Investigations on gametogenesis and gonadal indices in the veined squid doryteuthis forbesii (steenstrup, 1856) (cephalopoda -loliginidae)

Knowledge of the maturation process is vital to understand the relationship between spawning stock andrecruitment. The purpose of the present study was to validatethe reproductive cycle of Doryteuthis forbesii using histological and statistical procedures. The changes in gonad during sexual maturation permitted the determination of different histological stages for oogenesisin 12 phases and spermatogenesis in 7 phases. This species spawns throughout the year with two peaks during spring and summer. During oogenesis the oocyte becomes progressively more elongated, with a subsequent narrow elongation of the apical zone forming the oocyte peduncle. Finally the oocytes turn smooth (chorion becomes the outer surface when the follicular cells disintegrate) and free, finally reaching the oviducts. The spermatogonia and the primary spermatocytes are difficult to distinguish from each other, both being relatively large cells with a large, distinct nucleus. The first meiotic division occured, and the primary spermatocytes become secondary spermatocytes. A second meiotic division occurred immediately afterwards, so the secondary spermatocytes become spermatids. The transformation of the spermatids to spermatozoa occurs by a process of differentiation known as spermiogenesis. Morphologically, this differentiation involves the transformation of the cell from a round to an elongate shape. The spermatozoa are grouped around the lumen, towards the centre. As spermatozoa matured and released from the testis they passed directly to the spermaduct which is surrounded by complex accessory glands. The first glands inactivate the spermatozoa and others cover the sperm mass with different secretions to form the spermatophore. Spermatophores usually accumulate in the Needham sac. Spawning season was determined by calculating the different stages of oocyte development in the four seasons of the year using three methods. One Way Analysis of Variance (ANOVA) with p˂0.05 and Newman-Keuls Multiple Comparison Test with P < 0.01and P > 0.05 were applied to compare the different stages of oocyte development in the four seasons of the year. The gonadosomatic index (GSI) for both sexes and the nidamental gland–somatic index (NSI) for the females, were calculated and commented.This study provided evidence suggesting that Doryteuthis forbesii is an intermittentspawner.