Fish Hatchery Management - fisheries & aquaculture

HAI'CHERY REqUTREMENTSITheoretically, gas bubble disease can be caused by any supersaturatedgas, but in practice the problem is almost always due to excess nitrogen.when water is supersaturated with gas, fish blood tends to become so aswell. Because oxygen is used for respiration, and carbon dioxide entersinto the physiology of blood and cells, excess amounts of these gases in thewater are taken out of solution in the fish body. However, nitrogen, beinginert, stays supersaturated in the blood. Any reduction in pressure on thegas' or localized increase in body temperature, can bring such nitrogen ourof solution to form bubbles; the process is analogous to "bends" in humandivers. such bubbles (emboli) can lodge in blood vessels and restrictrespiratory circulation, leading to death by asphyxiation. In some cases,fish may develop obvious bubbles in the gills, between fin rays, or underthe skin, and the pressure of nitrogen bubbles may cause eyes to buluefrom their sockets.Gas supersaturation can occur when air is introduced into water underhigh pressure which is subsequently lowered, or when water is heated. waterthat has plunged over waterfalls or dams, water drawn from deep wells,or water heated from snow melt is potentially supersaturated. Air sucked inby a water pump can supersaturate a water system.All fish-coldwater or warmwater, freshwater or marine species-are susceptibleto gas bubble disease. Threshold tolerances to nitrogen supersaturationvary among species, but any saturation over 10091, poses a threat tofish, and any levels over 110% call for remedial action in a hatchery. Nitrogengas concentrations in excess of 1059t cannot be tolerated by troutfingerlings for more than 5 days, whereas goldfish are unaffected by concentrationsof nitrogen as high as 120114 for as long as 48 hours and 105lirfor 5 days. whenever possible, chronically supersaturated water should beavoided as a hatchery source.CARBON DIOXIDEAll waters contain some dissolved carbon dioxide. Generally, waters supportinggood fish populations have less than 5.0 parts per million carbondioxide. Spring and well water, which frequently are deficient in ,xygen,often have a high carbon dioxide content. Both conditions easily can becorrected with efficient aerating devices.carbon dioxide in excess of 20 parts per million may be harmful to fish.If the dissolved oxygen content drops to 3-5 parts per million, lower carbondioxide concentrations may be detrimental. It is doubtful that freshwaterfishes can live throughout the year in an average carbon dioxide contentas high as l2 parts per million.A wide tolerance range of carbon dioxide has been reported for variousspecies and developmental stages of fish. chum salmon eggs are relatively