Amazing strange red tail shark

[redtailshark1]

One of my red tail sharks, during the night time can change colour.
It some times turns golden green instead of black or half and half should i be worryed?
is this common?

 

[peewee]

i don't know if red tailed sharks are characins but if they are then it's pretty common for them to change color when it turns dark.

 

[phobull]

Probably for hunting.

 

[redtailshark1]

phobull dident you live in japan?
i might take a picture and post it one day