FISHERY BULLETIN: VOL. 71, NO. 4 



Table 13. — Percent of Apostle Islands sticklebacks mature 

 at each annulus with total number of fish in each group 

 in parentheses. 



I's I's 50 mm 



under 50 mm and over 



III 



IV 



Within the ovaries, several developmental 

 groups of ova can be distinguished. The ovaries 

 were classified into the following stages for 

 maturity: 



Immature (I) 



Preserved in Formalin, the ova was translu- 

 cent, spherical, and invisible to the naked eye. 

 Ova of this group are present in the ovaries 

 throughout the year. Ovaries in this stage are 

 slender, elongate, white organs. 



Intermediate (II) 



The first yolk granules appear in this stage 

 giving the ovary a pale yellowish tinge while 

 making the ova visible without magnification. 



Maturing (III) 



The yolk granules appear as highly refractive, 

 spherical bodies in the cytoplasm, and ova be- 

 come opaque. The ovary becomes turgid and 

 deep yellow in color, with ova readily visible but 

 firmly embedded in the follicles. The size of ova 

 in this stage varies widely. 



Ripe (IV) 



When the ova are about ready to be spawned, 

 a single conspicuous golden oil globule appears 

 in the yolk. The ova readily break from the fol- 

 licles in which they were formed and flow freely 

 from the oviduct when the sides of the fish are 

 pressed. In Formalin-preserved fish, mature ova 

 can readily be separated from ovarian tissue 

 with a dissecting needle, a procedure which was 

 almost impossible in Stage III fish. The fish is 

 very rotund. 



Partly spent (V) 



Partly spent fish contained ripe ova but not 

 the full complement. The ova are congregated in 

 the anterior ends of the ovaries, with the poste- 

 rior portion somewhat flaccid and lighter in 



Ovaries were gradually resuming the appear- 

 ance of those in the intermediate stage. Ova 

 maturing for the next reproductive period are 

 already visible to the naked eye. Following 

 spawning, resorbing ova remnants were some- 

 times found. 



Female fish were judged to be sexually mature 

 when their ovaries contained ova in develop- 

 mental Stage II or beyond. Male maturity was 

 established by noting the presence of breeding 

 color, an ink-black patch on the ventral surface 

 as noted by McKenzie and Keenleyside (1970), 

 remnants of which were detectable through the 

 year after its original appearance. 



Time of Spawning 



The first spent females were observed on June 

 6 with no great increase in percentage frequency 

 of occurrence until mid-July. By the end of July, 

 all but one of 38 fish were spent, and that one 

 was partly spent. It appears that the spawning 

 season for these fish is approximately 8 wk long. 

 Equally long spawning periods are reported by 

 Nelson (1968b) and Bigelow and Schroeder 

 (1953). 



Spawning Habitat 



The spawning act was not observed in the 

 lake, therefore the exact location and spawning 

 substrate cannot be identified. McKenzie and 

 Keenleyside (1970) saw Lake Huron Pungitius 

 spawning among rocks around the shore. No 

 such activity was noted in superficial observa- 

 tion in the Apostle Islands. Ripe station 3 fe- 

 males and males displaying vivid reproductive 

 coloration were found exclusively in the dense 

 growth of Nitella sp. At station 2, ripe fish of 

 both sexes were collected over highly organic 



1050 



