“STUDIES ON REPRODUCTIVE BIOLOGY OF SPINELESS CUTTLEFISH SEPIELLA INERMIS”
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Date
2019
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KARNATAKA VETERINARY, ANIMAL AND FISHERIES SCIENCES UNIVERSITY, BIDAR
Abstract
Sepiella inermis, also known as the spineless cuttlefish, is an emerging species in the
cuttlefish fishery. This species has been attracting international market in the recent years. The
present study was undertaken to investigate the reproductive biology of S. inermis off
Mangaluru, south-west coast of India. The S. inermis samples were collected from Mangaluru
Fisheries Harbour during September 2016 and May 2017. The relationship between dorsal
mantle length (DML) and body weight (TW) of Sepiella inermis was mathematically
expressed as TW= 0.9873×DML2.0828 (r² = 0.8683) and TW = 0.9725×DML2.1789(r² = 0.8622)
for male and female respectively. The species showed allometric growth. Maturity stages were
assigned by gross macroscopic examination of the gonad as 1) immature, 2) maturing 3)
mature and 4) spent. Apparently, female tend to gain more weight than male for a given
length. The female: male ratio ranged between 0.90:1 (September) to 1:1 (April). 50% of the
male matured at 50-55 mm and female matured at 60-65 mm. Fecundity varied from 172 to
560. Ova diameter varied between 0.29 to 6.12 mm, individuals in all the 4 maturity stages
were found throughout the year. However, maximum proportion of matured male and female
were encountered during September-October followed by February-April. Furthermore, the
highest Gonadosomatic Index (GSI) for male and female also coincided with spawning
season. Nidamental gland Index (NGI) peaked in the month of October. Based on the
proportion of each maturity stage, as well as the maturity indices (GSI and NGI), the spawning
seasons were inferred to be in the months of October-September and February-April