The statement that a fish is able to breathe outside of water but does not reproduce is not necessarily a disadvantageous mutation. It is important to consider the context and environmental factors in which this mutation occurs.
If the fish species lives in an environment with fluctuating water levels or occasional droughts, the ability to breathe outside of water could actually be advantageous. It would allow the fish to survive in temporarily waterless areas and potentially access new habitats or food sources. In such a situation, this mutation might increase the chances of survival and could be selected for by natural selection, hence impacting evolution.
However, if the fish lives in a stable aquatic habitat with no need to go out of water, this mutation might not provide any significant advantage and may not be beneficial for survival or reproduction. In such cases, if the fish does not reproduce, the mutation would not be passed on to the next generation and would not be inherited by other fish.
It's important to note that the impact of a mutation on evolution depends on various factors, including the environment, mating behaviors, and overall fitness of the organism. Mutations that increase the fitness and reproductive success of individuals are more likely to be passed on to future generations.