170 FISH HATCHERY MANAGEMENT 



equilibrium they become inactive. Opercular movement decreases. When 

 the fish can no longer make swimming movements, the respiration becomes 

 quite rapid, and opercular movements are difficult to detect. At this point, 

 the fish may be removed from the water and spawned. If gasping and mus- 

 cular spasms develop while a fish is being spawned, it should be returned 

 to fresh water immediately. If the fish has been overexposed to the drug, 

 respiratory movements will cease. Rainbow trout placed in a 264 parts per 

 million solution of MS-222 require 30 to 45 seconds to become relaxed. 

 Concentrations of 0.23 gram of benzocaine per gallon of water or 0.45 

 gram of MS-222 per gallon of water are commonly used to anesthetized 

 fingerling Pacific salmon. 



Use of MS-222 as an anesthetic for spawning operations is widespread. 

 However, concentrations as low as 18.9 parts per million have reduced 

 sperm motility. Therefore, the anesthetizing solution should not come in 

 contact with the reproductive products. Adult Pacific salmon have been 

 anesthesized with a mixture of 40 parts per million MS-222 and 10 parts 

 per million quinaldine. Carbon dioxide at concentrations of 200-400 parts 

 per million, is used in some instances for calming adult Pacific salmon. It 

 can be dispersed into the tank from a pressurized cylinder through a car- 

 borundum stone. 



Both ether and urethane have been used in the past, but both should be 

 discontinued due to the high flammability of ether and the possible carci- 

 nogenic properties of urethane. 



Artificial Control of Spawning Time 



Management requirements and availability of hatchery facilities often make 

 it desirable to spawn fish at times different from the natural spawning date. 

 Several methods have been used with success. 



PHOTOPERIOD 



Controlled light periods have been used with several species of fish to 

 manipulate spawning time. The Fish and Wildlife Service's Salmon Cultur- 

 al Laboratory, Entiat, Washington, conducted a 3-year study to determine 

 the effect of light control on sockeye salmon spawning. The study showed 

 that salmon exposed to shortened periods of light spawn appreciably ear- 

 lier. Egg mortalities can be significantly higher, however. Light, not tem- 

 perature, is apparently the prime factor in accelerating or retarding sexual 

 maturation in this species; although temperatures varied from year to year, 

 salmon receiving no light control spawned at essentially the same time 

 each year. 



