HUNTER and MACEWICZ: ATRESIA IN NORTHERN ANCHOVY OVARY 



were large, often consisting of 100 or more catches 

 of 10-20 females each. In all collections ovaries 

 were classed according to atretic characteristics as 

 well as on the basis of the presence of postovula- 

 tory follicles (age and age 1 d) and hydrated eggs 

 according to the method described by Hunter and 

 Goldberg (1980). All but two of the collections were 

 from the Southern California Bight or northern 

 Baja California, the region where the Central 

 subpopulation of the northern anchovy is concen- 

 trated (Vrooman et al. 1981). Two collections were 

 from the vicinity of Monterey and San Francisco 

 Bays. Fish from these areas appear to have a dif- 

 ferent spawning season from those of fish to the 

 south so they are listed separately in our seasonal 

 tabulations. All collections were classified using 

 histological criteria to determine the incidence of 

 ovarian atretic states as a function of female size, 

 season, and reproductive state. 



Histological Characteristics 



We describe below the histological characteris- 

 tics of four oocyte classes and four stages of atresia 

 in the northern anchovy. These stages and classes 

 are subsequently used to define various ovarian 

 atretic states in laboratory and sea-caught female 

 anchovy. 



Oocyte Classes 



The northern anchovy is a multiple spawning 

 fish (Hunter and Goldberg 1980) with asynchro- 

 nous oocyte development (oocytes in many stages 

 of development occurring simultaneously in re- 

 productively active ovaries; Wallace and Selman 

 1981). During the spawning season oocyte devel- 

 opment is a continuous process involving all 

 stages with a new spawning batch maturing every 

 week to. 10 d (Hunter and Leong 1981). Oocyte 

 development and maturation in teleosts, reviewed 

 recently by Wallace and Selman (1981), has fre- 

 quently been subdivided into many stages (An- 

 drews 1931^ Yamamoto 1956; Lambert 1970b), but 

 our work required a simpler histological classifi- 

 cation system. We have combined the stages of 

 past authors into four oocyte classes (unyolked 

 oocytes, partially yolked oocytes, yolked oocytes, 

 and hydrated oocytes), and we describe the his- 

 tological characteristics of each class below. 



"Andrews, C. B. 1931. The development of the ova of the 

 California sardine (Sardina caerulea). Unpubl. manuscr., 88 

 p. Stanford Univ., Stanford, CA 94305. 



1) Unyolked Oocytes — This class includes all 

 oocytes without yolk that are about 0.04 mm or 

 larger and range upward in size to about 0.35 mm 

 (U, Fig. la, b). Oocytes <0.04 mm are excluded 

 because they consist mostly of "oogonium nests", 

 do not have a true follicle layer, and do not seem to 

 undergo degeneration (o, Fig. lb). The smaller 

 oocytes within this class (0.04-0.15 mm) are spher- 

 ical, have a large nucleus with a narrow homoge- 

 nous very densely staining cytoplasm (Fig. lb). A 

 very thin single layer of elongated, spindlelike 

 cells (the beginning of the granulosa layer) sur- 

 rounds these small oocytes. The large oocytes in 

 this class are oval, the C5rtoplasm stains faintly 

 with hematoxylin and has a cloudy, mottled ap- 

 pearance (Fig. Id). The oval nucleus of these oo- 

 cytes contains several nucleoli and is surrounded 

 by a granular perinuclear zone. In these larger 

 oocytes a thin, definite, faintly eosinophilic stain- 

 ing, hyaline membrane (precursor of the zona 

 radiata) appears between the oocyte and the grow- 

 ing follicle. The follicle consists of a narrow single 

 inner layer of cuboidal granulosa cells and a single 

 outer layer of flat elongated thecal cells with some 

 blood capillaries. The larger oocytes also may have 

 some small vesicles in the periphery of the cyto- 

 plasm. These vesicles are at times difficult to dis- 

 tinguish and they seem to disappear in yolked 

 oocytes. No oil vacuoles exist as northern anchovy 

 eggs do not contain oil droplets. 



2) Partially Yolked Oocytes — Oocytes in this 

 class are in the early stages of yolk deposition 

 (vitellogenesis) and range in size from 0.3 to 0.5 

 mm (major axis) (P, Fig. Id, g). The class includes 

 oocytes in the initial stage of yolk deposition up to 

 and including those in which yolk granules or 

 spherules extend three-fourths of the distance 

 from the periphery to the perinuclear zone. Yolk 

 deposition starts at the periphery of the oocyte 

 cytoplasm as small eosinophilic staining granules 

 and then subsequently spreads internally until 

 they nearly reach the finely granular perinuclear 

 zone. Usually by this time the granules have be- 

 come small spherules. The oval-shaped nucleus of 

 oocytes in this class contains several nucleoli. 

 Delicate striations appear on the hyaline mem- 

 brane between the oocyte and follicle layer at the 

 time yolk appears in the oocyte. As maturation 

 proceeds, the follicle layer becomes wider due to an 

 increase in the width and proliferation of 

 granulosa cells. The thecal cells do not increase in 

 size but remain elongated, flat cells with occa- 

 sional blood capillaries and form a thin outer cov- 



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