sick saltwater blenny?

Question

I am looking after a friends saltwater fish tank and have a rainbow coloured blenny which when it is sick it goes dark brown with white patches on it. When I turn the lights on into the morning it is always brown and white and take about an hour to come right. Does anyone know what is the cause of this?

Answer 1

This rapid change in color is just a reflection of the stress of suddenly turning on a bright light. If you were sleeping and woke to find somebody shining a floodlight in your face, you'd be stressed too... It takes the fish a lot longer to adjust to lighting because they don't have eye lids, so the only way for them to escape the light is to hide (a very stressful process). This is normal. If you can call your friend and ask them, I'm sure they will tell you it does the same thing every day.

Soop Nazi

EDIT: If you're watching your friend's fish, you should probably not mess with anything, for fear of changing something incorrectly and killing, harming, or damaging your friend's fish or tank...

Answer 2

As the Soop Nazi said, it is the sudden change in lighting, they need time to adjust to the bright light, a way to avoid this happening is to use metal halides which gradually increase the light intensity rather than bright light immediately and so does not stress the fish.

Answer 3

I have had this problem before in my tanks. You need to have a dim light on in the room or on the tank to create a simulated "dawn" period. This is more natural and the fish will not get stressed. Worked for me!

Answer 4

I know some fish that doe this (cories, pencilfish, neon tetras, cherry barbs). I think it's a protection from predatory fish. I think that their body colors become dull so no light is reflected and the predators see them.