72 



Fishery Bulletin 94| 



1996 



E 



0) 



~ 60 



Ocl Nov Dec Jan Feb Mar Apt May Jul 



Month 



~ 60 



Oct Nov Dec Jan Feb Mar 



Month 



Apr May Jul 



Figure 3 



Percentage of mature European horse mackerel, 

 Trachurus trachurus, females classified into atretic 

 states (Al during the first reproductive season and (B) 

 during the second reproductive season. No ovaries were 

 sectioned in June (A). Five ovaries sectioned in May 

 (B) were not classified into atretic states because of their 

 low number. Open solid bar = atretic state 0; filled solid 

 bar = atretic state 1; diagonally hatched bar = atretic 

 state 2; cross-hatched bar = atretic state 3. 



tracting the number of days to the 50% spawning 

 point (67 days) from the number of days to the 50 r /£ 

 postspawning point (161 days) which resulted in a 

 spawning duration estimate of 94 days. 



An increase in the mean number of potential and 

 past-spawning stages per female occurred until early 

 May indicating a possible increase in spawning fre- 

 quency ( Fig. 5 ). By the end of May, when atretic states 

 2 and 3 were estimated to be very high, the mean num- 

 ber of these spawning stages decreased sharply. This 

 shows that no other oocytes were recruited into vitello- 

 genesis as the spawning period was ending. 



Gonadosomatic and hepatosomatic index From 

 the histological study we observed that no females 



of age less than 2 years spawned (Karlou-Riga 5 ). 

 Therefore, GSI and HSI were both calculated for fe- 

 males older than 1 year of age. The peak GSI value 

 occurred in February 1989, when the histological 

 data indicated that half of the mature females (52%) 

 were spawning (Fig. 6). GSI decreased in the follow- 

 ing months, whereas the peak HSI value was ob- 

 served near the end of the first reproductive period 

 (around May). During the summer and autumn of 

 1990, the two indices remained low, and an increase 

 occurred in December 1990 denoting the onset of the 

 second reproductive season (Fig. 6). During the sec- 

 ond season, the peak GSI value was about one third 

 of the respective value of the same index observed in 

 the previous period (Fig. 6). 



The correlation of the two indices was tested by 

 using Spearman's rank correlation procedure (Zar, 

 1984 ). Disagreement was found during the sampling 

 period (Oct. 1989-Nov. 1990: r=-0.2829, P<0.001, 

 n=551; Dec. 1990-May 1991: r=-0.1955, P<0.001, 

 «=429). The negative correlation between GSI and 

 HSI indicates that GSI and HSI did not follow the 

 same course, indicating most probably that ovarian 

 growth proceeds at the expense of liver content as is 

 the case for other teleost species (Wallace and 

 Selman, 1981), including Trachurus murphyi (Kai- 

 ser, 1973). 



Estimation of length at 50% mature 



The sex ratio was examined by applying the paired- 

 sample ^-test in both reproductive periods, and no 

 difference was found at 5% level of significance 

 (£=1.92, P=0.127). Length-frequency distributions of 

 females for the two periods were tested by applying 

 the Kolmogorov-Smirnov two-sample procedure. No 

 significant length differences were found between 

 females that were macroscopically staged (P=0.96 

 [>0.05]) and those that were histologically staged 

 (P=0.37 [>0.05]> for maturity status. Therefore, the 

 data from the two periods were combined, and the 

 ML 5(| values were estimated from the logistic curves 

 separately for histological and macroscopical data 

 (Fig. 7). 



Fish with lengths close to ML 50 were two to three 

 years old (Karlou-Riga 5 ). The macroscopically esti- 

 mated ML 5n (220 mm) was a little higher than the 

 histologically estimated ML- (211 mm), probably 

 owing to the macroscopical misclassification of some 

 mature females as immature. However, analysis of 



''Karlou-Riga, C. 1995. Age and growth of Trachurus 

 trachurus (L.) in the Saronikos Gulf (Greece I. Unpubl. 

 manuscr.. Fisheries Laboratory, Ministry of Agriculture, 15 

 Karaoli and Dimitriou St., GR-18531 Piraeus, Greece. 



