Molting enhances internal concentrations of fipronil and thereby decreases survival of two estuarine resident marine crustaceans

Triple jeopardy: The combined effects of viral, chemical, and thermal stress on kuruma prawn (Penaeus japonicus) juveniles

Growing concerns have emerged over the combined effects of multiple stressors on ecosystems. Empirical evidence shows that the sensitivity of aquatic invertebrates to insecticides varies under thermally fluctuating conditions. Additionally, field surveys in estuarine areas of western Japan confirmed the presence of juvenile kuruma prawns (Penaeus japonicus) carrying the white spot syndrome virus (WSSV). Given the potential of co-exposure to multiple stressors, we performed a combined exposure experiment using a full-factorial design with three stressors: WSSV infection (presence or absence: initial 2 h exposure), fipronil (insecticide) exposure (0 or 0.1 μg/L: 14 d exposure), and temperature (20, 25, or 30 °C). We observed the highest mortality (75 %) in the WSSV + Fipronil treatment at 30 °C, with the associated specimens showing significant changes in the internal load of WSSV and concentrations of fipronil and its metabolite, fipronil sulfone. Severe perturbations of metabolites associated with increased energy expenditure and fatty acid utilization have been identified as potential factors underlying lethality in juvenile kuruma prawns. The results demonstrate that WSSV infection increases the susceptibility of thermally stressed juvenile kuruma prawns to fipronil. Therefore, further studies are required to determine the combined effects of multiple stressors in environmentally relevant scenarios on juvenile kuruma prawns as well as in estuarine ecosystems.

Relationship closeness of tolerance to two neonicotinoids with their internal body burden in two estuarine resident marine crustaceans

The estuarine resident crustacean sand shrimp, Crangon uritai, has a higher tolerance to neonicotinoid insecticides than that of the kuruma prawns, Penaeus japonicus. However, the reason for the differential sensitivities between the two marine crustaceans remains to be understood. This study explored the mechanism underlying differential sensitivities based on insecticide body residues after exposing both said crustaceans to two insecticides (acetamiprid and clothianidin) with or without oxygenase inhibitor piperonyl butoxide (PBO) for 96 h. Two graded-concentration groups were formed; group H (1/15-1 times the 96-h LC₅₀ values) and L (one-tenth the concentration of group H). Results showed that the internal concentration in survived specimens tended to be lower in sand shrimp than in kuruma prawns. Co-treatment of PBO with two neonicotinoids not only increased sand shrimp mortality in the H group, but also altered metabolism of acetamiprid into its metabolite, N-desmethyl acetamiprid. Furthermore, molting during the exposure period enhanced bioconcentration of insecticides, but not affects survival. Collectively, the higher tolerance of sand shrimp than that of kuruma prawns to the two neonicotinoids can be explained by lower bioconcentration potential and more involvement of oxygenase in their alleviating lethal toxicity.