" Why do fish have scales?
The primary purpose of scales is to give the fish external protection.
How many types of scales are there?
There are four main kinds of scales, and numerous variations of each kind.
1. Placoid
2. Cosmoid
3. Ganoid
4. Cycloid and Ctenoid
Different fishes, different scalation
It is interesting to think about the lifestyle and habitat of a fish, then look at its scales. In the brain teaser page below, the scales of five shark species are shown, two are slow swimming bottom-dwelling sharks, one is a generalist predator, and two are fast swimming pelagic species. Can you work out which scale belongs to each shark?
Are all scales the same size?
No. Scale sizes vary greatly between species. Some fishes, such as the freshwater eels have tiny embedded scales. Fishes such as the tunas have tiny scales often found in discrete areas of the body. Many fishes such as the snappers have medium sized scales whereas the scales of others such as the Tarpon, Megalops cyprinoides are large enough to be used in jewelery. The scales of the Indian Mahseer, Tor tor are known to reach over 10cm in length.
How old is a fish scale?
As cycloid and ctenoid scales increase in size, growth rings called circuli become visible. These rings look a little like the growth rings in the trunk of a tree. During the cooler months of the year the scale grows more slowly and the circuli are closer together leaving a dark band called an annulus . By counting the annuli it is possible estimate the age of the fish. This technique is extensively used by fisheries biologists.
Can a fish have more than one type of scale?
Yes. Some species of flatfishes (flounders, soles, etc) have ctenoid scales on the eyed side of the body and cycloid scales on the blind side. "
The primary purpose of scales is to give the fish external protection.
How many types of scales are there?
There are four main kinds of scales, and numerous variations of each kind.
1. Placoid
2. Cosmoid
3. Ganoid
4. Cycloid and Ctenoid
Different fishes, different scalation
It is interesting to think about the lifestyle and habitat of a fish, then look at its scales. In the brain teaser page below, the scales of five shark species are shown, two are slow swimming bottom-dwelling sharks, one is a generalist predator, and two are fast swimming pelagic species. Can you work out which scale belongs to each shark?
Are all scales the same size?
No. Scale sizes vary greatly between species. Some fishes, such as the freshwater eels have tiny embedded scales. Fishes such as the tunas have tiny scales often found in discrete areas of the body. Many fishes such as the snappers have medium sized scales whereas the scales of others such as the Tarpon, Megalops cyprinoides are large enough to be used in jewelery. The scales of the Indian Mahseer, Tor tor are known to reach over 10cm in length.
How old is a fish scale?
As cycloid and ctenoid scales increase in size, growth rings called circuli become visible. These rings look a little like the growth rings in the trunk of a tree. During the cooler months of the year the scale grows more slowly and the circuli are closer together leaving a dark band called an annulus . By counting the annuli it is possible estimate the age of the fish. This technique is extensively used by fisheries biologists.
Can a fish have more than one type of scale?
Yes. Some species of flatfishes (flounders, soles, etc) have ctenoid scales on the eyed side of the body and cycloid scales on the blind side. "
