Goldfish do change colour as they get older and also due to enviromental reasons.
Good quality food, good lighting and good water quality mean nice brightly coloured fish. Black is a normal colour for a goldfish.
The opposite leads to them fading or loosing colour.
My fish used to have black flecks, dad neglected him when I moved away and he lost all his colour and was a pale orange. Now I have him he's nice and healthy, turning bright orange again and gaining his black flecks back :)
If your fish is sick he will probably be at the bottom of the tank alot with his fins clamped to his sides and will generally look dull. :)
This is not a Betta question so it belongs elsewhere.
fishs eddy
The fins help steer the submarine; making it be able to turn left or right.
You can see fish eggs because they are clear/transparent with a little black dot in each egg.
A black & orange fish.
Cooling fins on a refrigerator are typically thin, metallic and silver or gray in color.
NO
so they turn better and to keep the board strait
Your albino Oscar's fins should not be turning black under normal circumstances. They can be turning black due to conditions such as too much ammonia in the water. Get your water tested to make sure.
deers or fishs
The cooling fins of a refrigerator are painted black to improve heat transfer efficiency. Black color absorbs more heat than lighter colors, helping the fins dissipate heat more effectively. This process enhances the overall cooling performance of the refrigerator.
fishing nets and killing them for their fins