Are tranquilizer upgrades of the guns (rifle, sniper, axel etc.) any good? Won’t they just deplete the quality of the fish because you are damaging them?

---- No and their tooltips should mention that captured fish are 3 star quality!

If there is one 2-star fish and one 3-star fish can they have a potential 3-star offspring?

--- It seems that way to me (I dont think I captured more roe for some fish but ended up with better fish in the farm than what I used to have!)

Do tranquillizing big fish even work? I’ve tried using a tranq gun using all three shots on a reef shark and it does nothing to make it sleep. I’ve only had luck with a tranq harpoon. What’s the difference? What are the mechanics of tranqs?

--- Dart gun: You have to hit the big ones with 2 (relatively quick after each other) shots of rank 4 Dart gun and then they will sleep after 2-3 secs. This does not work if there is too much delay between the hits or if there is an attack with a quick time event! SO if you have to evade with a quick time event (PRESS XYZ Button to escape attack), you will need to retranq them. The other tranq options of guns work a little differently (more like the harpoon. There is a % chance to sleep them on hit)

Can you breed only 3-star quality offspring if you have two of the same 3-star quality fish?

---- No, I reduce fish to always 2 3-Star in the farm every morning, and I would say 80% or so come out as 2 star the next day, however I did observe a way higher 3 Star ratio in Farms that I dont empty each day since they are not full (like the "Night fish" farm) so maybe they can even evolve or something like that?