Hemolymph-Mediated Dynamics of Paralytic Shellfish Toxins and Tetrodotoxin in Scallops

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.