Effects of microplastics on early life stages of marine fish

Environmental plastic pollution is a major ecological and societal concern today. Over the last 10 years, a broad range of laboratory and experimental studies have complemented field observations in the hope of achieving a better understanding of the fate and impact of micro- and/or nano-plastics (MP/NP) on diverse organisms (e.g. birds, fish and mammals). However, plastic pollution remains challenging to monitor in the environment and to control under laboratory conditions, and plastic particles are often naturally or experimentally co-contaminated with diverse chemical pollutants. In fish, the most significant effects reported after exposure to MP / NP were observed on behavioral and neurological functions, intestinal permeability, metabolism and intestinal microbiome diversity. However, plastic pollution remains difficult to quantify in the environment and to control in the laboratory, and plastic particles are often co-contaminated naturally or experimentally with various chemical pollutants. Therefore, studies on the behavioral and physiological effects associated with ingestion of virgin MP / NP in early life stages of marine fish are still few at present. Thus, the purpose of this thesis is to study the effects of two types of plastic frequently encountered in the marine environment, namely polyethylene (PE) and polystyrene (PS), in the form of microplastics (from 10 to 100 μm), on the early life stages of marine fish, known to be particularly sensitive to environmental stresses. Thus, larvae and juveniles of different model fish species (Tropical: Acanthurus triostegus and Temperate: Sparus Aurata) were selected. Several physiological and behavioral parameters were studied after exposure to MP via different pathways (water and food) in various experiments on these model species. Current results do not show any marked effects of this stressor at environmental concentrations, however some results, such as increased mortality and metabolic disturbances, at higher doses, show toxicity following ingestion of these particles. Thus, this thesis reveals that the toxicity of virgin PM / NP on fish should be evaluated more systematically using rigorous laboratory methods, in order to gain a better understanding of the underlying mechanisms of this toxicity to fish.