Corydoras Bullying Another Cory?

Hi
I've been MIA for a few months for various reasons including my Mum passed away.  I was her carer for 9 years so it's been very difficult.  Anyway, I know where to come to ask fish-related qns! 

I have 5 panda corys in my 100l tank (for 5 months now).  4 are large but there is a runt in the litter that just does not seem to grow at all altho' I know it eats enough. 

I digress, my query is this:  I notice in the evenings 2 of the larger corys seem to pick on another large cory.  They swim either side of it and nudge it and generally get in it's way or chase it wherever it goes in the tank....even if it goes for a snooze.  Last night I couldn't take it anymore as they even rolled it onto it's back a number of times.  So not knowing what to do, I placed it in a small incubation tank overnight. 

This morning all seems calm and the isolated one looks like he is in one piece.  So I decided to put him back in the tank as it's only ever at night this 'bullying' occurs.  All 5 pandas are snoozing on the sand in a tight-knit group at present.

Any advice please?  I love my pandas!

Thanks Sue - yes, I was concerned about stressing all the fish trying to catch this one.  It isn't the small one being bullied, it's one of the large ones that is being bullied.  They all seem to leave the little one alone.

So 2 of the 3 larger ones are involved in this activity.  I will keep a close eye on them and see what happens and also look around for a friend with other pandas. 

Thanks so much for your help.   

Sounds exciting - wow, 1700s?!  Wishing you all the best with your ancestor hunt.   

Maybe it is the frisson of breeding happening - I'll try & see them from the top & see if that one is broader....hmmm interesting! 

Thanks!   

Welcome back, Sunshine.

One of the theories I had for my 6 pygmy cories' demise in the summer (lots of posts on here re that) was that, once one died, they weren't happy in a smaller shoal and it stressed them out, resulting in a domino effect of falling ill and dying.  Subsequently, I felt that a much larger shoal may have resulted in a much better outcome, and all the more so if the other fish were larger.  My hunch is that, with the other fish (tetras, harlequins) each being double the size of the cories, I might have been better off with 12 cories for every 6 fish that were double their size (in effect meaning that the small cories collectively would be the same size in fish cms/inches as the bigger fish collectively), and the cories might have fared better.

In your case, I wonder if increasing the shoal size to a minimum of 8 would help disperse or remove the aggression or competition or whatever's going on - it might improve the general group behaviour to be more natural at least, and it might also result in some similar-sized companions for your 'runt' or even ultimately for your larger ones.  If you happened to have more space, then you might even want to consider increasing the shoal size to more than that, depending on your other fish in that tank, their sizes (possibly along the lines of my untested hypothesis above) and area of the tank which they tend to inhabit (eg you wouldn't want the bottom over-crowded).

Just another option to add into the mix for you. Out of interest, what other fish do you have in that tank?

I know my males go through spates of 'hassling' my biggest female and it can look very aggressive. I read up on it and the males will keep nudging the female, forming a T shape of cories and when there's several males and 1 female in the mix it's a bit of a bun fight to be honest. Are they doing something like that?

They are peaceful but they're also vigorously amorous for want of a better description.

That's good news!

If you want to get them to breed, a trick a lot of people use is to do a water change when the pressure drops, and refill with cold water. This simulates melt water from the mountains, which signals spring. And feed them live food (or frozen live) at the next feed after the water change.

Congratulations! Sounds wonderful and must have been fantastic to witness.

Great news indeed and congratulations, I discovered I had an acquired extra cory once, I don't know where the little guy had been hiding until he was big enough to be seen.

Sue's tip with the cooler water works with celebes rainbows too btw.