8o BRITISH FRESH-WATER FISHES 



attention to the distribution and characteristics of our native 

 sticklebacks. 



The Three^spined Stickleback (Gastrosteus aculeatus) 



FIN FORMULA. 



First Dorsal : no membranes, 3 spines. 

 Second Dorsal : 10 to 12 rays. 

 Pectoral : 10 rays. 

 Anal : i spine, 8 or 9 rays. 

 Ventral: i spine, i ray. 



TEETH. 



Rather large, villiform, in 

 both jaws. 



The three-spined?: stickleback is the smallest of British fresh- 

 water fishes, probably never exceeding three inches in length, 

 but it makes up for its diminutive stature by exceeding abun- 

 dance, and avoids insignificance by reason of its destructive 

 habits and indomitable pugnacity. 



In shape this stickleback is very graceful ; the upper and 

 lower contours sloping symmetrically from the small mouth to 

 Appearance, the slender tail, which is set off by the brisk spring 

 of the fan-shaped caudal fin. The pectoral fins, which appear 

 to be the chief organs of locomotion, are set back about 

 one-third of the entire distance between the snout and the 

 margin of the caudal fin, and are large and fan-shaped. The 

 soft or posterior dorsal fin balances the anal fin, and both 

 combine to give the little creature a very smart appearance, 

 from the foremost ray in each being nearly three times as long 

 as the posterior ray. 



The foremost or spinous dorsal fin has disappeared, and its 

 place is occupied by three formidable curved spines, which give 

 the fish its distinctive name. Under the skin at the back 

 of the head, are three other spines, two with their points 

 directed forwards and one directed backwards. The ventral fins 

 have become purely defensive, consisting merely of a single 

 spine and a small ray. In front of the anal fin is an isolated 

 spine, short, stout, and sharp. 



