Recommended for grades 4-6

Have you ever watched a fish swimming effortlessly in the water and wished you could do the same? Fish have special fins and features that allow them to thrive in their watery habitat, but they also have some anatomical things in common with you. Let’s find out. WRITE AN INTRODUCTION HERE.

You have something in common with a fish. A fish — just like you — needs oxygen to live. You have Iungs that remove oxygen from the air. A fish has gills that remove oxygen from the water. Water flows into the fish through its mouth. It passes over the gills, the gills remove the oxygen, and the water flows out through the gill vents.

Moving through water is hard work! Many fish are streamlined or flat. This smooth shape allows them to slip through the water using the least amount of energy. The streamlined shape of salmon allows them to make their way up rapidly flowing rivers against the strong current. The flat shape of a flounder allows it to hide on a sandy or muddy bottom.

Fish prefer to go undetected by other fish. If they are predators, they do not want their prey to see them and flee. If they are prey, they don’t want the predators to see them! Irregular color patterns make fingerlings more difficult to see. Fish are usually darker on their backs and lighter on their undersides, making them harder for birds to see from above, and harder for larger fish predators to see them from below.

Fins allow a fish to move, to aim itself, and to balance:

  • Fins along the back of a fish (dorsal fins) and along the stomach (pelvic and anal fins) balance the fish and keep it upright.
  • Fins that stick out along the sides (pectoral fins) help a fish position or aim itself in the water. Pectoral fins can also act as brakes.
  • A fish uses its tail fin (caudal fin) to move itself forward through the water.
  • Many fish have another fin located about halfway between the dorsal fin and the tail fin (the adipose fin).

Most fish, including salmonids, have scales that cover their bodies. Scales protect a fish’s body like clothes protect your body. The scales slide over each other, allowing the fish to move and turn.

Some fish don’t have scales. These fish have thick, tough skin to protect themselves. Catfish and sharks are examples of fish that do not have scales.

A protective slime coats the body of many fish. Slime helps to protect fish from fungi, disease, and parasites.

Eyes – All fish have two eyes. Many fish have well-developed sight. They can see above, below, and ahead of them at any time. The only area they cannot see is directly behind their tail. Fish can use their eyes independently. One eye may be looking up, while the other is looking ahead and down! Some fish live in cloudy water, or are active only at night, so vision is not as important to them, having learned to rely on other senses to survive. Their eyes may be smaller, or less developed.

Smell – All fish have nostrils, and most have an extremely keen sense of smell. Smell is particularly well-developed in those fish that have poor vision. Salmon have an extremely strong sense of smell. There is strong evidence that they use this to return to the streams of their birth to spawn.

Hearing – Fish have ears, but they are located inside their bodies. Some fish use these ears for hearing, but they are mostly used for balance. Fish also have a lateral line, located along their sides. This organ senses pressure changes caused by things like the movement of another fish.

Taste – Just like you, fish can taste what they eat. Fish have taste buds in their mouths. Catfish even have taste buds outside of their mouth. They are located in their whiskers (barbels). Catfish can taste their food before they even put it in their mouths!

Recognizing Salmonid Species

The Exterior Anatomy of a Salmon
Look closely and you will find many clues about how to identify a salmon and the special names for all of their fins.

  • Dorsal fin
  • Adipose fin
  • Lateral line (row of special cells)
  • Anal fin
  • Gill cover
  • Nostril
  • Pectoral fins
  • Pelvic (ventral) fins
  • Caudal fin

Identification features of juvenile Pacific salmon (genus oncorhyncus)
Each species of salmon develops its own distinctive features, and these will help you identify which fish are migrating in the stream.


  • Parr marks oval, wider than interspaces
  • No spots
  • Dark spotting both lobes of tail
  • 13 or more rays in the anal fin


  • Parr marks oval, but narrower than interspaces
  • No spots
  • Long first rays often white
  • 13 or more rays
  • Little or no spotting in lower lobe of tail


  • Adipose fin clear, not pigmented
  • No spots
  • 13 or more rays


  • Faint parr marks, extend little, if any, below lateral line.
  • Leaves fresh water as fry
  • 13 or more rays


  • No parr marks
  • No spots
  • 13 or more rays

Learning Activity: Label the Anatomy of a Salmon


  • Print, add color to and label the anatomy of the salmon, and glue or tape it to a blank page in your journal; or
  • In your journal, draw this salmon and label the anatomy.

Identification features of juvenile trout (genus oncorhyncus)

Trout are similar to salmon but have a few important differences. These features will help you identify our local species of freshwater fish.


  • Spots in dorsal
  • Not more than 5 parr marks on dorsal ridge ahead of dorsal fin
  • Tail usually black spotted
  • Teeth on base of tongue
  • 8-12 rays
  • Red or yellow mark on throat
  • Maxillary extends past rear margin of eye


  • No teeth on base of tongue
  • Few or no spots in tail
  • 8-12 rays
  • No red or yellow mark on throat
  • Maxillary does not extend past rear margin of eye
  • 5-10 parr marks on dorsal ridge ahead of dorsal fin
  • Spots on dorsal