116 



Fishery Bulletin 88(1), 1990 



clarified by grinding and polisliing on both surfaces. 

 Growth rings were counted on the polished surface 

 with no further preparation. Rings were accentuated 

 by observing the specimen under polarized light and 

 were enumerated with a hand counter by following the 

 ring sequence with a pencil via a camera lucida. Speci- 

 men age in days (i.e., statolith ring number) was estab- 

 lished by taking the mean of at least three counts that 

 deviated less than 10%. Specimen age was rounded to 

 the nearest whole number. 



The statolith size and shape of a newly hatched S. 

 lessoniana were determined from a specimen which 

 was hatched from an egg trawled-up in Cleveland Bay 

 off Townsville. This specimen further provided infor- 

 mation on DML at hatching (5.3 mm). Growth rate of 

 aged specimens was thus taken as the increase in man- 

 tle length in mm/day minus 5.3 (i.e., DML-5.3/age). 



Results 



The notable characteristics oi Sepioteuthis lessoniana 

 statoliths are a rounded dorsal dome and a relatively 

 long, thin rostrum (Fig. IB). Unlike the sepioid Idio- 

 sepius pygmaeus in which rings were most obvious in 

 the lateral region of the statolith (Jackson 1989) or 

 Loligo (Photololigo) edulis (Natsukari et al. 1988) which 

 has a clearly countable ring sequence in the rostrum, 

 S. lessoniana statolith rings were most discernable in 

 the dorsal dome. Rings were very difficult to discern 

 in the rostrum. 



The ring sequence within the statolith commenced 

 from a prominent check, although some faint ring 

 structure was visible inside this check. This check ring 

 corresponded closely in size to the outer margin of the 

 statolith of the newly hatched S. lessoniana (which also 

 had some ring structure at hatching), indicating that 



this ring represents a hatching check. This feature has 

 also been documented in the loliginid .s(iuids/l//o/f')(///i.s 

 suhulata (Lipinski 1986) and Loliga (Phatoliiligo) edulis 

 (Natsukari et al. 1988). 



Tetracycline staining 



The growth ring sequence could be clearly visualized 

 and counted in the vicinity of the tetracycline or cal- 

 cein marks in seven specimens maintained in captiv- 

 ity. The counts of these specimens corresponded to a 

 daily periodicity in ring formation (Table 1). Rings were 

 generally more easily counted between two stain marks 

 (P^ig. IC) than from the stain inark to the edge, as the 

 edge rings are the most difficult to discern. A statolith 

 check was often induced within the statolith, which cor- 

 responded to the date of capture and staining (Figs 

 1A,C). 



When using high magnification or very sharp focus, 

 numerous subdaily rings could be discerned which often 

 made counting of daily rings difficult. This was espe- 

 cially true in areas of the statolith where rings were 

 quite thick (wide). Using a lower magnification or 

 changing the plane of focus helped to delineate the true 

 daily rings that were superimposed over the numerous 

 subdaily rings. A similar phenomena has been shown 

 to exist in the otoliths of the freshwater fish Coregonus 

 spp. (Eckmann and Rey 1987). 



Age and growth 



A total of 23 individual .squids were aged (Table 2) to 

 produce a growth curve (Fig. 2) and to ascertain 

 maturity. (Jrowth inS. lessoniana is rapid, with a large 

 size reached in less than 6 months. Growth rates deter- 

 mined for larger specimens were considerably greater 



