Experimental Validation of the Periodicity of Increment Formation in the Statolith of the Bigfin Reef Squid Sepioteuthis lessoniana (Cephalopoda: Loliginidae), Lineage C, from the Palk Bay, Indian Ocean

Abstract

Sepioteuthis lessoniana Lesson, 1831 is a neritic squid that inhabits coral reefs, rocky reefs, seaweed, and seagrass beds within the Indo-Pacific region. Increment validation, which determines the periodicity of increment formation in the squid statolith, is fundamental for age determination and understanding life-history traits; hence, it is critical for fishery management and stock conservation. Egg masses of S. lessoniana, Lineage C, were collected from the southeast coast of India and incubated in the hatchery. Post-hatching, the planktonic hatchlings ranged in dorsal mantle length (DML) from 3.9 to 5.49 mm (average 4.98 mm). The size of their statolith (total statolith length) ranged from 318 to 418 μm (average 360 μm). In the nuclear region, the increments formed during embryonic development numbered 9–14 (mean = 12). The first solid increment appeared one day post-hatching. Most of the increment counts (83%) were consistent with the actual age (days) of the squid post-hatching, while 17% of statolith counts were one or two days (increments) older than the actual age of the squid. The early growth rate ranged from 0.07 to 0.24 mm DML/day. The validation data presented here confirm the one-day-one-ring hypothesis in S. lessoniana, Lineage C.