HUNTER and MACEWICZ: ATRESIA IN NORTHERN ANCHOVY OVARY 



TABLE 3. — Mean and maximum duration of various 

 atretic characteristics of the ovaries of starved northern 

 anchovy. 



oocyte resorption than usually occurs under 

 natural conditions. Variation in the female nutri- 

 tional state, food ration, water temperature, day 

 length, and a host of other variables may affect 

 rates of atresia. In addition, field data indicate (see 

 next section) that some spavming may occur in 

 females with low to moderate levels of alpha 

 (yolked) atresia, indicating that such stages may 

 persist under natural conditions for extended 

 periods. Despite these uncertainties we believe 

 that our laboratory estimates of atretic rates are 

 useful for making a rough estimate of the mini- 

 mum time elapsed since the end of the spawning 

 season in sea-caught females. 



Natural Rates of Atresia 



In this section we analyze sea data taken since 

 1977 for the occurrence of four ovarian atretic 

 states in a northern anchovy population: 



Atretic state — no alpha atresia of yolked oo- 

 cytes (yolked oocytes present). 



Atretic state 1 — alpha atresia of yolked oo- 

 cytes where <50% of the yolked oocytes are af- 

 fected. 



Atretic state 2 — alpha atresia of yolked oocytes 

 where 50% or more of the yolked ooctyes are af- 

 fected (Fig. 5a, b). 



Figure 5. — Northern anchovy ovaries wath increasing atresia 

 states (bar = 0.1 mm), a) 50% of all yolkfed oocytes (Y) are in an 

 alpha (a) stage of atresia (both early and late are counted). This 

 is the division point between atretic state 1 and atretic state 

 2. b) 100% (all) yolked oocytes are in an alpha stage of atresia 

 (Ya). Also present are a few unyolked alpha atretic oocytes and 

 several beta (j8) stage atretic follicles. This is still in atretic 

 state 2. c) All yolk has been resorbed leaving only unyolked 

 oocytes (U) and many beta (/3) stage atretic follicles. This is 

 atretic state 3. 



Atretic state 3 — ovaries with no yolked oocytes 

 present and beta stage atresia present (Fig. 5c). 



In addition to the atretic condition of the ovary, 

 we also include histological evidence of recent or 

 imminent spawning using the system of Hunter 





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