HUNTER and GOLDBERG: SPAWNING INCIDENCE OF NORTHERN ANCHOVY 



The number of eggs per mode was estimated for 

 117 of the field-caught specimens by fixing a 

 weighed sample in Gilson's fluid and determining 

 the size-frequency distribution of yolked oocytes 

 (MacGregor 1968; Macer 1974). One-hundred and 

 fifty of the oocytes >0.20 mm on the major axis 

 were measured to the nearest 0.05 mm from each 

 sample and all the remaining oocytes ( >0.20 mm) 

 were counted. We shall use "diameter" to refer to 

 these measurements but since anchovy eggs are 

 longer than wide, it is not a diameter in a strict 

 sense but the major axis of an oblate spheroid. 



The form of the distribution of egg diameters 

 within an ovary was similar to those illustrated 

 for other multiple spawning fishes (Macer 1974). 

 Distributions varied from ones composed of two to 

 three distinct modal groups of eggs to ones with 

 only a single mode. Even in those with very dis- 

 tinct modal gi'oups the tails of adjacent modes 

 often overlapped. We used the program 

 NORMSEP (Abramson 1971) to separate modal 

 groups, estimate the mean egg diameter within a 

 mode, and estimate iteratively the number of eggs 

 within a mode. Although one must arbitrarily as- 

 sume egg diameters within a mode are normally 

 distributed, the program does eliminate some of 

 the subjectivity in judging the range of diameters 

 to include within a mode and how the tails of 

 adjacent modes should be proportioned. 



Just prior to ovulation and spawning the modal 

 group of eggs about to be spawned takes up fluid 

 and swells to three or four times its former volume 

 (Fulton 1898). These hydrated eggs greatly in- 

 crease the ovary weight and increase the total 

 weight of the female. To avoid this bias in female 

 weight we used female weight less ovary weight 

 (ovary-free wet weight) to express fecundity- 

 weight relations. We also provide fecundity esti- 

 mates based on total weight in tabular form so 

 that conversions can be made if desired. 



CLASSIFICATION OF OVARIES 



Ovaries of laboratory matured females that had 

 spawned within 24 h in all cases contained post- 

 ovulatory follicles. They were similar in appear- 

 ance to those described for a variety of teleosts 

 (Cunningham 1898; Wheeler 1924; Bowers and 

 Holliday 1961; Yamamoto and Yoshioka 1964; 

 Moser 1967; Scott 1974). In specimens killed 0-6 h 

 after spawning, postovulatory follicles consisted of 

 irregularly shaped structures composed of colum- 

 nar follicle cells and an underlying connective tis- 



sue theca (Figure 2A, B). In some cases the colum- 

 nar cells had hypertrophied slightly. The lumen 

 characteristically contained eosinophilic granules 

 of uncertain origin. 



Degeneration was pronounced in material 

 examined 24 h after spawning. The postovulatory 

 follicle (Figure 2C) had greatly shrunken or col- 

 lapsed on itself, vacuoles had become common, and 

 walls of the follicle cells were no longer distin- 

 guishable (Figure 2D). The granular material that 

 was observed in postovulatory follicles taken at 

 the time of spawning was still present but not as 

 abundant. The prominent underlying connective 

 tissue theca seen in new postovulatory follicles 

 was no longer distinct. Degeneration had progress- 

 ed further, 48 h after spawning. The follicle was 

 one-half to one-fourth smaller than at 24 h, the 

 lumen was very small or indistinguishable, 

 eosinophilic granules were absent, and nuclear 

 sizes were gi'eatly reduced. 



Owing to their rapid degeneration, postovula- 

 tory follicles were difficult to age in laboratory 

 specimens sampled 48 h after spawning. At this 

 time they may be confused with intermediate 

 stages of atretic oocytes (Lambert 1970). On the 

 other hand, classification of postovulatory follicles 

 into age day and age 1 day was done with an 

 accuracy of 76 to Si'^i (Table 1). In view of this, the 

 following system was established for classification 

 of ovaries from field-caught specimens; 



Hydrated: ovaries with many hydrated eggs (eggs 

 enlarged by fluid uptake just prior to ovula- 

 tion) and no postovulatory follicles. (Spawn- 

 ing considered to be imminent.) 



Age day: new postovulatory follicles, showing 

 no sign of degeneration as described above 

 (Figure 2A, B). Hydrated eggs may occa- 

 sionally be present. Elapsed time from 

 spawning <24 h. 



Age 1 day: regressing postovulatory follicles, 

 showing degeneration as described for 

 specimens (Figure 2C, D) sampled 24 h after 

 spawning. Elapsed time from spawning 3=24 

 h but <48 h. 



Nonspawning (mature): ovaries with many 

 yolked oocytes; may contain post- 

 ovulatory follicles in advanced stages of de- 

 generation which cannot be readily distin- 

 guished from other atretic structures. 

 Elapsed time from spawning 48 or more 

 hours. 



Immature: few or no yolked oocytes. 



643 



