HUNTER and MACEWICZ: ATRESIA IN NORTHERN ANCHOVY OVARY 



disintegrates, the thin prezona radiata (if present) 

 dissolves and the granulosa cells enlarge, and, 

 with only a slight proliferation, phagocytize the 

 unyolked oocyte. When resorption is complete, all 

 that remains is the follicle. 



2) Beta ((3) Stage Atresia — Initially the beta 

 stage atretic follicle is a compact structure com- 

 posed of numerous disorganized granulosa cells 

 surrounded by a thin thecal and blood vessel layer. 

 The nucleus of some of the granulosa cells is pyc- 

 notic and many of the cells contain a large in- 

 tracellular vacuole that may be empty or contain 

 amorphous particles. Occasionally one or more 

 large intercellular cavities may exist among the 

 granulosa cells (Fig. 3b, d). Preovulatory beta 

 stage atretic follicles containing such cavities may 

 easily be confused with postovulatory follicles 

 (older than 48 h) and, as a consequence, we do not 

 age postovulatory follicles older than 48 h (Hunter 

 and Goldberg 1980). In addition, small (older) beta 

 stage atretic follicles from yolked oocytes (Fig. 3c, 

 d) are indistinguishable from beta stage atretic 

 follicles from unyolked oocytes. Thus, we do not 

 identify the original oocyte type undergoing at- 

 resia in beta or subsequent atretic stages; such 

 distinctions are made only for alpha stage atretic 

 oocytes. 



Three different patterns of atresia may occur at 

 the conclusion of the beta stage: 1) The follicle 

 may follow the classic pattern outlined by 

 Bretschneider and Duyvene de Wit (1947) and pass 

 through subsequent gamma and delta stages (both 

 characterized by increased pigmentation, see be- 

 low); 2) the follicle may be completely resorbed 

 during the beta stage leaving no histological 

 characteristics that can be identified; and 3) the 

 follicle may pass directly from a beta stage struc- 

 ture to a delta stage structure without passing 

 through the intervening gamma stage. In north- 

 ern anchovy, either the duration of the gamma 

 stage is very short or few follicles pass through the 

 gamma stage into the delta stage, because in re- 

 gressing ovaries the incidence of gamma stages is 

 very low compared with those of either beta or 

 delta stages. 



3) Gamma (y) Stage Atresia — The gamma 

 stage atretic follicle is usually much smaller than 

 the typical beta stage follicle (Fig. 3e). The 

 granulosa cells contain flocculent material of 

 light-yellow hue and have nuclei of very irregular 

 shape. The granulosa cells are surrounded by 

 many fewer thecal cells and blood vessels than 



occur in the beta stage atretic follicles. Occasion- 

 ally we see an atretic follicle of quite different 

 appearance in anchovy ovaries which we classify 

 as a gamma stage atretic follicle; they are included 

 in the gamma stage because they also contain 

 flocculent material of light-yellow hue. In this 

 case, the flocculent yellow material is extracellu- 

 lar rather than intracellular, and the material is 

 encapsulated by a layer of granulosa and thecal 

 cells. It is possible that the extracellular flocculent 

 material is produced by the disintegration of 

 granulosa cells. 



4) Delta (6) Stage Atresia — The diagnostic 

 characteristic of this stage is the presence of a dark 

 yellow-brown, finely granular pigment in the 

 granulosa cells (Fig. 3f). The delta stage atretic 

 follicles are normally very small structures typi- 

 cally composed usually of 2-20 granulosa cells in 

 the ovarian connective tissue stroma. Thecal cells 

 and blood vessels no longer encompass the 

 granulosa cells. 



In our laboratory work 3-4 levels of abundance 

 were recorded for each of three atretic classes seen 

 in anchovy ovaries (alpha, beta, and gamma + 

 delta stages). The gamma and delta stages were 

 combined since gamma stages were rare. In addi- 

 tion, the alpha stage atretic class was further sub- 

 divided into three groups depending on the type of 

 oocyte undergoing atresia (unyolked, partially 

 yolked, and yolked oocytes). In the discussion that 

 follows we have combined some of the abundance 

 levels and have considered only what we believe to 

 be the most diagnostic atretic characteristics, al- 

 though all atretic characteristics as originally 

 tabulated are given in Tables 1 and 2. The system 

 of atretic classifications was further simplified in 

 our presentation of the analysis of sea-caught 

 specimens, but that will be discussed sub- 

 sequently. 



RESULTS 



Rates of Atresia in the Laboratory 



The speed at which yolked oocytes were resorbed 

 was striking. In the first sample (elapsed time 

 from onset of starvation = 3 d) the ovaries of 11 of 

 the 24 females (46%) had yolked ooc5d;es in the 

 alpha stage of atresia (Table 1). By the 13th day, 

 half of the females no longer had yolked oocj^s, 

 and in the rest of the females 50% or more of their 

 yolked oocytes were in the alpha stage of oocyte 



125 



