The sun was shining down into the water and I could clearly see that there were a number of fish darting around between the weeds.
They were very small fish and I wished I had a pinkeen net to catch one and identify it.
Then one of them swam towards the surface and turned, giving me a look at its profile. A stickleback.
To be precise, a three-spined stickleback. A bit of a surprise that. Ireland has three species of stickleback.
The fifteen-spined is the largest and is only found in the sea.
The nine-spined is sometimes called the ten-spined stickleback and can have anything from seven to 12 spikes along its back.
It’s mainly found in inland counties.
The three-spined (which sometimes has four spines) has the ability to move between fresh and salt water and is mainly found in coastal counties.
The surprise was that the placid river back-water I spotted the fish in was in the Midlands, about as far from the coast as you can get in this country, so they should have had nine spines not three.
But the truth of the matter is that very little study has been done and their distribution has not been properly mapped.
This is presumably because they are a fish with no obvious commercial or sporting importance, except perhaps to kids with pinkeen nets.
But they are found all across the temperate zone of the northern hemisphere and they’ve been much studied in other countries.
This is because they’re readily available and adapt well to life in a laboratory aquarium.
These studies have shown they’re a fascinating fish.
Their breeding behaviour is particularly interesting. In spring males abandon their dull colouring in favour of a gaudy mating livery.
They turn a brilliant blue or green with a red or orange patch on the chest and large, pale blue eyes. They then build a complicated nest into which they entice a female.
When she’s laid her eggs she leaves, but the male stays on and guards the eggs and the fry when they hatch, with great ferocity.
The biologists also discovered that, although male sticklebacks are very territorial during the breeding season, at other times of the year they display a surprising ability to cooperate with each other.
They are very small fish which are in constant danger of being eaten by larger species.
If a potential predator appears, sticklebacks, operating in pairs or larger groups, will approach it teasingly, rather like small birds mobbing a bird of prey, to test whether it’s hungry and therefore a possible threat.
One brave individual fish usually gather the information which benefits the whole group and they seem to take it in turns to go on the dangerous part of the mission of discovery.
This behaviour was first recorded by scientists in the United States who put a rainbow trout into a tank containing sticklebacks.
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