Fish Hatchery Management - fisheries & aquaculture

FISH HEALTH MANAGEMENT 283lice, and leeches. The application rate is 0.25 Part Per million active (0.84pound of 80% W.P. per acre-foot). One treatment will suffice for monogenetictrematodes, leeches, and fish lice. For effective control of anchorparasites, Masoten should be applied four times at 5-7-day intervals'Because Masoten breaks down rapidly at high temPeratures and highpH, it may give inconsistent results in summer. If it must be used then, applicationsshould be made early in the morning, and at double strengthwhen water temperatures are above 80"F.E q uipment D ec on tamina tionThe following procedures for the decontamination of hatchery equipment istaken from irout and Salmon Culture by Leitritz and Lewis (tgZO)'Equipment sometimes must be decontaminated. One of the best andcheapest disinfectants is chlorine. A solution of 200 Parts Per million willbe effective in 30-60 minutes; one of 100 parts per million may requireseveral hours for complete sterilization. Chlorine levels are reduced byorganic material such as mud, slime, and plant material; therefore, for fulleffectiveness, it is necessary to thoroughly clean equipment before it isexposed to the solution. A chlorine solution also loses strength when exposedto the air, so it may be necessary to add more chlorine or make up freshsolutions during disinfection.chlorine is toxic to all fish. If troughs, tanks, or ponds are disinfected,the chlorine must be neutralized before it is allowed to drain or to enterwaters containing fish.One gallon of 200 parts per million chlorine solution can be neutralizedby 5.6 grams of sodium thiosulfate. Neutralization can be determined withstarch-iodide chlorine test paper or with orthotolidine solution. A fewdrops of orthotolidineare added to a sample of the solution to be tested. Ifthe sample turns a reddish-brown or yellow color, chlorine is still Present.Absence of color means that the chlorine has been neutralized'Chlorine may be obtained as sodium hypochlorite in either liquid orpowdered (gT'H) form. The latter is the more stable of the two, but it ismore expensive. The amount of chlorine added to water depends on thepercentage of available chlorine in the product used. As an example, HTHpowder may contain either 15,50, or 65% available chlorine. Therefore, thefollowing amounts would be needed to make a 200 parts per million solution:2 ounces of l5% available chlorine HTH powder to 10.5 gallons of water;I ounce of 50% available chlorine HTH powder to 18 gallons of waterlI ounce of 65% available chlorine HTH powder to 23.25 gallons ofwater.