Fish Identification

I recently took part in a course to improve my Fish Id skills. Being able to identify the aquatic life that you see means that you can discuss what you have seen. Also knowing how to Id a fish properly means that you can then look it up and find out what it actually was.

So how do you Id a fish? Well first of all it is important to learn the different parts of the fish. The diagram below has the typical parts of a fish. Now it is important to realise that not all fish will have all the fins shown in this diagram.




Nemo had a lucky fin.

Nemo had a lucky fin.

A fish can have many different types of fin. They are either paired, a matching fin on the other side, or they are unpaired with no reciprocal fin on the other side.

Dorsal Fins

Dorsal Fins are unpaired. They can either be hard (with spines) or soft, and some fish have both. It acts as a keel keeping the fish upright. Some fish use their dorsal fins to swim, such as trigger fish.

Tail Fins

These are used for swimming. There are several different tail shapes that fish can have.

Lunate – this is the fastest shape

Forked – moderately fast

Squared – very manoeuvrable, capable of bursts of speed over short distances

Rounded – very manoeuvrable, capable of bursts of speed over short distances

Tapered – slow swimmers, uses body undulations to swim

Anal Fins

These are similar to dorsal fins in that they provide stabilization for the fish, they are also unpaired.

Pectoral Fins

These are paired fins. They provide the fish with turning and breaking.

Pelvic Fins

These are also paired fins. They provide the fish with stabilization and breaking.


Body Shape


Humans have several different body types, and so do fish.

There are four main types of body shape, though there are some other shapes but they are lesson common.


This is a torpedo shape. A fish with this body is streamlined and can easily move through the water.


These are fish that have been flattened from top-to-bottom.


These are fish that have been flattened from side-to-side.


These are fish with long and thin bodies, such as moray eels.


Mouth Position


The mouth position on a fish can tell you a lot about how and where a fish eats.


These are fish that either chase their food or eat what is directly in front of them.


These fish have upturned mouths and usually feed on what is above them.


These fish have downturned mouths and usually feed on what is below them.


Colour and Patterns


These different effects help to camouflage the fish.


These lines run from tail to head.


Bands run completely around the body of the fish from top to bottom.


Bars run partially around the body of the fish from top to bottom.


These are large spots.


These are small spots.


Colours that run together making it hard to discern any specific pattern or marking.


This is when it is dark on the top and light on the bottom, meaning that it is difficult to be seen from above or below.


The colours help to blend the fish into the coral that they are swimming past.


So to get better at Fish Id there are a fantastic set of powerpoint slides available from the Atlantic and Gulf Rapid Reef Assessment. Or you can pop down to your local dive shop and take a Fish Id course. Make sure that your instructor goes through in detail the above points, if he just hands you a card with pictures of fish on it and tells you to note what you see then they aren’t really doing their job.

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