Fish Hatchery Management - fisheries & aquaculture

FISH HEAL'IH MANAGEMENTDECONTAMINA'f IONThe actual administration of chlorine varies among hatcheries, so only generalprocedures will be given here. Decontamination methods should assurethat the full strength (200 parts per million) of the chlorine is maintainedfor at least I hour, and that a concentration of not less than 100 parts permillion is maintained for several hours. Many hatcheries are so large thattotal decontamination cannot be completed in one day. Treatment thenmust be carried out by areas or blocks, and started at the upper end of thehatchery.Before chlorine is added, all ponds, raceways, and troughs are drained.Additional dam boards are set in certain sections to hold the water to thevery top of each section. Rearing troughs are plugged, so they will overflow,and drain outlets from the hatchery blocked. The required quantityof chlorine then is added gradually to the incoming water that feeds thehead trough. The solution flows to the various rearing troughs' which areallowed to fill and overflow until there are 3 inches of the chlorine solutionon the floor. The incoming water then is turned off or bypassed. Thechlorine solution is pumped from the floor and sprayed on the sides andbottoms of all tanks and racks, the walls and ceiling, head trough, and anyother dry equipment for I hour. The same procedure must be used in allrooms of every building, with special attention being given to the foodstorage room. Undergroundpipelines must be filled and flushed severaltimes. If the hatchery must be decontaminated in sections, the work shouldbe so planned and timed so that all buildings, springs, supply lines, andraceways contain maximum chlorine at the same time, so that no contaminatedwater can enter parts of the system already treated. While a maximumconcentration of chlorine is being maintained in the raceway system,all loose equipment such as pails, tubs, trays, splashboards, and other materialmay be immersed in the raceways. Care must be taken that woodenequipment is kept submerged.Throughoutthe course of the project, checks should be made on theapproximate chlorine strength with the orthotolidine test or chlorine testpapers. If any section holds a concentration below 100 parts per millionchlorine after I hour, the solution should be fortified with additionalchlorine. Finally, the solution is left in the hatchery until no chlorine canbe detected in the holding unit. This may take several days.MAINTENANCE OFTHE HA'TCHERYAfter a hatchery has been decontaminated and is pathogen-free, recontaminationmust be prevented. The movement of any live fish into the hatcheryshould be forbidden absolutely and production should be restarted onlywith disinfected eggs. The spread of disease can be prevented only by rigid