How do you reduce aggression in your fish tank?

Answer 1

AnswerYou haven't said what kind of fish you have, but it appears they are either fresh- or salt-water tropicals. I can't speak from experience about Saltwater Fish, but freshwater tropicals come in 3 basic temperaments - community (which means peaceful), semi-aggressive and aggressive. (They are labeled this way at PetsMart, for instance, if you want examples.)

• Community fish are usually totally peaceful, tend to school (prefer several of their species) and do not establish dominance within their school or across species. If you don't want to deal with aggression, pick these kinds of fish.
• Semi-aggressive fish can be single or schooling and can either give or deal with pesky, aggressive behavior to/from other fish, whether their own or other kinds. Several of these kinds of fish can only be kept one of a species (and these are often the more colorful males of the species), though you may be able to mix several species in one tank This kind of aggressive behavior includes chasing and nipping and can lead to the death of other fish if they are not nimble enough to outrun/hide or otherwise be impervious to this kind of behavior.
• Aggressive fish can usually only be kept one or a very few of one or only up to a couple of other species they are compatible with, tend to grow large, require lots of space, be carnivorous and will eat other fish, especially smaller ones. There is no good defense against this kind of behavior in the long run, you can only keep certain numbers and kinds of aggressive fish in one tank.

The key to dealing with this kind of aggressive fish behavior is balance, not a question of reducing it (as you have asked.) You have to know how many of each kind you can keep (one, a few or a school), what kinds are compatible, and then, based on the temperament of your particular fish you may have to fine tune it from there.

For instance, I keep a pretty aggressive, 'semi-agressive' planted freshwater tank. It includes an African Leaf Fish which has become full grown, large for his species, and definitely wants to be top-dog in the tank. Because he's pretty well-matched with the other fish (who either don't interest him or keep out of his way) he was picking almost exclusively on my Redtail Shark (full grown and quite a large fish.) Redtail sharks usually know how to avoid trouble - that's their ability to live in a semi-aggressive tank - so this poor guy was spending all day in the corners with the tubes and plants I put there to give him a protected place - but I was never seeing him except at night! So I decided to try to distract the Leaf Fish with another top-doggish type species and chose a (single) Gold Gourami.

I used to have a Blue Paradise Gourami with the Leaf Fish (when he was smaller) and those 2 were pretty well paired and fought almost exclusively between themselves. So what happened when I put in the Gold Gourami? He started picking on the Killifish, usually placid top-dwellers that don't interest or bother other inhabitants. So I have had to sequester the Killifish to give their fins a respite and see who the Gold Gourami will go after next. Meanwhile - the Redtail Shark has come out of hiding because on some level I haven't observed the Leaf Fish must not be chasing him back into the corner every time he sees him, probably sizing up the Gourami... So on it goes - balance.

Even with compatible semi-agressive species in the right numbers you are going to need to create hiding places and keep an eye on things. From what I have seen, once a balance has been established (either between 2 bullies or between a bully and a coward, they leave most of the other fish out of the fighting, predominantly) it stays that way until one of those 2 fish changes (dies or whatever) and then a new balance is sought. Balance, distraction, observation, fine-tuning - or keep Neon Tetras!