ASPECTS OF THE BIOLOGY OF THE GIANT FORM OF STHENOTEUTHIS-OUALANIENSIS (CEPHALOPODA, OMMASTREPHIDAE) FROM THE ARABIAN SEA

An investigation was carried out on the recently discovered 'giant' ex tra large (XL) form of the squid Sthenoteuthis oualaniensis from the A rabian Sea. The sample consisted of 2 males, which have not been previ ously described, and 13 females. Diet composition, parasite loading, s ucker ring dentition, bioluminescence and sexual dimorphism were exami ned and compared to known parameters of the medium (M) form. Reproduct ive strategy, potential fecundity, egg size distribution in the ovary and oviducts were examined in mature XL females. Evidence of multiple spawning in the giant form was also investigated. Overall body shape, bioluminescent structures and coloration of the giant form were simila r to the M form, though the XL form had a smaller fin angle than the M form. The mature female XL form has a dorsal mantle length about twic e that of a mature female M form. Adult females of the XL form have a dorsal mantle length about twice that of adult males of the same form. Differences between males and females were found in arm sucker ring d entition and parasite load, suggesting a difference in diet. This coul d be linked to size differences between the sexes. A strong correlatio n between ovary mass and mantle length was found (r(2) = 0.64). Poor c orrelation was found between mantle length and oviduct mass (r(2) = 0. 128) and potential fecundity (r(2) = 0.07). Potential fecundity ranged between 2-5 million eggs and the holding capacity of the oviducts was approximately 300,000 eggs. This combined with the presence of sperma tangia and the presence of food in the stomach suggest that the XL for m is a multiple spawner. S. oualaniensis appears to have a plastic phe notype and has adapted to the Arabian Sea conditions by evolving the c apacity to grow to a giant size.