The reproductive biology of female Logigo Forbesi Steenstrup (Cephalopoda: Myopsida)
Aspects of the reproductive biology of female Loligo forbesi were investigated. The species is dioecious and females are generally smaller than males. The maximum size attained by females in Scottish waters is 330 mm and the largest size attained by the males is 550 mm. Variations in sex ratios do not indicate any seasonality. The demography is complex and apparently not consistent from year to year. Recruitment is possibly all year round and is associated with an extended spawning season (December to May). It is not known whether different spawning groups contribute to spawning. Maturation is associated with an increase in the size of the reproductive structures (ovary, proximal oviduct, oviducal gland, distal oviduct, nidamental glands and accessory nidamental glands) relative to body weight. This is not associated with a decrease in the wet somatic and visceral components. The glands of the female reproductive system show histological changes associated with maturation. The epithelia of these glands become secretory with maturation and their secretions are thought to provide the egg coats. An exception is the proximal oviduct which is apparently involved in the transportation of eggs and possibly has an absorptive function. Examination of eggs from the ovary of females at different stages of maturation suggests that eggs are spawned continuously over an extended period. The function of the accessory nidamental glands is unknown but they exhibit a secretory cycle associated with maturation. The accessory nidamental glands harbour symbiotic bacteria which change colour with maturation. This colour change has potential for use in experiments investigating factors controlling maturation in those species which have accessory nidamental glands. Preliminary experiments have shown that the colour of these bacteria can change when grown on a medium to which extracts of optic glands (cultured in a medium) were added. A total of twelve strains of bacteria were isolated from the accessory nidamental glands of females from different maturity stages. Based on physical and biochemical characteristics, the bacteria were tentatively identified as species of Vibrio and Pseudomonas.