Farming aquatic organisms is called Aquaculture. Fish and algae farming could be beneficial to a settlement. Aquaculture is more resource intensive than plant-based agriculture, but is often more efficient than growing terrestrial animals, especially as part of a wastwater and biomass recycling program.
Fish will likely be grown in enclosed tanks in dedicated areas of a settlement. Once resources are sufficient, some fish may be grown in community areas in open pools or in private aquariums as pets.
Single celled algae is grown in tanks of aerated (with carbon dioxide, nutrient rich water. Waste biomass and wastewater can be used as a nutrient source, as long as they ae free of toxic chemicals. When the algae has reached the desired population density, the water is filtered, and the algae removed for processing.
Multicelled algae, such as seaweed, can be grown in tanks.
As long as clean water and food is continually cycled, many sedentary species of mollusc can be grown at a relatively high population density. Commonly farmed molluscs include geoducks, abalones, and clams.
The various forms of aquaculture may be integrated with each other, or even with plants.