TRANSPORTATION OF LIVE FISHES 355 



The formation of scum and foam on the surface of transport water may 

 result from drug usage or excessive mucus produced by large numbers of 

 fish hauled over long distances. Excessive foaming interferes with observa- 

 tion of fish during transit and inhibits aeration. To alleviate this problem, a 

 10"o solution of Dow Coming's Antifoam AF emulsion should be used at 

 the rate of 25 milliliters per 100 gallons of water. For maximum effective- 

 ness, the compound should be mixed in before drugs are added or fish 

 loaded. Antifoam is nontoxic to fish. 



Water Quality 



Oxygen 



The most important single factor in transporting fish is providing an ade- 

 quate level of dissolved oxygen. However, an abundance of oxygen within 

 a tank does not necessarily indicate that the fish are in good condition. 

 The ability of fish to use oxygen depends on their tolerance to stress, water 

 temperature, pH, and concentrations of carbon dioxide and metabolic 

 products such as ammonia. 



The importance of supplying sufficient quantities of oxygen to fish in 

 distribution tanks cannot be overemphasized. Failure to do so results in 

 severe stress due to hypoxia and a subsequent buildup of blood lactic acid, 

 and may contribute to a delayed fish mortality. Ample oxygen suppresses 

 harmful effects of ammonia and carbon dioxide. Dissolved-oxygen content 

 of transport water preferably should be greater than 7 parts per million, 

 but less than saturation. Generally, as long as the oxygen concentration is 

 at least 6 parts per million, salmonids have ample oxygen; however, should 

 carbon dioxide levels increase, more oxygen is required by the fish. Oxy- 

 gen consumption by fish increases dramatically during handling and load- 

 ing into the transportation tank. For this reason, additional oxygen (as 

 much as twice the flow normally required) should be provided during load- 

 ing and the first hour of hauling. The oxygen flow can be reduced to nor- 

 mal levels (to provide 6 parts per million in the water) after this acclima- 

 tion period, when the fish have become settled and oxygen consumption 

 has stabilized (see Stress, page 358). 



The addition of certain chemicals such as hydrogen peroxide has been 

 effective in increasing the oxygen concentration in water. However, a more 

 practical and economical method is to introduce oxygen directly from pres- 

 surized cylinders into the circulating water. 



Control of water temperature, starving fish before they are transported, 

 and the addition of chemicals and anesthetics to the water have reduced 

 hauling stress. 



