10 



become completely inert and hang limply in the hand while being 

 inspected. Such fish recovered slowly when returned to the water. 



Lewis (1969) observed what he called fighting, with con- 

 sequent mutilation among catfish when stocked in cages at den- 

 sities of less than 50 to 75 fish per cubic yard (65 to 98 fish 

 per cubic meter) , and recommended stocking cages at a density of 

 150 fish per cubic yard (196 fish per cubic meter) to eliminate 

 this problem. Collins (1970) used cage densities of 160 per 

 cubic yard (209 per cubic meter) with no fighting or mulilation, 

 and Schmittou (1969) used densities as high as 382 fish per cubic 

 yard (500 fish per cubic meter) with no loss attributed to mutila- 

 tion of one fish by another. Our cage densities were in the range 

 of 180 to 185 fish por cubic yard (235 to 242 fish per cubic meter) . 

 In our case, hov;ever, mutilation occurred quite erratically and 

 was not the principal cause of death. For example, mutilation of 

 fishes was much more prevalent in cages suspended in ponds 1 and 

 5 than in pond 2, but pond 2 fishes had a higher rate of mortality 

 (46.1%) than those in either pond 1 (21.0%) or pond 5 (36.6%). 



In an effort tc more clearly define the problem, we decided 

 to add beef liver to the diet of some fish, and to increase the 

 density of others, A divider was placed in one cage in each of 

 ponds 1 and 5 so that the fish v/ere crowded into an area having 

 2/3 of the former volume. These fish were fed the normal ration, 

 with no liver. In the remaining cage in each of these ponds the 

 fish were maintained at their former density and their pellet diet 

 was supplemented by a substantial amount of beef liver. In 14 days 

 it became clear that less mutilation v;as occurring among the liver- 

 fed fish than among the more crov;ded fish, and all caged popula- 

 tions were placed on a liver diet. The series of observations 

 seemed to indicate that the problem v/as more one of diet than of 

 density, and this sesmed to be confirmed in our later study in 

 which caged populations receiving Purina trout chow, a more complete 

 diet, exhibited no fighting or mutilation in any of the caged pop- 

 ulations . 



CAGED CHANNEL CATFISH IIT PUBLIC FISHING WATERS 



Materials and Methods . — We conducted a test to determine 

 if channel cctfish could be successfully reared in cages floated 

 in a congested area of a public fishing lake. A cage of 1/4-inch- 

 mesh (6 .4-millimster mosh) hardv/are cloth was suspended in a boat 

 slip in the center of a complex of docks in 585-acre (236 . 7-hectare) 

 Stephen A. Forbes reser'v'oir where both pedestrian and boat traffic 

 passed within a few feet (meters) of the cage. The cage was 8-feet 



