Abstract

To investigate the dynamics of paralytic shellfish toxins (PSTs) and tetrodotoxins (TTX) in scallops, PSTs and TTX were analyzed in the hemolymph supernatant (hemolymph-S) and digestive gland in Yesso and Akazara scallops cultured in eastern Japan. In Yesso scallops sampled between 22 April 2025 and 21 October 2025, the PST concentrations in the hemolymph-S were 1.6–17% of those in the digestive gland, showing a positive correlation (r = 0.753). However, the PST composition in the hemolymph-S and digestive gland differed; the hemolymph-S composition initially resembled that of laboratory-cultured dinoflagellates, coinciding with typical onset of toxic dinoflagellate blooms in late April. Following this period, the PST composition in the hemolymph-S gradually converged with that of the digestive gland, via chemical transformation in the digestive gland followed by release into the hemolymph. The ratios of 11β-OSO3H toxins (C2, GTX4, GTX3) to 11α-OSO3H toxins (C1, GTX1, GTX2), which exist in chemical equilibrium, exhibited a similar trend. TTX was detected in both tissues of Yesso and Akazara scallops collected from 28 August 2025 to 27 January 2026, with the hemolymph-S concentration being 0.5–5.4% of that in the digestive gland. These results suggest that these toxins are sequestered into the digestive gland from the PST-producing dinoflagellates and certain TTX-bearing organisms, and then they partially flow into the hemolymph for circulation throughout the body.

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