Dedicated To The Tribal Aquaculture Program

September 1997 - Volume 21

Topics Of Interest:

KeweenawBay Tribal Hatchery and Service Enter New Trout Agreement

Liming Of Ponds

Reducing Fish Production Cost

Using Bentonite Clay To SealLeaking Ponds

Guidelines for the Use Of Rotenone

Silicones Show Promise As Net Antifoulants

TheUse Of Ozone In Hatcheries

Hatchery Tip

KeweenawBay Tribal Fish Hatchery and the US Fish and Wildlife Service Enter Into New TroutAgreement

By: Nancy Besonen, L'Anse Sentinel, L'Anse, Michigan, Edited By: MTAN

The United States Fish and Wildlife Service (USFWS) picked up approximately 15,000trout from the Keweenaw Bay Indian Community's Tribal Hatchery on June 10, and delivered anew two-year agreement for the hatchery to serve as a brood stock isolation facility. Thetrout transfer and signing ceremony marked the successful culmination of a two yearagreement between the tribe and the USFWS that included:

The hatchery would receive and raise lake trout and brook trout eggs collected by theUSFWS from wild stocks of Lake Superior fish. Only after these fish passed a two yeardisease clearance could they be transferred to other disease free Federal or State fishhatcheries. Once these fish mature their eggs will be used for Lake Superior stockingprograms. During this two year period, the USFWS took the responsibility of meeting theKeweenaw Bay's yearly objectives for local lake trout stocking.

Keweenaw Bay Tribal Hatchery Manager Mike Donofrio said the agreement constitutes anequal trade of goods and services. Except for additional fisheries training and some minormodifications needed at the hatchery, (which was paid for by the USFWS) the tribe,government and the angler benefit equally from the collaboration, simply because itimproves the fishery.

"This fish isolation concept was brand new in '95," Donofrio said of thetribe's agreement with the USFWS. "As far as I know, they didn't have a federalprotocol for bringing wild fish into a hatchery system" This fish isolation programresulted from a fish rearing disaster in the early 1980s, when a virus (EEVD) wiped outlake trout fingerlings and brood stock, in the federal and state hatchery system. Thatloss ultimately lead to the government's securing "fish isolation facilities"for its federal hatcheries.

The lake and brook trout fingerlings transferred from Keweenaw Bay hatchery were firstbrought into the system as fertilized eggs in September, 1995. Those eggs were collectedfrom spawning coaster brook trout at Isle Royale National Park, and lake trout fromCaribou Island in Ontario, Traverse Island in Michigan and the Apostle Islands inWisconsin. The Keweenaw Bay hatchery's fish stocking priorities, consisting of introducing100,000 lake trout yearlings into Keweenaw Bay each year, were met by the Iron RiverNational Fish Hatchery.

The approximately 3,000 coaster brook trout and 12,000 lake trout transferred from thehatchery averaged 7-10 inches in length, Donofrio said, and had passed their three diseaseinspections with flying colors. Persons present at the ceremony, including federal andhatchery employees, the media and private citizens, viewed the loading of the trout fordelivery to the Iron River National Fish Hatchery in Wisconsin, along with the signing ofthe second two-year agreement between the USFWS and the Keweenaw Bay Indian Community.Donofrio said the Tribal Hatchery is the only facility in its region, including Michigan,Iowa, Minnesota, Wisconsin, Illinois and Missouri, currently under contract with thegovernment to raise brood stock. While a long-term solution for raising disease-free troutis currently under review by the USFWS, no final decision has yet been made.

Two federal hatcheries would need to be converted in order to maintain the program,Donofrio said, or the government must continue to contract out the raising of its wildbrood stock. In the meantime, the Tribal Hatchery will continue in its new agreement withthe government through 1999. "It's a way to cooperate with the management of afishery," Donofrio said. "We're just helping them out."

Liming Ponds

Forrest Wynne, Area Extension Specialist, Aquaculture Kentucky State UniversityCooperative Extension Program, P.O. Box 3327 Somerset, KY 42564-3327 (606) 679-2090

Ponds built in areas which have acid soils and soft water may not always perform wellfor fish production. Such ponds may benefit from liming if the water has a totalalkalinity of less than 20 mg/l (20 ppm). If alkalinity is more than 20 mg/l, liming maynot be beneficial. Alkalinity measures the buffering capacity of the water and is usuallya good indicator of productivity. Carbonates, bicarbonates, hydroxides, phosphates, andorganic substances are the main components of water alkalinity. Water hardness is causedby calcium, magnesium, iron, and aluminum salts, most often in the form of carbonates,sulfates, or chlorides. Alkalinity and hardness can be measured with commerciallyavailable water test kits, or by State Fisheries or Extension Service AquacultureSpecialists. Generally, total alkalinities of 100-120 mg/l, water hardness concentrationsof 100-250 mg/l, and pH values between 6.5 - 9.0, are considered desirable for freshwaterfish production.

Liming a pond properly will raise the pH of bottom muds and water, and make phosphorusmore available for plant production. Ponds should be limed during the late fall or winter,especially if a pond fertilization program is begun the following spring. If lowalkalinity ponds are fertilized before being limed, much of the phosphorus may be lost tothe bottom muds. Therefore, the effort and expense of fertilization could be wasted.However, lime should not be added to a pond which has been recently fertilized as it tendsto remove phosphorus from the water.

Low levels of phosphorus may limit the growth of a pond's microscopic plants which arethe foundation of the aquatic food chain and pond productivity. Fish populations shouldbenefit from liming. Liming can enhance nutrient cycling; the breakdown of organic matterand may also help clear muddy pond water. Liming may be less effective if the pond has alarge watershed and water is exchanged more than once every 3 or 4 weeks. Surface, coalmining spoils contain pyrites which can produce sulfuric acid when exposed and weathered.Ponds should not be constructed on these watersheds unless the soil has been tested or theacidic runoff water can be diverted away from the pond.

Ponds can be limed with liquid lime, basic slag, or agricultural limestone. The acidneutralizing value represents the ability of a liming material to neutralize acid whencompared with pure calcium carbonate (which represents 100%). Liquid lime works rapidlybut contains 50% water which doubles the amount of material to apply. Basic slag has aneutralizing value of 50-79%. The values for agricultural limestone range from 95 to 108%.Hydrated or slaked lime has a value of 136% and calcium oxide has a value of 179% andshould not be used to lime fish ponds. Calcium oxide or hydrated (slaked) lime will notincrease carbonate alkalinity and could drastically raise water pH, which may kill fish.Agricultural limestone is usually the best choice. It is inexpensive ($9.00-$22.00/ton)and safe to use in fish ponds. Agricultural limestone should be ground fine enough to passthrough a 10 mesh sieve. Small particles will dissolve more readily in water. A sieveanalysis may be required to determine particle size and assign the lime an efficiencyrating.

The amount of lime required per surface acre of pond is determined by analyzing pondmud samples. Samples should be taken randomly from deep and shallow areas; making an"S"-shaped pattern over the entire length and width of the pond. Mud samples canbe collected from existing ponds using a boat and an 8-oz. can attached to a long pole orby taking small plugs of mud with a length of PVC pipe. In ponds greater than 5 surfaceacres, three to six similar sized mud samples should be taken per acre. Smaller pondsrequire 10-15 mud samples per surface acre. The samples should be mixed together andallowed to air dry on a flat surface. Pond mud samples should then be pulverized andplaced in a soil sample box marked "fish pond". These samples can then besubmitted to a private soils testing lab or to your county extension office to be sent outfor processing (for a small fee).

Lime application rates will usually be made on the basis of 1,000-10,000 lbs./ surfaceacre. Lime should be distributed as evenly as possible over the entire surface of a fullor dry pond. The best time to lime a pond is before filling, lime can be applied with aspreader and mixed into the pond bottom with a disc-harrow. Small, full ponds can be limedby spreading bagged lime from a boat or by broadcasting it from the shore. Large ponds mayrequire greater amounts of lime which is more economical when purchased in bulkquantities. Lime can be loaded onto a inch plywood platform placed over the bow of alarge boat or between two small boats. The material can be shoveled or washed off theplatform using a water pump, while moving slowly across the pond. A boat 18 feet long by 6feet wide can carry 1,500 lbs. of agricultural limestone.

Considering the relatively low cost involved in the maintenance of a pond's limerequirement, ponds should be limed before implementing a pond fertilization program. Ifliming does not improve fish production to a satisfactory level after one year, afertilization program should then be tried.

Ponds may need to be limed every 3-5 years. A good general rule for liming ponds is toapply lime at rates similar to those used for alfalfa field preparation. To maintain apond's pH and alkalinity at desirable levels, the lime should be applied annually byadding one-fourth of the initial application. Pond alkalinity and pH should be checkedeach year to evaluate the effectiveness of supplemental liming. Total alkalinity shouldnot be less than 20 mg/l with pH values between 6.5-9.0.

Reducing Fish Production Costs

By: G. William Klontz, M.S., D.V.M., Technical Services Advisor, Nelson and Sons,Inc., 118 West 4800 South, P.O. Box 57428, Murry, UT. 84157-0428, 1-800-521-9092

In this day of diminishing profit margins for foodfish producers, it is essential tocut production costs wherever possible - and practical. Many fish farmers takelabor-saving measures by purchasing, for example, demand feeders and mechanical graders.These measures might be effective to some degree, but it seems only logical to reduce themajor production cost factors, the chief among which is feed. And the most frequentcost-reduction measure in feeding is to increase the feed conversion; i.e., decrease thefeed conversion ratio (FCR).

Most commercially available trout and salmon feeds are capable of generating FCR's of1.1:1 - 1.2:1 if fed properly. The costs of feeding a 55-cent/kg pellet at decreasing feedconversions are quite significant.

Poor feed conversions are the result of overfeeding the population for the followingreasons:

• Overestimating the biomass in the population
• Overestimating the length and or weight increase
• Improperly calculating the daily feeding rate
• Improperly weighing or not weighing the daily feed

The majority of cases of over or underestimating the biomass and/or growth rate stemfrom not acquiring reliable inventory data. This presentation describes several inventorymethods and their limitations.

Sampling Methods

Before implementing one of the following methods to sample a population of fish, thefish should not have been fed for at least 18-24 hours.

"Grab" Sampling With Crowding:

The fish are crowded to the inflow end of the pond. Insert a fish crowding screen justdownstream of the inflow to reduce the injury to the fish from the turbulence. If thewater is clear, the fish are crowded to the point where the bottom of the screen is notvisible. If the water is not clear, the fish are crowded to the point where they seemquite "unhappy" about the situation.

Three to five nets of fish are taken from the population at different points. The fishare either weighed in total and counted or individually weighed and measured. Ineither event, the fish should be returned to the area outside the crowded population topreclude their being handled twice.

"Grab" Sampling Without Crowding:

A few (2-3) handfuls of feed are cast into one area of the pond. When there is a"feeding boil", fish are sampled using a long-handled dipnet or a cast net. Thefish are either weighed in totaland counted back into the pond or are individuallyweighed and measured. The process is repeated 2-3 times in different areas of the pond toensure representative sampling of the population.

The "5-by-5" Sampling Method:

Of the different methods of population sampling, this method is the best for obtainingstatistically representative samples of the population. The process begins with crowdingthe population toward the inflow end of the pond. A livebox (1 meter x 1 meter x 1 meter)is placed just downstream of the crowding screen. Five nets of fish are removed fromdifferent areas of the crowded population and placed into the livebox. One net of fish isremoved from the live box, weighed and counted into the area downstream from the crowdingscreen. The remaining fish in the livebox are released downstream also. This process isrepeated 5 times. The fish in at least one and preferably two of the weighed and countedsamples should be individually weighed and measured.

Fish Size Determination Methods

Individual Lengths and Weights:

Anesthetize, weigh ( 0.1 g), and measure at least 40 fish from each of 2-3 samplings.Of all the inventory data analyses, the individual weight and length values provide thegreatest degree of sensitivity. Using the mean (average), median, and midrange values,sampling bias can be detected. If the three values are equal, then there was no bias. Ifthe mean and/or median values are greater than the midrange value, then the samplingfavored larger fish. Correspondingly, if the mean and median values are less than themidrange value, the sampling favored the smaller fish.

Sampling bias can be viewed from several aspects. At one extreme it can be dismissed,while at the other extreme it can mean collecting more data. Most people choose to ignoreit and plan to do better next time. Some, on the other hand, will use it as an indicationthat the population should be size-graded to reduce its impact. This is by far the bestinterpretation and the most effective in the long run.

This method is quite time consumptive and requires more attention to detail than othermethods. To be most effective, individual weights and lengths should be a routinepractice. If this method is implemented once every month or so, its effectivenessdiminishes. Then staff loses interest and reverts to simpler, less effective methods. Theterm "less effective" is not to be equated with "ineffective".

Lot Weight Method:

A net of fish is weighed (1-5 pounds) and the fish counted back into area of the pondoutside the crowded population, if applicable. otherwise, return the fish to the pond.

Weighing can be accomplished by one of the following methods:

• Tare a hanging or platform balance with a bucket containing water. Either count the fish into the bucket before recording the weight or place fish into the bucket, record the weight and count the fish out of the bucket.
• Tare a platform balance with an empty bucket and a wet net. Weigh a group of fish in the net placed in the bucket. Count the fish out of the net. Record the new tare (water from the fish the bucket) with the wet net. This value is subtracted from the fish weight.
• The weight of a group of fish can also be determined by the water displacement method. In this method the displacement container should be calibrated for the size of the fish being inventoried.

1. Select a 35-40 liter straight-sided container. Mark 1 mm increments on the inside ofthe container. Calculate the cross sectional area and the volume of 1 mm increase in waterdepth.

2. Place the container on a platform balance having a sensitivity of 10 g. Put aknown volume (liters) of water into the container and record the mm level at the top ofthe water. Tare the balance to zero.

3. Put a net of fish into the container, record the weight, record the new water level,and count the fish back into the pond.

4. Calculate the biomass of fish which displaces 1 mm of water depth.

5. Weigh and count 3-5 samples per pond. Samples should come from different areas inthe pond.

One disadvantage of the water displacement method is its lack of sensitivity andaccuracy, especially if the unit is not calibrated. In addition, active fish in the unitcan make estimating the displacement level very difficult. To reduce this effect, it issuggested that an external sight-tube be installed and calibrated.

DATA ANALYSES

A. From the individual weight and length values, the following parameters can becalculated:

1. Mean (average) length and weight per fish

2. Median values for length and weight in the samples.

3. Midrange values for length and weight. The value lying halfway between the largestand smallest value.

• Condition factor (weight in g divided by the cube of the length in mm)

Using the data from the previous inventory and the data collected during the precedinggrowth period, the following parameters can be calculated:

1. Average weight (g) gain per fish.

Gain = ending weight minus starting weight.

2. Total biomass (kg) gain in the population

Biomass = (headcount X mean g per fish) / 1000. Gain = biomass at end minus biomass atstart

3. Average length (mm) gain per fish

Increase = end length minus start length

4. Average daily length (mm) increase

Increase (mm/day) = total increase (mm) / days

B. Using the lot weight data, the following parameters may be calculated:

1. Determine the number of fish per kilogram by totaling the number of fish and lotweights and dividing the total lot weight by the number of fish. The result is the meanweight per fish which is divided into 1000 to generate number of fish per kg.

The methods used to determine the number of fish per kg are not very time or laborconsumptive. The data acquired are quite accurate and reliable - however, only if thelimits of the procedures are followed. The methods provide only a limited amount of data;e.g., there can be no determinations of mean, median, and midrange length values orcondition factor values. Without such data, it is very difficult to assess size variationin the population and daily length increase.

The presence or absence of sampling bias may be identified by determining the number offish per kg in each sample lot. It is not unusual in a raceway population to have thelarger fish near the inflow end and the smaller fish at the outflow end of the pond. Thisactually does not indicate bias. In this case, the composite no./kg would be quiterepresentative of the population as a whole. If samples taken from a circulating or staticpond indicated quite a variation in fish size, then sampling bias would be indicated.

2. Weight gain per fish during the preceding growth period can be calculated bysubtracting the beginning weight (g) per fish from the ending weight (g) per fish.

3. The ending biomass (kg) and the biomass gain (kg) in the population can becalculated by multiplying the headcount by the average fish weight (g) and subtracting thestarting biomass from the ending biomass.

4. The feed conversion ratio can be calculated by dividing the amount of feed (kg) fedduring the preceding growth period by the biomass gain (kg).

5. The Specific Growth Rate (daily % weight increase) can be calculated using theequation presented above.

6. Using the mean weight of individual fish calculated using the number per kg method,it is not advised to calculate the length or condition factor using a mathematicalequation or a weight length table.

SUMMARY

A suggested approach to inventorying a population of fish throughout their productioncycle is to implement several of the methods described.

Begin the process when the pond is stocked. Determine the number per kg and weigh thefish into the pond. At the completion of the pond stocking determine the number per kgagain. Also, anesthetize a group of 40 fish for individual lengths and weights. Calculatethe mean, median, midrange and standard deviation values for lengths and weights. Also,calculate the mean condition factor. This will detect size bias from the originalpopulation to the new population. It will also facilitate constructing the daily feedingregimen.

The population should be inventoried at 14-day intervals. The first 2-3 inventoriescould be done with grab samples with crowding. One of the samples (at least 40 fish)should be weighed and measured individually. At intervals of 2-3 months or when the pondpopulation is reduced and or graded, the "5 by 5" inventory method should beused.

If performance data are used to their fullest advantage, the feed conversion ratio andthe fish quality should improve measurably, thus reducing the production costsaccordingly.

Using Bentonite To Seal LeakingPonds

By: John W. Jemsen and Brandon Foster, The Aquaculture News, January 1994

Nothing is more frustrating to landowners than to find that their recently constructedpond leaks like a sieve. No matter how much planning and care is taken in building a pond,there are no guarantees that it will hold water. Leaky ponds can sometimes be repaired butremedies are almost always costly.

If you have a new pond that leaks, sometimes just simple settling of the soil in thedam over time may cure the problem. in many cases another core constructed to cut ofseepage channels beneath the dam can be engineered to seal off the leak. Leaks along drainpipes can also be identified and repaired. Exposed sand and gravel seams in the pondbottom are common sources of leaks. Sometimes these areas can be found and covered with alayer of good quality clay.

Bentonite clay is often recommended to help seal porous pond bottom soils. When wet,bentonite swells 12 to 15 times its original size, effectively sealing off the spacesbetween soil particles. Bentonite can be the solution to a leaky pond. However, it isusually expensive and it doesn't work under all circumstances. Here are some things youshould know about bentonite and its use for sealing ponds.

• Don't confuse calcium bentonite with the swelling type sodium bentonite from Wyoming. Calcium bentonite also causes rapid changes in pH, which can lead to fish kills.
• Western swelling type sodium bentonite is sold under various trade names. It can be obtained in limited quantities from local dealers. The price is about $7.50 per 100-pound bag. At a minimum application rate of one pound per square foot, a 100-pound bag would be applied to 100 square feet of pond soil. Therefore, about 20 tons, or 400 bags, would be needed to cover an acre of pond bottom. Bentonite may also be purchased in bulk directly from Wyoming at a cost of approximately $150 per ton. This works out to about $3,000 per acre. Because of its high cost, bentonite use may be limited to patching leaky spots in ponds.

Three general methods can be used to apply bentonite to ponds. They are the blanketmethod, the mixing method, and the sprinkle method. When the blanket method is used, thetop 4 to 6 inches of the dry pond bottom needs to be removed. The Freshly exposed surfaceis then smoothed and covered with a layer of bentonite. The bentonite layer is thencovered with the previously removed soil and the whole thing is compacted by rolling ortamping. If possible, water flow into the pond should be controlled to prevent damage tothe treated surface before the pond fills. It will take several days before the bentoniteforms a barrier to prevent water seepage.

When the mixing method is used, the bentonite is mixed with the soil. The pond bottommust be cleared of all rocks and vegetation before the bentonite can be applied to thesurface. The bentonite is spread evenly and then tilled or disked 4 to 6 inches into thesoil. The soil is then compacted by rolling or tamping. No topcoat of soil is requiredwith the mixing method.

Bentonite can also be sprinkled on the water surface over a suspected leak. Althoughthis is the least effective of the three methods, it eliminates the need to drain thepond.  Application rates range from 1 to 8 pounds bentonite per square foot. Theapplication rate is determined by the seepage rate.

To best determine the minimum amount of bentonite required to prevent or reduce waterseepage to an acceptable rate, perforate the bottom of a bucket and place 1 to 2 inches ofgravel in the bottom. Cover the gravel with 6 to 8 inches of the pond soil you will betreating. Tamp down the soil, add water, and observe to determine the seepage rate in yourpond. Once you have determined the seepage rate, you can test for the effectiveness of thethree possible methods of bentonite application.

If the blanket method is to be used, remove the top 4 to 6 inches of soil from thecontainer, add pound bentonite per square foot to the freshly exposed surface, and thenreplace the soil that was removed. Tamp it down, add water, and observe the results. Ifthe mixing method is to be used, mix the top 3 to 4 inches of soil in the bucket with pound bentonite per square foot. Tamp it down, add water, and observe the results. If thesprinkle method is to be used, prepare the container with gravel, soil, and water asbefore, then sprinkle the bentonite on the water surface and observe the results. Continueto repeat the method you have chosen, progressively using more bentonite until anacceptable minimum amount of bentonite is reached that appears to control seepage.Finally, add 25 to 50 percent more bentonite to the actual pond soils than shown by thetests to allow for the greater water depth of the pond and the inefficiency of large-scaleapplications.

Bentonite may be purchased in one of two forms. The granular form is more effectivewhen sprinkled on the water surface than the pulverized form because the larger particlesare able to sink quickly to the bottom before they are saturated with water and swell.Because the powder can create a lot of dust when it is spread out or disked into dry soil,the granular form may be easier to use than the powdered form when applied in this manner.However, the powdered form may be more effective when it is disked into the soil becauseit does a better job of filling in the spaces between soil particles. Bentonite is onlyabout 40 percent as effective at sealing leaks when it is applied to wet soils as when itis applied to dry soils. Patching leaks is almost always expensive and not alwayseffective. Therefore, preventing leaks initially with properly designed and constructedponds is essential.

Guidelines For The Use of Rotenone

By: Chris K. Hyde, Extension Aquaculturist, Alabama Cooperative, Extension Service

Many pond owners will at some time want to eliminate some or all of the fish from theirponds. Common reasons for eradicating pond fish populations include elimination of wildfish from ponds prior to stocking for aquaculture or sportfishing, contamination of pondswith an overabundance of undesirable fish species, and renovation of out-of-balancesportfish populations.

Rotenone is the compound approved by the Environmental Protection Agency (EPA) for thepurpose of fish eradication. Rotenone is a natural substance derived from the roots ofcertain types of tropical and subtropical plants. It is highly toxic to fish at very lowconcentrations but has low toxicity to most other organisms at the rates used forfisheries work.

Used in the United States since 1930, rotenone is available in both liquid and wettablepowder formulations and is marketed in concentrations of 2.5% and 5.0%. Treatmentconcentrations range from 0.5 parts per million (ppm) to 5 ppm of commercial product (5%concentration) depending upon target species and environmental conditions.

A common misconception about rotenone is that it kills fish by removing oxygen from thewater. Rotenone has no effect on dissolved oxygen levels. In fact, it does not even"suffocate" fish. Rotenone is readily absorbed through the gills and transportedby the blood to the cells, where it kills fish by interfering with their cellularchemistry.

Several factors affect the toxicity of rotenone to fish. It is important for pondowners to understand these factors in order to use rotenone effectively, especially whentotal fish eradication is the goal. Timing of application to coincide with favorableenvironmental conditions can significantly lower treatment cost by reducing the quantityof rotenone needed to achieve the desired results. Factors affecting toxicity of rotenoneinclude water temperature, alkalinity and pH, turbidity and organic matter, aquaticplants, water depth, fresh water source, sunlight, oxygen and resistant species.

The best pH for rotenone effectiveness is near neutral or about 7.5. Rotenone is moretoxic to fish in acidic water, but its time of effectiveness is reduced because it bindsto acids. However, basic water helps fish to overcome rotenone's toxic effects. Withregard to alkalinity, rotenone is more toxic to fish in water of low alkalinity whilewater high in alkalinity will require more rotenone to achieve the same results. Thepresence of clay turbidity or heavy algae blooms can cause rotenone to bind with thesuspended particles and reduce its effectiveness.

An abundance of aquatic plants will negatively affect treatments as plants absorbrotenone and interfere with treatment and mixing. Deep ponds tend to be thermallystratified during warm months. This layering of temperatures can hinder the mixing ofrotenone. Pumping the chemical through weighted hoses may be necessary to adequately treatthe bottom layer of deep, stratified ponds.

Water temperature during treatment should range from 45 to 75. Complete kills will beexperienced more often when the water temperature Is between 46 and 65. The most favorabletemperature for rotenone use is reported to be 61. The paradox with water temperature isthat the warmer the water, the more toxic rotenone is to fish. However, rotenone isdetoxified or broken down very rapidly In warm water. Therefore, for maximum toxicityoverall, it's better to have slightly lower toxicity in cooler water over a longer periodof time.

Streams, springs, or seeps either flowing into the pond or coming up from the pond bottom can provide safe havens for fish until the rotenone has detoxified. Rotenone breaks down quickly in the presence of sunlight. The lower the level of dissolved oxygen, the more toxic rotenone is to fish. Species such as common carp and bullhead catfish are very resistant to rotenone. Ponds containing these species will require higher concentrations than ponds containing other, less resistant fish such as bass, shad, crappie, or channel catfish. Fish eggs are also more resistant to rotenone than fish. Of course, not all of the previously discussed conditions can be controlled by the pond owner. However, careful timing of a rotenone treatment can often combine several favorable conditions to help achieve the best results with the least cost.

Rotenone is labeled for use as a fish toxicant at rates of 0.1 to 5.0 ppm for the 6percent formulation with the 2.5 percent formulation approved for use at a rate of 0.2 to10.0 ppm. Labeled rates vary because environmental conditions and fish tolerance can be sovariable. For example, on a cloudy day with water temperatures around 60 with pH near 7.5and no resistant species present, a treatment level of 0.5 ppm would be very effective.However, during the summer with slightly turbid water, at least 2.0 ppm would be requiredto achieve the same results. This same combination of environmental factors with bullheadspresent may require the highest concentration of 5 ppm (See CHART on next page).

Three of the main causes of poor success using rotenone are:

• miscalculation of pond volume and/or dosage;
• poor distribution of the toxicant; and
• presence of unknown subsurface springs or other freshwater inlets.

Also keep in mind other considerations when planning a rotenone treatment.

• Treat on an overcast day, avoiding sunlight, which detoxifies rotenone.
• Treat early in the morning before pH and oxygen levels increase.
• Avoid treating during periods of turbidity, following rain or if plankton bloom is heavy. Avoid treating ponds with heavy aquatic weed growth. Weeds absorb rotenone and interfere with mixing.
• Avoid treating ponds during the summer. Warm water quickly detoxifies rotenone.
• Use the higher treatment rates when either common carp or bullheads which are resistant species, are known to be present.
  

ROTENONE TREATMENT RATE GUIDELINES

Although rotenone has an extremely low toxicity to humans, EPA has not set a safetolerance level in fish and consumption of fish killed by rotenone cannot be recommended.

Wait one to four weeks following treatment before restocking the pond, depending uponwater temperature and alkaline. It's always a good idea to place a sample of fish to bestocked in a cage within the pond to test for residual toxicity. If the fish are notkilled within 24 to 48 hours, the pond may be restocked. If immediate restocking isdesired, rotenone can be detoxified quickly by adding potassium permanganate to the waterat a rate of twice that used in the rotenone treatment.

Sand Filters

From: Aquanetics

By: The Aquaculture News

Extra-large, high-flow sand filters, ideal for hatcheries and other aquacultureapplications, are now available from Aquanetics Systems, Inc. The filters are available ineither horizontal or vertical configurations and are made of non-toxic plastics. The42"-diameter filter chambers feature attractive, smooth, gelcoated exterior surfaces,and are certified to handle working pressures of 50 p.s.i.g. and hydrostatic testpressures of 75 p.s.i.g.

The vertical model provides 9.6 sq.ft. of filter surface area and handles a maximumflow rate of 144 GPM. Horizontal models 84" or 100" long provide 20 or 25 sq.ft.of surface area and handle maximum flow rates of 300 or 375 GPM, respectively.

Flanged inlet and outlet plumbing connections are provided, and all filters havepressure gauges. Horizontal models have easily accessible manholes. The units arehydraulically balanced to prevent displacement of the filter media during normal operationor while cleaning.

Individual units can be fitted with side mounted, 3" rotary backwash valves, or4" butterfly valves and multiple filters may be ganged to handle the largestfiltration jobs.

For information on the high-flow-rate sand filters and related aquaculture equipment,contact: Aquanetics Systems, Inc., 5252 Lovelock St., San Diego, CA 92110. Or callAquanetics at (619) 291-8444 (voice) or (619) 291-8335 (Fax).

Silicones Show Promise As Net Antifoulants

By: Geoffrey Swain and Nagahiko Shinjo

Biofouling of aquaculture nets presents serious maintenance and operational problems.It reduces water circulation, increases drag forces, increases weight, and may act as areservoir for parasites and disease. At present, the usual solutions are to applyAntifoulants that use biocides (substances that kill organisms) or to clean and replacethe nets as necessary. An alternative remedy, however, may soon be available in the formof silicone coatings.

The ability of silicones to control fouling was first recorded in the early 1970's,although they weren't considered a serious alternative to organotin and copper antifoulingpaints due to their high cost, inferior performance, and poor mechanical properties. Now,however, regulations restricting the use of the organotin biocides and recognition of theproblems associated with the uncontrolled release of chemicals into the environment haveresurrected interest in silicones. The most attractive aspect of the silicone elastomersis that they are nontoxic and function by reducing the adhesion strengths of thebiofouling communities. This means that, while they may foul, the fouling is easy toremove.

Field test

To provide a better understanding of how these coatings might perform in real lifesituations, two large nets were coated with commercially available silicones asdemonstration projects. One, a 12' x 12' x 10' net with " mesh, has been in serviceon the east coast of Florida for 15 months. There have been no serious fouling problemsand the marine growths that do occur are easily removed by a diver with a soft bristlebrush. The second is a 40' diameter, 10' deep net of " mesh. This net has yet to beplaced in service but test samples exposed at the site have exhibited good performance.

The coatings were applied using a simple dip technique. The nets were then hung tocure. The amount of material, including waste, required to coat the nets was aboutone-half gallon per 100 square feet. This corresponds to a coating cost of approximately90 cents per square foot. There is still much to be learned about the performance ofsilicone net coatings and improvements need to be made with regard to cost andperformance. We believe, however, that the nontoxic, elastomeric and foul releaseproperties of silicones make them an ideal candidate for reducing the fouling problemsassociated with nets and aquaculture. For more information, call us at (407) 768-8000 ext.7129.

The Useof Ozone as a Disinfectant in Fish Hatcheries and Fish Farms

By: ULRICH EUGSTER, Ministry of Hunting and Fishing Zurich, Switzerland and BRUCESTANLEY, Ozonia Ltd Duebendorf, Switzerland, Submitted By: Mary LaMarca, Ozonia NorthAmerica, Inc., P.O. Box 330, 178 Route 46, Lodi, New Jersey 07644, 201-778-2131

The ever increasing load on the fish hatchery environment calls for more intensivemeasures to maintain the natural equilibrium. In order to maintain indigenous fishpopulations it has become necessary in many countries to introduce stocking programs forcoarse fish in addition to the ever increasing activities involving game fish. Thesedemands have placed extreme pressures on hatcheries and farms already operating withlimited facilities. The easiest way to increase production without vast capital outlay isto increase the number of fish being reared in a given volume.

It is obvious that when the fish density per cubic meter is raised, the risk ofinfection increases proportionally. In order to maintain the survival rate as high aspossible it is of vital importance to ensure that no water borne disease can enter thesystem - this applies to recirculating as well as single pass systems. An ideal method ofdisinfecting water is by ozonation in a contact tank prior to use. Ozone is a verypowerful bactericide and viricide and, unlike other agents, it leaves no undesirableresidues. The latest available advanced ozone technology, which will enhance efficiencyand be environmentally beneficial, now lies within the reach of all operators.

Introduction

In the modern world of today it is not unusual for man to give nature a helping hand toovercome certain difficulties in order to maintain a natural equilibrium. Over the lastdecades, pollution, mainly from industry, has taken its toll and some of the hardest hitresources are our lakes and rivers. One of the worst things that can happen to surfacewater is direct pollution - a typical example of this is the fire at Schweizerhalle inBasle, Switzerland and the result it had on the River Rhine. Even without direct pollutionour waters are still subject to varying degrees of contamination that have a directnegative bearing on the life forms that these waters support.

In an attempt to compensate for the effects of our modem world, and to maintainindigenous fish stocks, it has become standard practice to introduce stocking programs forlakes and rivers that are in danger of becoming fishless. Depending on the water inquestion, these stocking activities can be anything from a short-term program lasting afew years until a water has re-established itself, or a permanent restocking program tomeet commercial or sporting needs.

Methods

In the Canton of Zurich many different types of fish are reared to replenish stocks inthe area's rich abundance of rivers and lakes. One of the hatcheries involved in thesestocking activities is located in the village of Greifensee on the shore of Lake Griffinfrom which the water for the hatchery is drawn. The quality of the water contained in anylake or river is continually changing - this is partly due to natural causes and partly topollution. In order to achieve the highest possible efficiency it is essential that theinlet water to a hatchery be clean, free from contamination and micro-organisms that coulddamage the fish stock being reared. In the Greifensee hatchery the water has been treatedwith ozone for many years with excellent results.

As the hatchery water is drawn it's pumped directly into contact chambers - these wereinitially fitted with porous diffusers and later fitted with an apparatus very similar toa radial diffuser. Following ozonation in the contact chambers, the water is pumpedthrough a sand filter in order to remove any fine materials carried along with the waterflow and any precipitated or flocculated matter. Finally, the water is passed through anactivated carbon filter in order to remove traces of residual ozone, biodegradableby-products and to adsorb non-polar substances. After treatment the water is pumped intothe hatchery where it is distributed to the hatching trays and fry tanks.

The hatchery in Greifensee is in a position to rear virtually any type of freshwaterfish. As a rule, however, the demand on the individual fish types by the professionalfishermen and anglers determines the actual stocking program. The main species reared arebrown trout, powan and northern pike.

The cultivation process follows established methods in aquaculture: selected rearingstock is caught during the spawning season. After stripping and fertilization, dependingon the type of fish, the eyed eggs are placed either in hatching flasks, or on hatchingtrays, where they are incubated until hatching. It is during this critical stage that thequality of the water is of primary importance - not only is it important for the actualefficiency with regard to the number of eggs hatched but also to the quality of the fryproduced.

Why Ozone

In general, the main reasons for using ozone in water treatment are:

• Partial or total oxidation of dissolved matter
• Precipitation of dissolved matter
• Micro-flocculation of organic matter
• Destabilisation of colloidal matter
• Disinfection

Unlike such agents as chlorine, or any of its derivatives, oxidation with ozone leavesno hard to handle or toxic residues requiring subsequent complex treatment. In practice,ozone immediately starts to attack the oxidizable components it comes into contact with.This property makes it a very powerful disinfectant. Because the process only leaves"oxygenated" products and oxygen, it is particularly well suited forapplications such as hatchery water where the presence of undesirable elements aftertreatment could have grave consequences.

Ozone Generation

The traditional method of producing ozone is by means of Dielectric Barrier Dischargeor so called Silent Electrical Discharge. Ozone generators working on this principle arebasically arrangements of high voltage electrodes separated from the earth electrodes bygaps and dielectric layers. Modem ozone generators using oxygen as the feed gas and,consequently, producing ozone at higher concentrations, are of particular interest tohatchery managers:

• The units themselves are more compact than generators using dry air as the feed gas.
• The controversial issue concerning nitrous oxides does not exist because there is hardly any nitrogen in the feed gas.
• If "Advanced Technology" dielectrics are fitted to the generator units, energy savings between 25% and 60% can be expected.

Contacting System

Apart from the ozone generator proper, the next most important part of any ozone plantor ozonation system is the equipment that brings the ozone in contact with the medium tobe treated. The purpose of the contacting or diffusion equipment is to create a largegas/medium contact area so that, under specific conditions, the highest possible masstransfer is achieved. Basically, there are 3 methods of achieving this effect:

• Porous diffusers: probably the most popular method of introducing ozone
• Radial diffusers: specially designed equipment for use in restricted areas
• Venturi injectors: simple means of introducing ozone with a high transfer efficiency

Ozonation in aquaculture is unique because it is a rare application where livingcreatures are exposed to disinfected water more or less immediately after it has beendisinfected. Because of this, hatchery operators have to be particularly careful how theyintroduce ozone to the medium being treated. One of the major problems encountered withthe contacting system is fry mortality caused by the over aeration of the hatchery water.

Because of this problem, operators have to look for a system that will ensure themaximum mass transfer (ozone to water) without introducing large quantities of non-ozonegas to the water. Of the 3 popular methods of diffusion only 2 come into question for thisapplication: the porous diffuserand the radial diffuser. The venturiinjector, although it has a high transfer efficiency, is unsuitable because itintroduces large quantities of ozone generator feed gas to the water that could cause frymortality.

A typical contact system for hatchery application will have 3 chambers. The firstchamber is a counter flow diffusion chamber where the ozone is introduced. In this chamberthe fast oxidation processes, i.e. the oxidation of dissolved matter such as iron andmanganese, and a fraction of the slow reactions takes place. The second reaction volume,without diffusers, is designed for the disinfection and the slow chemical reactions. Thelast chamber is where the slow reactions are completed and a major portion of the residualozone decomposes.

Conclusion

Experience gained over the years with numerous plants have provided a betterunderstanding of the criteria relating to applications in aquaculture. In the future, anincrease in the use of ozone is expected not only in fish hatcheries but also in:

• Farms where fish are reared to a certain size and then culled for culinary purposes
• Salmon smolt stations
• Large domestic and zoo aquariums
• Tanks for other aquatic species such as dolphins, seals, etc.

Ultimately, circulating closed systems will become the norm and the over loading ofrearing systems sometimes associated with fish farming will also be avoided.

Acknowledgment

Special thanks are given to Max Straub, Manager of the Ministry of Hunting and Fishingin Zurich Switzerland.

Hatchery Tip

Is your hatchery program so well funded that you don't even bother trying to find thebest/cheapest way to accomplish a task? Are you tired of dealing with all that money youcarry over from one year to the next? If so, you need not bother reading these next twohatchery tips. However, if you are interested in cutting your electrical power cost anddiverting several thousand dollars to your program/staff, you may just want to continuereading. Greg Fischer (Tribal HatcheryManager-Red Cliff Reservation) informed the MTAN of two great ways to lower yourelectrical power cost:

• If your hatchery has a backup generator to supply electrical power, you may want to ask your power company if you would qualify for a lower base rate if you used your generator during periotic "High Peak" power loads. This program is not well advertised so you will need to specifically inquire about it. Greg told the MTAN he will save more then $8,ooo this year.
• The Red Cliff hatchery will be making additional savings because they plan to pay for the entire year's propane needs "this summer." The good news is that the propane dealer will deliver the gas as it is needed. The savings is made because the entire years purchase is made during the period when gas rates are the lowest, thus cutting out those seasonal rate increases we all have learned to hate.

For more detailed information you may want to call Greg at 715-779-3728.

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