Before the Gods divided the fish in different places, our cave stronghold survived mostly on fish. That was the best time we had. After that, we lost our main food resource. Many of us died. Others gone to upper world.
Good old times...
Also, mussels spawn only in shallows, they cannot spawn in deep water. Maybe it spawned by shallow tile, but very close to deep tile, so you wasn't able to step on it.
I think i'm good with your letters now.