Investigation of Microplastics Ingestion and Effects in Striped Red Mullet in East Mediterranean Sea Danae Patsiou∗1, Nikoletta Digka1, and Catherine Tsangaris1 1Hellenic Centre for Marine Research { Street Address : 46,7 km Athens Sounio ave., P.O. Box 712, P.C. 19013 Anavyssos Attiki, Greece Abstract Marine plastic debris is increasing and so does the microplastic (MP) ingestion by marine organisms. Detection of MPs in the marine environment is ongoing, however, there is lack of consensus regarding the effects of MP ingestion in marine organisms. The aim of the present study is to assess MP ingestion together with cellular and biochemical biomarkers in native Mediterranean fish species proposed as bioindicators of MPs, at coastal sites under different human pressure intensity in the Ionian Sea, and to investigate whether biomarker variations can be related to the occurrence of MPs in their gastro-intestinal (GI) tract. Striped red mullets Mullus surmuletus, were sampled along the tourist coast of Zakynthos island and inside the Zakynthos National Marine Park. The fish GI tracts were digested using 15% H2O2 at oC and then filtered to detect ingested MPs. The polymer identification analysis using Fourier-Transform Infrared Spectroscopy analysis of the samples is ongoing. Blood samples were collected from alive M. surmuletus to evaluate DNA damage, and the results so far indicate no differences in the micronuclei occurrence in fish blood cells among sampling sites. The investigation of biochemical biomarkers includes: acetylocholinesterase in muscle tissues to evaluate neurotoxicity, and catalase and glutathione S-transferase in the liver tissues to assess antioxidant defence and biotransformation responses. The present study carried out in the framework of the Plastic Busters MPAs project intends to measure the extend of MPs pollution by in situ investigation of cellular and biochemical parameters of native Mediterranean species, to attribute the animal health status directly to the presence of MPs in the animal. Keywords: microplastic ingestion, ecotoxicological biomarkers, Mullus surmuletus, Ionian Sea, Greece ∗Speaker sciencesconf.org:micro2020:334424.