We had about 40 fancy guppies in a tank. 50/50 male/female. We realized the ratio was off and so we moved all the males to a new tank. These formerly peaceful males are now picking on eachother severely. Lots of tattered fins. We are kind of shocked because we expected them to get along better with more space and zero females. Is this normal for an all male guppy tank? Is there anything we can do to keep them friendly with no females in the tank? I did notice that the water temperature was a little high in the male tank. Is that related to aggression?

imo the females are dominant i dont know bout the guppies but thats the law of the land with mollies-well for my upkeeeping.my ratio was the other way for awhile alot of males than they started being stuck to power head intakes
hmmso i got a few more females to put the ratio right and now i have 1 male leftpoor guy hes 12-1 dont stand a chance my 1 female hold her brood forever than spits them out 3 at a time shes the queen i guess.my male is original came from the fw-moved up to bw.male mollie life is not that long from what i read.2-3yrs seems about right but wow these woman are killers they dont take no crap,i have a dalmation female ,well got 2 together and one is 4"shes monster but shes passive.these fish are very active thats what i like drink some coffee whatch thefishvery friendly

Guppies are always sex driven and if there is no females in the tank they will try to mate with anything around even other males. That is what is probably causing the damage to the fins.

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Gives a whole new meaning to getting tail.

ironbone: LOL Maybe you should limit the coffee before posting!!

IMO, they are probably fighting because no females. Did the set up you had before 50/50 work?? If so, I suggest you just go back to that. The books might say that the ratio is off but guppys don't read. Most likely sexual aggression causing the fin nipping. Guys are getting all revved up and no one help them out. Ever seen an all male prison where no one is having sex-not even in the showers with the other guys same thing. Get these poor guys some girls. Call in a few prostitutes if you have to LMAO!!! I try to keep a 3 to 1 ratio (3 females to 1 male) but my most basic rule is just whoever fights gets kicked out. I had 3 mollys in my daughters tank 1 female and 2 males (accidentally), The sail fin kept picking on the black molly or the sailfin got moved to a new tank in the living room and now has a female sailfin to pal around with....although he is usually pretty hard on her too but it seems a little more territorial then aggressive.

So, basically, keep an eye on them and either change the set up to something less aggressive or remove the nippers. But don't leave it too long. Fin nipping will probably lead to stress and the next thing you know you'll have sick guppys and then dead ones.

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10gal fry tank planted with Wisteria, Java Moss, Anuabis and Anacharis
35gal Sponge Bob tank with live bearing tropicals (daughters tank)
15gal planted with Swords, Java Fern, Wisteria and Red Rubin housing 10 fry and 2 bladder snails
55 gal with Oscar (future planted tank with angels and flowerhorns)
55 gal Community tank (platys, mollys, guppys, glass catfish, angels, phantom tetra, red eye tetra and swordtails)

I'm a long time guppy breeder. Yes, the males will smack each other around in the absence of females. One solution would be lots and lots and lots of plants so they can get away from each other. In a breeding program where you want any control, all male tanks have to happen. The only solution I've found is to under stock the tank and to over plant so the fish can get away from each other.

The proper ratio for guppies for peace and health is really 2 females for every male. 1 to 1 tends to lead to dead females, the males tend to harass them to death if there aren't more females than males.

Shredded fins doesn't tend to happen from fish to fish aggression, however. I would look at water chemistry, to make sure you don't have any water quality issues, such as ammonia, ph, carbonate hardness. Think about adding a little salt, guppies are actually a touch brackish ideally. Also check to see that you don't have too aggressive a water flow. I used to have torn fins in my 55 then I turned down my power head and the torn fins went away. They may like to dive head first into current, but their big fancy fins can't handle a lot of fast water.

I think I have over 100 adult guppies in the 220 and fry being born everyday. I put some angels in there for fry control. If I want fry I will put a few in a 15 gal tank and as soon as the fry are born I'll remove the adults.

__________________
SUCCESS IS MEASURED BY YEARS, NOT MONTHS!!!
220 Tank build
http://www.aquariumforum.com/f15/sta...late-3253.html