NOTE Tserpes and Tsimenides. Determination of age and growth of Xiphias gladius 



595 



to dry completely. A section about 2 cm thick was cut 

 with an electric saw from each dried spine at the point 

 where the spine flares (condyle). Each section was 

 placed in a plastic cylinder (3 cm diameter and 2 cm 

 height) which was then filled with liquid resin. These 

 were left to dry for at least 12 hours, the plastic case 

 was removed, and two or three sections about 1 mm 

 thick were cut distally with a "Stuers" accutom. 



Age determination 



Spine sections were read under a binocular micro- 

 scope at 12x magnification by using reflected light 

 and a dark background. The distances from the fo- 

 cus to the edge of the section on the dorsal rim (spine 

 radius) and from the focus to each annulus were 

 measured with an optical micrometer. Sections were 

 read by two readers and identical counts were ob- 

 tained in >80% of the cases; samples were consid- 

 ered unreadable and were excluded from the analy- 

 sis if discrepancies in counts could not be resolved. 



Typically, broad opaque bands and narrow trans- 

 lucent ones could be seen alternating outwards from 

 the central core. Translucent bands that form around 

 the entire circumference of the spine were consid- 

 ered to be annuli and the total number of these bands 

 was recorded (Fig. 1). 



Age classes were assigned on the basis of the num- 

 ber of annuli and the following characteristics of the 



bands: 1) the disappearance of the first annulus from 

 older fish and 2) the existence of multiple bands 

 mainly in larger fish. Preliminary analysis of LJFL 

 measurements taken in nursery areas of the Aegean 

 sea have shown that swordfish reach a length of 

 about 80-90 cm at one year of age. The first annulus 

 could be seen in fish of this size at an average dis- 

 tance of 1.5 mm (SD=0.08) from the focus, but it was 

 usually not visible at lengths greater than 100 cm 

 (Fig. 1). In such cases, and if the total spine radius 

 was greater than 1.5 mm, one year was added to the 

 assigned age. As described by Berkeley and Houde 

 ( 1983), multiple bands are those which form around 

 the entire circumference of the spine such that the 

 distance between them is substantially less than that 

 of the preceding and following annual bands. In these 

 cases, the clearest band was considered an annulus 

 and the others were ignored. However, if it was not 

 possible to identify such a band, the specimen was 

 considered unreadable. When the opaque-translucent 

 zonation was such that annuli could not be defined, 

 such specimens were also considered unreadable. 



Data analysis 



The marginal increment ratio (MIR) was estimated 

 for each specimen according to the formula: 



MIR = (S-r)/S, 



Figure 1 



Sections of second anal-fin spine with five growth zones (A) and one growth zone (B) used for age 

 determination of swordfish, Xiphias gladius, from the eastern Mediterranean. First annulus is miss- 

 ing in section (A) whereas it can be clearly seen in section (B). Estimated location of first annulus in 

 section (A), based on its location in section (B), is indicated by an arrow. Lower-jaw fork lengths 

 (LJFL) of animals (A) and (B) were 162 and 95 cm, respectively. 



