In these times the cost of seafood is pretty high, not to mention all the contaminants they absorb. If you have the setup and the skills, you can run a shrimp or a crab farm, but it can be laborious. The best bet is a freshwater fish farm. There are many different fish that are great candidates for the task. Catfish, Talapia, perch, bream, etc. But it does take more than just putting fish in a barrel and letting them grow, if you're looking for sustainability. Planning a fish farm takes a bit of forethought and ingenuity. A stable sustainable farm has a multitude of uses. It serves also as a water source if all other sources are exhausted. The droppings are a superb fertilizer for your garden. And even better, the slurry at the bottom of the tank can be pumped directly into the trays of aquaponic garden setups. Most of the slurry will bet absorbed into the roots, and the remainder can be filtered and returned to the tank. The size of the tank has to be generous. Keep in mind, in a sustainable tank setup, there will be fingerlings and frye also. Having a filter net array will keep the frye from predating by the fingerlings. And the fingerlings will be separated from the adults. Keeping the fish isolated from other species and outside contaminants will assure they become a long term food source. In feeding your school, it is also a good idea to maintain a worm farm (in another article) or a mosquito trap will serve well.

For a simple tank, you can start with an elongated trough made of cement. It need only be a few feet deep and a few feet wide. The length is all your decision. For example, in a 10' (inside measurement) tank, a frye barrier at 2' and a fingerling barrier at another 2' will keep a majority of them separated. That gives you a 3'x3'x6' adult fish area, which can hold quite a bit since they are predominantly schooling fish to begin with. You can even use an above ground pool for the adults and keep the fingerlings/frye in the concrete tank.
For the fry barrier, a 1/4" mesh will do fine, while a 3/4" mesh will serve to keep the fingerlings from the adults. The longer they survive, the better their chances of becoming a providing adult. Another thing to consider is a 1/8" mesh 6" from the bottom. During their spawning, the fertilized eggs will fall through the screen, keeping them seperated from the other predators. It will be a task also to keep the breeding slurry from betting caught up in the droppings so you may have to use an anderwater hose to stir up the sediment so it can be picked up in the aquaponics pump.
If you feel so inclined, you can net the tank and separate the different sizes by hand. Once you have all the details worked out, the more efficient you will be in supplying/maintaining it. The main thing to keep in mind is making sure there is proper oxygen in the water. A common fountain setup will fix this.

There are a boatload of articles on the web about creating and running a fish farm, so I'll not bring them here