Assessment of deltamethrin toxicity in Macrobrachium nipponense based on histopathology, oxidative stress and immunity damage.

Deltamethrin (Del), a commonly used broad-spectrum insecticide, has been reported to have a toxic effect on aquatic animals, but knowledge in freshwater prawns is limited. This study revealed that Del is highly toxic to Macrobrachium nipponens with the 24 h, 48 h, 72 h, and 96 h LC50 values to be 0.268, 0.165, 0.104, and 0.066 µg/L, respectively. To further investigate the toxic effect of Del in M. nipponense and the reversibility of damage, prawns were exposed to 0.05 µg/L Del for four days and then transferred into fresh water for seven days. Histopathological examination, oxidative stress, hepatopancreas function, respiration system, and immune system were analyzed through multiple biomarkers. Results showed that Del exposure caused severe histopathological damage to hepatopancreas and gill in M. nipponense, and the prominent decrease of acid phosphatase (ACP) and alkaline phosphatase (AKP) activity further enhanced the hepatopancreas damage; the accumulation of malonaldehyde (MDA) and hydrogen peroxide (H2O2), and the decrease of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity, indicated severe oxidative stress caused by Del. Besides, Del exposure also induced remarkably increased lactic acid (LD) level, decreased lactate dehydrogenase (LDH) activity, and decreased expression of immune-related genes, which demonstrated the respiration disruption and immunosuppression caused by Del. After 7-day decontamination in freshwater, the indicator of hepatopancreas function (ACP and AKP activity) and respiration (LD level and LDH activity) improved to the control group level. However, the histopathological damage and the biomarker in oxidative stress and immune system did not recover to the initial level.

Multi-biomarker assessment in the giant freshwater prawn Macrobrachium rosenbergii after deltamethrin exposure.

Deltamethrin (DM) is a synthetic pyrethroid used for agricultural purposes to control insects. However, its extensive use contaminates the aquatic environment and results in serious health problems in aquatic organisms. Knowledge about the toxic effect of DM in freshwater prawns is limited; therefore, this study aims to assess the toxicity of DM in Macrobrachium rosenbergii based on multiple biomarkers. Four-day acute toxicity tests showed that DM was highly toxic to M. rosenbergii with the 24 h, 48 h, 72 h and 96 h LC50 values to be 1.919, 0.603, 0.539, and 0.449 µg/L, respectively. According to 96 h LC50, prawns were exposed to DM at three concentrations (0.02, 0.08, and 0.32 µg/L) for 4 days, and then moved into fresh water for decontamination to investigate the toxic effect of DM in M. rosenbergii. At low concentration (0.02 µg/L and 0.08 µg/L), DM did not cause obvious histopathological damage to hepatopancreas and gill tissue, while at high concentration (0.32 µg/L), the histopathological harm was serious and the damage did not recover to the initial level after 7-day decontamination. 0.02 µg/L DM exposure did not induce significant changes in most of the biomarkers except the increased lactate dehydrogenase (LDH) activity, lactic acid (LD) level, and the first increased then decreased mRNA expression of immune-related genes, indicating the stimulation of DM on energy production and immunity. 0.08 µg/L and 0.32 µg/L DM exposure resulted in varying degrees of damage on prawns, but overall, their toxic effects showed similar trends based on the biomarkers. Increase in malonaldehyde (MDA) and hydrogen peroxide (H2O2) content and decrease in superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity after DM exposure demonstrated the oxidative stress caused by DM. The significantly increased acid phosphatase (ACP), alkaline phosphatase (AKP), LDH activity and LD level indicated hepatopancreatic dysfunction and respiration disruption. The first increased and then decreased expression pattern of immune-related genes indicated the immunosuppression caused by DM. After 7-day decontamination in freshwater, the activity/level of the biomarkers partly recovered. This study revealed the severe toxic effect of DM on Macrobrachium rosenbergii based on multiple biomarkers, providing fundamental knowledge for the establishment of DM toxicity assessment system with proper parameters in freshwater crustaceans.