THREESPINE STICKLEBACK OF KODIAK ISLAND 



555 



salmon. It occurs either free or in a cyst on the 

 viscera. Presumably it is the worm, the adult 

 form of which has been reported from bears and 

 mergansers as Diphyllobothrium. 



A nematode, identified by Morton 4 as Dacmtis 

 1/ievis Zschokke and Heitz, is fairly common in 

 the stomach and intestine of the stickleback, 

 usually occurring in small numbers. This worm 

 is found in both species of charr (Salvelinus 

 alpimts and S. malma). Morton reports also an 

 acanthocephalan worm, Neoechinorhynckus rutili 

 (Miiller), in the Karluk Lake stickleback and 

 states that Meyer (1032) has found this worm in 

 sticklebacks (Gasterosteus) in Europe. 



A parasitic copepod, identified by Wilbur M. 

 Tidd as ErganilvH cotti Kellicott, is found on the 

 Karluk Lake sticklebacks. A large proportion of 

 the fish carry from 1 to 5 of these copepods each, 

 attached to the skin at the base of the pelvic or 

 dorsal fins or more often in the gill chamber and 

 gills. 



Bigelow and Schroeder (1953) state that the 

 stickleback "is a proverbially pugnacious fish, 

 using its spines with good effect as weapons of 

 offense and defense, even on fishes much larger 

 than itself." We have not observed any demon- 

 stration of this pugnacity in the sticklebacks in 

 Karluk and Bare Lakes. As will be discussed 

 under food habits, the stickleback in these waters 

 is not known to feed on other fishes large or small. 

 It is preyed upon by the arctic charr, but the act 

 of capturing a stickleback by a charr has not been 

 observed. We may surmise that the act takes so 

 little time that the stickleback has no opportunity 

 for defensive action. Juvenile red salmon have 

 been found with sticklebacks in their mouths or 

 stomachs, but the act of capture has not been 

 observed. 



According to our observation, the stickleback 

 depends to a large extent for protection on a 

 sort of camouflage. In clear, calm water, over 

 a shoal, it will lie at the surface, perfectly mo- 

 tionless for many minutes at a time. In such 

 a position, it resembles a floating stick or twig. 



It is possible that the male stickleback makes 

 effective use of his spines in chasing females 

 into the nest and in guarding the nest after the 

 eggs are laid. 



Food Habits 



Norman (1936), Jordan (1905), and others 

 have remarked on the voracity of Gasterosteus 

 acuJeatus and stated that it is strongly preda- 

 ceous on the eggs and young of other fishes. 

 However, Markley (1940) found the sticklebacks 

 of Sacramento River (sample taken in October) 

 to be feeding mainly on insects and other inver- 

 tebrates, especially amphipods. Carl (1953) ex- 

 amined a small number of stickleback stomachs 

 from Cowichan Lake, British Columbia, and 

 found zooplankton (Cladocera, copepods, amphi- 

 pods) and insect larvae to be the chief items in 

 the diet. Bigelow and Schroeder (1953) list as 

 food for the threespine stickleback in the Gulf 

 of Maine copepods, isopods, small shrimp, young 

 squid, diatoms, small fish fry, and fish eggs. It 

 is evident that the stickleback will eat a wide 

 variety of (animal) foods depending on what is 

 available. 



Stomach examinations of sticklebacks in Kar- 

 luk and Bare Lakes are summarized in tables 

 8-10. The larvae and pupae of chironomid flies 

 (Diptera) were found, often in considerable 

 numbers, in a large percentage of the stomachs. 

 Other insects, such as caddis-fly larvae and dam- 

 selfly and stonefly nymphs, occurred irregularly. 



Also of importance were copepods, of the gen- 

 era Diaptomux and Cyclops; and Cladocera, of 

 the genera Daphnia and Bosmina. Stomachs 

 were examined that contained well over 200 in- 

 vertebrate plankters of 1 one more of these 

 4 genera. 



Table 8. — Contents of stickleback stomachs, Bare Lake, 1951 

 (Numbers in parentheses are range of number of organisms per stomach] 



' See footnote 2, p. 543. 



