HOW TO ID FISH
Identifying fish can sound pretty tricky, especially when you flip through an ID book and see that there are hundreds of other similar fish. However, if you know a few key areas to look at and take note of, it gets a lot easier. You don't have to worry about remembering exactly every detail of the fish. It always does help however, if you have a camera and can take a photo of the fish to refer to later, or if you have an underwater slate to jot down quick notes about your fish.
There are four key pieces of information you need to gather when identifying fish. Two of them have nothing to do with appearance and are done quickly and usually without thought. Those two are the habitat and the behaviour. The other two piece of information are the body shape and size, and the distinctive features. So lets break these four things down further.
Habitat:
- What is the bottom composition?
- What is the depth?
- Demersal (living on the bottom) vs. Pelagic (living in open water)
- Inner vs Outer coast
- Regional differences
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Behaviour:
- Singular vs schooling fish
- Predator and prey relationships
- Is it territorial?
- Are they guarding eggs?
- Nocturnal vs diurnal
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Most of the habitat and behaviour information we gather without even being aware of. It's generally we don't need to take notes on these kinds of things, as when we think back to the fish we saw we can imagine the rest.
For example, think of your favourite fish you've seen while diving. Odds are when you thought of it, you thought of it where it should be; along a sand bottom, in a rocky reef, inside some sponges. You'll also have imagined whether it was many fish or just the one, if it was night or day, if the fish was hiding or chasing something. Your dive log would have told you where in the world you were, and potentially what your depth was. If you know your dive had very varying depth it may be a good idea to write that down.
Now that you know where your fish was and what it was doing, you need to look at the fish itself.
Body Shape and Size:
- Many ID books are broken up according to body shape
- Is the body long, and eel-like?
- Is the head bigger than the body
- Is the fish flat?
The list goes on and on with this one, but try to get a general outline of how your fish looks, as well as it's size. I find comparing it's size to a body part helps me visualise it later.
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Distinctive Features:
- Colour and markings
- Cirri and barbel (we'll get more into what these are in a moment)
- Fins, spines and tail shapes
Most fish can vary significantly in colour, so it alone is not suitable for identifying fish. Also many species change colour and markings when going from a juvenile to an adult, or from male to female. That being said, colour and markings are the two easiest things to take note of and will most definitely assist in identifying. Most ID books usually show or describe male / female or juvenile / adult variations if that species of fish does vary a lot.
When we're talking about markings, there are six main terms to use. Bar, Stripe, Band, Speckles, Spot and Blotches. Some people will use a few other terms, but for basic ID practice only worry about these six.
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Bars are vertical markings up and down a fish's body. This is a very common kind of marking and we see it in many fish, like Tiger Rockfish, and Kelp Greenling.
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Stripes are horizontal markings that go along a fish's body. These may completely cover the fish, like a Striped Perch, or there may only be one or two stripes, like on a juvenile Yelloweye Rockfish.
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Bands are diagonal markings. In most cases a fish will only have a couple bands, usually near their head, like on a Almaco Jack, or a Blue Rockfish.
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Speckles are small clusters of marks. They may be all in a singular area, or spread out over the fish's entire body, like on a female Kelp Greenling, or a China Rockfish.
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Spots are well defined circular markings. These may be in specific areas, according to the species, like Yellowtail Rockfish and Olive Rockfish which have them below their dorsal fins, or all over the body, like a Wolf Eel.
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Blotches are poorly defined or irregular markings. Like speckles, they may be in one specific area, or all over the fish's body. Many species of Rockfish have blotches, including Quilback Rockfish, Brown Rockfish and Grass Rockfish
Once you've identified the markings, you want to look for other distinctive features. Some of these are very obvious and you may have noticed straight away, some are less so. The two main ones on the face to take note of are Cirri and Barbel.
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Cirri are appendages that stick out of the fish, usually on its head. They are usually branched, or "bushy". They may be large and the defining feature of the fish, like on a Decorated Warbonnet, or smaller and barely noticeable like on a Rock Greenling.
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A Barbel is a slender whisker like sensory organ near the mouth of the fish. The most common example is the catfish
Finally we need to look at fins and spines. Many people may think of spines as a separate feature, however they are generally a part of the fins, which is why we're talking about them here. We should also quickly mention the Lateral Line. Although the lateral line may look like a stripe, it is actually a system of sensory organs, used to detect movement, vibration and water pressure. Some species, like Lingcod and Copper Rockfish have a stripe directly on their lateral line.
There are five main fins to be aware of. The Dorsal Fin, the Tail Fin, the Anal Fin, the Ventral Fin and the Pectoral Fin.
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The Dorsal Fin is the one on the top of the fish. It can be one long fin, or broken up into two separate fins. The front part is called the Spiny or Fore part, and the back part is called the Soft or Rear part. As those names suggest, generally if that species of fish has dorsal spines, they will be in the front section. The dorsal fin is used to stabilise the fish while it's swimming, as well as to assist with turns and stops
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Next is the Tail Fin. It is more properly called the caudal fin, however because many people and ID books just refer to it as the tail, we will do so here. The tail is used for propulsion, so the shape of it will dictate how fast a fish can move. The more forked the tail is the faster the fish can move. The more rounded it is, the slower it is.
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Beside the tail is the Anal Fin. Some fish may also have spines on their anal fin, as shown in the picture. The anal fin helps stabilise the fish while it's swimming.
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The Ventral Fin is at the bottom centre of a fish. It is usually fairly small, and it helps control the direction of a fish's movement. It is also sometimes referred to as a Pelvic Fin.
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Lastly there is the Pectoral Fin. These fins are on the sides of the fish just behind the gills. They are used for balancing and braking. Some species also use them to jump out of the water.
Once you know your basic features of a fish and what to look for, identifying it is fairly easy. Most ID books are very user friendly and break down sections by body shape, or the location the fish may be found in. This makes it simple to start sorting out the different species you've found. As you get more familiar with different fish, you can generally know what family a fish is in just by looking at it.
The real key to fish identification however, is familiarity. The more you do it the easier it will get. Personally when I am trying to learn a new area's fish, I make sure I look up and write down the scientific names for the fish I see on a dive; even the common ones that I see all the time. This forces me to actually look up the species, and ensure I am correct in what I think it is while I'm getting the scientific name. After I've done this for a few dives I start only looking up the unusual ones. I find this is a great way to cement the local fish knowledge in my mind.