Had to last night give my rainbow shark to a mate who had a spare tank. Almost overnight it changed its behaviour. Last week it was a really placid fish, almost timid. Suddenly it was chasing everything (bronze corys, bristlenoses and guppies)

It was nibbling them and even butting them with his head! Suddenly every other fish was cowering.

Anyone else seen this sudden change in behaviour?

New territory suddenly thrust upon it. Very stressed with his new situation and possibly different water parameters. Hopefully he will settle down again.

i had 3 mollies all male, they got along well for 5 weeks since i got them. Then two weeks ago the largest attacked and killed the other mollies

It was really wierd it kind of snapped like it was hypnotised without the red eyes :evil:

hear is a quote about red tailed black sharks which i believe are from the same family

' ...this popular aquarium fish can be a nightmare - aggressive and quarrelsome with its own kind and prone to terrorizing companion fish. Keep with a group of 5-6 with other species only if they are large enough to fend for themselves.'

from: The Aquarium Owner's Manual - Gina Sandford

Maybe the same applies for your rainbow shark :-?

new info

'This freshwater cyprinid originates in Thailand and may not be a good choice for a community tank. They like to stake out their own territory in the tank. This territory can be in the form of small caves, rocks and even plants. They will become aggressive with smaller fish that invade this territory. Only keep one of this species in your tank because they will not tolerate another Rainbow or Red Tail Sharks in the same tank. They may exist together for awhile, but one will end up chasing the other relentlessly until the other succumbs.'

Fishlore.com

RTB sharks can be very peaceful until they reach a certain size, or age, then get very territorial. This is so of a number of species.

Yes, so maybe the Rainbow isn't quite right for the current tank :-?

Thanks, I guess he isn't right right for this tank. Pity as I really enjoyed watching him cruise around the tank.