Ferreira and Vooren Age. growth, and structure of vertebra in Galeorhmus galeus 



27 



formed by a hyalin, unmineralized cartilage (Fig. 17). 

 A 45cm TL juvenile shark's vertebra showed some 

 mineralization of the intermedialia, but unmineralized 

 areas were still present. Two rings were observed (Fig. 

 18). The first ring was probably formed during the first 

 winter after the birth in November (Peres 1989). The 

 most recent one was just forming on the margin. In 

 adult individuals the largest number of rings was 41, 

 observed in a female of 155cm TL. 



Histological observations revealed the presence of a 

 thin uncalcified layer at the very edge of the vertebrae, 

 peripheral to the outermost narrow or wide calcified 



Figure 16 



Microradiograph of a sagitally sectioned vertebral column 

 from a Galeorhinus galeus embryo, showing calcification 

 (white zones) of double cone in centrum (50 x). 



zones at the margin (Fig. 18). This indicates that the 

 marginal growth of the vertebra starts with the for- 

 mation of an unmineralized layer of cartilage which is 

 subsequently mineralized. This layer is probably pres- 

 ent throughout the year and does not by itself indicate 

 periodicity of ring formation. 



Back-calculation 



All linear regressions of total length on vertebral radius 

 were significant (p<0.05). The regression slopes were 

 significantly different between juveniles and adults 

 (j0<0.05) and between adult males and females (p< 

 0.05). Therefore, a power relationship was found to be 

 more adequate to fit the pooled data for juveniles and 

 adults of each sex. The following equations were ob- 

 tained: Females (AT = 26), TL = 32.59 x R om and 

 males (AT = 33), TL = 25.07 x R - 897 , where N indi- 

 cates sample size and R radius of vertebra, with TL 

 in cm and R in micrometric units (1 m.u. = 10~ 3 cm) 

 (Fig. 19). 



Lengths were back-calculated by age class and did 

 not reveal the occurrence of Rosa Lee phenomenon 

 (Gulland 1977), so the lengths at age were averaged 

 (Table 3). The von Bertalanffy growth parameters 

 were: females, k = 0.075, L M = 163cm, and t = -3.00; 

 males, k = 0.092, L 00 = 152cm, and t =-2.69. The 

 growth curves calculated from these parameters are 

 shown in Fig. 20. 



Using the ELEFAN software, several attempts were 

 made to find the growth curve best fitted to the length- 

 frequency data. In order to obtain a data set contain- 



Figure 17 



Sagittal section of vertebra from a 

 Galeorhinus galeus embryo, showing 

 (a) perichondrium, (b) hyaline cartilage 

 in intermedialia, and (c) calcified car- 

 tilage of cones. (Haematoxylin. 100 x) 



