Principle #1 : Genetic Variation Some clownfish are orange with white stripes while others are more of a black/gray color with white stripes. Also, some of these fish grow to be big and some are small.
Principle #2 : Overproduction & the Struggle for Existence Clownfish produce many other fishes, they usually produce more that what will actually survive since most get eaten by sharks or eels. They also struggle to survive when they have to combat diseases and even competition.
Principle #3 : Differential Survival & Reproduction Orange and smaller fish are more likely to survive since they have a better ability of blending in inside an anemone since that's where they usually hide. These anemones are mostly of orangish and yellowish colors and are not too big.
Principle #4 : Changes in Gene Pool. Overtime,the population of black/gray and larger clownfish will drop in number. The population of orange and smaller clownfish will increase since they arent getting eaten as often. Although this is going to happen, it doesn't mean there will be absolutely no black/gray larger fish.