Dedicated To Tribal Aquaculture Programs
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September 1998 ~ Volume 25 | |
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Topics of Interest:
Matters of Fish Health
Matters of Fish Health
Fish diseases constitute one of the most important problems and challenges confronting fish culturists. Fish in intensive culture are continuously affected by environmental fluctuations and management practices such as handling, crowding, transporting, drug treatments, undernourishment, fluctuating temperatures, and poor water quality.
Fish diseases do not occur as a singly caused event but are the end result of interactions of the disease, the fish and the environment.
All of these factors can impose considerable stress on the homoeostatic mechanisms of fish rendering them susceptible to a wide variety of pathogens. Parasites, viruses, and bacteria are all causes for concern to aquaculturists. Many of these pathogens are easily treatable and are not transferrable to humans. On the other hand, there are fish diseases that are not treatable and cause widespread mortality both in the hatchery and wild fish. Disease also reduces hatchery efficiency and production, which in turn, increases costs and reduces profit.
Another major issue pertaining to fish health is the concern over the introduction of infectious diseases, particularly those that are not endemic to the area, through fish culture facilities to wild fish populations. The impacts of infectious diseases are generally misunderstood or seriously underestimated, and it is not uncommon to find resistance to their assessment and control. Many of the fish health programs, guidelines and regulations are simply regarded as another bureaucratic impediment and cost placed in front of the aquaculture industry. This attitude is due, in part, to the "old school of thought" that significant epizootics rarely if ever occur in wild populations and to the abiding faith that once fish are released into the wild they will recover. Wild fish stocks can become infected and suffer high mortalities through the release of pathogens in untreated hatchery effluent or through the stocking or escapement of diseased fish into aquatic systems.
For example, the State of Colorado stocked hatchery-reared trout known to be infected with whirling disease (Myxobolus) on a population of wild trout in a major Colorado river fishery. Result: the wild population was infected and suffered high mortalities. Three state fish & wildlife officials lost their jobs for introducing these disease infected fish.
A state fish hatchery in Paradise, Utah, withdraws water from the Little Bear River for culture purposes and discharges it back into the river. Biologists were made aware of deformed wild fish in the Little Bear. Upon investigation 8-22 percent of the native population had been infected by the disease Myxobolus. The source of disease was traced back to the Paradise Hatchery.
In Michigan, a pathogen-contaminated hatchery discharging into a nearby river infected the wild fish population in that river. All fish in the hatchery and river were eradicated to prevent further spreading of the pathogen throughout the watershed. The state of New York last year ordered that 43,000 pounds of fish be destroyed from four state hatcheries because they were infected with whirling disease. This same disease is also now plaguing state fish hatcheries in Connecticut.
All responsible fish hatchery managers should consider fish diseases a serious potential threat to the health of our public aquatic resources.
Some of the measures we should all employ at our Tribal facilities relative to fish health include annual diagnostic inspections, standard disinfection procedures on tanks, raceways and fish hauling trucks, inter-hatchery fish movement restrictions and requiring a fish health certificate from any facility conducting a fish/egg transfer.
What Every Fish Hatchery Worker Should Know about Zebra Mussels
The zebra mussel is a freshwater clam native to the Caspian Sea of western Russia. First discovered in 1988 in the Great Lakes region, it has spread at an alarming rate throughout the eastern North American continent and has been reported as far south as New Orleans. A single mature female zebra mussel can release over a million eggs in a season. Because of its diverse genetic background, the zebra mussel is highly adaptable to a wide range of environments.
Densities approaching 100,000 ft2 and 10 inches thick have been reported in industrial water intake pipes. Cost to fishermen and consumers in the Great Lakes region is estimated to be 5 billion dollars by the year 2000.
The greatest physical impact that the zebra mussel will have on fish farmers is as a macrofouler. Hatcheries, raceways, intensive recirculating systems and holding facilities will probably sustain most of the anticipated damage.
Impact On Fish Farmers
Zebra mussels will clog filters, screens, cages and pipes. Zebra mussels have been identified as the intermediate host for at least one species of parasitic trematodes which can infect cultured fish species. Zebra mussels have also been found to be attached to aquatic plants such as coontail, hydrilla, Naiad and milfoil and have the potential of surviving in mud-bottomed aquaculture ponds having macrophytes. Because they are highly efficient filter feeders, dense populations of zebra mussels in ponds could conceivably reduce primary production such that fry and fingerlings are literally starved to death.
Preventive Measures
The adage, "An ounce of prevention is worth a pound of cure" could never be truer when it comes to zebra mussels. Once established, zebra mussels can be difficult, costly and sometimes impossible to eradicate. Here are steps you can take to protect your Tribal hatchery operation:
Keep out Contaminated Equipment and Fish Shipments. Zebra mussels can enter your facility either as microscopic larvae transported in water, or as adults attached to boat hulls, motors, trailers, harvesting baskets or catfish holding socks. Strictly prohibiting boats and other equipment from contaminated waters onto your property can eliminate most sources of zebra mussels. Allow only shipments of fingerlings and brood stock from operations which are certified zebra mussel-free.
Clean, Dry and Quarantine. Steam clean or immerse in hot water (140 F) for 3-4 minutes, dry and quarantine all contaminated equipment that comes on your premises. This includes seines, nets, buckets, hauling tanks and pumps. Bulky equipment like seines should be spread out in the sun for 3-4 days since adult zebra mussels can live more than a week out of water in warm, moist areas.
Remove Aquatic Weeds. Remove, inspect and properly dispose of aquatic weeds that inadvertently are carriers into your facility. Don't allow either of these pests to become established in your ponds.
Protect Your Water Supply. Since most surface waters will eventually be infested by zebra mussels, fish farmers should use ground water from a well or spring where feasible. Water taken from creeks or rivers should be filtered using sand filters or buried infiltration beds. In extreme cases, a constant-flow treatment of chlorine/sodium thiosulphate can be used to treat contaminated waters. Needless to say, keeping zebra mussels out of your fish farm will eliminate unnecessary headaches and expenses.
Control Measures
Several non-chemical practices that can help control zebra mussels at your farm are:
Filtration Systems. Filtration is probably the most effective and economical method for operations that use surface waters. Sand filter, submerged infiltration beds and in-line filters will eliminate most stages of the zebra mussel.
Desiccation. Hatchery ponds are typically drained and allowed to dry during the off season. This practice will kill all stages of zebra mussels.
Heat Treatment. Contaminated equipment can be steam cleaned or immersed in hot water (140 F) for 3-4 minutes to kill juvenile and adult zebra mussels.
Biological Controls. Freshwater drum, blue catfish, redear sunfish and common carp are all known to feed on indigenous clams. A polyculture arrangement using one or a combination of these species should be effective against juvenile and adult zebra mussels.
Chemical Controls. Several chemical treatments have also proven to be effective in killing zebra mussels. Those that tested positive by Ohio State University and the National Fisheries Research Center-La Crosse researchers are as follows:
Salt. Common table salt at a 1% (10,000 ppm) treatment rate for 24 hours had a 100% mortality for larval and juvenile stages of the zebra mussel.
Benzalkonium Chloride. This chemical is recommended for use on contaminated equipment at 100 ppm for 3 hours or at 250 ppm for 15 minutes. It will kill all stages of the zebra mussel.
Rotenone. This should be used to treat infected ponds. Depending on temperature, a treatment of 1-5 ppm for 24 hours will kill adult zebra mussels.
Chelated Copper. Treat at 2 ppm for 48 hours to eliminate adult zebra mussels from ponds. Toxicity of copper compounds does vary with the pH and alkalinity.
Hydrated Lime. Addition of calcium hydroxide to a newly drained pond at a rate of 1000-2000 lb/acre will kill larval and juvenile zebra mussels.
Should you decide on a chemical treatment, conduct a simple on-site bioassay to protect the environment and your investment.
No chemical treatment has proven 100% effective against all stages of the zebra mussel without harming other aquatic life forms. Be sure to contact your state environmental agency as well as your local EPA or FDA office to determine the latest regulations before using any chemical treatment. For information on a particular compound, contact the Technical Information Officer, National Fisheries Research-La Cross, WI at 608/781-6200.
Muskrat Control
By: Jim Steeby
Now that the cooler temperatures are only a few months away many producers need to think about controlling nuisance muskrat populations. The animals are particularly active between November and February when feeding and breeding activity is at its peak, and food sources become scarce. Trapping is the best control and, fortunately, muskrats are relatively easy to trap. These rodents are particularly attracted to floating or partially submerged objects and, consequently, leg-hold traps placed on naturally occurring or man made structures close to the water line are very effective. Traps should be attached to the structure with a foot or two of wire to establish a drowning set. A piece of plastic netting or hardware cloth 3'x3' nailed to some 2x4s makes a good structure to set traps on. Place this platform at water level and stake it out with some rebar, metal fence posts or attach larger boards so it will float. Place two to three traps on top and attach each with wire. Good locations for the float are in areas of high muskrat activity that is easily accessible in wet weather. A "colony trap" can also be made and works well. Trapping licenses are usually required for these activities and can be obtained anywhere hunting licenses are sold. Be sure to contact local conservation officers before you start a program of control to make sure that the trapping is legal.
Bird Damage at Aquaculture Facilities
By: W. Paul Gorenzel, Fred S. Conte and Terrel P. Salmon, Department of Wildlife, Fisheries and Conservation Biology, Univ. Of California Davis, CA
Reduction of the damage caused by fish eating birds requires accurate bird identification and some knowledge of avian biology and habits. Responsible bird management requires knowledge of both the problem species and other birds that use the aquatic habitat without harming aquaculture efforts. Not all birds are harmful to production efforts. Birds only become a problem if their activities directly or indirectly result in fish loss. Many species benefit from the association with production facilities without interfering with production efforts.
Large open-water areas are natural attractants to many birds. Birds can have a significant economic impact on fish culture operations. Fish-eating birds are highly mobile and adaptable predators, able to rapidly exploit situations of food abundance. Aquaculture facilities are ideal feeding sites for these predators.
The severity of bird problems will vary with the species and number of birds present and whether the birds reside only seasonally or tend to remain at the facility throughout the year.
The proximity of nearby nesting or roosting sites and the availability of alternative feeding sites are also important factors. Problems are compounded when drought impacts alternative feeding sites, especially as the number and size of available wetlands continue to diminish due to human activities.
Besides consuming fish, birds can injure fish, disrupt their feeding activity, disturb broodstock, and contribute to the spread of diseases and parasites in aquaculture ponds and raceways. Bird feces can degrade water quality and through bacterial activity, lead to reduced oxygen levels. It can result in significant expenditure of time and funds in establishing bird management programs and training personnel.
The birds commonly responsible for most damage are herons, cormorants, pelicans, gulls, egrets, mergansers and other diving ducks, blackbirds, and kingfishers. Other problem species reported less frequently include dippers, grebes, ospreys, and dabbling ducks. Because most species of fisheating birds are diurnal, or active during daylight hours, direct observation is the usual means of confirming bird presence and damage. Obvious signs of hunting and feeding birds include birds perched on trees or wires near raceways or ponds, hovering overhead and then plunging into the water, standing or stalking along the edges of ponds, or swimming and diving in the ponds.
Some species, including the black-crowned night-heron and the yellow-crowned night-heron in particular, feed at dusk and night, when aquaculture personnel may not be present to observe damage. Because most fish are swallowed whole, often few direct signs of damage are left behind. The decrease in the number of remaining fish may not be obvious for some time. In these cases, the presence of whitewash (bird excrement), bird feathers, and/or bird footprints may be the only signs of bird predation. Additional observations at night should be made to verify bird depredation. Some fish may show scars from predatory attempts. Cormorants often injure fish, allowing access to fungal and bacterial disease organisms. Herons sometimes spear but do not kill or eat larger brood stock. Chewed or partially eaten fish may be a sign of predatory animals including raccoon, mink, and otters.
Legal Status and Permit Protocol
Resolution of bird depredation problems is complicated. All fisheating birds that frequent aquaculture facilities are classified legally as migratory and thus are protected by federal, and in most cases, state laws. These laws were developed to protect US interest in migratory birds in concert with the interests of other nations that provide habitat to these same avian populations. The migratory Bird Act (16 USC 703-71 1) consists of agreements made with foreign governments concerning migratory species and influences US domestic laws and regulations concerning these species.
Damage Prevention and Control Methods
With the exception of total exclusion, control methods rarely solve a bird control problem. Results obtained from nonexclusion techniques may vary.
Keep in mind that all methods succeed or fail to some degree, and a combination of methods is usually required.
The choice of control methods will be determined by a number of factors, including the species of birds involved, the extent of the damage, the projected cost of the control program, the type of facility to be protected, the species of fish grown, the size of the water impoundments, and the long-term effect on facility management. Finally, economics plays a role in the selection process; the expected cost of the control program must be less than the value of anticipated damage.
Exclusion
Exclusion is the complete enclosure (caging) of ponds and/or raceways with screen or net. It is effective for small facilities, but is not practical for protecting most ponds larger than 5 acres (2 ha). Total exclusion is the only legal method available that provides complete, long-term control. Complete screening or netting is effective in excluding all problem birds and has been adopted by a number of state and federal hatcheries. Some commercial producers have adopted complete facility exclosure or partial exclosure in combination with other management practices. This choice is based primarily on the monetary damage caused by the birds and/or self-protection from potential legal consequences associated with migratory, threatened, and endangered bird species.
Impediments
Impediments are partially covered systems with overhead wire, line, net, or screen, and devices that discourage birds from entering a feeding zone or perching nearby. Impediments such as overhead lines are usually less expensive than enclosures, but do not exclude all bird species.
Overhead Wires or Lines
Ponds or raceways can be covered with overhead lines of braided or other extruded polypropylene material, or stainless steel wire, suspended horizontally in one direction or in a crossing pattern. These lines should be made visible to the birds by hanging streamers or other objects at intervals along the wires.
The objective is to discourage bird feeding activities and not cause bird injury or death. Overhead wire networks generally require little maintenance other than maintaining proper wire tension and replacing an occasional broken wire. Reflecting tapes are also used in overhead networks, but they are prone to wind damage.
Perimeter Fencing or Wires
Perimeter fencing or wire around ponds and raceways provides some protection from wading birds and is most effective for herons. For ponds, erect fencing at least 3 feet high in water 2 to 3 feet deep. Small mesh material can be used to prevent fish from entering the shallow water, but maintenance costs associated with algae buildup and accumulated debris can be substantial. Fences built in shallow water will not prevent birds from feeding on the pond side. Great blue herons have been deterred in Great Britain with a 2-strand fence with wires at 8 and 14 inches around a pool supplemented with floats spaced under 1 foot apart around the pool.
Fences surrounding raceways should be high enough to prevent feeding from atop the fence. Occasionally blackbirds will cling to fencing or screening near the water and feed on small fish. A slick surface created by securing plastic over the fence or screen will eliminate the problem.
Electric fences with nonlethal levels of electric current have also been used but with varying success. Problems include maintenance and preventing the system from becoming grounded, commonly caused by vegetation interference and blowing debris. Wires are strung on supports that suspend the wire over the water's edge near the natural shelf that often forms in shallow areas of the pond margin. This system discourages wading birds from feeding on fish while walking along the shelf.
Metal Spines
For some situations, sharp, metal spines, sometimes called porcupine wires may be used to deter perching and roosting by birds. The spines prevent birds from settling on the growout or holding structures, and the fish are protected from fecal contamination by the birds. These devices are used on fish farms to prevent birds from perching on a structure near the water.
Homemade versions of these commercial products can be built by hammering nails through wood lath and attaching the lath at the appropriate location. Poles or posts may be guarded against perching birds by sharpening the end, by insertion of a guard spike, or by use of a sheet-metal cone over the end. These devices are useful in discouraging species that hunt from an elevated perch or at roosting sites where fecal deposits are unacceptable.
Fish Management
Fish management and the ability to adjust programs based on changing bird habits are as important as facility design.
Since fingerlings are more susceptible to bird predation, they should be located close to the center of human activity and near buildings that might be incorporated in a bird exclusion system. Larger fish usually need less protection because they are better able to avoid bird predators. A compromise strategy is to concentrate the more susceptible fingerlings under nets covering smaller ponds, and use larger ponds and an intensive bird harassment program to protect the larger fish.
Frightening
Frightening devices and techniques modify behavior and discourage birds from feeding, roosting, or gathering at a location. Many visual and sound-making devices are commercially available for scaring birds. These include gas operated exploiters, pyrotechnics, electronic noisemakers, bird distress calls, standing or pop-up effigies, eyespot balloons, raptor models, strobe or flashing lights, reflective plates or lines, and water spray devices.
The value of these devices is usually limited to short-term control. Although bird damage can sometimes be reduced by using only one type of frightening device, better results over longer periods are often achieved by using a combination of devices and/or by changing methods frequently.
In addition, scaring equipment, especially sound-making devices, is usually more effective when moved often to prevent birds from becoming accustomed to the device. Birds will eventually ignore any scaring device that is left in the same place or that emits sound in the same regular pattern over a long period of time.
Further Assistance
The Animal and Plant Health Inspection Service (APHIS) of USDA will provide assistance to aquaculture facilities that experience losses to birds. If required, on-site advice and instruction in the actual use of damage control methods is provided by the APHIS-ADC personnel. Kill permits are not routinely issued and are contingent on approval from APHIS and the US Fish and Wildlife Service. For information concerning assistance, permit applications, and sources of equipment and supplies, contact the appropriate state director of USDA APHIS-ADC.
Maximize Your Hatchery's Budget To Train Your Staff
By: MTAN
How often do you find yourself faced with the dilemma of having insufficient revenues to spend on your hatchery program? How frequently do you wish you had the opportunity to find good affordable training for your hard working staff? The MTAN would like to offer one option which may save your hatchery program training dollars that could be channeled to other areas.
Fish hatchery supervisors from state and federal hatchery systems are excited about sharing information with Tribal hatchery workers. One of the ways this exchange is taking place is through an "On The Spot Hatchery Experience." If you feel that your staff would benefit from a training visit to one of these hatchery facilities, please give a call to the MTAN so we can help to made the arrangements. Depending on your specific needs, this kind of training could be one or several days in length and could even be spaced out over a broad cross section of the fish rearing cycle. The only expenses incurred to your program would be for travel, meals and lodging.
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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. |
