Impact of Fish Diseases and Environmental Changes

1. Fish diseases and the environmentPaul R. Earl and Arcadio Váldez GonzálezFacultad de Ciencias Biológicas Universidad Autónoma de Nuevo León San Nicolás, NL 66451pearl@dsi.uanl.mx

2. Healthy fishes are compromised by unfavorable changes in their habitatThe major feature of the epidemiology of fishes is the rise of the proverbial opportunistic pathogen. Fishes are normal in healthful environments, and this is obvious. The same fishes and the waters they live in usually carry the same microorganisms, many of which are opportunistic pathogens. Overcrowding leading to disease is quite likely in commercial ponds of fishes.

3. Overcrowding with low oxygen and high secreted ammonia is the major cause of disease, and ciliated protozoa can be leading pathogens as aeromonads and other bacteria might be. Viruses are much less often causes of disease. Nonetheless, viruses like Salmon Anemia Virus cause millions of dollars of quick losses without considerations of environmental deterioration.

4. Billions of humans demand more and more nitrogen-based fertilizer to make food. Some consequences are: 1. elevated CO2, 2. climate change via greenhouse gases, 3. land-use change, 4. loss of biodiversity, 5. biological invasions, and 6. increased N fixation. Human activities are having global consequences.Nitrogen and other gases of the global warming trend are poorly studied in regard to fishes. Nearly one third of the Earth's land surface is devoted to raising crops and domestic animals. Large areas of diverse natural vegetation with soybeans, peas, alfalfa and other leguminous crops have changed the environment. The burning of fossil fuels such as coal and oil releases previously fixed nitrogen, causing the further escalation of atmospheric nitrogen.

5. The waters of some streams and lakes are also being acidified by industrial pollutants like sulfides. Excess nitrogen is being transported by rivers into estuaries and coastal waters. Has this unprecedented nitrogen loading contributed to long-term declines in coastal fisheries and accelerated losses of biological diversity in both aquatic and land-based ecosystems?Overextraction of freshwater by pumping in many places can lead to salination, and the invasion of salt tolerant fishes as in the Rio Grande. Pollution and overextraction of freshwater are foremost problems and relate to human overpopulation.

6. References for fish healthThe purpose of this lecture with its Spanish version is to acquaint you with fish diseases (fds), assuming you are interested in fresh or saltwater fishes as food, sport or in decorative aquaria. As a scientific field of interest fds are poorly developed, lacking organization and cohesiveness.

7. More literature on the netSouthern Regional Aquaculture Center (SRAC), the University of Florida (UF) and the University of Texas (TAMU) are congratulated for their excellent contributions to fish health.SRAC 4700, “Saprolegniasis (winter fungus) and Branchiomycosis of Commercially Cultured Channel Catfish”SRAC 472, “Submitting a Sample for Fish Kill Investigation” SRAC 473, “Medicated Feed for Food Fish”SRAC 474, “The Role of Stress in Fish Diseases”SRAC 475, “Proliferative Gill Disease(Hamburger Gill Disease)”SRAC 476, “Ich (White Spot Disease)”SRAC 477, “ESC—Enteric Septicemia of Catfish”SRAC 478,“Aeromonas Bacterial Infections-Motile Aeromonad Septicemia”SRAC 479B, “Columnaris Disease”

8. NutritionWide ranging fishes can choose a balanced diet, whereas confined fishes cannot. Complete rations sometimes called aquafeed must be formulated to meet all nutritional requirements. About 3,500 kilocalories per kg of diet with 100 mg protein daily is also needed.Minerals and vitamins are of course needed. The growth should be 2 times the ration per kg of gain. Blood hemoglobin is 10 g/dL, hematocrit 32 %. The erythrocyte count is 1 million per cm of blood.

9. Aquaculture and moreGlobal production of farmed fishes and clams has more than doubled during the past 25 years, growing from 10 million metric or megatons (mt) to over 29 mt at the turn of the century. Meanwhile, harvests of ocean fishes have remained at around 90 mt. Regardless, wild fish stocks are overfished. Today aquaculture— the farming of fish, shrimp, clams and oysters — supplies more than one-fourth of all commercial fishes. A kilogram of the high-market-value species like salmon can cost 3 kg of cheap fishes.

10. Between 1986-97, 4 of the top 5, and 8 of the top 20 wild species harvested from the ocean were small fishes used in production of animal feed: anchoveta, Chilean jack mackerel, Atlantic herring, chub mackerel, Japanese anchovy, round sardinella, Atlantic mackerel and European anchovy.As aquaculture production continues to increase and intensify, both its reliance and impact on ocean fisheries are likely to expand even further. The future balance between farmed and wild-caught fish, the total supply of fish available for human consumption, and the health of the marine environment will depend on trends in aquaculture practices.

11. Deterioration of the environment and toxicityDifferent fishes live in a) fresh, b) brackish and c) saltwater. Seawater can have salts at g/L as :NaCl 28.014 MgCl2 3.812 MgSO4 1.752 CaSO4 1.283 K2SO4 0.816 CaCO3 0.122 KBr 0.101 SrSO4 0.028 H2BO3 0.028 as 3.5 % NaCl.

12. Fish killsTypical questions on a fish kill are: Where and when was the fish kill discovered? Size and depth of the pond? Source of water? What is the water temperature? What type and how many aquatic plants? Any recent agricultural spraying or animal waste runoff? Any recent thunderstorm or hot, cloudy weather? What species of fish were killed? Was just one species of fish killed?

13. A simple explanation of a fish killThe 100 % disaster was likely due to the shortage of oxygen. A fish kill can occur in fresh, brackish or saltwater. The degradation of domestic waste absorbs oxygen and promotes nitrite that uses oxygen to go to nitrate. Algae and protozoan dinoflagellates bloom enormously. A marine fish kill happens at the shore.In sunlight, microorganisms produce oxygen. At night, this plankton community uses it.You can see what will happen to the fishes and invertebrates in the early morning hours,More than one million fishes, primarily menhaden, were reported killed on August 20, 2003 in Narragansett bay, Rhode Island, USA. A fish kill of this magnitude demonstrates the fragility of the environment.

14. Organic wastes, nitrogen and acid lakes Coal-fired electric utility plants are the major source of pollution in the US, especially via the production of acid rain. Coal is of course the major competitor of oil.Our culture depends upon burning fossil fuels.Also nitrogen, relating to food demand, increases and supports the global warming trend. Aquaculture and overfishing are merely the RESULTS of social changes, including human overpopulation. However, the invention of ammonia production by Fritz Haber (1868-1934) for fertilizers solved the food shortage problem as visualized by Malthus (1766-1834). About 1900, the human population skyrocketed and so did nitrogen production thanks to the Haber process.

16. Pesticide toxicityMany of these compounds are anti-enzymes. For instance, mammals and fishes do not have the same enzymes that the invertebrate pests have. Lack of specificity is the main fault of the disinfectants formalin, copper sulfate, potassium manganate and outcompetimg introduced rainbow trout; rotenone might be used to eliminate all fishes, and trout reintroduced over a year later. Abate?

17. Immune responseFishes do not have lymph nodes and do not produce gamma globulin. Otherwise, they are rather similar to mammals. B & T lymphocytes are seen. Vibrio spp. and other bacterins have been commercially introduced. However, research in vaccines is far behind what it might be and this implies lack of incentive. One successful example is given. The disease ich or white spot can be controled by injecting vaccine of ground Ichthyophthirius multifilis. ALSO ! cilia from related Tetrahymena thermophia (T. pryriformis) give protection. By 3 weeks, injected or bathed fish were protected. Still, protection duration is merely guesswork.

18. Cancer Some fishes, particularly bottom-feeding ones, develop papillomas on the skin, lips, opercula and fins. These growths are infections caused by viruses that are sometimes intimately associated with carcinomas in man, i. e., papilloma viruses. Regardless, cancers (tumors) like visceral granuloma and fibromas and other neoplasms (cancers !) are rare in fishes, possibly because they don't live long enough.

19. Endangered speciesHealthy fishes are of course compatible with their environment. Fishes fill a given niche within ecological limits. Pollution diminishes their survival. Diseases can be approached with concern for physical factors like osmotic pressure, temperature, pH and oxygen saturation that are often neglected. The viability of fish eggs is still another inquiry.

20. The world fisheries are not sustainable.Large marine sanctuaries have been suggested. Georges banks at northeastern USA near the Canadian Grand banks has been closed for several years, because of depleted stocks of cod, haddock and flounder. Herring & mackerel have rebounded in 10 years. However, the species composition changed ! Will herring & mackerel now compete strongly with cod and other large fishes ? The food chain has changed.