146 



FISH HATCHERY MANAGEMENT 





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Figure 45. Rotational line-crossing system based on three 

 lines. Each box represents a pool of fish belonging to a 

 specific line. Solid lines show the source of females used to 

 produce the next generation. The dotted lines represent the 

 males used in the mating system. Generations of offspring 

 from the original lines are presented on the left of the 

 columns. (Source: Kincaid 1977.) 



strains or the subdivision of a first generation strain hybrid is the preferred 

 method for line formation, because either of these tends to maximize the 

 initial genetic diversity within the base population. After the three lines 

 have been formed, the rotational line-crossing system can be implemented. 

 At maturity, matings are made between lines. Females of line A are mated 

 to males of line C to advance line A. Females of line B are mated to males 

 of line A to advance line B, and females of line C are mated to males of 

 line B to advance line C. Each succeeding generation is advanced by re- 

 peating this procedure (Figure 45). 



The rotational line-crossing system is flexible enough to fit into most 

 broodstock operations. At least 300 fish (50 males and 50 females from 

 each of the three lines) are needed for maintenance of the population, but 

 this number could be set at any level necessary to meet the egg production 

 needs of a particular hatchery operation. 



