I would say that there's a great number of investors looking at two things: the use of technology to forward sustainable seafood and to improve aquaculture. Those are things where it solves a problem and can scale quite rapidly.
There's a need for new fish feeds, because fish feed prices are really high. There is a need for new technologies to prevent disease in aquaculture, because otherwise there is too much risk in aquaculture production. There are growing local markets for seafood, especially in Asia.
"Sustainable" is a great word, but its use in this context is meant to obscure the actual truth: human beings are exceeding the limits of the Natural World in virtually every way (including by over-fishing our oceans). The right reaction to our "unsustainable" behavior would be to reduce our consumption, and to find a way to live within the limits of nature. Taking over natural processes, making them more dependent, in the end, on human action, is not the right approach. In Nature, it works the other way around.