Molting inhibition in Calanus finmarchicus from exposure to the chitin synthesis inhibitor teflubenzuron

Abstract

Within the aquaculture industry, various chemotherapeutics and treatment strategies have been applied to protect farmed fish in open cages against parasites and diseases. Among the most common strategies for management of parasitic copepods is the use of chitin synthesis inhibitors (CSI) such as teflubenzuron. In addition to controlling salmon lice infestations of salmon, exposure to teflubenzuron can cause adverse effects in non-target organisms within the surrounding marine environment. Teflubenzuron causes inhibition in the synthesis of chitin resulting in premature molting and molting-associated mortality. In the marine boreal ecosystems, the copepod Calanus finmarchicus is essential in interconnecting trophic levels and constitutes a substantial part of the total zooplankton biomass in the northern oceans. The copepod depends on molting between life stages to grow and is a potential non-target organism to teflubenzuron. As climate changes, an increase in environmental stress and anthropogenetic pollution in the arctic and boreal areas is expected. Likewise expected is the future need for knowledge of the potential effects increased anthropogenic activity and presence has on the northernmost environment and the life in it.

Adverse outcome pathways (AOPs) is a tool that provides insight into the mechanistic processes of complex systems by examining, evaluating, and organizing key events and the relationship between them into linear sequences of events. There is currently a wide network of AOPs used in hazard identification of numerous typical stressors. As a continuation of the work in AOP 360, “Inhibition of chitin synthase 1 leading to increased mortality in arthropods”, this thesis aims to investigate the relationship between exposure to the veterinary insecticide teflubenzuron and the negative effects on molting in the copepod C. finmarchicus. To achieve this, an extended sub-acute exposure study of C. finmarchicus has been carried out, supplemented by a gene expression study of genes relevant to the molting process and its regulation. Additionally, a novel method is being developed for fluorescent chitin imaging and measurement of chitin content in marine copepods. Based on these sub-studies, this thesis aims to describe the effects of teflubenzuron on molting in C. finmarchicus.

The main findings suggest that exposure concentrations of 0.03 µg/L teflubenzuron and higher causes inhibition of normal development and growth, morphological deformities, and molting-associated mortality in C. finmarchicus. Correcting this effect concertation from nominal to measured (0.127 µg/L), our findings suggest that C. finmarchicus can experience substantial adverse effects on multiple levels of biological organization at environmentally relevant concentrations. Despite multiple indications of the possible effect teflubenzuron has on chitin synthesis in C. finmarchicus, no statistical significance was found for the expression of chs1 at teflubenzuron exposures of 0.01 µg/L -0.03 µg/L. Thus, this study was unable to link molecular inhibition of chitin synthesis, by chs1, to the adverse effects found in the other levels of biological organization related to molting.

In summary, teflubenzuron causes adverse molting-associated effects in C. finmarchicus at environmentally relevant concentrations. Future efforts to link teflubenzuron to the inhibition of chs1 are needed to assess the applicability of AOP 360 to C. finmarchicus.

Within the aquaculture industry, various chemotherapeutics and treatment strategies have been applied to protect farmed fish in open cages against parasites and diseases. Among the most common strategies for management of parasitic copepods is the use of chitin synthesis inhibitors (CSI) such as teflubenzuron. In addition to controlling salmon lice infestations of salmon, exposure to teflubenzuron can cause adverse effects in non-target organisms within the surrounding marine environment. Teflubenzuron causes inhibition in the synthesis of chitin resulting in premature molting and molting-associated mortality. In the marine boreal ecosystems, the copepod Calanus finmarchicus is essential in interconnecting trophic levels and constitutes a substantial part of the total zooplankton biomass in the northern oceans. The copepod depends on molting between life stages to grow and is a potential non-target organism to teflubenzuron. As climate changes, an increase in environmental stress and anthropogenetic pollution in the arctic and boreal areas is expected. Likewise expected is the future need for knowledge of the potential effects increased anthropogenic activity and presence has on the northernmost environment and the life in it.

Adverse outcome pathways (AOPs) is a tool that provides insight into the mechanistic processes of complex systems by examining, evaluating, and organizing key events and the relationship between them into linear sequences of events. There is currently a wide network of AOPs used in hazard identification of numerous typical stressors. As a continuation of the work in AOP 360, “Inhibition of chitin synthase 1 leading to increased mortality in arthropods”, this thesis aims to investigate the relationship between exposure to the veterinary insecticide teflubenzuron and the negative effects on molting in the copepod C. finmarchicus. To achieve this, an extended sub-acute exposure study of C. finmarchicus has been carried out, supplemented by a gene expression study of genes relevant to the molting process and its regulation. Additionally, a novel method is being developed for fluorescent chitin imaging and measurement of chitin content in marine copepods. Based on these sub-studies, this thesis aims to describe the effects of teflubenzuron on molting in C. finmarchicus.

The main findings suggest that exposure concentrations of 0.03 µg/L teflubenzuron and higher causes inhibition of normal development and growth, morphological deformities, and molting-associated mortality in C. finmarchicus. Correcting this effect concertation from nominal to measured (0.127 µg/L), our findings suggest that C. finmarchicus can experience substantial adverse effects on multiple levels of biological organization at environmentally relevant concentrations. Despite multiple indications of the possible effect teflubenzuron has on chitin synthesis in C. finmarchicus, no statistical significance was found for the expression of chs1 at teflubenzuron exposures of 0.01 µg/L -0.03 µg/L. Thus, this study was unable to link molecular inhibition of chitin synthesis, by chs1, to the adverse effects found in the other levels of biological organization related to molting.

In summary, teflubenzuron causes adverse molting-associated effects in C. finmarchicus at environmentally relevant concentrations. Future efforts to link teflubenzuron to the inhibition of chs1 are needed to assess the applicability of AOP 360 to C. finmarchicus.