Regional differences in intra-body distribution of saxitoxins in freshwater pufferfish Pao sp. A from Cambodia

The Mekong River in Cambodia is inhabited by approximately ten species of freshwater pufferfish of the family Tetraodontidae. However, limited information is available regarding the toxin profile of these fish. In this study, to obtain sufficient information on the intra-body distribution of toxins in Cambodian freshwater pufferfish, one species of Pao freshwater pufferfish (Pao sp. A) were collected from Phnom Penh (PNH) in November 2019 (n = 23) and from Kratie (KTI) in March 2023 (n = 21). Toxin analyses of these samples revealed that individuals from both regions possessed saxitoxins (STXs) and contained no tetrodotoxin. Pao sp. A specimens from PNH possessed high STXs levels in the skin, muscle, liver, and gonads, whereas those from KTI showed relatively low levels of STXs concentrated in the skin. STXs amount in the ovaries in PNH individuals increased exponentially with increasing the gonadosomatic index (GSI). We also clarified that STXs concentration in the skin became increasingly higher as KTI individuals grew. These results suggest that differences in living regions may affect the intra-body distribution of STXs in Pao freshwater pufferfish, with maturation and/or growth contributing as well.