FISHERY BULLETIN. VOL. 77, NO 3 



could be determined by the presence of postovula- 

 tory follicles but the estimate would have to be 

 made soon after spawning. Through techniques of 

 Leongi 19711 it was possible to induce spawning in 

 the northern anchovy, Engraulis mordax, in the 

 laboratory, making it possible to characterize the 

 histological degeneration of postovulatory folli- 

 cles on a time basis. Thus, it seemed feasible that 

 spawning frequency of natural populations oi E. 

 mordax could be estimated from incidence of post- 

 ovulatory follicles in females once the period in 

 which they could be detected was established. 

 Moreover, once recently spawned fish were iden- 

 tified, the rate of maturation of subsequent egg 

 batches as well as the number of eggs produced per 

 batch could be estimated. 



The objectives of this study were to establish the 

 detection period for postovulatory follicles in 

 northern anchovy and to estimate the incidence of 

 natural spawning through histological examina- 

 tion of these structures. In addition, by using this 

 information to guide our selection of specimens, 

 we provide a new estimate of the number of eggs 

 released per spawning or batch fecundity, and the 

 time required for subsequent spawnings. Previous 

 estimates for anchovy based on frequency dis- 

 tributions of yolked oocytes include those of Mae- 

 Gregor (1968) and Norberg.'^ 



METHODS 



The period over which postovulatory follicles 

 can be detected in the ovary was determined from 

 anchovy held in the laboratory. Groups of anchovy 

 reared to sexual maturity were induced to spawn 

 using the method of Leong (1971). A total of 119 

 females were sampled; fish were killed at the time 

 of spawning and thereafter at 24-h intervals up to 

 9 days after spawning. Ovaries were fixed in 

 Bouin's fixative or 10% neutral buffered Forma- 

 lin"^ and embedded in Paraplast. Histological sec- 

 tions were cut at 6 ixm and stained with Harris' 

 hematoxylin followed by eosin counterstain, Mas- 

 son's trichrome, periodic acid-Schiff reagent, or 

 Heidenhain's iron hematoxylin. A classification 

 system for postovulatory follicles was established 

 and laboratory specimens were classified without 

 prior knowledge of their age to estimate the accu- 

 racy of the technique. Field samples were then 

 classified using the same criteria. Three field col- 

 lections of anchovy females from the Southern 

 California Bight were examined to determine the 

 frequency of spawning in natural populations: 

 3 commercial purse seine samples of 38-65 temales 

 each from March 1977; 4 research trawl samples of 

 1-11 females from September 1977; and 29 re- 

 search trawl samples of 10 or 11 females from 

 February 1978 (Figure 1). 



■■^Norberg, R. H, 1975. Investigations on the fecundity of 

 northern anchovy, jack mackerel and Pacific maciter- 

 el. Unpubl. manuscr., 2,3 p. Calif. Dep. Fish Game, 350 Golden 

 Shore. Long Beach, CA 90802. 



"Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



FiCURE I. — Location of samples of 

 fftnaie northern anchovy taken off 

 southern California in March and Sep- 

 tember 1977 and February 1978. 



642 



