540 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



observations have been made as a means of assess- 

 ing the effectiveness of fertilization in increasing 

 lake productivity. 



BIOLOGY OF THE STICKLEBACK 



Since it was named and described by Linnaeus 

 in 1758, Gasterosteus aculeatus has had a long 

 and involved nomenclaturalhistory. Specific and 

 subspecific names have been based in the main on 

 variations in the numbers of bony plates and of 

 fin rays, on length of spines, and on selection of 

 environment. 



The threespine stickleback in Karluk and Bare 

 Lakes is of the partially armored form. For 

 present purposes, we shall not assign to it a name 

 designating a subspecies or variety, but shall sim- 

 ply refer it to the species Gasterosteus aculeatus. 



The ninespine stickleback, Pungitius pungitius 

 (Linnaeus), is the only other member of the 

 family which occurs in the waters of the North 

 Pacific area, and it is found only in small num- 

 bers in Karluk Lake. 



The sticklebacks as a group (family Gas- 

 terosteidae) differ considerably in morphology 

 and appearance from even their nearest relatives 

 among the fishes. They are small fish and have 

 as a distinguishing character a number of iso- 

 lated (free) stout spines in front of the dorsal 

 fin. These spines are short but sharp pointed. 

 At the posterior side of each spine is a small, 

 triangular fin membrane. The dorsal spines can 

 be erected or depressed by the fish and will lock 

 weakly in the erect position. There is one short 

 anal spine, and the pelvic fin consists of one 

 heavy spine and one or two rudimentary rays. 



There are no scales, but some of the species have 

 bony plates. 



Gasterosteus aculeatus, the threespine stickle- 

 back, is a moderately slender, streamlined fish. The 

 snout is somewhat pointed. The caudal peduncle 

 is slender, the tail shallowly forked (fork length 

 of fish equals approximately 0.97 times total 

 length). The anal fin originates well back of 

 the dorsal fin (almost even in Pungitius pun- 

 gitius). The species is extremely variable in 

 numbers of lateral bony plates and fin rays. 

 Figure 2 represents an adult threespine stickle- 

 back from Karluk Lake. 



The color varies with the locality and the type 

 of water. Except for spawning males, dull tones 

 predominate. Generally the upper surfaces are 

 olive, greenish, or brown, the colors becoming 

 lighter on the sides. The ventral surface is light 

 yellow, white, or silver. Dark-brown pigmenta- 

 tion occurs in small indefinite blotches and in a 

 variable pattern of transverse patches along the 

 sides. The fins are pale. The rays of the pec- 

 toral fin are outlined by lines of small dots of 

 black pigment. The breeding female in Karluk 

 and Bare Lakes does not assume any bright color- 

 ation. The male, in breeding season, from the 

 snout to the back of the pelvic fin, is red to 

 yellowish-salmon colored. The color tones are 

 clear but not bold. Bluish tints may appear 

 along the sides and on the face. Vrat (1949) 

 mentions the iridescent blue-green color in the 

 iris of the eye of the breeding male and indicates 

 that this color is noticeable for a period of many 

 days or weeks. We have found this condition to 

 hold for the Kodiak Island sticklebacks. 



Figure 2. — Adult threespine stickleback (Gasterosteus aculeatus). 



