Respuesta :
Genetic variation is the variation in the DNA sequence in the genome of an organisms. Organisms of a species have similar characteristics but they are not identical due to genetic variation. Genetic variation is important in the survival and the adaptability of a given species of organism. Therefore, in this case lack of genetic variation necessary to adapt to change in the environment will lead to extinction of the fish species that lacks the variation.
The most likely outcome for any species lacking the genetic variation necessary to adapt to a changing environment is to become extinct over time. While other scenarios are possible (many fish species can change gender if the need arises), the basic premise of the question states that the fish lacks the ability to adapt.