FISH HEALTH MANAGEMEN I 285 



DECONTAMINATION 



The actual administration of chlorine varies among hatcheries, so only gen- 

 eral procedures will be given here. Decontamination methods should assure 

 that the full strength (200 parts per million) of the chlorine is maintained 

 for at least 1 hour, and that a concentration of not less than 100 parts per 

 million is maintained for several hours. Many hatcheries are so large that 

 total decontamination cannot be completed in one day. Treatment then 

 must be carried out by areas or blocks, and started at the upper end of the 

 hatchery. 



Before chlorine is added, all ponds, raceways, and troughs are drained. 

 Additional dam boards are set in certain sections to hold the water to the 

 very top of each section. Rearing troughs are plugged, so they will over- 

 flow, and drain outlets from the hatchery blocked. The required quantity 

 of chlorine then is added gradually to the incoming water that feeds the 

 head trough. The solution flows to the various rearing troughs, which are 

 allowed to fill and overflow until there are 3 inches of the chlorine solution 

 on the floor. The incoming water then is turned off or bypassed. The 

 chlorine solution is pumped from the floor and sprayed on the sides and 

 bottoms of all tanks and racks, the walls and ceiling, head trough, and any 

 other dry equipment for 1 hour. The same procedure must be used in all 

 rooms of every building, with special attention being given to the food 

 storage room. Underground pipelines must be filled and flushed several 

 times. If the hatchery must be decontaminated in sections, the work should 

 be so planned and timed so that all buildings, springs, supply lines, and 

 raceways contain maximum chlorine at the same time, so that no contam- 

 inated water can enter parts of the system already treated. While a max- 

 imum concentration of chlorine is being maintained in the raceway system, 

 all loose equipment such as pails, tubs, trays, splashboards, and other ma- 

 terial may be immersed in the raceways. Care must be taken that wooden 

 equipment is kept submerged. 



Throughout the course of the project, checks should be made on the 

 approximate chlorine strength with the orthotolidine test or chlorine test 

 papers. If any section holds a concentration below 100 parts per million 

 chlorine after 1 hour, the solution should be fortified with additional 

 chlorine. Finally, the solution is left in the hatchery until no chlorine can 

 be detected in the holding unit. This may take several days. 



MAINTENANCE OF THE HATCHERY 



After a hatchery has been decontaminated and is pathogen-free, recontami- 

 nation must be prevented. The movement of any live fish into the hatchery 

 should be forbidden absolutely and production should be restarted only 

 with disinfected eggs. The spread of disease can be prevented only by rigid 



