SPAWNING INCIDENCE AND BATCH FECUNDITY IN 

 NORTHERN ANCHOVY, ENGRAULIS MORDAX^ 



J. Roe Hunter^ and Stephen R. Goldberg^ 



ABSTRACT 



Histological criteria were developed to age postovulatory follicles from examination of laboratory- 

 spawned northern anchovy and used to estimate the frequency of spawning of natural populations. 

 One-day-old. postovulatory follicles were the preferred estimator of spa wnmg frequency; 48 hours after 

 spawning postovulatory follicles could not be consistently identified because of their rapid degenera- 

 tion; and the occurrence of postovulatory follicles less than 24 hours old was affected by hour of 

 sampling and sexual composition of the school. The nightly spawning incidence was estimated to be 

 16±4'7r of the northern anchovy population in February and 12'7, in March. Thus, females spawned 

 about every 6-8 days during the peali of the breeding season . The rate of oocyte development corres- 

 ponded with this reproductive rate, indicating that a new mode of yolked oocytes matured about once a 

 week. Nearly all eggs in the most advanced mode in the ovary were spawned in one night and the 

 number of eggs spawned was estimated to be 389 i59eggs/g of female I ovary-free wet weight). The high 

 spawning frequency and the prolonged breeding season of the northern anchovy indicate that total 

 fecundity may be limited by food availability and energy reserves. 



Ichthyoplankton surveys have become one of the 

 standard methods' for estimating biomass of 

 marine fish populations. At high latitudes many 

 fishes produce a single spawning batch per year 

 (Qasim 1956) and spawning biomass may be di- 

 rectly estimated from total fecundity and produc- 

 tion of eggs and larvae. Multiple (fractional) 

 spawning fishes are characteristic of subtropical 

 and tropical seas (Nikolsky 1963) and estimation 

 of spawning biomass from egg and larval produc- 

 tion is dependent upon the number of spawnings 

 per year and the number of eggs per spawning. At 

 present, no adequate method exists for estimating 

 these two parameters for pelagic, multiple spawn- 

 ing fishes. 



Past methods have employed measurements of 

 size-frequency distribution of yolked oocytes ( usu- 

 ally eggs >0.2 mm in diameter). Eggs are often 

 distributed in one to three modes and the number 

 of eggs in the most advanced mode has been as- 

 sumed to be equal to the number of eggs produced 

 per spawning (Clark 1934; MacGregor 1968). 

 Another approach has been to count all yolked 

 oocytes in reproductively active females and to 



'Supported in part by the Marine Research Committee of the 

 State of California. 



^Southwest Fisheries Center La JoUa Laboratory, National 

 Marine Fisheries Service, NOAA. P.O. Box 271, La Jolla, CA 

 92038. 



'Department of Biologv, Whittier College, Whittier. CA 

 90608. 



assume that these are equal to the number of eggs 

 spawned in a season (Macer 1974). Neither ap- 

 proach provides conclusive evidence for the 

 number of spawnings nor total egg production. All 

 eggs in the most advanced mode may not ovulate 

 (Clark 1934; Yamamoto and Yamazaki 1961) 

 and atresia may reduce the number of eggs per 

 spawning (Macer 1974; Ivankov 1976). Further, 

 the total number of yolked oocytes may not pro- 

 vide an estimate of total fecundity because some of 

 the small unyolked oocytes, not included in such 

 counts, could mature later during the same breed- 

 ing season. 



It has long been known in teleost fishes (Cun- 

 ningham 1898) that at ovulation a remnant of the 

 ovulated follicle (empty or postovulatory follicle) 

 remains in the ovary. Postovulatory follicles are 

 believed to be transitory because of their rarity in 

 field-collected material (Wheeler 1924; Yamamoto 

 1956; Gokhale 1957; DeVlaming 1972; Goldberg 

 1977; Andrews'*), but actual measurements of 

 their longevity are rare because the time of spawn- 

 ing must be known. Yamamoto and Yoshioka 

 ( 1964 ), using Oryzias latipes which spawns every 3 

 days, reported postovulatory follicles were barely 

 distinguishable on the third day after spawning. 

 They suggested that the frequency of spawning 



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

 California sardineiSardina caerijlea\ Llnpubl. manuscr., 88 p. 

 Stanford University, Stanford, CA 94305. 



Manuscript accepted March 1979 

 FISHERY BULLETIN: VOL. 77. NO. 3, 



1980. 



641 



