BIOLOGY OF THE MUTT0NFI8H 



73 



5. AGE ESTIMATION AND EATE OF GROWTH. 



An estimation of the age and rate of growth of the muttonfish has been made 

 from a study of the otoliths. The scales are very small and show no uniformity in 

 annual growth area-. The vertebrae were found to be very unsatisfactory in the older 

 fish because of the difficulty of distinguishing the rings toward the margins. How- 

 ever, in the younger specimens they were a valuable check on the otolith counts. 

 The otoliths sire comparatively small and regular in form and show clearly alternate 

 light and dark areas. Final counts of the bands were made with the low power objec- 

 tive of the compound microscope upon ear-stones cleared and mounted in glycerine. 

 No grinding down of the stones was necessary. In all, otoliths from ninety -one speci- 

 mens have been examined. The method of computation has been somewhat the same as 



Fig. 



3. 



(a) 



(h) 



(c) 



(d) 



(e) 



(/) 



e 



Muttonfish otoliths drawn to the same scale. 



No. 119: 

 No. 124: 

 No. 41 : 

 No. 9'8 : 

 No. 31: 

 No. 33; 



llx -7 

 1-5 X -8 

 2-2 X 1-4 

 3-2 X 2 

 4-2x 2-5 

 4-7 X 30 mm. 



mm. 

 mm. 

 mm. 

 mm. 

 mm. 



Fish in first summer, 9'0 cm. in length. 

 " " second summer, 12-6 cm. in length. 



" third summer. 21- cm. in length. 

 " " sixth summer, 33-5 cm. in length. 

 " " tenth summer, 51-5 cm. in length. 

 " " seventeenth summer. 61-5 cm. in length. 



that used by Fryd" (1901) for Zoarces vivipanis. He assumes that during the winter 

 a comparatively small amount of material is added to the otolith and this shows as a 

 narrow opaque band or line. During the summer a comparatively large amount is 

 added, which shows as a broad and much less opaque area. The dark centre 



