I have a MAJOR problem with my oscars and I'm not real sure what to do . Here's the problem:
It started two nights ago.. I did what I always do, feed the fish and in a hour or two later turn the lights out and go to bed. The 1st night I heard a loud crash.. I didn't know it was from the fish tank so I'didn't check it when I turned the light on in the morning ... My 4" Oscar (Female) had chunks missing off her head and side not life threating but it must hurt. The male 3" oscar had no chunks missing but had a few scrapes. When light's go off she is sitting at the bottom moving gravel.. when any fish swims by her she shoots to the top of the tank and hit's her face .... Can someone please tell me what's going on. I had all the fish for quite some time. Other then that the JD's they have been in there 2 months I got them as fry.

They are in a 75g
Water is great never a problem test weekly with water/change and vac
Tank mates are all smaller by a long shot. GT,2 JD's, 2 small Plecos
Female Oscar is about 4" inches / Male is Maybe 3" inchs
Temp is 78
JD's are the newest to join the tank have been in there 2 months I got them as fry.
The only thing I did differnt is started adding Krill along with there other foods.

could be there are getting spooked by something when the lights are off. my guess would be the plecos but it really could be any of them. i doubt that the krill you have added for food has anything to do with it.

now you do know that your tank is way too small for all the fish you have listed. to house all of them for life you shoud look into to a tank in the 180 us gallon range.(along with proper filtration)

also how do you know you have a male and a female oscar. since they are to young to have bred did you have success in venting them? just curious

My female is a rescue had (HITH,Fins rot,and what I think was bad salt burns)... the place I got her form told me. My little O has been paired up with bigger O from the sec he was added to the tank , from what I've read it's a match. My fish are still very small I understand that they will need a bigger tank soon.. and I have that in the works. Not 180g but I do have 125g in the working. GT was a rescue as well he. Just curious, But you said "US GALLON" I'm guessing your not in the states ? I Follow the 1 inch per gallon rule... Is there more to it then that.. I would love some feed back

your right im not in the us im a little north of you.

as for the one inch rule this might apply to small community fish but large cichlids like oscars require large tanks. many people here will tell you that for 2 oscars no tank mates you will need a tank around 100 gallons add 2 jacks 2 plecs and a gt and you looking for even bigger like i said around 180. think of it like this your jacks and gt will grow toabout 8-10 inches, add 2 plecos and if there common plecos your looking at about 20 inches each add 2 more 14 inch oscars and suddenly a 125 is not as big as originally thought. big fish need big tanks. and huge filtration to go with it.

there are 2 major probs you will run into when these fish mature. the first is bioload. your water maintenace will be huge many water changes per week. secondly there will be the aggression problem. too many big fish not enough room to hide. a 125 might be ok if you rehome a couple of fish(im thinking the plecos myself).


whatever you do decide to do bestof luck with it.

The problem is, you are keeping both nocturnal and diurnal fish together in quite a small tank. Where the Oscars will normally sleep at night, plecs will be swimming around the tank, my guess is the Oscars are getting spooked by the fish that are active. When this happens, they could just swim into anything and hurt themselves. The other thing you've got to bear in mind is plecs can in some cases latch onto the side of a fish and remove the slime coating, this is when ulcers suddenly appear and people don't know why.

If it keeps happening, I would remove the pleco and see if things improve. However it must be said that your tank is too small for the fish you got so my advice would be either upgrade, or reduce the fish you've got before they get too much bigger.

That's my advice for what it's worth:)