The University of the Basque Country Cell Biology in Environmental Toxicology group has conducted research using thick-lipped grey mullet and in six zones and report acquisition of feminine features by male fish in all the estuaries, not only in the characteristics of the gonads of the specimens analyzed but also in various molecular markers.
According to Miren P. Cajaraville, director of the research group, the results - Arriluze and Gernika in 2007 and 2008, Santurtzi, Plentzia, Ondarroa, Deba and Pasaia since then -show that "endocrine disruption is a phenomenon that has spread all over our estuaries, which means that, as has been detected in other countries, we have a problem with pollutants."