The XV European Congress of Ichthyology (ECI XV) has been organized by the Interdisciplinary Centre of Marine and Environmental Research (CIIMAR) and took place in the HF Ipanema Park Hotel, Porto, Portugal, from the 7th to 11th of September 2015. The congress given particular emphasis to the scientific areas historically covered by ECI. The scientific program has include sessions in four main areas: i) Phylogeny, systematics and genetics; ii) Ecology, conservation and invasive species; iii) Life cycles, migration and connectivity; and iv) Physiology, behaviour and toxicology. A specific symposium on fish otoliths has been also included. The Conference has been organized with two parallel oral sessions and daily poster exhibitions. The congress included eight invited plenary lectures made by world renowned fish researchers in addition to 138 regular oral presentations and 171 poster exhibitions. We had 284 registered participants that came from 44 countries (Portugal: 56; Brazil: 22; Spain and Poland: 21; Hungary and Italy: 13; Czech Republic: 11; Estonia, Germany and USA: 9; Croatia and France: 8; Belgium, Greece, Kazakhstan, Lithuania, Russia and Sweden: 5; Austria and Australia: 4; Finland, Israel, Iran, UK, Netherlands, Switzerland and Turkey: 3; Mexico, Norway and Tunisia: 2; Algeria, Argentina, Bosnia, Canada, Chile, China, Columbia, Georgia, Greenland, Latvia, Morocco, Romania, Slovakia and Slovenia: 1). In addition to the scientific component to the meeting, several social events have been arranged, and we hope that you take some time to discover Porto, an ancient city classified as an UNESCO world heritage site. Some selected papers will be published in a special issue of the Journal of Applied Ichthyology (Wiley Online Library) following peer-review in the beginning of 2017.