First I would test the pond to see what kind of organisms live there that could be food for these fish, such as algae, insects and other microbes that could be in the water. I would also examine other fish to see if one of the two the similar species could have evolved from another species. I would also see if the similar fish in a control area would mate. They could be competitors for mates, nesting grounds and food source or they could both have evolved from one species and adapted to the environment over time being they are secluded in a small pond. By checking the biotic and abiotic factors, the community ecology, nutrients, energy source, temperature and oxygen. This could all give us an idea of where near by did these fish come from before they got secluded in a pond.