Prevention 



In hatcheries 



Care of Ponds and Utensils 



In the care of ponds, troughs and raceways arrangements should be 

 made, wherever possible, to disinfect them thoroughly at least once a 

 year. This procedure is a "must" after a severe epidemic and 

 disinfection should begin at the upper waters first. Chlorine, because 

 of its efficiency in killing pathogenic organisms and of its low cost 

 has been found to be the most desirable chemical disinfectant for hatchery 

 use (Davis 1938, Fish 1939, Connell 1939, Hagen 19^0, VIolf 1940, 

 O'Donnell 1944 )• Before chlorination is begun all fish should be 

 removed. Chlorine is available in powder or fluid form which liberates 

 various amounts of "available" chlorine. 



One of the best papers on the disinfection and maintenance of 

 hatcheries is that vjritten by O'Donnell (1944) and for more complete 

 treatment of this subject the reader should consult that paper as only 

 general procedures will be given here. The concentration of chlorine 

 found by O'Donnell (1944) to be m.ost effective in all hatchery vrork is 

 200 p.p.m, When clean surfaces ai'-e kept moist with such a concentration, 

 O'Donnell (1944) found that disease producing organisms were killed in 

 less than 30 minutes. Although it is desirable to maintain the solution 

 at full strength, occasionally this is impossible, such as in the 

 treatment of raceways, owing to dilution, but under no conditions should 

 the concentration fall below 100 p. p.m. according to O'Donnell (1944). 

 At 100 p. p.m. disease producing organisms are killed in one hour or 

 less. O'Donnell (1944) says that mud, muck and other organic material 

 dissipates chlorine at a rapid rate and as much of such material as 

 possible should be removed. Before starting the actual chemical 

 disinfection of the hatchery, a number of preliminary operations are 

 necessary. All ponds, racevrays, and troughs should be measured for 

 capacity and calculations made of floor surfaces in the buildings, 

 allo\Ting for 3 inches of solution on all floors. After determining the 

 type of chlorine solution or powder to be used, calculations are made of 

 the quantity needed to produce a concentration of 200 p. p.m. In the 

 event that the chlorine solution runs into fish-bearing rraters after 

 leaving the hatchery, neutralization T.all be necessary to render the 

 chlorine inactive and harmless. Commercial sodium thiosulphate ("hypo") 

 is used as a neutralizer, 5-6 grans being required to neutralize each 

 gallon of 200 p. p.m. chlorine solution. 



Before adding chlorine, all ponds, racevirays, and troughs should 

 be drained, Davis (1938) suggested allOYri.ng ponds to dry in the sun for 

 several days. Additional splash boards are to be provided in certain 

 sections to allow raising of the vfater to the top of each section. After 

 draining, the splash boards are installed and water is allowed to rise 

 until the particular section is about half filled. Then one-half of the 

 calculated amount of concentrated chlorine is emptied into the raceways. 



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