Fish Hatchery Management - fisheries & aquaculture

276 FISH HATCHERY MANAGE,MENltoxicity of formalin to fish. Above 70'F, formalin becomes more toxic; theconcentration used for channel catfish should not exceed 167 parts per millionfor I hour (S.g ^ilhliters per l0 gallons;43.8 milliliters per l0 cubicfeet). At such high temperatures, concentrations higher than 167 Parts permillion should be used for bluegills or largemouth bass only with caution.In water temperatures above 50"F, salmonids become more sensitive tohigher concentrations of formalin, and treatment levels should not exceed167 parts per million for I hour. At higher temperatures and lower concentrationsof formalin, it may be necessary to repeat the treatment on two ormore successive days to effectively control ectoparasites without damage tothe fish. Aeration should always be provided during bath treatments toprevent low oxygen conditions from developing. At the first sign of stress,fresh water should be added to flush out the treatment.Formalin also can be used effectively as an indefinite treatment of mostfish species in ponds, tanks, and aquaria at 15-25 parts per million if certainprecautions are used. Do not exceed 10 parts per million as an indefinitetreatment for striped bass fingerlings because the 96-hour LC50 (theconcentration that kills 509il of the fish in 96 hours) is only 12 parts permillion. Formalin removes 1 part per million oxygen for each 5 parts permillion formalin within 30-36 hours, and it should be used with extremecaution, particularly during summer months, to minimize the chance of anoxygen depletion in the unit being treated. Formalin also is a very effectivealgicide so it should not be used in ponds with moderate to heavy phytoplanktonblooms. If it is necessary to use formalin in a pond that has aphytoplankton bloom, drain out one-third to one-half of the water prior totreatment. Within l2 to l6 hours after treating, start adding fresh water tobring the pond level back to normal.Fish treated with excessive concentrations of formalin may suffer delayedmortality. Rainbow trout yearlings, channel catfish fry and fingerlings, andbluegill fingerlings often are vulnerable in this way. onset of deaths canoccur anytime within I to 24 hours after treatment but may not occur until48 to 72 hours later, depending on species of fish, size and condition offish, and water temperatures. clinical signs associated with delayed mortalitiesinclude piping at the water surface, gaping mouths, excess mucus' andpale color. Formalin also is toxic to humans but the strong odor and eye irritationusually warn of its presence. A few people develop allergicresponses to formalin'COPPER SULFATECopper sulfate (registered by the Food and Drug Administration only as analgicide) is one of the oldest and most commonly used chemicals in fishculture and is considered to be 100'/o active. It has been applied widely in