Pomacea canaliculata is an introduced aquatic animal which has transformed into a malignant aquatic animal of paddy and other aquatic plants in China. In addition, the snail also acts as an intermediate host of Angiostrongylus cantonensis, and the main causative agent of human eosinophilic encephalitis. Moreover, the snail consumes dissolved oxygen in freshwater, causing destruction of the aquatic environment. As a result, P. canaliculata was listed as an invasive species in China by the Chinese State Environmental Protection Administration in 2003. It is necessary to prevent the species from spreading further and expanding its population. Pueraria peduncularis Grah. is a traditional Chinese medicine that belongs to the Pueraria family within the Leguminosae, and distributes widely across southwestern China. In terms of agricultural activity, the herb is biologically active against a variety of agricultural pests, and has insecticidal, bactericidal, and slug-killing activities. In our previous study, we found that P. peduncularis extracts had extremely strong toxicity against the apple snail and further identified the active compound as pedunsaponin, which has LC₅₀ value of 3.89 mg/L and great molluscicidal potential.
To explore the effects of pedunsaponin on the respiratory metabolism of P. canaliculata, the oxygen consumption rate, ammonia excretion rate, and the ratio of oxygen to nitrogen (O:N) were examined after treatment with pedunsaponin. The correlations of these processes with pedunsaponin concentrations, treatment temperatures and snail sizes were also evaluated in this study.
The results showed that both the oxygen consumption rate and ammonia excretion rate decreased in the pedunsaponintreated groups compared with the untreated group (P＜0.05). When the temperature was 28 ℃ under 40 mg/L pedunsaponin, the oxygen consumption and ammonia excretion rate were 0.19 mg/(g·h) and 0.02 mg/(g·h) in the treated snails, while for the normal snails, they were 0.88 mg/(g·h) and 0.07 mg/(g·h), respectively. In addition, pedunsaponin significantly reduced the O:N ratio of the snails, shifting away from protein, fat and carbohydrate metabolism to main protein one.
In conclusion, this study demonstrates that pedunsaponin is able to reduce the level of respiratory metabolism of P. canaliculata, which may inhibit fat and carbohydrate metabolism, thus forcing the snail to increase protein metabolism for an immune response. As a result, the snails died due to the lack of an energy supply. The study provides a theoretical basis for further research into toxic mechanism of pedunsaponin on P. Canaliculata.