Distribution, age and growth of the diamondback squid, Thysanoteuthis rhombus (Cephalopoda: Thysanoteuthidae) from the tropical Arabian Sea

Sajikumar, K K and Sasikumar, Geetha and Venkatesan, V and Vidya, R and Alloycious, P S and Jestin Joy, K M and Sahib, Karamathulla and Nataraja, G D and Mohamed, K S (2020) Distribution, age and growth of the diamondback squid, Thysanoteuthis rhombus (Cephalopoda: Thysanoteuthidae) from the tropical Arabian Sea. Fisheries Research, 224. pp. 1-9.

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Abstract

Individuals in all life stages of the large oceanic diamondback squid Thysanoteuthis rhombus were observed in the southeastern Arabian Sea. A total of 82 individuals were collected from the Arabian Sea between February 2013 and December 2018. The length-weight relationship follows an allometric growth pattern. Age and growth were estimated by statolith increment analysis (n = 77) and demonstrated a rapid growth rate ranging from 1.42 to 4.80 mm dorsal mantle length (DML)/day. Based on back calculated hatch dates, T. rhombus spawned from May to December with a peak in July. Male and female squids matured at 6 months of age. The oldest individual was a mature female (655 mm DML) that was 220 days old with a growth rate of 2.97 mm DML/day. Differences in size-wise (DML) instantaneous growth rates were evident. Stomach content analysis revealed that fish and squid were the major prey of adults and sub-adults, while in juveniles, crustaceans were the dominant prey item. Ontogenetic differences in the diet were apparent.

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