Journal of the Marine Biological Association of the UK

Research Article

Estimated life span of the Japanese pygmy squid, Idiosepius paradoxus from statolith growth increments

Noriyosi Satoa1 c1, Takashi Kasugaia2 and Hiroyuki Muneharaa3

a1 Division of Biosphere Science, Graduate School of Environmental Science, Hokkaido University, Kita-ku, Sapporo, Hokkaido 060-0810, Japan

a2 Port of Nagoya Public Aquarium, 1-3 Minatomachi, Minato-ku, Nagoya 455-0033, Japan

a3 Usujiri Fisheries Station, Field Science Center for Northern Biosphere, Hokkaido University, 152 Usujiri-cho, Hakodate, Hokkaido 041-1613, Japan

Abstract

Growth increments in statoliths of Idiosepius paradoxus were observed for aging analysis. The rate of increment formation was examined by staining the statoliths with tetracycline at 5–14 d intervals. In 6 of 16 specimens, increments formed daily, but in the other specimens, increments formed less than one per day. The maximum number of increments observed in males and females were more than 150 and 140, respectively, suggesting a life span of ≥150 and ≥140 d. During the cool season (from November to April), the dorsal mantle length (DML) and the number of increments gradually increased. Specimens collected in June showed bi-modal patterns in DML and the number of increments. Only small specimens were collected from August to October. These results suggest that two generations alternately occurred in the cool season and in the warm season.

(Received March 16 2007)

(Accepted November 26 2007)

Correspondence:

c1 Correspondence should be addressed to: Noriyosi Sato Division of Biosphere Science Graduate School of Environmental Science Hokkaido University Kita-ku, Sapporo Hokkaido 060–0810 Japan email: norico@fish.hokudai.ac.jp