108 FISH HATCHERY MANAGEMENT 



Figure 39. An essential instrument in any fish rearing opera- 

 tion is an oxygen meter. Catastrophic fish losses can be 

 avoided if oxygen concentrations are checked periodically and 

 the optimum carrying capacity of the hatchery can be deter- 

 mined. Several brands of meters are available commercially. 

 (FWS photo.) 



lost to the air. The water has a lower capacity for oxygen, and little of it 

 may reach the pond bottom. Planktonic animals have short life spans; as 

 more are produced during warm weather, more also die and sink to the 

 bottom, where bacteria decompose them — utilizing oxygen in the process. 

 Respiration levels are high, meaning that more metabolism is occurring 

 and more wastes produced. These also are stimulants to bacterial produc- 

 tion. So is any uneaten food that may be provided by the culturist. Both 

 oxygen production and consumption are very rapid, and the balance is 



