The male butterfly blenny blows water over the eggs to oxygenate them
Underwater photographer Paul Kay, co-author of Marine Fishes of Wales, highlights some of the more unusual species in our seas.
North Cardigan Bay is very interesting because it's one of the places which remains reasonably pristine; it's a special area of conservation.
Consequently, you get interesting fish species there as they're not disturbed.
One little fish is the butterfly blenny. It's only three or four inches long and the females lay eggs in big old whelk shells. Then the males go in to guard the eggs.
Most people have never seen or heard of them as they can't be caught by anglers, and if they were trawled or dredged up, the fishermen would probably throw them back.
So only divers get to see them. You can swim over and see a whelk shell with a pair of eyes looking out at you!
A friend from Bangor University Ocean Sciences who goes out on their research vessel in Liverpool Bay says he's seen some scaldfish. We do know they're caught off Conwy Bay.
They're called scaldfish because when they're caught they come up with all their scales off and they look like they've been scalded.
The clingfish clings on to things, like the inside of empty shells, with the suckers underneath them. You find them off north Llŷn; they're red, with ice blue dots.
One of the few fish which can change sex is the cuckoo wrasse
We've also got some incredibly brightly coloured fish off Bardsey.
The male cuckoo wrasse is bright orange and blue and the females are duller brown and orange, but with a little black and white zebra stripe on their tails.
The male fish has a harem of females, but when he dies, the leading female changes sex and becomes a male, taking on their bright colours.
One fish that's now rare is the common skate. It's big, almost a metre in length, but they don't travel very far and are slow to reproduce; they have hand-sized mermaid's purses for eggs.
They're also very vulnerable to trawling and dredging and are now classed as almost extinct in the Irish Sea. A hundred years ago, they were very commonly caught off Llanfairfechan.
A transparent goby has been photographed off north Wales. There are very few records of them, but this summer (2009) I saw a shoal of a couple of thousand of them.
Southern species are coming up into the Channel Islands, Cornwall and will eventually appear in the north of Wales. If they come in large numbers, it could indicate that the sea temperature is rising because of global warming.
The first tompot blenny to be found in Britain was found off Anglesey and in Victorian times the Natural History Museum would get a standard specimen which described that species of fish. Some of their gobies came from Colwyn Bay.
All this information might be hidden away, but when you start looking you can discover what a great marine heritage we've got here, and hopefully a great future, too.
Marine Fishes of Wales by Paul Kay and Frances Dipper costs £19.95 and is available from the Marine Conservation Society and other outlets.