Fish move fast and can be tricky to identify. Taking photos from the side, top, front and underside can help a lot.
Make sure you keep your fish in a bucket of seawater and only as long as you need to identify it – fish need to stay cool, wet and well-oxygenated.
Here’s a handy guide to some of our most common rockpool species.
Identify your fish here…
1. Does it have two dorsal (back) fins, the first with a yellow tinge on the top?
You have a Rock goby. These are one of the most common rockpool fish. You’ll find them in all different sizes swimming round pools and darting under stones. There are lots of other species of goby. On sandy beaches you are more likely to see sand gobies or common gobies.
2. Does it have one long dorsal fin and fat lips with no ‘antennae’ on the head.
You have a Shanny (or Common Blenny). This is another of the most common rockpool fish. Its fat lips give it a cheerful appearance and these fish are very curious. They like to sit on stones propped on their fins. They can also survive in damp places out of the water between the tides so look into holes in the rock to spot them.
3. Do you have a blenny like the one above but with two feathery antennae on its head?
This is a Tompot blenny. Their big eyes and lips and headgear of this species make them a favourite with marine photographers. In the spring the males guard clutches of eggs on the lower shore.
4. Or a blenny with just one antennae on its head?
This is a Montagu’s blenny. These are small so you need to look closely to spot the headgear.
5. Does your fish look a bit like a lumpy armoured car, with some small spines around its cheeks and a small barbel at each corner of the mouth (look closely)?
This is a Sea scorpion. Don’t be alarmed, it doesn’t sting. This fish has no swim bladder which means that it only floats when it’s swimming and sinks when it stops. It’s very variable in colour which gives it good camouflage.
6. Is it long and thin with a head like a seahorse and small fins on its back?
You have a pipefish. The most common sort on the shore is the Worm pipefish. This has a short snub nose that sticks up a little and no tail fin. It’s a cousin of the seahorse and the male carries the eggs in a slit along his belly rather than a pouch.
Another species you may find is the Greater pipefish. This one can be as long as your arm and has a hexagonal cross section. The nose is very long and sea-horse-like. There are several other species.
7. Is it long with one long dorsal fin and no chin barbels or spots?
This is an eel. The Common eel is sometimes found on the lower shore among seaweed. Silvery-coloured Sand eels are another species frequently found in pools. If disturbed they jump along the surface of the water.
8. Is it long with big spots along its back and very slippery to the touch?
This is a Butterfish. This is a very distinctive fish, which is unlikely to be confused with anything else.
9. Is it long and slender with three or five barbels (like whiskers) on its chin?
This is a rockling. There are two species on the shore, the Five-bearded rockling (with 5 barbels as the name suggests) and the Shore rockling, which has three barbels. These fish are slippery and eel like and specialise in making rockpoolers jump by thrashing around in seaweed.
10. Does it have a sucker on its belly? (You can tell without looking if your fish sticks firmly to the rock or container).
This is probably a cling-fish. The most common species, the Cornish Clingfish, has a duck-bill shaped nose, two blue spots on its head, which may not be obvious, two small antennae on its nose and a tapering shape towards its tail.
Another species with a sucker is a Montagu’s sea snail. This fish looks like a large tadpole with small eyes.
11. Is it a flat fish?
On the rocky shores around Cornwall this is likely to be a Topknot. These fish have specially adapted fins to help them cling onto the underside of the rocks.
Otherwise the most common species are the Plaice (which has bright orange spots on its back) and the Flounder.
There are lots of other species of flatfish, so if you’re unsure send me a photo.
12. Does it look like a shark with a clear dorsal fin (set back near the tail) and cat-like eyes?
You have a Catshark (also known as Dogfish). These small sharks are harmless although their skin is sandpaper-rough. They sometimes become stranded in lower shore pools at the lowest tides. Look out also for their eggcases (mermaid’s purses) which take around 7-9 months to hatch out.
13. Not found your fish?
There are many more species of fish that can be found in our rock pools – have a look at more photos below. In summer you may find the young (fry) of many open water species like Grey mullet, Haddock and Pilchard.
Discover the secret world of fish and other rock pool creatures with my book Rock Pool: Extraordinary Encounters Between the Tides.
Have your own beach adventures and see the underwater world as never before with my hands-on children’s activity book, Beach Explorer: 50 Things to See and Discover.