168 BULLETIN OF THE BUEEAU OF FISHERIES 



summer'^ on the shores of the Gulf, for in northern Europe its breeding season occurs 

 in June and July. The male often but not always builds a nest attached to grass or 

 weeds in which the female spawns, and he guards nest and eggs until the latter 

 hatch, which occurs in about 12 days, the newly-hatched larvpe being about 6 mm. 

 long. 



Commercial importance. — This stickleback is of no commercial importance in 

 America, but it is sometimes tried out for oil in north Europe when enough can be 

 caught. 



64. Three-spined stickleback {Gasterosteus aculeatus Linnaeus) 



Two-SPiNED stickleback; Stickleback; Pinfish; Hornpout; Ghoster; 



Thornfish; Thornback 



Jordan and Evermann, 1896-1900, p. 747. 



Description. — The three-spined stickleback is a stouter fish than its nine- 

 spined relative, being about one-fourth as deep as long, and is more compressed, but 

 resembles it in fusiform outline, very slender caudal peduncle, and square tail fin. 

 Its most diagnostic characters are the number of dorsal spines, of which there are 

 three (occasionally four and very exceptionally five) , with the first two usually much 

 the larger, and each with a small triangular fin membrane; the small size of the anal 

 spine (in the nine-spined stickleback this is long and free; in the four-spined long but 

 attached to the fin by the fin membrane) ; and especially the presence of a series of 28 to 

 33 bony plates on the sides, and of a ventral plate between and behind the ventral fins. 

 The fact that the dorsal fin originates some distance in front of the anal is also 

 diagnostic, while its ventral spines are longer and stouter than those of the nine- 

 spined stickleback. This is one of the most variable of fishes, Smitt "" mentioning 

 no less than 32 "species" or races based on its varieties. Its dorsal spines, for 

 example, may be long or short and vary in number as noted above. Its bonj- plates 

 range from none at all to very well developed ones. Its caudal peduncle may or 

 may not be keeled. Most American authors have recognized an American as con- 

 trasted with a European species at the least, the former supposedly with longer 

 dorsal spines, each of them reaching to the next behind when depressed, and the 

 latter with shorter spines; but inasmuch as the long-spined as well as the short- 

 spined form is known to occur on the other side of the Atlantic, with every possible 

 gradation between the two, and seeing that we ourselves have found both in the 

 Gulf among fish otherwise indistinguishable, we incline to the belief that all the 

 various forms are but environmental races of the one species. And this is well 

 established for the relative strength of the dermal armature, which is M'eak in fresh 

 water and strong in salt water. 



Color. — This fish is extremely variable in color, a fact hardly mentioned in 

 most American accounts. Fundamentally it is deep graj'ish, olive, greenish-brown, 

 or sometimes blue above, paler and often with silvery reflections on the sides, its 

 belly silvery, and the fins pale, except that the fin membrane is often red. In 

 .breeding season the males are described as turning reddish below from nose to vent 



" It spawns in April and May at Woods Hole. 

 » Scandinavian fishes, 1892. 



