Leo, I am going to have to disagree with some of the information you are receiving. I agree with some of it, but let's clarify some things. You mentioned that everything you are reading about sunfish (as a whole) can be fine in a 55. This is true, but as others mentioned, this depends on species, and doesn't talk about stocking levels (how many of that species can live in a 55). Yes sunfish are aggressive, particularly when they reach sexual maturity. There are two schools of thought when it comes to stocking sunfish, and I've used them all. Let's use a 55 gallon for example.
1) You could stock 1-2 medium-sized sunfish and provide plenty of vertical structure. This means you'd have plenty of room for fish to establish territory and break up line-of-sight (to prevent aggression).
2) You could stock 5-8 medium-sized sunfish. This crowds them to the point where no territory can be established, and no single (small, weak, or less aggressive) fish gets harassed. Just make sure you have sufficient filtration, and keep up with vacuuming the waste out because you will need to feed a lot the keep the fish full.
There is also a happy-medium that I really like and have done before with great success. Do 3-4 sunfish along with a small shoal of large-bodied, fast minnows (think Luxilus, large Cyprinella, or Nocomis or Semotilus chubs). The minnows are too large or fast for the sunfish to eat, and also provide a visual distraction that keeps sunfish occupied so they won't be harassing others all the time.
I've found that warmouth are the most passive of the Lepomis sunfish, and you won't have to worry about aggression from them. Most other sunfish can be vicious and harass others until they die. I can't speak for crappie, though. Just to let you know, I've used all three methods described above. My last sunfish setup was a 46 gallon bowfront with 5 western dollar sunfish and 3 warmouths (see my avatar). The setup lasted 3 years without a single hiccup. After three years, I moved the warmouth out because they were too big, but by then the dollars had reached there max size. Aggression immediately broke out, so I added two bluehead chubs. Once I did that, the tank lasted another year until I had to move cities.
1) You could stock 1-2 medium-sized sunfish and provide plenty of vertical structure. This means you'd have plenty of room for fish to establish territory and break up line-of-sight (to prevent aggression).
2) You could stock 5-8 medium-sized sunfish. This crowds them to the point where no territory can be established, and no single (small, weak, or less aggressive) fish gets harassed. Just make sure you have sufficient filtration, and keep up with vacuuming the waste out because you will need to feed a lot the keep the fish full.
There is also a happy-medium that I really like and have done before with great success. Do 3-4 sunfish along with a small shoal of large-bodied, fast minnows (think Luxilus, large Cyprinella, or Nocomis or Semotilus chubs). The minnows are too large or fast for the sunfish to eat, and also provide a visual distraction that keeps sunfish occupied so they won't be harassing others all the time.
I've found that warmouth are the most passive of the Lepomis sunfish, and you won't have to worry about aggression from them. Most other sunfish can be vicious and harass others until they die. I can't speak for crappie, though. Just to let you know, I've used all three methods described above. My last sunfish setup was a 46 gallon bowfront with 5 western dollar sunfish and 3 warmouths (see my avatar). The setup lasted 3 years without a single hiccup. After three years, I moved the warmouth out because they were too big, but by then the dollars had reached there max size. Aggression immediately broke out, so I added two bluehead chubs. Once I did that, the tank lasted another year until I had to move cities.
