Do the new anglerfish only spawn when the area is loaded in, or can you also fish them up?
Could you add grilled fish recipes (with FEP bonuses similar to cheeses) made from rare deep-catch cave filets? You could then add a chance to fish up a scary creature rather than a fish. The combat encounter could balance the rewards a bit and would discourage bots/early-world deep cave fishing?
This system would also make it easier for you to add more scary deep water creatures, since you'd just have to model it and then add it to the list of potential monsters that can be fished up (this would also prevent situations of overcrowded tunnels of annoying water monsters, as well as slimes)
Also, could you give the angerfish a skinnable hide sometime? They're large enough to deserve one imo