A comprehensive study of fipronil toxicity in the marine fish European sea bass, Dicentrarchus labrax, in a global change scenario

Abstract

Fipronil (FIP) is a broad-spectrum phenylpyrazole insecticide known to block the gamma-aminobutyric acid (GABA) receptor system, particularly in insects. It is used to control pests in agriculture although it could be harmful to other non-target species in nearby aquatic systems. To confirm this hypothesis, the effects of oral administration (10 mg FIP /Kg feed) of commercial Regent®800WG (80% fipronil) to European seabass juveniles were studied under two temperature regimes. These temperatures were a) actual natural temperature in winter time (around 13ºC) and b) +3 ºC above natural winter temperature (i.e., 16ºC, as predicted by the IPCC panel for the NW Mediterranean by 2100). A wide array of physiological and metabolic biomarkers including feeding rate, general condition indices, plasma and epidermal mucus metabolites, immune response, osmoregulation, detoxification, neurotoxicity, oxidative-stress markers, digestive enzymes were considered. Moreover, endocrine disruption at the histological, hormonal and gene expression level was also assessed. These endpoints were measured at different times: a) right before FIP administration (time 0), b) 7 and 14 days after administration of a daily feed spiked with FIP and c) one-week after FIP withdrawal from the diet (depuration period). In addition to the disruption of the GABA system, as shown by changes in the expression of key genes involved in GABA synthesis, FIP administration resulted in a significant alteration of several biomarkers including enhanced metabolism, oxidative stress, apoptosis, osmo-regulatory activity, several digestive enzymes, and more important, a disruption of the reproductive system that persisted after depuration. Notwithstanding, the bile analyses confirmed a rapid clearance of FIP but the persistence of the more toxic metabolite fipronil-sulfone even after depuration. Altogether, these results revealed a notable impact of fipronil on the physiological condition of this species. Since the European sea bass as well as other commercial fish species in both fisheries and aquaculture practices inhabit highly productive estuarine ecosystems, particularly during early and juvenile stages, the discharge of agriculture runoffs can lead to unwanted economic and ecological consequences