Killer Guppies

[blb69]

We bought 10 guppies several weeks ago made up of two females and eight males. In the first two weeks the female killed three males before a male killed her. The tank settled down for a week or two, but now the males are back to attacking each other to the point that it looks like we're going to lose another guppy. Everyone keeps saying they can be aggressive while establishing a pecking order, but don't kill each other. Ours are. The only change is that we added some more plants in the last week, so I can understand that they may need to establish a new pecking order in the altered environment, but can anyone explain why our guppies are actually killing each other? These aren't tropical guppies - they were bred in cold water & so live in a cold water tank at 20 degrees celsius.

 

[rpgmomma8404]

Hmmm, that is interesting. I know I've been told you should have a ratio of one male to two females to keep the aggression down. I learned this after I got two male guppies for my ten gallon. They didn't really fight but the bigger one did pick on the smaller male guppy. There was enough hiding places in the tank though that the smaller guppy could easily get away from him when he was being mean. The bigger guppy ended up dying first but I think it was due to not having the tank fully cycled when I added them (shouldn't listen to the people at the pet store). 

 

[KittyKat]

Guppies can be quite agressive. The reason that it is recommended that at least two females are kept per male is that otherwise, the females can be over harrassed as the males have a pretty one-track mind. What you're seeing is exactly that.
 
FWIW, 20°C is really lower end of tropical when it comes to keeping fish.

 

[Lillefishy]

If you keep all males there will be less aggression as there'll be no females to fight over, they'll still bicker but will soon establish a pecking order & settle down