If push ever actually comes to shove, bugs are way more efficient than fish. The fact you can’t buy a soldier-fly larva burger even if you want to, makes me think we’re far from peak meat.
Promising technology from aquaculture are algefarming which can be used for carbon capture or ecological alternative for animal feed, seaweed farming which can either be used directly in human diet or as animal feed, molluscs, shellfish and fish farms. Some shellfish are already heavily involved in water treatment and water quality control.
Insect farms in comparison seems more limit in use, and harder in terms of cultural change. There has already existed plenty of cultures that have depended on the ocean for their diet, similar to cultures in the past which primarily depends on vegetarian diet. All that might be required for a cultural shift is a nudge in the right direction with economical incentives.
What we need to do is make the externalities created by farming part of the food price, including the pollution they create. The artificial fertilizers, the fossil fuels, the energy costs, water pollution, eutrophication, the destruction of biodiversity and land usage. All of it need to be part of the price so that it incentivize a change in the dietary culture towards more sustainable production.
Getting people to change their culture is the hard part. Convincing people to eat less meat is like convincing a vegetarian to eat more molluscs. Almost impossible.