66 



Abstract.— Histological sections of 

 European horse mackerel, Trachurus 

 trachurus (L.) ovaries were used to fol- 

 low oogenesis and to describe the 

 atretic states. Atretic states were used 

 to examine the reproductive cycle dur- 

 ing two successive reproductive sea- 

 sons. During the first season, spawn- 

 ing lasted from December to May, with 

 peak spawning occurring between the 

 end of March and the beginning of 

 April. The duration of the spawning 

 season for the average female was es- 

 timated to be about 3 months. Atretic 

 state 1 (yolked oocytes where <50'7r 

 were in alpha ( a) stage atresia ) was the 

 most common atretic condition during 

 the spawning season. Atretic states 2 

 (yolked oocytes where >50% were in a- 

 stage atresia) and 3 (no yolked oocytes 

 present but ji atresia or later atresia 

 stages) increased near the end of the 

 season, and at the end of the season, 

 females in atretic state 3 were predomi- 

 nant. The mean number of potential 

 and past-spawning stages per female 

 increased throughout the spawning 

 season, indicating an increase in 

 spawning frequency. During the second 

 season, spawning occurred from Janu- 

 ary to May. High numbers of females 

 in atretic states 2 and 3 were noted dur- 

 ing the period considered to be the 

 middle of the season, followed by an 

 increase of females classified in atretic 

 state (yolked oocytes with no a-atre- 

 sia stage), indicating a species flexibil- 

 ity to different conditions. The use of 

 traditional macroscopic methods, such 

 as gonadosomatic and hepatosomatic 

 indices, revealed a conformity with the 

 histological data concerning the iden- 

 tification of the spawning season. To- 

 tal body lengths at female maturity 

 (ML 50 ), estimated histologically and 

 macroscopically, were found to be 211 

 and 220 mm, respectively. 



Ovarian atretic rates and sexual 

 maturity of European horse 

 mackerel, Trachurus trachurus (L.), 

 in the Saronikos Gulf (Greece) 



Constantina Karlou-Riga 



Fisheries Laboratory. Ministry of Agriculture 

 1 5 Karaoli and Dimitnou St 

 GR- 18531 Piraeus, Greece 



Panos S. Economidis 



Department of Zoology, Aristotle University 

 PO. Box I 34, GR-54006 Thessaloniki, Greece 



Manuscript accepted 20 July 1995. 

 Fishery Bulletin 94:66-76 (1996). 



In the Greek seas, the genus Trach- 

 urus is represented by three species: 

 European horse mackerel, T. trach- 

 urusCL. ); Mediterranean horse mack- 

 erel, T. mediterraneus (S.); and blue 

 jack mackerel, T. picturatus (B. ). The 

 first two species are of commercial 

 value and are very abundant, where- 

 as the third is very scarce. Their av- 

 erage catch over the years 1987-90 

 constitutes about 10% of the total 

 annual yield of the country and 15% 

 of the total Saronikos Gulf catch 

 (NSSG, 1989-93). Although these 

 species are commercially important 

 fish for the entire Mediterranean re- 

 gion, little is known about their biol- 

 ogy, especially their reproduction. The 

 genus Trachurus comprises multiple 

 spawners with a prolonged spawning 

 season (Polonsky and Tormosova, 

 1969; Kaiser, 1973; Macer, 1974; 

 Andrianov, 1985; Eaton, 1989; Liso- 

 venko and Andrianov, 1991; Mace- 

 wicz and Hunter, 1993; Komarov 1 ). 



The most convenient method of 

 determining the reproductive cycle in 

 a female is to observe the seasonal 

 developmental changes of the gonads. 

 Until recently these changes for spe- 

 cies of Trachurus were examined by 

 studying the seasonal variations of 

 maturity stages or the gonadosomatic 

 index, or both (Kaiser, 1973; Macer, 



1974; Nazarov, 1977; Arruda, 1984; 

 Andrianov, 1985; Kerstan, 1985; Ko- 

 marov 1 ). However, for multispawners 

 the use of gross anatomical criteria 

 provides a less accurate assessment 

 offish maturity and reproduction in 

 comparison with that of histological 

 methods ( Hunter and Macewicz, 1985a; 

 Dickerson et al„ 1992; Eltink 2 ). Histo- 

 logical examination is essential for de- 

 tecting maturing females, partly 

 spawned fish, the postovulatory fol- 

 licles, and atretic oocytes. 



In the present work we used the 

 ovarian atretic states defined by 

 Hunter and Macewicz (1985b) in 

 order to follow the reproductive 

 cycle of European horse mackerel. 

 Specifically, we estimated the rate 

 at which females spawn and pass 

 from the active (when fish are ca- 

 pable of spawning in the current 

 season) to the inactive state (when 

 fish have completed their spawning 

 cycle), the peak period of spawning, 

 and the duration of the spawning 



1 Komarov, J. A. 1964. On the reproduc- 

 tion of horse mackerel (Trachurus trach- 

 urus) off the southwestern coast of Africa 

 ICES Council Meeting 94, 5 p. (Mimeo. I 



2 Eltink, A. 1991. Batch fecundity and 

 fraction spawning of horse mackerel 

 ( Trachurus trachurus L. I. European Com- 

 munity Study Contract BO-1990-207, 71 p. 



