A comprehensive study on freshwater pufferfish Pao baileyi: profiles of toxin possession, accumulation, and uptake.

Freshwater pufferfish, primarily belonging to the genus Pao, constitute an important branch in the family Tetraodontidae. Toxic freshwater pufferfish contain saxitoxin (STX) but lack tetrodotoxin (TTX), which is commonly found in marine pufferfish. Here, we focused on the freshwater pufferfish Pao baileyi and assessed the toxicity and toxin distribution patterns in wild individuals. Subsequently, we conducted intrarectal toxin administration in vivo and tissue slice incubation in vitro using artificially bred nontoxic individuals. Toxin analyses showed that wild P. baileyi possessed only STX, with relatively high STX concentrations in the intestine and muscle. In the intrarectal toxin administration, nontoxic individuals acquired a dose of 5 nmol STX/individual and the STX amount in the intestine, liver, muscle, and skin was quantified at 24, 48, and 72 h. At 24 and 72 h, the sum of relative STX amount across all tissues investigated was 59.52 and 56.49%, respectively, obviously higher than that observed at 48 h (21.37%). In the tissue slice incubation, slices of these four tissues prepared from the same batch of nontoxic P. baileyi, were incubated in solutions containing TTX and STX and toxin taken up in the tissue was quantified over time. The dynamic changes of STX within the liver and skin over the 24-to 72 -h period are similar between in vivo and in vitro experiments, however, those of STX in the intestine totally differ. Tissues of P. baileyi could selectively take up STX. This study reveals the profiles of toxin possession, accumulation, and uptake of representative Pao freshwater pufferfish.