Relative growth of the broadclub cuttlefish Sepia latimanus (Quoy & Gaimard, 1832): Implications for somatic size reconstruction, sex discrimination, and age class identification from the cuttlebone

Molluscan Research 31(3): 176-182; published 30 Nov. 2011
Copyright © The Malacological Society of Australasia & the Society for the Study of Molluscan Diversity
Relative growth of the broadclub cuttlefish Sepia latimanus (Quoy & Gaimard, 1832): Implications for somatic size reconstruction, sex discrimination, and age class identification from the cuttlebone

SHIGEKI DAN¹, KATSUYUKI HAMASAKI^2*, TAKASHI YAMASHITA¹, MASAKAZU OKA³& SHUICHI KITADA²

1Tamano Laboratory, National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, Tamano, Okayama 706-0002, Japan

^{2Department of Marine Biosciences, Tokyo
University of Marine Science and Technology, Minato, Tokyo 108-8477,
Japan
^{3Research Center for Tuna Aquaculture, Seikai
National Fisheries Research Institute, Fisheries Research Agency,
Nagasaki, Nagasaki 851-2213, Japan
^{* Corresponding author—Email: hamak@kaiyodai.ac.jp}}}
Abstract

As a basis for improving our knowledge about the growth and age of the broadclub cuttlefish Sepia latimanus, we used cuttlebones to determine the somatic size, sex and age classes of this species. We collected 663 individuals and measured their dorsal mantle length, body weight, and cuttlebone dimensions. The age classes were inferred from the relationship between the number of lamellae and the length of the cuttlebones. Sexually dimorphic growth was characterised by faster thinning and widening of the cuttlebone in females than in males; no differences were found in the weight of the cuttlebone between the sexes. The gonado-somatic index was higher in females than in males. Thus, the morphology of female cuttlebone adapted to ovarian maturity. Sex discriminant equations based on cuttlebone measurements assigned 76% of the individuals to their own sexes, and the accuracy increased when the shell length was greater than 270 mm. Two distinct groups were found in the relationship between the number of lamellae and the length of the cuttlebones, suggesting that the cuttlebones of S. latimanus provide information on age classes and can assist in reconstructing the somatic size of each sex.

Key words: Sepia, Cephalopoda, Japan, Ishigaki Island, relative growth, maturity, stock management

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