Adaptability is built in on many organisms, rather than a random blind search process. Anoles lizards introduced to a Mediterranean island developed cecal valves within 35 years(!). Recently some insects were found to have actually borrowed genes from plants that helped survival. The old "Nature makes no leaps" evolutionary paradigm is in dire need of revision.
I used a similar word, "adapted", but probably the way to describe this is that there is plasticity where the genetics are always there and are ready to respond through an epigenetics response that is triggered by environmental cues both in the fish experiencing the environmental factors and their offspring. This is why even genetic clones, eg human twins, have notable differences that arise because of different epigenetic response arising from different environmental cues.
