Karlou-Riga and Economidis: Ovarian atretic rates and sexual maturity of Trachaurus trachurus 



67 



season for the average female. In addition, anatomi- 

 cal maturity stages and the gonadosomatic index 

 were compared to histological results in order to show 

 the extent that these data can provide accurate infor- 

 mation concerning the reproductive cycle. Finally, we 

 estimated the length at which 50% of females are ma- 

 ture, using both histological and macroscopic criteria. 



spent. Gonads and livers were removed and weighed 

 to the nearest 0.1 gram. 



Ovaries classified into maturity stages greater 

 than II (about a third of the length of the body cav- 

 ity) were preserved in 7% neutral, buffered formalin 

 for histological examination. A number of randomly 

 selected ovaries in maturity stages I and II were also 

 preserved in 7% buffered formalin. 



Materials and methods 



Sampling and macroscopic classification 



Samples of European horse mackerel were collected 

 in the Saronikos Gulf (Fig. 1) by a commercial trawler 

 operating from October through May. In the study 

 area, the mean annual temperature and salinity at 

 a depth range of about 100-200 meters were 14°C 

 and 38%c, respectively. At this depth range, which 

 characterizes European horse mackerel distribution 

 (Fischer et al., 1987), there was little monthly tem- 

 perature variation during the sampling period 

 (Georgopoulos 3 ). The samples were taken almost 

 monthly, from October 1989 until May 1991, but they 

 were taken more often during the peak spawning 

 period until the end of the sampling period. Supple- 

 mentary samples were obtained with a purse seiner 

 during the period closed to trawling (i.e. June-Sep- 

 tember) (Table 1). 



European horse mackerels were ran- 

 domly selected from the catch, and the to- 

 tal length of the fish was measured to the 

 nearest centimeter. Ten fish from each 1- 

 cm length class (throughout the available 

 range) were retained. These fish were 

 measured (total length) to the nearest 

 millimeter, sexed, and weighed (total 

 weight) to the nearest gram. After gross 

 examination of the gonads, the fish were 

 classified into maturity stages according 

 to Macer (1974). Because some of the 

 stages used by Macer were difficult to dis- 

 tinguish macroscopically, (such as devel- 

 oping virgin (maturing/immature) versus 

 resting, ripe versus running, and spent 

 versus recovering), three pairs of Macer's 

 stages were grouped into single stages. 

 Thus, the maturity scale used consisted 

 of seven stages: I = virgin, II = resting, 

 III = early developing, IV = later develop- 

 ing, V = ripe, VI = partly spent, and VII = 



3 Georgopoulos. D. 1993-95. National Centre for 

 Marine Research, Aghios Kosmas, 16 604 Hellini- 

 kon, Greece. Personal commun 



Histological method and classification 



A small piece (about 0.5-1 cm long) of each preserved 

 ovary was removed, dehydrated, and embedded in 

 paraffin. Subsequently, 3-/im sections were cut and 

 stained with Harris hematoxylin followed by eosin 

 counterstain (H+E). In each sectioned ovary we re- 

 corded the following characters (Wallace and Selman, 

 1981; Mayer et al., 1988; Macewicz and Hunter, 

 1993): (a) oocytes that had not begun vitellogenesis; 

 (b) oocytes in early vitellogenic stages; (c) advanced 

 yolked oocytes; (d) migratory-nucleus-stage oocytes; 

 (e) hydrated oocytes; and (f) postovulatory follicles. 

 Postovulatory follicles were aged following the crite- 

 ria used for T. symmetricus (Macewicz and Hunter, 

 1993; Macewicz 4 ). The ovarian sections were also 



4 Macewicz, B. J. 1993. Southwest Fisheries Science Center, 

 Natl. Mar. Fish. Serv., NOAA, P. O. Box 271, La Jolla, CA 

 92038. Personal commun. 



Yugoslavia 



Figure 1 



Map of the Saronikos Gulf (Greece) 



