Rainbow Problems

hi

hope you can help with this problem. i have a well-planted, 300L tank with a mixture of medium-sized fish. just recently my rainbows (2 reds and 3 bosemans) have started showing what look like scratches. fish are about 4 inches long and have half inch scratches along their sides. have attached a photo of the reds. scales are missing along a line - looks pretty nasty in the flesh. any ideas on whats happening?

i havent had any disease in the tank for about a year. no obvious signs of parasites. other fish include 2 angles, 2 clowns, pictus cat, 2 bronze cats, 2 plecs, 2 keyhole cichlid, 1 firemouth, 4 congo tetra and flying fox etc. no other fish show any damage and there is no sign of any aggression (at leat not during daylight hours). have had rainbows 2-3 years and last fish added (plecs and keyholes) about the time this started.

thanks for your help

tony

Looks nasty.
Water stats would be good in ammonia,nitrite,nitrate,and ph.
If there no signs of flicking and rubbing I would treat it as bacterial.
What do the gills look like.
Can you enlarge the pic.

thanks for quick reply

no sign of any abnormal behaviour. gills look fine - certainly no sign of swelling.

have attached better pic. guy at the shop thought it might be bullying by firemouth or one of the catfish?

water change (about a quater) last week but no effect. will test water. if it is them scratching themselves why only at night?

its bad get treating with a bacterial med.
Keep an eye out for bullying.
Good luck.
Does it look fluffy to you.

thanks - no not fluffy at all

ok, pics can be deceiving at well as helpful at times.