Levels and distribution of tetrodotoxin in the blue-lined octopus Hapalochlaena fasciata in Japan, with special reference to within-body allocation

The toxins present in poisonous and venomous animals have both offensive and defensive functions. The blue-lined octopus Hapalochlaena fasciata has tetrodotoxin (TTX) in various organs, including the salivary glands, muscles and skin, and TTX is assumed to be used in both offence and defence. In this study, we explore the evolution of toxicity in H. fasciata by measuring the levels and distribution of TTX in H. fasciata specimens collected in Japan and by investigating the TTX allocation within the body. TTX was detected in all 13 adults and 3 paralarvae studied. The concentration of TTX was highest in the anterior and posterior salivary glands, and the total amount of TTX was highest in the muscles and skin. Larger individuals had significantly higher amounts of TTX, but the TTX concentrations in the muscles and skin were not correlated with body weight. There were large individual differences in TTX concentration and some individuals showed extremely low TTX levels. These individual differences may be related to regional, seasonal and sexual differences, although the origin of TTX in this species is still unclear. Furthermore, we found a strong positive correlation between TTX concentrations in the posterior salivary gland and TTX concentrations in muscles and skin, with the former being c. 20 times greater than the latter. This suggests that the allocation ratio may not result from a plastic allocation, reflecting the TTX needs of each organ or the amount of available TTX, but rather may, at least partly, be evolutionarily fixed.