It's unlikely an aquatic species can achieve technological breakthroughs needed to spread like humans can. It would be very difficult for them to build fires, smelt metal, and create the advances based off of those tools.

While they can be extremely smart and adaptable, it's difficult to imagine how a species like that could develop machines.

Sure, there's possible ways around it, like natural vents and geothermal power, but why would they utilize these resources without a benefit like cooking?