primarily through windows and interior heat generation) can't change the temperature of the heat capacity material rapidly. Thus, little heat is let in or out, and the high capacity material slowly stores heat. The building's thermal mass damps out temperature fluctuations."

Dome Technology has developed the technology to economically place the urethane insulation on the outside of the concrete while protecting the urethane from the harsh weather conditions and the degradation of the sun's ultraviolet rays. The end result is a Super Insulated concrete facility. This method of technology has proved itself time and time again in reducing expensive energy costs to the owner 25%-50% and more.

Dr. Arnold Wilson, professor of civil engineering at Brigham Young University has engineered over 500 thin-shell concrete domes throughout the world and has this to say about the strength of the concrete dome.

"Thin-shell, reinforced concrete domes are probably the most disaster resistant buildings that can be built without going underground or into a mountain.

"It is predicted that a wind of seventy miles per hour blowing against a thirty foot tall flat walled building in open flat terrain will exert a pressure of 21.97 pounds per square foot. If the wind speed is increased to 300 mph the pressure is increased to 404 pounds per square foot. Wind speed of 300 mph is considered maximum for a tornado. It is far greater than that of a hurricane.

"Against that much pressure a dome 100 feet in diameter 35 feet tall would still have a safety margin of nearly 1 times its minimum design strength. In other words, the stress created by the 300 mph wind would increase the compressive pressure in the concrete shell to a 1098 psi. The shell is allowed 2394 psi using design strengths of 4000 psi.

"The fact is, the thin-shell, concrete dome is not flat; therefore, the maximum air pressure against the dome of 404 pounds per square foot could not be realized. The strength of the dome is much greater than 4000 psi. The margin of safety is probably more like 3 or 4.

"The thin-shell dome at Port Arthur, Texas, has been hit by three hurricanes. A hurricane does not exert enough pressure on a dome to even be noticed. As shown above, the dome can easily withstand the stresses of a tornado; however, debris carried by a tornado could cut the surface membrane. If the debris contained a large timber or metal object, it might be possible, if conditions were just right, puncture the dome. But the puncture would be very local and would certainly never cause a serious collapse of the dome. Possible damage to the doors or windows may occur if there was a rapid decompression caused by the tornado.

"For most domes, the likely disaster will be earthquakes. The worst areas in the United States are listed as seismic zone 4. Earthquake forces do not even approach the design strength the thin-shell, reinforced concrete dome which is built for every day usage. It would take an external force many times greater than an earthquake to approach the design strength of the concrete itself.

"Nuclear fallout is another disaster consideration. It is interesting to note that the only structure left standing near ground zero at Hiroshima was the concrete skeleton of a dome. Certainly, the thin-shell dome would be superior to most buildings if a nuclear fallout condition occurred. Rain would tend to wash the radiation off the building much better than conventional buildings.

Generally, domes are quite tall. Radiation strengths are inversely proportional to the square of the distance from the source. The roof of the dome would hold the radiation further from the occupants than many other structures. Also, concrete itself absorbs radiation very well. The concrete dome would greatly reduce the effects of fallout on the occupants.

"It is interesting to note that German thin shell structures stood up to allied Bombing in the second world war better than most other structures. When a bomb would hit a thin shell, it would either bounce off the resilient exterior or would puncture a hold through it. Since there are no single components that carry large loads, there is nothing that can be knocked down like a beam or column. Therefore, repair was a simple patch to cover the hole that was made when the bomb would go through.

"The forces caused by a major earthquake are considerably less than normally provided for when a dome is designed for nominal vertical loads.

"The forces caused by wind and earthquake on a concrete dome generally do not control the design. Domes are very strong and durable and in a realistic situation would probably still be standing when all conventional structures had failed."

HUMIDITY'S EFFECT ON THE CONCRETE DOME

When the dome is used as a cover for sewer treatment ponds, swimming pools or aquaculture centers, the concrete shell is subject to a great amount humidity. This humidity is hardly harmful to the concrete but actually helps the concrete cure. Concrete will cure for many years. When the moisture from the humidity is added to the curing process, the concrete simply gets stronger and stronger year after year.

LOW MAINTENANCE

Roof repair and maintenance of heating and cooling plants-traditionally the two highest maintenance costs for traditional structures are cut dramatically in concrete dome structures. Snow and water inflict relatively little stress on the exterior of the dome. Concrete dome structures need only a fraction of the HVAC equipment required in conventional structures to maintain comfort levels and maintenance costs are proportionately reduced.

SUMMARY

The insulated reinforced concrete dome is possibly the most energy efficient, economical, environmentally friendly, durable and low maintenance building on the market. It is the ideal building to meet the needs and circumstances of those in the business of commercial fish farming.

Methods of Controlling Growth Rate of Rainbow Trout

By: George W. Klontz, Aquaculture Specialist, Nelson and Sons, Inc., 1908 East E. Street, Moscow, Idaho 83843, 208-882-2617

Based upon the results of a recently completed two-year controlled growth study, the following feeding regimen could also be implemented to provide fish of uniform size over extended periods. In this example, the production plan calls for a monthly harvest of 7,400 (450 g) trout. The process starts with 60,000 eyed eggs which should result in 6 months of market-size fish. In this scenario, the water temperature is a constant 15⁰C, which makes production forecasting much easier.

The first-feeding fry are raised in shallow troughs (3 m x 0.33 m x 0.1 m deep) suspended over deep tanks (5 m x 1 m x 1 m deep). When the fry are approximately 2,000 per kg they are to be transferred to deeper tanks.

Daily feedings are to be such that the fish receive all they can eat several times during the day. When the fish are 500-1,000 per kg, one-sixth of the population is to be transferred to another deep tank and fed full daily rations. The remaining fish are put on a novel feeding regimen of 7 days of feeding at 50% of the full-feeding level and 7 days of no feed. This feeding level provides little more than the daily maintenance requirement. Thus, there will be little weight gain. However, there will be some length increase as skeletal growth is more a function of temperature, genetic and hormonal activity rather than metabolizable energy.

At monthly intervals, another group is to be removed from the reduced feeding regimen lot and put onto a full-feeding regimen. Thus, the last group should be of marketable size 6 months after the first fully fed group was harvested.

If the foregoing is considered to be a little too rigorous to implement on such small fish, then a feeding regimen of 7 days of full feeding followed by 7 days of no feeding could be implemented. Other days of feeding followed by days of no feed could be used. The fish will have reduced weight and length gains, thus necessitating some thoughtful planning of harvest schedules. For example, this feeding regimen will require more rearing space than the 50% feeding regimen because the fish will be larger throughout the growing-on period.

The main concern with the foregoing is to determine when to reinstate a full-feeding regimen so that the market date and size can be met. This is not too difficult if the water temperature is constant and one understands that under such situations the daily length increase is linear. If the water temperature is not constant, then the calculated daily length increase must reflect that allowed by the water temperature.

To calculate the approximate date to reinstate full-feeding under constant water temperature conditions, the length of the fish at market size minus the length of the fish on reduced feeding divided by the daily length increase will indicate the number of days of full feeding required. To calculate the approximate date to reinstitute full-feeding under varying water temperature conditions, the average monthly or, better, weekly water temperature-dependent length increases should be available. The process is then the same as for the constant water temperature conditions.

In summary, the step-by-step process to implement the suggested feeding regimen is:

• Disinfect the eyed eggs with an appropriate iodophor upon receipt and adjust the water temperature to that of the incubation system.
  
• Incubate and hatch the eggs. It is advisable at hatching to remove the egg shells from the system as soon as possible to prevent transmission of any bacterial or viral pathogen in/on the egg shells. Upwelling incubators are ideal for accomplishing this by merely increasing the water flow to flush the shells out. With tray or basket incubation, the shells usually require manual removal.
  
• When the fish are ready for feed they should be fed several times during the day. Ideally, feeding should be done by belt feeders to provide a constant feeding. Uneaten feed, fecal solids, and dead fish must be removed several times during the day. It is especially important to remove dead fish expeditiously to prevent transmission of any bacterial or viral pathogen to the fish dining on their fallen brethren.
  
• When the mean weight per fish is 2-3 g (or larger if fingerlings are purchased), transfer an appropriate amount by weight to another container and put them on a full feeding regimen until they are the desired size for the market.
  
• The remainder of the lot is to be fed 50% of the daily requirement for 7 days followed by 7 days of no feeding. Or the fish may be fed at the 100% daily level for 7 days followed by 7 days of no feeding. On the day of resumed feeding following the 7-day feed deprivation, care should be taken to feed in a fashion that all fish receive their share. This will reduce the potential for unwanted size variations in the population. Population inventories of length and weight should be done at the end of the 7 days of feed deprivation so that the daily feeding regimen for the ensuing 7 days can be calculated properly.
  
• At monthly intervals, appropriate portions of the controlled growth population are removed and put on full feeding. During the growing-on period, strict attention should be paid to not exceeding the population density or dissolved oxygen limits of the system.
  
• The end result should be the production of uniform-sized fish over a period from a single lot of eggs or fingerlings. If the process is implemented and maintained with care, size grading should be necessary only at harvest times.

During the production cycle, the following performance indicators should be monitored at 14-day intervals (preferred) or 28-day intervals:

• Size variation within the population: This is obtained by weighing and measuring at least 40 fish during the inventory process. From these data the following can be calculated:

a. Average, mid-range, and variance of fish lengths/weights.

b. Daily length increase and specific growth rate.

c. Biomass and weight gain of the population.

• Condition factor: This is the length to weight relationship. It is calculated by dividing the average weight (g) per fish by the cube of the average length (mm³). As time passes in the reduced feeding groups, the condition factor will decrease. After the fish are put on 100% feeding regimens, the condition factor will increase to the appropriate level of approximately 0.0000126.
  
• Feed conversion: Most commercial trout and salmon feed formulations are capable of providing feed conversions of 1.2:l. Feed conversions less than this; i.e., >1.2:1, should indicate that something is amiss. The most common causes are over-estimating the pond population and/or the allowable growth rate.
  
• Mortality: The daily mortality should not exceed 0.02% in well-managed populations of trout. Mortalities greater than this should be thoroughly evaluated for causal factors.
  

As the fish approach market size, the following performance indicators should be monitored:

• Dress-out as percent recovery after removal of the gills and viscera. For most strains of rainbow trout, there should be a recovery of 83-86%. Boned, skin-on fillets should have a yield of 51-54% .
• Gross appearance of the fish is judged by the body coloration, body conformation, and fin condition .
• Flesh quality (taste, color, and texture) of table-fish .
• Calculate production costs versus sales income to estimate net profit.

In closing, there is a caveat. Should one decide to implement this procedure, it is recommended that (1) small lots (<20,000 2-3 g fish) be used initially; (2) the pellet size fed throughout the growing-on period remain at one level less than the manufacturer's recommendation (thus, there will be more pellets to go around); (3) the fish be fed attentively to assure that all fish in the population receive their fair share to preclude unwanted size variation. The procedure presented has been evaluated extensively under laboratory conditions for two years. It has yet to be formally evaluated under commercial production conditions, although there are reports that limited attempts are being conducted without mishaps.

The bottom-line is - are you, the reader, satisfied with the way your fish perform? If not, then something should be done. I have offered an idea. Others have offered ideas. Gather them in, evaluate each in terms of the situation, and, as they say here in The Colonies, "Go for it!"

The Effects of Density On Fish Growth Performance

- Abstract Only -

By: Lawrence C. Belusz, Alexandria Technical College, Alexandria, Minnesota,

Above a specific temperature, which varies by species, a fishes' metabolic processes cannot keep up with increased demands for energy, and growth rate begins to decrease. The result of these demands is that for each fish species there is an optimum temperature for growth. Not as well understood is that each species of a specific size has an optimum density, or degree of crowding per unit of space, which also produces an optimum growth rate. For fish culturists attempting to maintain fish density or loading rates (carry capacity) as high as possible, it is important to realize that management and production tradeoffs are made in return for maximizing the pounds of fish raised per cubic foot of space or gallon of water. These tradeoffs can be observed as: reduced rate of growth which results in a longer time to market, decreased feed conversion efficiency which results in more feed to grow an equal weight of fish, less uniformity in growth which results in fewer fish reaching market weight and increased time spent in size-grading, lower survival of fish which results in more cost per fish, more incidence of disease which results in added operational costs for treatments, and increases in water quality emergencies which result in added operational cost and more stress for fish which in turn leads to reduced growth. An understanding of the optimum spatial requirements of fish and the performance factors which are affected, will enable the fish culturist to produce a given crop of fish at optimum levels of management input which will be reflected in an optimum cost of production.

Walleye Spawning in Michigan

By: James A. Copeland and Martha M. Wolgamood, Michigan Dept of Natural Resources, Wolf Lake Hatchery, 34270 CR 652, Mattawan, MI 49071

Michigan Dept of Natural Resources has been utilizing walleye from the Muskegon River as a source of walleye eggs for many years. Fish migrate upstream and are captured by DC electrofishing below a barrier dam. Spawning techniques have evolved to the point where we can normally rely on >80% development to the eyed egg stage (eye-up in 1986 was only about 27%). Between 80 and 100 million eggs are taken annually.

Broodfish are selected and captured by district field crews when the Muskegon River water reaches 36F. Fish are then sorted by sex visually and taken to a spring-fed pond which is 50F. Most females are "green" upon arrival, and are all placed in 54 cu ft holding nets. Average weight of the females is about 7 lbs.

Fish are collected daily from the river and transported to the holding nets until 500-600 fish have been captured. Females in each net are examined daily to check for ripeness, and ripe females are spawned daily until egg take goals are met. Experience has shown that all fish will be ripe within 2-3 days after capture.

Ripe fish are anesthetized with MS 222 prior to spawning. Spawning is done on a small dock at the pond. No protection from wind, sun, rain or snow is provided for the eggs during stripping. Anesthetized fish are rinsed in fresh water and wiped with a towel before spawning. One female is stripped into a stainless steel 5 qt pan. The number of eggs per female ranges from 160,000 to 200,000. If a female produces > 200,000 eggs, they are usually split between two pans for fertilization.

Prior to 1990, two males would be stripped into a pan of eggs and a small amount of water (about one cup) was added. The eggs were stirred for 5-10 seconds and then allowed to set approximately 2 minutes before being poured into a 5-gal pail with Fuller's earth and water. If eggs were allowed to set for more than 2 min, they would begin to stick together. The fuller's earth mixture we used was: one cup to about 3.5 gal water.

Beginning in 1990, a new fertilization technique was used. Two males would be rapidly stripped into a 1.6 qt plastic jar ( full of lake water). This mixture is vigorously shaken and poured into a pan of eggs. The eggs are stirred with a feather and allowed to set for 30 seconds, if eggs begin to stick before 30 sec, they must be poured into the Fuller's earth mixture immediately or they will form clumps. It is believed that fertilization is almost instantaneous. The Fuller's earth mixture is stirred with a feather as the eggs are poured into it. This procedure is repeated until 8 or 10 females have been stripped and fertilized, and the eggs put into a 5-gal pail.

After the last pan of eggs has been added to the Fuller's earth mixture, the pail of eggs is allowed to set for a maximum of 5 min. At this time, the eggs are poured into a floating 30 cu ft holding net (with 1/16 in mesh) to allow the eggs to water harden. Eggs from up to 100 females are put into each water hardening net. The net also serves to wash excess Fuller's earth out of the eggs. The eggs are packaged for shipment I hr after the final lot of eggs have water hardened. Fish that have been stripped are held in 54 cu ft nets in the spring-fed pond for 24 hours and are then returned to the Muskegon River.

Water-hardened eggs are dipped from the net using one of the spawning pans. Eggs are put into 12 in x 10 in x 9.5 in styrofoam boxes. A box is initially filled about half full with water. Eggs are gently poured into the box until the water overflows. At this point, water is poured off the eggs and this process continues until the eggs in the box are about I inch from the top. The eggs are just covered with water for shipment. Each box contains about 16 qts of eggs. The trip to the hatchery is approximately 100 miles and takes about two hours.

Upon arrival at the hatchery, the eggs are measured into plastic hatching jars. Five quarts of eggs are added to a jar, and the volume of eggs in this jar is used to fill the remaining jars. The eggs are siphoned into the jars. The jars are then put on the hatching battery to incubate the eggs. Each jar is supplied with 1.06 qt/min of 50F spring water. Eggs will not be rolled at this low flow.

Eggs are treated daily with 1:600 formalin for 15 min. On day ten, treatments are discontinued, and water flow is increased until the eggs roll gently. This allows dead eggs to migrate to the top of the egg mass and allows them to be siphoned. It may take 3-4 days before most dead eggs will roll to the top. During this period, eggs should be monitored for saprolegnia infestation. If one does occur, formalin treatment should again be given. In 1986, the average eye-up was 27%. In 1990, 1991, and 1992, the mean had risen to 63%, 78%, and 83%, respectively.

Eggs will be very near hatch on day 15 of incubation. At this time eggs are transferred to a heated water 62F battery. After about 3 days at this temperature, eggs will hatch. Hatching fry are directed into rectangular 9.7 ft x 13 ft long troughs. This allows the egg shells to settle. If tannic acid is used to eliminate egg adhesiveness, egg shells will not break down at hatch and settle in the troughs. The overflow from this trough leads into a 8-foot (100 cu ft) circular tank. The egg shell settling trough is covered with a black cover and a light bulb is placed at the outlet. Fry are attracted to the light and are quickly pulled into the overflow. The carrying capacity of the circular holding tank is about three million fry. Fry are held in these circular tanks for 2-3 days and are then shipped to rearing ponds or stocked.

The same styrofoam containers that were used to transport eggs are used to ship fry. Approximately 2 gal of water and 50,000 fry are put into a plastic bag in the styrofoam container. Fry are measured using volumetric displacement in a 500 ml graduated cylinder. The number of fry/ml is determined using a 3-4 ml sample of fry in a 10 ml graduated cylinder and averaging 3-5 samples from each tank. Oxygen is then added and the bag is sealed.

Examination of External Signs and Behavior Patterns of Fin Fishes for Disease Problems

By: Terry Ott, U.S. Fish and Wildlife Service, La Crosse Fish Health Center, La Crosse, Wisconsin

The Chinese philosopher, Confucius once said, "the happiest hatchery worker is the one who feeds all fish by hand". For someone living so long ago Confucius was wise to know the value in hand feeding. He knew how important it was to watch fish feed and how they behaved during the feeding period. He also understood the value of having a front row viewing seat into the clinical signs fish may express if something is not just right with them.

According to Webster's Dictionary, disease can be defined briefly as any deviation of the body from its normal or healthy state causing discomfort, sickness, inconvenience, or death. When microorganisms that cause diseases in fish become numerous they may cause changes in behavior or produce other obvious signs. Some of which give valuable clues as to the nature of the disease.

Individual diseases do not always produce a single clinical sign or characteristic that is diagnostic in itself. Nevertheless, by observing the signs exhibited by fish one usually can narrow down the cause of the trouble to a particular type of causative problem.

It should be emphasized, that many external signs and behavior patterns are common to a multitude of fish diseases including nutritional and environmental anomalies. The appearance of every sick fish tells a story, which fits into the proverbial jigsaw pattern of disease diagnosis. Good observation uncovers many useful clues.

Following is a list of common external clinical signs, or changes in behavior a hatchery worker can look for in fish suffering from a disease. Each sign or behavior observed can occur as a direct result of fish experiencing one or more of the following disease categories; viral, parasitic, bacterial, environmental, or nutritional disease.

Sluggish behavior - fish may become very inactive and often cease feeding. Lie listlessly on the bottom of the tank or float just below the surface of the water. This behavior is the first observed in fish experiencing a disease. All five disease categories should be suspect with this behavior. Flashing, scraping, darting, whirling - fish may have protozoan parasites or neurological damage. Faded pigment - fish become very pale in color, suspect a nutritional or environmental problem. Darkened pigment - fish become very dark in color look for viral, bacterial, or nutritional problems. Exophthalmia (popeye) - fish are showing one (unilateral) or two (bilateral) protruding eyes. Suspect first an environmental problem. Then look for bacterial, viral, or nutritional problems. Hemorrhaging in the eye - fish have blood spots in the eyes. Environmental, bacterial, or if the species is young lake trout suspect viral (EEVD). Hemorrhaging in the mouth - blood spots become apparent on the roof of the mouth and along the jaws. Suspect a bacterial agent especially if the fish are young rainbow trout. The microorganism could be Yersinia ruckeri the cause of Enteric Redmouth disease. Erosion of the jaws/mouth - necrosis of jaw muscle in salmonids, suspect bacterial infection. Hemorrhaging in opercula region - redness on the gill covers and throat of fish. If fish have just been hauled suspect hauling stress (environmental); otherwise suspect a systemic bacterial infection. Gill damage - presence of swollen gill lamellae, clubbing and gill rot. Check for bacterial infection, environmental (gas supersaturation), ecto-protozoan parasites, or nutritional problems. Fin rot - fish have badly damaged fins or frayed fins, exposing the fin rays. Nutritional, bacterial, or environmental anomalies are to be suspected. Saddle-like lesions - necrotic tissue on dorsal surface. Generally located behind the dorsal fin. Look for nutritional, environmental, or bacterial problems. Distended abdomen - the abdomen is often filled with ascitic fluid (serous fluid). The fish may have a bacterial or viral infection. Hemorrhaging on the surface - the fish has redness around the base of the fins, on the ventral surface and along the sides. A systemic bacterial infection or nutritional problem would be the categories to seek help on. Furuncles (boils) - blood filled blisters on the skin. This condition is a result of the disease Furunculosis caused by the microorganism Aeromonas salmonicida. Protruded anus - swollen/redden vent with some discharge. Viral, bacterial, or an intestinal parasite may be the cause. Eye cataracts - eyes become cloudy, leads to blindness. Suspect a nutritional, environmental, or eye fluke (parasite).

All these external signs and behavior patterns which were discussed above require no specialized equipment or fish health biologist to point out to you. All that is required is some extra time spent when you are feeding your fish to look for any behavioral changes or signs which may indicate a disease problem developing in your fish. If you are working at a hatchery that is using demand feeders spend a few minutes at each pond during the day to watch the fish feed, and don't be alarmed, if you notice one or two fish within a pond expressing some abnormalities. Look for many fish expressing the same behavior or clinical signs then talk to your manager immediately.

If a serious disease problem is suspected a fish health biologist should be contacted for assistance in isolating and identifying the causative agent or problem. Clinical signs can be helpful, but also misleading. In almost all instances an accurate evaluation can be made only at a diagnostic laboratory.

Control of diseases in hatchery fish can be achieved best by a program of good management. Correct the problem before it starts! This involves maintaining the fish in a good environment, with good nutrition and a minimum of stress.

Tribal Hatchery Updates

Both the Lac Vieux Desert (LVD) and the Sokaogon Chippewa (Mole Lake) Bands are starting construction of a walleye fry rearing/distribution program. The LVD project has already set the foundation for the hatchery rearing facility, while the Mole Lake Band is still in the designing phase for its rearing building. For those MTAN readers who have gone through this designing and construction process, you will recall how frustrating the process can be. If you can find a few relaxed moments during your busy day to call and offer your sympathy and advise, I'm sure it would be well received.

Hatchery Tip

New Publication:

Zebra Mussels and Aquaculture

Zebra Mussels: A Crisis in Aquaculture is a new four-page pamphlet discussing potential problems zebra mussels can cause for aquaculturists. Written by North Carolina State University Extension Fisheries Specialist Jim Rice, the pamphlet provides suggestions for protecting aquaculture water supplies and discusses ways to prevent the contamination of water used for hauling fish and fingerlings. Other topics include the use of disinfectants, control measures for infested facilities and the implementation of inspection and monitoring programs to detect the presence of zebra mussels. The publication is available from North Carolina Sea Grant, P.O. Box 8605, North Carolina State University, Raleigh, NC 27695-8605, phone 919-515-2454, Email: harriss@unity.nesu.ede.

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Last updated: August 28, 2009

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