358 FISH HAICHERY MANAGEMENT 



distressed. However, elevated concentrations of CO2 can be tolerated if the 

 rate of buildup is slow. 



Adequate ventilation, such as air scoops provide (Figure 111), is a neces- 

 sity for distribution units. Tight covers or lids on the units can result in a 

 buildup of CO2 which will stress the fish. Aeration of the water will reduce 

 concentrations of dissolved CO2, if there is adequate ventilation. As men- 

 tioned previously, antifoam agents reduce foaming, which inhibits aeration 

 and contributes to the buildup of CO2. 



Buffers 



Rapid changes in pH stress fish, but buffers can be used to stabilize the 

 water pH during fish transport. The organic buffer trishydroxymethyl- 

 aminomethane is quite effective in fresh and salt water. It is highly soluble, 

 stable, and easily applied. This buffer has been used on 29 species of fish 

 with no deleterious effects. Levels of 5-10 grams per gallon are recom- 

 mended for routine transport of fish. The least promising buffers for fish 

 tanks have been inorganic compounds such as phosphates. 



Handling, Loading, and Stocking 



Stress 



Stress associated with loading, hauling, and stocking can be severe and 

 result in immediate or delayed mortality. When fish are handled vigor- 

 ously while being loaded into distribution units, they become hyperactive. 

 They increase their oxygen consumption and metabolic excretion. The first 

 hour of confinement in the unit is critical. Oxygen consumption remains 

 elevated for 30-60, minutes then gradually declines as fish become 

 acclimated. If insufficient oxygen is present during this adjustment period, fish 

 may develop an oxygen debt. The problem may be alleviated if oxygen is 

 introduced into the distribution tank 10 to 15 minutes before fish are 

 loaded, especially if the water has a low dissolved oxygen content. When 

 fish are in the unit, the water should be cooled. After the first hour of the 

 trip, the oxygen flow may be gradually decreased, depending on the condi- 

 tion of the fish. 



The total hardness should be raised in waters used to hold fish during 

 handling and shipping. The addition of 0.1-0.3% salt and enough calcium 

 chloride to raise the total hardness to 50 parts per million is recommended 

 for soft waters. Calcium chloride need not be added to harder waters, 

 which already contain sufficient calcium. 



Striped bass are commonly transported and handled in a 1.0% salt solu- 

 tion. Fingerlings should be held in tanks for 24 hours after harvest to allow 



