Kids' Corner, Fish & Life Cycles

Fish Anatomy | Life Cycle | Native Species

Skagit Watershed Education ProjectFish are AMAZING creatures! Fish live, eat, and BREATHE in the water! Do fish actually breathe the WATER? Not really. Fish have a different way of getting air than we do--they filter it OUT of the water with GILLS. If people could do that, we could stay underwater all day too! But to swim as well as they do, we'd have to grow strong tails and fins!

Fish Anatomy

Fish Anatomy Diagram:

[Image]: Fish Anatomy

Some descriptions of the different parts of a fish are listed below.

Types of FINS

Each fin on a fish is designed to perform a specific function.

Fins are important for helping fish to stabilize themselves (so that they don't flop over!) and help them do almost everything else they do also! A fish can use its fins to help it find food, or to escape from becoming food themselves!

Adipose fin

  • There is one kind of fin that isn't on the picture above that many fish have. It is called the adipose fin, and is located on top of the fish, in between the dorsal fins and the caudal fin. The adipose fin is sort of a mystery to people who study fish. What does it do? Why is it there? We don't really know! This fin could help the fish with stability in the water. The adipose fin is the fin that is often clipped so that people can tell the difference between hatchery fish, and natural fish.

Pelvic fins

  • Pelvic fins (also known as ventral fins) are paired so that there is one on each side of the fish. These fins are very important for stability and some fish have adapted these fins for their own special purposes (such as a sucking appendage which helps anchor them to the ocean bottom, or into strong "walking" appendages!).

Pectoral fins

  • Pectoral fins are also paired, one on each side. These fins are used for many different things, depending on which fish is using them, but in general, they help in balance, swimming, and turning.

Dorsal fin

  • The dorsal fin is not a paired fin like the pelvic and pectoral fins, but some fish have more than one of them. Although the dorsal fin is also used in balance and steering for the fish, it can also be adapted for other purposes. In one kind of fish (called the angler fishes) it looks like a fishing lure and attracts prey for the fish to eat. Some fish have sharp spines in their dorsal fins which they use to protect themselves against predators.

Tail fin (Caudal fin)

  • The tail fin (called the caudal fin) is the main source of movement for most fish. It's like the motor on a boat. It shouldn't be surprising then, that it is shaped differently according to how the fish needs to move most of the time. This helps the fish to move more efficiently through the water.

Fin Shapes

There are four main shapes of tail fins. This picture illustrates the differences.
[Image]: Fin Shape
Not all fish have all of these kinds of fins, but all bony fish have at least some fins


  • Fish with tails that are rounded or truncated are usually slow swimmers, but these tails are powerful so that these fish can swim far and long.


  • Fish with lunate tail shapes (pointed but not sharply forked) are some of the fastest fish and can maintain rapid speeds for long durations. This would be very helpful for out-running larger predators!


  • Truncated fins end in a more-or-less vertical edge. Salmon have truncated tail fins.


  • Fish that are continuous swimmers usually have a forked caudal fin, and the more active the fish is, the deeper the fork tends to be.


  • The last kind of fin is called the anal fin. Like the other fins, it often plays an important role in stability and balance for the fish. It can also be used for other things, and in some species, it is used to aid in reproduction.

Other Fish Parts

Fish have eyes, noses (called nostrils), scales, a mouth, and gills too. These are all a little different depending on which species of fish you want to know about. This is because they often become very specialized (just like many of the fins do) to help the fish do what it does most.


Anadromous Fish Life Cycle

Anadromous Fish

[Image]: Fish Life Cycle

Anadromous Fish

Anadromous (pronounced an-aa-dro-mus) fish, have an interesting life cycle. They are neither saltwater fish, nor freshwater fish, but they are actually BOTH!! They are born in fresh water, and grow up there (different kinds stay in freshwater longer than others). Some kinds will stay a few weeks, others will stay 2 or 3 years, but after they have lived in freshwater for a while, they swim downstream to the estuary (a place where brackish water--or diluted saltwater--is formed from the mixing of the ocean water with the stream or river).

In the estuary, their bodies change so that they can live in the ocean. This is called the SMOLTIFICATION process, and the fish going through it are called SMOLTS. The fish have to go through this change gradually, which is why it is so necessary to spend time in the estuaries (where the water is a mix of fresh and salt water). After their bodies have changed, they swim out to the ocean. They live in the ocean for most of their adult lives.

But anadromous fish aren't done when they get to the ocean. In order to keep the cycle going, the adults must lay and fertilize their eggs (spawn) back in FRESHWATER!! When they are ready to spawn, then, they must return to the freshwater stream or river where they were born. Most anadromous fish die after they spawn, but some types (like steelhead and Atlantic Salmon) actually repeat this cycle SEVERAL times during their life.


Native Species

(Illustrations by Ron Pittard)

 [Image]: Rainbow TroutRainbow Trout are actually a land-locked form of the anadromous steelhead. They can grow up to 2-5 lbs. eating such things as minnows, crayfish, insects, and other small aquatic life.


[Image]: Rainbow TroutThe female Rainbow Trout (pictured first) are generally lighter in coloring, while the males (pictured second) are brighter. Spawning generally occurs in April and May upriver in gravel beds.


[Image]: Sockeye SalmonSockeye Salmon also have a land-locked relative. These are called Kokanee Salmon and are very common in this area. Kokanee are much smaller than Sockeye and eat plankton.


[Image]: Coho SalmonCoho Salmon are an anadromous fish that usually live one year in fresh water (after hatching) and then go out to the ocean to live for a year or two before returning again to fresh water to spawn again. Coho mostly eat small fish. 

Visit "Fish Resources" on this site to learn more about these Native fish!