Answer: Those which can adapt and withstand the high acidity levels of water.
The pond slowly becomes more acidic due to release of chemicals from a nearby factory. The chemicals released are acidic and toxic which will cause biomagnification in the pond water. Those organisms which can withstand the high acidic pH of water will survive. Others which can undergo adaptations can also survive.
pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction :)
