How do you get fish into the hatchery?

You put them in, one of each type you want. It will say that if you go up to it with a fish in your inventory. Salmon meat is not an entire fish, you need salmon roe if you want salmon, they are bugged and will probably give you nothing, so I would keep your salmon roe for alchemy. You can use clam meat though if you want clams, they never respawn though, or at least they never did for me, same with the slaughterfish eggs.

I wonder if Nordic Barnacles would work?

They don't unfortunately. I have tried

If you put slaughterfish in there does it attack you if you go in.When I go down to the dock Belrand likes to go swimming.I also have a fishing mod.I wonder if they would tear the net.

Hmm, never thought about slaughterfish to tell the truth. Try them out and see, then let us know.

I was attacked once by slaughterfish, but every other time they just let me collect everything, maybe it depends on how long you stay in one spot. But it takes a while to collect the clams if you put them in, and still they never attacked. The slaughter fish eggs never respawned, so apart from some eggs and the scales off the creatures when you kill them they seemed a waste of time. But still I suppose they look good swimming around in there.

Sheesh, I didn't think about the clams either!

I'm definitely going to throw some clams in the next time I'm there.I need to think about the slaughterfish.

The hatchery slaughterfish are totally tame in my game.

Nice.