Question
Hello,

I have a 30 litre coldwater Biorbe, in it I have 2 x 3" orfes, one
gold, one blue, and 4 minnows. One of the minnows has always
been noticably smaller than the rest of the shoal. All the fish
have been living together for over 3 months now. It was last
week that I noticed some sort of shannigans in the tank, the
smallest minnow was swimming up to the other minnows and
splaying his fins out, and in they did it back in return, it kept
following/chasing the rest of the minnows, and occasionally the
blue orfe would chase it back. I thought maybe this was either
some kind of mating ritual or it trying to make itself appear
bigger i.e. territorial. A couple of days after, I went to the tank to
feed them, and none of the minnows were to be found, for
hours! I saw them all hiding in the ornament on top of the filter.
Eventually the 3 biggest ones came out, but not the smallest.
The next day they were all out for feeding time, and I thought
the smallest minnow looked a bit raggy around its face and gills
and not smooth like the others. This morning when I fed them,
the small raggy looking minnow was balancing on some artifical
plants and breathing quite rapidly, and then the blue orfe came
right up to him and started frantically chasing him around the
tank almost to the point where I wanted to stick my net in and
poke the blue orfe away! Is my minnow getting bullied or do you
think its ill and what can I do?

Best Regards

Kelly Chapman

Answer
That is less than 8 gallons, very small.  The orfes may just fit in there now but they grow fast to about 1.5 feet long.  Add to that 6 minnows, and your tank is too small for 6 minnows or 2 baby orfe let alone both.  Fin displays can be fish trying to show off dominance and/or breeding related.  What species are the minnows and how big are they?  The orfes are way too small to have any reproductive desires.  The weak minnow is being bullied.  Orfe are predatory fish by nature.  Although they are too small to eat the other fish, they may chase them around.  I would get the orfe to a pond as soon as possible where they can grow and swim fast as they were meant to.  I would also check the pH, ammonia, and nitrite levels in the tank to see if they are too high which could explain the fish hiding.  You should do 30-50% water changes a few times a week to try to keep such a small tank under control.  The raggety minnow is probably in that shape from a combination of water quality issues and being chased and bothered by the other fish.  Good luck!

Robyn
fishpondinfo.com