who is killing my cories?

[odobenus]

short version:
Our 55 gallon tank houses 1 red tailed black shark, full grown, 1 gold severum, about 2.5 inches long, 6 Buenos Aires tetras, each about 1 inch long, and 2 ottos. On Thursday (5 days ago) we added 6 small (about 1/2 inch long) pseudo Julii cory cats. Today I found two of them dead, and one missing its tail. Who is attacking them?


long version:
A while back I asked for advice on stocking our new 55 gal. You can read the topic here.

We moved the fish from the 10 gal, added more tetras, and one gold severum. Everything was fantastic. We did not lose a single fish.

We put off adding the cory cats until last week. We bought 6 Julii cory cats from the LFS. (They are not true Julii, but they are still really, really cute.) We do not have a quarantine tank (which I am well aware is a terrible thing) so they went right into the 55 gal. I let the bags float in the water for a while, then added some tank water and let them sit a while longer before netting them into the tank. The tetras nipped at them for a while, then settled down.

Today I did a pwc and found two dead cories. Their tails were missing, which I assumed was from being nibbled on after death. I noticed one of the remaining cories, however, is missing its tail. That means either (a) someone else in the tank bit it off, or (b) it rotted off. I checked the tank parameters: 0 ammonia, 0 nitrites, <5 nitrates. (I had been cleaning the tank well in preparation for the cories.) Other than the nipping tetras when they were first introduced I have not seen any aggression.

Did I just buy sick cory cats, or is someone harassing them? What steps should I take to protect the remaining cories? We have a 10 gal planted tank, with a gravel substrate, with a male betta. Would it be better to move the cories to the 10 gal, even though the gravel might be hard on their barbels?

 

[JustOneMore20]

Red tail black sharks are really territorial. My guess would be that it attacked your cories.

I think I would move them to the 10g. As long as the gravel isn't sharp, it will be fine. I have cories in my 29g with gravel and it is more rounded so it doesn't bother them.

I don't think I'd try to keep any more bottom feeders with the RTBS unless they can hold their own against him...that leaves cories out. I'm not sure about loaches...I don't think I'd try it. Really, its hard to stock other bottom feeders when you have a RTBS. They don't like to share their space.

 

[lovemybarbs]

my shark was fine until I introduced new fish. I'd say it is him.

 

[odobenus]

grrr. Silly shark.

I know that my cory cats should be in at least a 30 gallon tank when full grown. How long will they be okay in the 10 gallon tank? Until they are about an inch long?

 

[Menagerie]

With only 3 or 4 cory cats in a 10 gal tank and proper tank upkeep, they should do fine for a while. Since you do not know the true species of cory, it's hard to judge how long they can stay in a 10 gal before growth is restricted. If they are smaller cories, then a 10 gal may be fine for a long time. Keep in mind that the betta may not like its new tank mates and you may need yet another backup plan

 

[lyquidphyre]

Is it possible they died because they were new (just couldn't handle the stress) and then someone (like the tetras or the RTB shark) ate their tail AFTER they were dead?

EDIT- reread the post

I have a RTB shark, and when I first got cories, their tails were nibbled at but after a while whoever (assuming my shark) left them alone after territory was established. Its possible the RTB shark was picking on them, but the stress of being new AND being picked on killed them

 

[odobenus]

Phoey, phoey, phoey.

If there is a chance the betta would be unhappy with them, too, along with the size-of-tank issues, maybe I should try to work something out in the 55 gal. I rearranged the rocks a bit. (It is a fairly large rock structure, and I couldn't move too much.) I also moved some of the plastic plants. I am hoping that will be enough of a change to tone down the RTB shark's aggression. (I still have not seen any of the fish pestering the cories.)

Which is less risky: hoping the RTB shark calms down (and part of it was just stress, like lyquidphyre suggested), or moving them to the 10 gal with a male betta who has never had a tankmate?

 

[lyquidphyre]

I would see how it works out- do the cories have their own hiding place?

My RTB shark has his own little place in my driftwood, and he gets slightly ticked (only sometimes) when fish hang out under the driftwood... but he especially does it to the newer fish until he gets used to them.

I would just wait it out a few more days and see how it goes.

 

[odobenus]

Well, it has been a couple of days now. I left the cories in the 55 gal with the potentially murderous RTB shark. The cory with the missing tail died, but the remaining three seem just fine. I think you were right, lyquidphyre, that it was a combination of stress/newness/being picked on.

Next question: If these three cory cats continue to do well, should we eventually add a couple more to bring their numbers up to 6? If so, how long should we wait before adding more cories?