88 



FISH HATCHERY MANAGEMENT 



Figure 35. Diagram of a V-trap. Fish follow the wire screen into the V and 

 enter the cage, where it is difficult for them to find a way back out through the 

 narrow opening in the V. 



Physical characteristics of earthen ponds play an important part in the 

 efficient harvest of fish. Removal of all stumps, roots, and logs is necessary 

 for harvesting with seines. The pond bottom should be relatively smooth to 

 provide adequate and complete drainage. Low areas that will not drain to- 

 wards the collection basin should be avoided. 



Rearing Unit Management 



Sanitation 



Sanitation is an important phase of any animal husbandry. A number of 

 undesirable situations can arise when waste feed and fecal material collect 

 in rearing units. If fish feed falls into waste material on the pond or race- 

 way bottoms, fish will generally ignore it and it will be wasted. Excessive 

 feces and waste food harbor disease organisms and can accumulate in the 

 mucus of the gills, especially during disease outbreaks. Disease treatment is 

 also difficult in filthy rearing units because treatment chemicals may react 

 with the organic matter, reducing the potency of the chemical. The waste 

 material may become stirred up as the chemical is mixed in the water; this 

 can be hazardous to the gills of the fish. Tanks, troughs, and raceways 

 must be cleaned frequently, whatever species — cold-, cool-, or warm- 

 water — is grown in them. 



In large earthen ponds, accumulated waste may reduce the oxygen con- 

 tent of the water. This can become a severe problem during periods of re- 

 duced water flow in the warm summer months. 



