When good fish go bad...

[jz]

Hello,
I'm just getting started in the hobby and have spent a lot of time reading this board while slowly setting up an FO tank. After many months, I have finally encountered a dilemma that I can't resolve through research. About 4 weeks ago I finally stocked my tank with 2 Lemon Butterfly fish (Chaetodon milliaris). I was told that they were good "beginner fish", and since butterflies have peaceful dispositions, I figured they would be great fish to start with. Anyway, the first 3 weeks went by smoothly. The fish adjusted well to the tank and each other. They exhibited great personality and appeared very healthy. Nevertheless, about a week ago the little one just snapped! A complete 180-degree role reversal. Suffice to say I was surprised to see the fish ripping around the tank, fins flared, bullying the other. It did remind be of all the cichlids that I used to keep in the tank from my fresh water days. Anyway, I was able to separate the two with a divider and, all is now temporarily well. Has anyone witnessed this sort of change in behavior with butterflies? Also any possible solutions besides finding a new tank for the little guy? I was thinking that adding new tank-mates might change the dynamics a little. Anyway, here are the tank specs:

75 gal AGA
Return Pump: Mag12
DIY Wet Dry: 4 gal bio balls
Skimmer: AquaC EV-90
UV Sterilizer: 25W Aquanetics

[BrianD]

Hi JZ

You might pick up a copy of this month's FAMA. There is a feature article by Scott Michael on butterflys, and he discusses many species.

As for your immediate question, juvenile butterflys can have a more aggressive disposition than adults. It may be that your smaller butterfly is still a juvenile, and may outgrow his mean streak. However, he may cause the other butterfly to stop feeding. I would remove him, and maybe replace him with a larger specimen.

FWIW, a 75 gallon tank is probably better suited to just one butterfly. They need plenty of swimming room.

Brian

[FMarini]

Hi:
i'll throw in some other ideas:
1) both B'flies were getting used to the tank, their tankmates and new surrounding. So they both were timid or scare. Now 1 month later, they feel comfortable, food is plentiful, no harassment, and the normal temperment of the fish is coming out. One B'fly sees the other as food competition.

2)-In that your dominant butterfly just reach sexual maturity, and the submissive one is a competitor(males).

Brians right on the money, butterlfies love room to swim. Time to decide which one you want to keep and return the other...else you 'll end up w/ one dead B'fly and a tank sick from the stress.
my opinion
frank

[jz]

Thanks for the input guys. They are still definitely juveniles (maybe 1.5"-2" long), but it would also appear that the aggresive butterfly felt comfortable and thus, competitive. I'll take him/her back to the lfs. Wouldn't be right to keep both of them penned up with a divider in the tank.
One last question. Any suggestions for tank mates? I was thinking of a snowflake moray, or maybe a radiata. Both seem pretty mellow, as long as they can't eat their neighbors.

Jeremy