AGE, GROWTH AND REPRODUCTIVE-BIOLOGY OF DIAMOND-SHAPED SQUID THYSANOTEUTHIS-RHOMBUS (OEGOPSIDA, THYSANOTEUTHIDAE)

Age and growth of the large oceanic squid Thysanoteuthis rhombus were estimated by statolith increment analysis of 72 specimens [mantle leng th (ML) ranging from 25 to 805 mm] and reproductive biology was studie d on 162 T. rhombus (ML 150 to 850 mm) captured in the eastern tropica l Atlantic and southwestern Pacific between 1976 and 1990. The maximum ages found in our samples were observed in a mature female of 750 mm ML (305 d) and in a mature male of 770 mm ML (309 d). The life span of T. rhombus was estimated to be about 1 yr; males and females matured at age 6 to 8 mo. T. rhombus is one of the fastest-growing squids: by age 300 d, they reached 750 to 800 mm ML and 17 to 17.5 kg body weight (BW). The increase in both ML and BW during ontogenesis was best fitt ed by a logistic growth curve. T. rhombus has high potential fecundity (up to 4.8 million oocytes), but a rather small maximum volume of ovi ducts (up to 140 000 eggs) and egg masses (35 000 to 75 000 eggs). It is suggested that T. rhombus is an intermittent spawner with multiple filling and evacuation of oviducts. The main function of the (for squi d) unusual behaviour of T. rhombus, i.e. living in pairs consisting of a male and female, is reproduction and is optimal given the low densi ty of T, rhombus populations and low active movement of squids.