vats aerated by compressed air and by agitators 

 lost 69.0 and 42.0 kg per metric ton (6.9 and 

 4.2 lb. per cwt) , respectively; those in the cool- 

 er pond water incurred a 20.0 kg per metric ton 

 (2.0 lb. per cwt) loss. 



DISCUSSION 



All groups lost weight during the test period. 

 However, during the last few days of the test 

 some positive weight change readings were ob- 

 tained, indicating some of the groups, partic- 

 ularly those in Test "C", were regaining weight. 

 This seemed highly unlikely as none of the fish 

 were being fed and all were under stress be- 

 cause of the holding situation. We surmised 

 that these positive weight changes were caused 

 either by the test gear or procedure and were 

 not the result of fish growth. 



Perhaps some of these positive observations 

 could be attributed to misreading the weighing 

 scales; and, as the scale was calibrated prior 

 to each day's weighing, there could have been 

 some misadjustment. Another possibility was 

 that the scale itself was inaccurate. However, 

 this unit had been sent to the manufacturer 

 prior to the beginning of these tests for clean- 

 ing and reconditioning. It has since been 

 checked against other scales and found to be 

 accurate. It is doubtful any of these factors 

 would account for the large percentage 

 (23.0%) of positive daily observations ob- 

 served. 



We speculated that wind blowing on certain 

 days might have affected the suspended scale. 

 The weighing operations were conducted in an 

 open shed, and perhaps wind pressure on the 

 lift cable might be biasing the test results. 

 However, examination of meteorological obser- 

 vations for the general area does not support 

 this. 



One of the most reasonable explanations for 

 the positive weight gains was the possibility 

 that the fish became infected with hemorrhagic 

 septicemia, a bacterial infection which can im- 

 pair kidney function and cause water retention 

 and which would result in a weight gain. As 

 each test progressed, the condition of the test 

 population deteriorated and some of the fish 

 in all the test groups exhibited outward signs 

 of bacterial infection. However, none of these 

 fish was examined by anyone qualified to make 



a positive diagnosis of hemorrhagic septicemia, 

 nor was it determined that kidney damage oc- 

 curred. One other consideration that lends 

 support to a disease-caused weight increase 

 was that positive weights did not occur until 

 the third day of holding in any of the tests, in- 

 dicating a build-up time was required, as would 

 be expected in a bacterial disease. 



One known factor that biased our figures 

 was the presence of dead fish in the containers 

 at the time of weighing. We determined that 

 dead fish held in the plant's holding vats gained 

 weight. Samples of fish that averaged 764.0 g 

 (26.9 oz) were sacrificed, and, over a 24-hr 

 period, gained an average of 62.5 g (2.2 oz). 

 This weight increase amounted to 8.2% of the 

 beginning weight. A complication in utilizing 

 this information to adjust data when dead fish 

 were present was the fact that it was not known 

 when individual fish succumbed nor how long 

 they had been dead. Without this information, 

 appropriate weight adjustments for mortality 

 could not be allocated. 



Two additional factors that could aflTect 

 weight changes have been suggested for our 

 consideration; the time of last feeding and the 

 state of sexual maturity. During the period 

 the weight loss study was conducted, mid-De- 

 cember to late March, the influence of both 

 these factors would be minimal. However, at 

 other seasons of the year, particularly in late 

 spring, both these variables would have to be 

 accounted for in studying weight changes dur- 

 ing holding. 



Regardless of the cause, weight losses, par- 

 ticularly in the last days of Test "C", were 

 masked by unknown factors and losses would 

 probably have been greater than shown. We 

 are suspicious of the figures showing slightly 

 more weight loss in vats with compressed air 

 than those having agitators, and would like 

 further verification of this before accepting 

 this as fact. 



This study did not determine whether the 

 weight losses that occurred during holding 

 were evident in the finished product, the dressed 

 fish. This point and other factors encountered, 

 such as the eff"ect of fish density on mortality, 

 the damage caused by handling, and the possi- 

 bility of using cool water to reduce mortality 

 and weight loss would be worthwhile research 

 projects for future programs. 



