Mdthbs

It makes sense to me that the best food in an underwater dome complex would be fish. Considering the massive amounts of aquatic life in the vicinity, it could work pretty well.

However, I can't think of how the people would actually catch the fish. They need to be able to breathe, so an airlock leading into a section of ocean wouldn't be useful (assume there is no underwater breathing technology nor submersibles available).

I've thought about some sort of net to catch them, but I'm not sure how the fish could be moved into the dome from there without flooding the place. If there were a way to catch fish on the sea floor (lobsters, crabs, etc.) easily, that would also work.

Assume the technology level when building the domes is that of today, but there will be no communication or supply deliveries from anywhere outside the domes (so nothing that would require extensive maintenance or consume too many non-renewable supplies).

Any ideas?

Fish traps are a convenient way to catch fishes and other sea creatures.

A fish trap is a trap used for fishing. Fish traps can have the form of a fishing weir or a lobster trap. A typical contemporary trap consists of a frame of thick steel wire in the shape of a heart, with chicken wire stretched around it. The mesh wraps around the frame and then tapers into the inside of the trap. When a fish swims inside through this opening, it cannot get out, as the chicken wire opening bends back into its original narrowness. Contemporary eel traps come in many shapes and sizes and are constructed of many materials. In earlier times, traps were constructed of wood and fiber.

Just put a suitable lure into the trap, and when the catch is done, pull the trap into a load-lock which you will evacuate from water before letting human access it.

Underwater domes will probably be located deep in the oceans. If you are under one of the major oceanic currents, then all you need is some dynamite.

Find a school of fish far enough from home for a blast to be safe and... well, blast. The fish will all die or be stunned, and they will float to the surface where a ship can gather them. The oceanic current will make sure that more fish will eventually pass by.

The advantage of this method is that since water is incompressible, explosions tend to have a far greater blast radius than in air, making fish much easier to catch with explosives than birds or game.

They need to be able to breathe, so an airlock leading into a section of ocean wouldn't be useful

Well, not so much. Freediving is very much a thing, after all, and has been for quite a considerable length of time. People have been able to variously dive to over 100m, swim hundreds of metres and hold their breath for about 10 minutes (probably not all three at once, mind you). You can look back centuries to find traditions of people diving without breathing gear to recover wrecks, pearls or food. Plenty of interesting stuff out there... have a read about ama divers, for example.

Once you're out in the water, spearfishing is a reasonable technique, and one often used in combination with free diving.

So all you really need is a moon pool or fast cycling airlock and a bunch of people willing to practise apnoea.

Now, the issues of diving illness and long term human viability at depth, that's a different matter...

Depending on the level of scientific realism you want, it should be possible to enable rod and reel "sport" type fishing activity from your underwater dome (even if the dome itself is kept at surface pressure, i.e. the humans inside aren't "saturation divers" spending long periods at depth pressure.

First, you need a "waldo" type manipulator system. These have existed for decades in deep diving submersibles; in this case, it would be optimized for the movement of the reel crank, a little casting motion, a sensor to feel the line tension (to detect bites). This lets the fisher operate the rod and reel in a "moon pool."

The "moon pool" is a sea-pressure chamber with an opening at the bottom to the sea. In surface vessels, these allow launching submersibles and ROVs from inside the hull, broadening the range of weather conditions for operations. In your colony dome, it provides a pressurized access to a water surface. The rod would be mounted by remote manipulators, or with the moon pool closed and the chamber pumped down to dome pressure.

When all is ready, the pressure is brought up to match the exterior, and the moon pool opened, so that the bait or lure can be cast into the pool and allowed to trail in the outside water. Assuming a continental shelf location (as opposed to abyssal), there is still some outside light, which might be augmented by floodlights outside the dome (to attract fish).

Once the bait is in the water, fishing operation would work much like surface rod and reel ocean fishing. Fish recovered through the moon pool would be stored in live wells (as are used in offshore recreational fishing), which could be sealed and brought inboard to be gradually depressurized (to cut down on exploding fish), before the fish are extracted to be consumed or sold.