Final answer:
The fish experienced sympatric speciation and were reproductively isolated due to male coloring differences. Pollution causing water cloudiness could lead to interbreeding and a breakdown of reproductive isolation, resulting in hybrid offspring or gene flow between species.
Step-by-step explanation:
The sympatric speciation mentioned refers to the process where new species evolve from a single ancestral species while inhabiting the same geographic region. In the scenario presented, two species of fish that have undergone sympatric speciation have become reproductively isolated due to differences in their mating signals, specifically male coloring. However, the introduction of pollution is likely to reduce the visual clues that the females use to differentiate males, potentially leading to a breakdown in reproductive isolation.
Reproductive isolation can occur in various forms, one of which is temporal isolation, where different species have different mating seasons. However, in this case, the reproductive barrier is initially based on visual mate recognition, which the pollution interferes with. If females can no longer distinguish between males of their own species and the other, they may interbreed, creating hybrid offspring or leading to gene flow between the species. This could ultimately result in the merging of the two species or the emergence of new hybrid species.