Types of Diseases and Parasites

Transcription

1 Types of Diseases and Parasites Handout 11.1a Parasitic Diseases More than 1,000 species of parasites are found in or on North American freshwater fishes. Some are extremely harmful, even causing death, and some produce no detectable damage. The environment, as well as the condition of the fish, often has an effect on the parasite. In one situation it may cause no harm, but under other circumstances it may be very dangerous. Crowded fish conditions existing in hatcheries or small ponds are conducive to the production and spread of a large population of parasites. The result is usually damaging to fish. Algae Algae are one-celled plants that are rather unusual parasites of fish. An excess of algae decreases the dissolved oxygen level of the water, thereby suffocating the fish. Fungi A water mold is the most common fungus infection in fish. This mold, along with several related forms is often found on injured fish. These fungi eventually kill the fish. Fungi may infect dead fish eggs, enclose the adjacent healthy ones, and kill them. Protozoa All major groups of these one-celled (usually microscopic) animals have representatives as fish parasites. Trematodes (flat worms) Trematodes is a large group of parasitic flat worms, often called flukes. Tapeworms and Roundworms Fish may have adult tapeworms in the intestine or larval forms in the body organs or muscles. No one has determined if the intestinal forms do damage, but the larval forms, particularly the bass tapeworm, are often very damaging. Parasitic roundworms are often present in large numbers, both as adults and larvae. Some thorny-headed forms thrust their heads into tissue of the intestine, producing great damage. Leeches Leeches can be damaging if present in large numbers. Fish-lice These are parasitic copepods sometimes worm-like in appearance. The anchor worm, Lernaea 235 cont d

2 cyprinacea, is the most dangerous one. It has a large, forked head, which is anchored in the tissues of the fish. The wound often becomes infected with bacteria, fungi, or algae. Large numbers of this parasite will kill fish. Bacteria Mycobacterial fish diseases are of particular importance because they are so common and destructive. The most important are columnaris disease and gill disease. These are often triggered by stress caused by environmental conditions. Mycobacterial fish diseases are bacteria related but not identical to those which cause tuberculosis in humans and domestic animals. Fish are not considered a significant source of human bacterial diseases unless eaten improperly cooked or in a spoiled condition. Viruses There are a number of serious viral diseases of fish. Among them are the following: Infectious pancreatic necrosis (IPN), which has been reported from every major trout hatchery and trout producing area in the United States. Channel catfish virus (CCV), found primarily in the southeastern United States. Infectious hematopoietic necrosis (IHN), a disease reported only a few years ago, but now spread to at least four states. 236

3 OVERVIEW: FISH DISEASES AND PARASITES Transparency 11.1a Disease and parasite problems have arisen in nearly all of the 100 national fish hatcheries and in the 500 state and 1,200 commercial production units. The number of outbreaks has increased in recent years. The millions of sport and food fish lost each year to disease create a tremendous financial impact that is difficult to estimate. Diseases continue to spread around the globe. Whirling disease, a crippling and sometimes fatal disease to trout and salmon, was known only in Europe for many years. In the late 1950s, the disease was discovered in the United States, but how it spread to this country is unknown. 237

4 Transparency 11.1b COMMON CATFISH DISEASES The two most common serious and quite common diseases affecting cultured catfish are Hemorrhagic septicemia and Columnaris disease. A description of each follows. Hemorrhagic septicemia Symptoms of this disease include red streaks at the base of the fins and the underside of the fish, and, at times, bulging eyes. The disease occurs most frequently in the spring and summer as the water temperature rises. The disease is usually treated with medicated feed containing the antibiotic terramycin. Columnaris Characteristics of this disease include frayed fins and discolored grayish-white patches or sores on the skin. This disease also occurs most frequently in the spring and summer as the water temperature rises. Columnaris is treated in the same way as Hemorrhagic septicemia. 239

5 Transparency 11.1c WARNING SIGNS OF DISEASE Warning signs of fish suffering from disease or parasite infection include the following: a general loss of appetite or refusal to feed abnormal coloration and the erosion of the fins, scales, or skin abnormal activity such as flashing, twisting, whirling, or erratic swimming movement listlessness, weakness, and a lack of activity. Fish exhibiting any unusual form of behavior should be examined for the following: sore discoloration bleeding swollen areas tumors popeye small black or white spots abnormal growths on the head, body, or fins 241

6 Handout 11.2a Treatment of Fish Diseases Once the diseases or parasites have been identified, successful treatment depends on selecting the most therapeutic drug or chemical, calculating the correct dosage level, and administering it in an appropriate manner. Use caution many drugs or chemicals used to control fish diseases or parasite infections will kill fish if the dosage level is miscalculated. In addition, therapeutic chemicals react to environmental conditions such as water temperature and chemistry, and these conditions may cause the chemicals to become toxic. Producers recommend isolating and treating a few fish to determine the effectiveness of the selected chemical prior to treating all of the fish. Many of the substances available for the treatment of disease and parasites have not been approved by the U. S. Food and Drug Administration and by the U. S. Environmental Protection Agency for use on food fish. Certain drugs and chemicals used to treat fish are considered unsafe for human consumption (some are suspected cancer-causing agents). Producers should contact federal and state agencies to determine if the drugs or chemicals have been approved. Two Preventive Treatments Considered Effective When Transferring Fingerlings from a Hatchery 1. Place fingerlings in 10 parts per million (ppm) potassium permanganate for 1 hour, then wash with fresh water. Follow this with an application of 15 ppm formalin for 5 to 12 hours. Follow this with 1 ppm acriflavin for 5 to 12 hours. 2. Place fingerlings in 15 ppm formalin for 24 hours. Treat briefly with percent acriflavin. (The second step can be done during transit). 245

7 Handout 11.2b Estimating Water Quantity Knowing how to determine the volume of tanks and ponds is necessary for treating fish. To calculate the volume of a square or rectangular body of water, multiply length by width by depth of water. This will result in cubic measurements for volume. Cubic feet is the measurement most commonly used. Use the same units of measure for each unit to be treated. To obtain the volume of a pond, determine the surface acreage and the average depth of the pond. Multiply the number of surface acres by the average depth in feet to get the volume of the pond in acre-feet. Since one acre-foot of water weighs 2.7 million pounds, then 2.7 pounds of any material dissolved in one acre-foot of water gives a solution of one part per million (1 ppm). The chart below presents weights of chemicals that must be added to one unit volume of water to give one part per million. Conversions for One Part Per Million Amount of Active Unit of Parts Per Ingredients Volume Million 2.7 pounds acre foot 1 ppm 1,235 grams acre foot 1 ppm 1.24 kilograms acre foot 1 ppm grams cubic foot 1 ppm 1 milligram liter 1 ppm 8.34 pounds million gallons 1 ppm grams gallon 1 ppm Factors to consider in calculating the amount of chemical needed include The Fish What are the tolerable limits of the fish to the chemical? The Water What water quality factors characteristic to the water will affect the chemical being used? 247 cont d

8 Could hardness or cloudiness increase the effect of, or render ineffective, the chemicals being used? The Chemical What percent active ingredients does the chemical have? The Pond Size What is the exact volume of water to be treated? Many fish have been killed because pond volumes have been exaggerated. A slight increase in calculated pond size over actual size will cause an overdose. On the other hand, an underestimation in size may result in an ineffective treatment. 248

9 Handout 11.2c Controlling Diseases No known effective cures exist for some fish diseases and parasite problems. Further, treatment of diseased or parasitized fish is often expensive, complicated, and rarely successful. Fish are very susceptible to a wide variety of disease-causing viruses, bacteria, and fungi, as well as parasitic worms, leeches, grubs, and lice. All of these occur naturally in fresh water ponds. The most effective control is prevention. Preventive measures include the following: Stocking healthy fish from disease-free commercial hatcheries Excluding wild fish Refraining from transferring fish from one pond to another Following recommended stocking rates to prevent overcrowding Avoiding adding fertilizer to ponds containing caged fish to prevent growth of nuisance algae and increased plant respiration Avoiding environmental stresses such as crowded conditions, improper handling, low oxygen levels, poor feeding practices, temperature shock, and high waste product build up. State and federal governments, as well as private industries are working together to provide closer inspection programs similar to the livestock industry system coordinated by the U. S. Department of Agriculture. Proposals to control fish diseases include the following: Authorizing legislation to establish a national fish disease-control program Expanding fish disease research and chemical registration Improving diagnostic and fish inspection services Increasing use of current control knowledge Maintaining cooperative efforts by all segments of the fisheries industry. 249

10 Transparency 11.2a CONVERSIONS FOR WATER TREATMENTS 1 acre-foot = 1 surface acre of water 1 foot deep 43,560 cubic feet 2,718,000 pounds of water 326,000 gallons of water 1 cubic foot = 7.5 gallons 62.4 pounds of water 28,355 grams of water 1 gallon = 8.34 pounds of water 3,800 cubic centimeters 3,800 grams of water 1 quart = 950 cubic centimeters 950 grams of water 1 pint = 475 cubic centimeters 475 grams of water 1 cup = 240 grams of water 1 tablespoon = 14.8 grams of water 1 teaspoon = 4.9 grams of water 1 pound = 454 grams 16 ounces 1 ounce = grams 1 liter = 1000 grams of water 251

11 Transparency 11.2b PREVENTIVE MEASURES Monitor Water Quality Environmental factors such as water temperature, dissolved oxygen content, and ammonia content are key elements in determining the quality of water. Avoid Handling Fish are stressed by being handled and are especially susceptible during hot weather. Monitor Population Density The possibility of contagion and of nutritional deficiencies increases as population density increases. Disinfect Equipment Equipment used in more than one body of water is a contributing factor to the spread of disease or parasites. Spray or immerse nets and other equipment in a solution of chlorine bleach, lime water, and diluted formalin. Wash in soap and water items such as feed and fish containers, water quality instruments, and boots and other items of clothing. During disease breakouts, keep equipment used in an infected pond separate from other equipment. Inspect Fish and Water Visit each culture site daily to inspect the condition of the fish and the quality of the water. 253

12 Transparency 11.2c PROBLEMS IN DIAGNOSIS Accurate diagnosis requires expensive, time-consuming tissue culture preparation, blood chemistry analysis, microscopic examination, and laboratory tests. Factors that complicate accurate diagnosis include the following: Fish may be stricken by more than one disease or parasite. Hundreds of types of diseases and parasites affect fish. Tissue decomposition in dying fish often masks the symptoms. Pollution, poor nutrition, rough handling, and other stress-related factors may be the initial source of the problem. 255

13 Transparency 11.2d AID IN DIAGNOSIS Producers sometimes seek help from local fisheries, biologists, or fish hatchery managers in diagnosing fish diseases and parasite infections. These specialists need as much information as possible to determine the cause of problems. Provide the following information when seeking help in diagnosis: County Pond owner Phone number Address Pond acreage Average pond depth (or maximum pond depth) Presence of wild fish in the pond Number of fish stocked in pond Number of each species lost each day Estimated percentage of population lost Day and time of day when losses started Description of symptoms or signs of sickness Day when the symptoms first occurred Size of fish affected Total number of fish affected 257