Fish: A Closer Look
by Caitlin Shannon

How do fish use their gills? Why do they have fins? How does a fish see?
Do fish have ears? Why do they have scales? What makes them different colors?

These are only a few of many questions that you may have about fish. Fish are no different from any other living organism on the planet, so all of their structures have specific functions that they perform that have been adapted to their living environments. This page is meant to give you a closer look at all of these structures and their functions, through photography and written descriptions.


Fish Structures and Their Functions: An Overview


The nostrils of fish do not open into the back of the mouth and are not used for breathing. They actually lead into organs of smell which are very sensitive, so that a fish can detect the presence of food in the water at considerable distances.

The eyes of a fish have large round pupils which do not vary in size.

The mouth serves for taking in food; also for the breathing current of water. Carnivorous fish’s mouths differ from herbivorous fish’s mouth because of their differences in diet.

The gills serve as the breathing mechanism for the fish. Water passes over the gills and they absorb the oxygen that is dissolved in the water.

The operculum is a bony structure covering and protecting the gills; it plays an important part in the breathing mechanism.

Fins give stability, and control the direction of movement during swimming


Crown Tail Betta
Family: Belontiidae

The first fish I decided to photograph was the Crown Tail Betta Fish.

They are resilient fish that are native to Thailand but found all over the US because they make very good pets due to the fact that they are so low maintenance. I also found that they tend to be very calm and easy to photograph when they are by themselves. These fish are primarily known for their elaborate tail that differentiates it from other bettas and all other fish. The males are usually more colorful than females, although some females can be just as elaborate. Males have been known to be very aggressive and combative and have been bred over the years in order to enhance their fins and vary in color.

Here are some of the specific structures and their functions...

These fish are carnivorous and therefore have a mouth that is turned slightly upward in order to tear apart their prey. Although they are carnivorous, for domestic purposes they will also feed on dried flaked food.

These are the scales of the Betta fish. As you can see, the color in the body is extraordinary and one of their most well known characteristics.


This is the pectoral fin. It is used by all fish to control the upward and downward movements of the fish
In this image the tail fin (or caudal fin) is depicted and the structure of the tail is quite clear. The tail fin accounts for about 40% of a fishes movement, as it exerts the most power than any of the other fins. You can see the amount of colors in the tail as well.

A calm betta
An agitated betta
An unprovoked betta with its fins and tail completely relaxed.
This betta shows its anger by puffing out its gill coverings and tail. By increasing its size, it can intimidate attackers.

Betta fish are known for their aggressive and combative behavior. They can be provoked many different ways. One way I got them to react was by putting certain color filters over the light source and because they see different wavelengths, different colors would cause them to react. They seemed to get most annoyed when the red filter was over the light. As shown in the image above, they show that they are agitated by puffing out their gill coverings and making their tail and fins larger. They also do this often in their natural environment, when confronted by an enemy or in an instance of courtship in order to impress a female.


The image on the right shows in more detail in how the gill coverings look when they are extended and the image on the left shows how the betta's gills would look normally.


How the Crowntail Betta got its name...

Obviously their most known and admired characteristic, their tail is
both colorful and entrancing

Bubble Eye Goldfish
Family: Carassius auratus

For this project I also decided to photograph a bubble eye goldfish.

These are strange, very distinct looking fish with original origin from China. They are one of the only fish that lack a dorsal fin and contain air bubbles directly underneath each eye. These bubble sacs are their most distinctive characteristic. They are filled with fluid and develop in about 6 to 9 months after hatching. Their entire body is symmetrical, you can see this best in the caudal fin, which is divided and forked. All of its other fins are also symmetrically paired on its body. Like any other goldfish, they are scavengers and will feed off pretty much anything. Because of this, they have a larger mouth that is structured for bottom feeding. They are extremely friendly fish and thrive in any community environment


A side view of their symmetrical caudal (tail) fin.

These are the metallic scales of the goldfish. You can also see how the
pelvic fins are symmetrical like the caudal fin.

These bubble sacs may seem awkward but they do not harm or
disadvantage the fish in any way.
They are delicate but will regrow fairly quickly if punctured.






Contact Information

Please feel free to contact me with any comments or questions

Caitlin Shannon -
Michael Peres -


Return to index of articles by students on the 'Principles and techniques of photomacrography' course, November 2008,
Biomedical Photographic Communications (BPC)
program at the Rochester Institute of Technology (RIT).

Article hosted on Micscape Magazine (Microscopy-UK).