Final answer:
The transfer of fish from one lake to another causes gene flow, which is the movement of alleles between populations and can introduce new genetic variation into a gene pool.
Step-by-step explanation:
When fisheries managers move fish from one lake to another, this causes gene flow, which is the correct answer to the question. Gene flow is the movement of alleles between populations and is an essential factor in evolution and biodiversity. When individual fish or their gametes are transferred from one lake to another, they carry their genetic information with them, which can then mix with the genes of the local population, potentially introducing new variation into the gene pool. This movement of alleles from one population to another can be due to various factors including wildlife migration, plant pollen dispersal, and human activities such as the intentional relocation of fish between bodies of water by fishery managers. It's crucial to realize that such actions can have significant ecological and evolutionary consequences on both the source and destination populations.