Stress to cause scratch?

[guille2007]

.Can fish to scratch against objects if get frighten?

I have notice my fish to do that after turning off the light at night, don't know if it is stress related or so since they don't do it during the day while light is turned on, they have been doing this for a long, at the begining I though that it was something related with WC, but have seen this even during days with no WC. They show a normal behaviour, good appetite, no white feaces.

[Graham]

They are probably being startled when the lights go out and they bang around into things.

G

[guille2007]

Yes Graham, that's the word, they do that after get startled, they scratch against bottom tank, air tube, heater cable, they always select the gill area to do it, no all fish do that either, just some of them, never have seen it doing that during a day under normal conditions.