THREESPINE STICKLEBACK OF KODIAK ISLAND 



551 



spawned sticklebacks are found along the shores 

 of the lakes or at the outlets. These fish are 

 either dead or in a weak, emaciated condition. 



The proportion of sticklebacks that spawn at 

 age 1 year is not known with certainty. Judging 

 from egg development in females (ages obtained 

 by reading otoliths of 1-year-olds), fewer than 

 one-half spawn at 1-year-old. Moreover, it is not 

 known whether a stickleback that spawns at 1 

 year dies, or lives another year without spawning 

 again, or spawns again the next year. 



Bertin (1025) believed that the life cycle of 

 the stickleback in Europe is accomplished in 1 

 year (in other words, that the fish spawn at the 

 age of 1 year), and that the fish die after breed- 

 ing. He stated, however, that in some localities 

 the fish may live longer. Leiner (1034) wrote 

 that Gasterosteus acuJeatus breeds at least 2 or 

 3 times during its life. Jones and Hynes (1050) 

 found the sticklebacks in England to live 3 years 

 and to show gonad maturation from the first 

 year, but did not indicate how many times the 

 fish spawns during its life. 



The sexually mature sticklebacks are struc- 

 turally hermaphroditic. Schneider (1004) re- 

 ported an instance of hermaphroditism in Gas- 

 terosteus in which one of the paired gonads 

 contained both ovarian and testicular tissue. 

 0. W. Huver in 1955 discovered that the stickle- 

 backs at Bare Lake and Karluk Lake have gonads 

 of both sexes present in the same fish, and Green- 

 bank in 1056 examined a large number of mature 

 specimens and found all of them to show this 

 condition. In the ripe male (fig. 11), the testes 

 are enlarged to occupy at least one-third of the 

 abdominal cavity. Between the testes and the 

 other organs, there is a thin septum. Against 

 the ventral side of this septum lie the paired 

 ovaries. These are 8 to 12 mm. long. They con- 

 tain no cells which can be identified under low- 

 power magnification as ova. No staining or 

 sectioning has been done. 



The oviduct is Y-shaped and apparently enters 

 the cloaca separately from the vas deferens. The 

 cloaca is simple and is continuous with the hind 

 gut. There is a single external opening. 



Just anterior to the cloaca and ventral or 

 slightly lateral to the posterior portion of the 

 gut, there is a pear-shaped, thin-walled sac some 



8 to 12 mm. long. This sac, as spawning time 

 approaches, becomes filled with a clear, viscous 

 fluid, presumably the material which is used to 

 cement the nest. 



The ovaries of the ripe female (fig. 12) occupy 

 a large proportion of the abdominal space. There 

 is a septum as in the male. The testes are not 

 prominent but definitely are discernible as rib- 

 bonlike structures and readily distinguishable 

 from the darker streak of the kidney. Xo cyto- 

 logical examination of the testes has been made. 

 The vas deferens and the oviduct apparently 

 enter the cloaca separately as in the male. 



A female stickleback, 70 mm. standard length, 

 captured in Karluk Lake on July 25, 1056, had 

 ovaries well distended with eggs. Among the 

 eggs were several which were well eyed (fig. 13). 

 While it may be possible that sperm cells had 

 entered the cloaca from the water outside and 

 had made their way up the oviduct, there is the 

 possibility that the spermatozoa were derived 

 from testicular material in the same fish. 



Aside from the change in coloring in the male 

 discussed earlier, and a visible swelling of the 

 ripe female, secondary sex characters attendant 

 on maturity are lacking. 



There is little agreement in the literature about 

 the time of spawning of Gasterosteus aeuleatus 

 or external factors with which it may be related. 

 Roule (1045) states that the stickleback spawns 

 in the latter part of spring or the first part of 

 summer. Carl (1053) says that the spawning 

 period is prolonged from the first week in April 

 to the first week in September. In the estuaries 

 and streams tributary to the Gulf of Main (Bige- 

 low and Schroeder, 1953), the fish is said to 

 spawn probably in May to June. 



Eechhoudt (1047) was able to induce a con- 

 siderable degree of sexual development in the 

 stickleback by exposure to artificial light. Ap- 

 parently this development did not reach the point 

 of actual spawning. 



We do not have information to fix the spawn- 

 ing date of the sticklebacks in Karluk and Bare 

 Lakes with any degree of precision. In Karluk 

 Lake in 1948 stickleback eggs were recovered 

 from a stickleback stomach on June 7. On the 

 other hand, females still carrying ripe eggs were 

 taken from Karluk Lake as late in the summer 



