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The Reproductive Biology of the Squid, Sepioteuthis Lessoniana ( Lesson, 1830 ) in the Coastal Waters of Zanzibar

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The Reproductive Biology of the Squid, Sepioteuthis Lessoniana ( Lesson, 1830 ) in the Coastal Waters of Zanzibar The reproductive biology of the squid, sepioteuthis lessoniana ( lesson, 1830 ) in the coastal waters of Zanzibar. Hassan Ahmed Mhitu Master of science (marine biology) University of Dar es salaam, Institute of Marine Science, 1997 A study on the reproductive biology of the bigfin reef squid, Sepioteuthis lessoniana f Lesson, 1830) in the coastal waters of Zanzibar, was conducted with a view to obtaining basic information that will be relevant to proper management of the squid fishery in the area. Data collection involved field sampling and laboratory work. A total of 664 specimens of the species were collected from artisanal fisheries at Chwaka, Zanzibar during 1994/1995. The body weight and the morphometric length measurements (DML, FW and FT) of S. lessoniana taken before and after freezing had no significant difference (P>0.05). However, the difference between the measurements made on 20 specimens while fresh and after freezing was less than 4%. The maximum size of S. lessoniana was 347 mm DML and 277 mm DML for males and females, respectively. The minimum size for males was 63 mm DML and 72 mm DML for females. The maximum weight was 1617.3 g for males and 969 g for females whereas the minimum weights were 20.8 g and 26.3 g for males and females, respectively. Mature squids migrate from the coastal waters from July to offshore waters to spawn. The length-weight regression equations were: Males W=0.0005L2547 , Females W=0.0004L2576 and Combined W=0.0005L2 555. The slopes for length-weight regression lines for both males and females showed no significant difference (P>0.001) when compared. Both male and female S. lessoniana exhibited allometric growth. The mean condition factor was generally higher for females than for males in all months except for August. Females were therefore heavier than males. Sexual dimorphism was evident in this species where 344 females and 320 males were identified. Sex ratio in S. lessoniana was not significantly different from 1:1 throughout the year except in May, June and November. Two maturity indices, the gonadosomatic index (GSI) for both sexes, and the ratio of nidamental gland length to dorsal mantle length (NGL/DML ratio) for females coincided in their peaks in July. This coincidence may imply that, the individuals were mature and were ready to spawn. Statistical and graphical methods were used to determine size at maturity. Size at maturity for S. lessoniana was 138.9 ± 6.4 mm DML for males and 162.9 ± 4.3 mm DML for females through the statistical method. The graphical method yielded 149.5 mm DML and 162.8 mm DML for males and females, respectively. The estimated fecundity for female S. lessoniana from Zanzibar ranged from 450 to 1180 with a mean of680 eggs for individuals of 140 mm to 249 mm DML. The number of eggs in a capsule was 6 and mean size of the eggs was 6 mm in length and 4.5 mm in breadth. Fecundity was related to the size of the female. .
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