BROODSTOCK, SPAWNING, AND EGG HANDLING 171 



Artificial light has been used successfully to induce early spawning in 

 brook, brown, and rainbow trout. The rearing facilities are enclosed and 

 lightproof, and all light is provided by overhead flood lamps. Broodstock 

 should have had at least one previous spawning season before being used 

 in a light-controlled spawning program. Eggs produced generally are small- 

 er and fewer eggs are produced per female. The following light schedule is 

 used to induce early spawning in trout. An additional hour of light is pro- 

 vided each week until the fish are exposed to nine hours of artificial light 

 in excess of the normal light period. The light is maintained at this 

 schedule for a period of four weeks and then decreased one hour per week 

 until the fish are receiving four hours less light than is normal for that 

 period. By this schedule, the spawning period can be advanced several 

 months. Use of broodfish a second consecutive year under light-controlled 

 conditions does not always prove satisfactory, and a controlled-light 

 schedule must be started at least six months prior to the anticipated 

 spawning date. 



Most attempts at modifying the spawning date of fish have been to 

 accelerate rather than retard the maturation process. However, spawning 

 activity of eastern brook trout and sockeye salmon have been delayed by 

 extending artificial light periods longer than normal ones. Temperature 

 and light control are factors in manipulating spawning time of channel cat- 

 fish. Reducing the light cycle to 8 hours per day and lowering the water 

 temperature by I4°F will delay spawning for approximately 60-150 days. 



The spawning period of largemouth bass has been greatly extended by 

 the manipulation of water temperature. For example, moving fish from 67° 

 to 61°F water will result in a delayed spawning time. 



HORMONE INJECTION 



Spawning of warmwater and coolwater species can be induced by hormone 

 injection. This method has not proven to be as successful with coldwater 

 species. Fish must be fairly close to spawning to have any effect, as the 

 hormones generally bring about the early release of mature sex products 

 rather than the promotion of their development. Both pituitary material ex- 

 tracted from fish and human chorionic gonadotropin have been used suc- 

 cessfully. 



Use of hormones may produce disappointing results if broodfish are not 

 of high quality. Under such conditions, a partial spawn, or no spawn at all, 

 may result. It also appears that some strains of fish do not respond to hor- 

 mone treatment in a predictable way, even when they are in good spawn- 

 ing condition. 



Injection of salmon pituitary extract into adult salmon hastens the de- 

 velopment of spawning coloration and other secondary sex characteristics, 



