Imidacloprid induces adverse effects on fish early life stages that are more severe in Japanese medaka (Oryzias latipes) than in zebrafish (Danio rerio)

Highlights

• Imidacloprid impacts on fish at environmentally relevant concentrations.

• At the same developmental stage, medaka are more sensitive than zebrafish.

• Our study supports the importance of taking species sensitivity differences into account.

Abstract

Neonicotinoids are widely used insecticides that have frequently been found in freshwater with concentrations ranging from ng to μg/L. It is known that these compounds impact non-target invertebrates, such as bees and gammaridae, in terms of toxicity and behavior, but impacts and species differences on vertebrates such as fish are little explored. The aim of this study was to investigate and compare the effects of one widely used neonicotinoid, imidacloprid, on development and behavior of two fish model species: Zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). Fish were exposed for 5 (zebrafish) and 14 (medaka) days from 0.2 to 2000 μg/L imidacloprid by aqueous exposure. Survival, development, behavior and histological features were monitored and organism-internal concentrations and biotransformation products measured. Imidacloprid caused sublethal effects in both species but the effects were much stronger in medaka with deformities, lesions and reduced growth being the most prominent impacts. Due to the overall longer time of development, time-integrated exposure of medaka was about 2-fold higher compared to zebrafish, potentially accounting for parts of the sensitivity differences. Our results underline the importance of taking species sensitivity differences into account especially when considering that medaka responded at imidacloprid concentrations that have been measured in the environment.

Introduction

Neonicotinoids are one of the most produced pesticide families, even after the partial ban in Europe since 2013 (Van Dijk et al. 2013; Simon-Delso et al. 2014; Bonmatin et al. 2015; Wood et al. 2017). They are low molecular weight and highly hydrophilic insecticidal chemicals that are applied in agriculture in various ways, including foliar sprays and seed treatments (Bonmatin et al. 2015). The intended mode of action of these molecules is to bind to nicotine acetylcholine receptors (nAChR) in nervous tissues in insects, causing dysregulation of neurotransmission at cholinergic synapsis, which can lead to overstimulation, tremors, paralysis and death (Sánchez-Bayo, 2012; Simon-Delso et al. 2014). Yet, based on this mode of action, neonicotinoids could affect signal transmission and behavior of other organisms with a developed neuronal system (Sánchez-Bayo, 2012). These include animals living in aquatic environments (Tennekes, 2011; Sánchez-Bayo 2012, 2014; Roessink et al. 2013).

Imidacloprid is one of frequently detected and well-studied neonicotinoids. It has been detected up to several hundred μg/L after agricultural use but has most commonly been found in the low ng/L range in continental water bodies (Moschet et al. 2014). Morissey et al. (2015) reported up to 320 μg/L imidacloprid in drainage ditches in the Netherlands while Anderson et al. (2015) documented a peak concentration of 0.7 μg/L in a Canadian surface water over a general background concentration of 0.04–0.05 μg/L. As demonstrated by aquatic species sensitivity distribution on survival after a few days of exposure (SI Fig. S1), insects are the most vulnerable organism group, followed by crustaceans, while fish appear several orders of magnitude less sensitive to direct short-term exposure of imidacloprid. Indirect effects on fish, such as a loss of the quantity and quality of crustaceans serving as food (Hayasaka et al. 2012a; Gibbons et al. 2014; Chagnon et al. 2015), have been proposed. However, direct sub-lethal effects on fish, especially during early developmental stages, have rarely been explored. Reduced locomotion was reported in zebrafish larvae continuously exposed to imidacloprid from fertilization to five days (Crosby et al. 2015). No impact was reported for zebrafish development when exposed to imidacloprid from fertilization to 48 h (Tišler et al. 2009) and 96 h (Scheil et al. 2009) of development, whereas growth of medaka adults and juveniles was reduced after long term exposure in mesocosms (Hayasaka et al. 2012b). Another study showed stress syndrome in medaka juvenile and increased parasite infestation after exposure to imidacloprid (Sanchez-Bayo et al. 2005). All these studies used exposure concentrations in the mg/L range, which is much higher than the concentrations found in the environment.

The aim of our study was to test if direct sub-lethal effects can be elicited by imidacloprid at concentrations that include environmentally realistic exposure levels during critical stages of development, i.e. early life, in model fish species: Zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). While both species share common features such as large broods, breeding all year and transparent eggs that develop outside the mother, a distinct difference is their time of development (SI Fig. S2) (Kimmel et al. 1995; Furutani-Seiki et al. 2004; Iwamatsu, 2004). While zebrafish hatch after 3 days post fertilization (dpf), medaka require an average of 9 dpf to emerge as free-swimming larvae. Thereafter, free swimming larvae are completely established within 5 dpf in zebrafish where it takes 14 dpf in medaka. We thus hypothesized that potential sub-lethal effects would be stronger in medaka because of the longer developmental time and consequently greater time-integrated exposure. To test this hypothesis, internal imidacloprid concentrations and physiological and histological alterations were examined for both species at similar developmental stages. Medaka indeed was more severely affected than zebrafish by imidacloprid exposure which led us to explore the relative abundance of metabolites involved in energy metabolism and neurotransmission in this fish.