On the Bahamian island of Andros, mosquitofish populations live in various, now-isolated, freshwater ponds that were once united. Currently, some predator-rich ponds have mosquitofish that can swim in short, fast bursts; other predator-poor ponds have mosquitofish that can swim continuously for a long time. When placed together in the same body of water, the two kinds of female mosquitofish exhibit exclusive breeding preferences. Which type of reproductive isolation operates to keep the mosquitofish isolated, even when fish from different ponds are reunited in the same body of water

In the question, it is given that the mosquitofish of different habitat shows different behavior as per the availability of predators in the particular habitat. For instance, some mosquitofish can swim continuously for a long time in fewer predators area whereas predator-rich ponds have mosquitofish that can swim in short, fast bursts.

It is evident that they diverged from common species that isolated in different regions, their behavior got changed according to the presence of predators. Thus, the isolation is here, behavioral isolation.