- Scientific name: Spinachia spinachia
- Also know as: Fifteen-spined stickleback
- Size: Up to 20cm but typically 5-12cm
- UK minimum size: N/a
- UK shore caught record: 10 grams
- IUCN Status: LC (Least Concern)
- Distribution: All around UK and Ireland with range extending throughout European waters.
- Feeds on: Small invertebrates and marine worms.
- Description: Small fish with elongated scaleless body. Small square dorsal and anal fins are set quite far back on the body. Upper body usually bluish to grey in colour with paler underside, which is sometimes yellowish in colour in males. Tail section is thin running towards the small tail fin. Usually fourteen to eighteen spines along the back, with the average number being fifteen – hence the alternative name fifteen spined stickleback.
Altogether there are sixteen species of stickleback, but the majority of these live in freshwater. However, the sea stickleback is a small fish species found in saltwater and is common all around the coasts of Britain and Ireland. They are generally found in shallow waters in depths down to ten or twenty metres deep, and can thrive in brackish water meaning they are often found fairly far up rivers and in estuaries, although they are a saltwater species and will never be found in completely fresh water. Being a small fish the sea stickleback does not hunt and instead will spend time scavenging through the shallows and will feed on any dead animal matter, tiny invertebrates or marine worms which it finds.
Sea stickleback can reproduce after around one year of life and – like their freshwater cousins – the sea stickleback will build a nest in a shallow area where the female will lay her eggs. After this she will soon die but the male will stay and, despite his small size, will attempt to defend the eggs from any predators which try to feed on them. A true mini-species the sea stickle back has one of the lowest shore caught records with the current record standing at just over a third of an ounce (5.6 drams, 10 grams). It is therefore only caught by anglers using the smallest freshwater hooks and who are specifically targeting tiny species such as this. Unsurprisingly the very small size of this species means that it has no commercial value. The sea stickleback is classed as a species of Least Concern with a stable population by the International Union for the Conservation of Nature (IUCN). This species is thought to be abundant along the coastlines of the UK and Ireland.