Answer:
The correct answer is - Resource partitioning.
Explanation:
Resource Partitioning is the method of differentiating in which there is differentiating in the resource and the source of nutrition so that there is no or less competition among the closely related species.
In this case, one of the species of the same size fishes spends more time on the surface of the tank, and the other spends on the bottom of the tank. This shows the example of Resource partitioning to avoid competition.
