HOWELL: SEASONAL CHANGES IN YELLOWTAEL FLOUNDER OVARIES 



section is proportional to its size as well as its abun- 

 dance, large oocytes tend to be overestimated and 

 small oocytes underestimated when percent fre- 

 quencies are calculated. The calculated percentages, 

 therefore, may not be exact, but they do provide in- 

 dications of seasonal changes. 



Size-frequency distributions of oocyte diameter 

 were constructed for each sample by dividing the 

 diameters into 10 ju.m categories. The number per 

 category was then divided by the total number of 

 measurements and expressed as a percentage. 



To test the hypothesis that no differences existed in 

 either frequencies of oocyte types or diameters be- 

 tween different regions within an ovary, or between 

 ovaries of the same fish, chi-square contingency tests 

 were employed to compare both size- and percent- 

 frequency distributions from portions of tissue taken 

 from the anterior, middle, and posterior regions of 

 both ovaries from eight fish collected in October. 

 Since no significant differences were found (P>0.05), 

 the anterior portion of the eyed-side ovary was 

 assumed to be representative, and this region was 

 used exclusively in the study. 



Two samples were collected in November; one in 

 1977 and one in 1978 (Table 1). In order to facilitate 

 data analysis it was desirable to combine them. Mean 

 length, weight, and GSI for both samples were com- 

 pared using a Student's t-test (Snedecor and Coch- 

 ran 1973). Since no significant differences were 

 found (P>0.25), the samples were combined for all 

 further analyses. 



RESULTS 



Macroscopic Structure and 

 Maturity Stages 



The paired ovaries lie, one on either side, in an 



ovarian cavity between the haemal spines and the 

 body wall musculature. Each is shaped like an elon- 

 gated cone, with the apex oriented toward the tail 

 and the enlarged anterior end protruding slightly into 

 the abdominal cavity. They are anchored by both 

 connective tissue fascia and a suspensory ligament 

 that runs from the cleithrum to the anterior end of each 

 ovary. Very short oviducts arise from the anterior end 

 of each ovary and terminate at the cloaca. 



Percentages offish in each of the different maturity 

 stages are given in Table 3. Stage I (Immature virgin) 

 females were observed only in the collection made in 

 April by the National Marine Fisheries Service. None 

 were found among those fish landed commercially, 

 since fishermen generally discard small immature 

 fish. Stage II (Developing virgin, recovering spent) 

 females were seen from May through early October. 

 Their percentage was relatively low in May, but in- 

 creased to 66% by June. In July and August all fish 

 were in this category. A rapid decline in the percent- 

 age of Stage II females occurred from September 

 (81%) to October (7%). Stage III (Developing, matur- 

 ing) females were present from September through 

 May. In early September, 19% of the fish were in this 

 stage. The percentage increased to 93% by October, 

 and all fish were in this stage from November through 

 at least February. Percentages then declined from 

 91% in April to only 7% in late May. Stage IV (Ripe) 

 females were observed only in April (9%), early and 

 late May (17 and 31%, respectively), and June (2 4%). 

 Stage V (Spent) females were seen only in May 

 and June. 



Gonosomatic Index 



When the relationship between GSI and fish length 

 was examined using functional linear regression 

 (Ricker 1973), a significant positive relationship was 



Table 3. — Seasonal changes in gonosomatic index (GSI) and percentages of yellow- 

 tail flounder in the different maturity stages. Stages are modified from Hjort 

 (1910). 



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