In the past, I have kept peaceful fish, that ends up being semi agressive, I have been told that water conditions can make some fish unnaturally agressive. Do you agree?

I have had platies who would fight all day and sneak up behind the cories to nip their fin, rasboras beating each other up, even guppies, I noticed that different guppies have different behaviors I have a tank with all male guppies and they never fought (same mother) I have brought new guppies and some can be quite aggressive to others. Is it the fish itself? the genes?

do you agree?

I do think that especially with common livebearers, much of it is down to the individual fishes personality and the number and genders of the fish of its own kind that its kept with. When i used to keep mollys, i never had any problems with them and they were amongst some of the most peaceful fish in the tank- but on the other hand i have heard reports from people here on the forum complaining that a molly/s of theirs is being very aggressive towards other fish.
When it comes to unusual aggression with peaceful livebearers, one of the only ways (which is not even a guaranteed success) to sort it out is to increase the numbers of certain genders of the livebearers type, so that the pecking orders become more complex and even between the fish etc.

I think the problem with a lot of common livebearers is that for countless years now most of them have been bred for appearances rather than robust health or good temperament. I'm sure the high level of inbreeding that so many common livebearers suffer from probably affects their mentality in a negative way to some degree- inbreeding does this with other animals at least a lot.
But i would still say that generally speaking guppys, mollys, platys and swordtails are still generally peaceful fish if stocked properly , although there's no doubt in my mind that there are certainly abnormally/unusually aggressive ones amongst these peaceful species out there.

Seems like my obvervations are correct!

I would love to get Cardinals, but the back of my head reminds me that they are fin nippers, they ARE tetras, same family as the piranha, I wouldnt want a tank of mini piranhas.

I used to have a school of 15 harlequins, the most dominant one killed everyone harlequin until there was 1 left. I do NOT want this to happen again.

Advices?

For those interested, out of all the small tropical community fish I have kept before, the Corys are the only fish that I can gaurentee to be peaceful. (Excluding the few rare aggressive cory species) and I have kept ALOT of species before.

This post has been edited by kevin007: Jun 13 2008, 07:31 AM

with any species of fish you will get the odd 'rouge' specimin who has clearly not read the book about how he's supposed to behave. There's very little you can do to counter against this, if you get one you can either accomodate it or re-home it.

As stated above the overbreeding and in breeding has caused some personality traits to become exaggerated so fish which used to be occasional fin nippers are now known for being trouble.

Environment is definitely a concern though, if you back any animal into a corner it’ll fight to get out, if you don’t provide a fish with the correct environment it will fight, this can be incorrect shoal numbers, water quality, lack of cover etc etc.

If you are experiencing a lot of problems with supposedly peaceful fish there may be a deeper problem with your tank, can you give us some more details on your set up and we’ll see if we can spot what the problem is

My fish are generally peaceful now, but in the past I have faced these problems and i have recently read someone explain the unusual aggression and i thought i could relate.

I guess I'm not the only one with this problem then.