High‐salinity water use of euryhaline catfish Genidens genidens revealed by otolith microchemistry

Abstract

Migratory patterns of the catfish Genidens genidens in four estuaries along theBrazilian Atlantic coast are reconstructed from otolith Sr/Ca, a salinity proxy,to test estuarine-dependency.To facilitate interpretation of this proxy in otolithcore-to-edgeprofiles, a Sr/Ca Reference Value for High Salinity (RVHSSr/Ca) of4.88 mmol/mol was established experimentally, from fish specimens reared inwater with a salinity level (33 psu) between estuarine and high salinity (marine)water. All wild specimens exhibited otolith Sr/Ca values higher than RVHSSr/Ca,suggesting that G. genidens utilizes environments with marine salinity. Ourresults reveal highly variable environmental histories, with at least five majorhabitat usage patterns. Most distinctive among these, we find that (a) fish fromParanaguá Estuarine Complex (PEC) exhibit high intraindividual heterogeneity;(b) most fish (57%) from Guanabara Bay (GB) exhibit prolonged exposure tovery high salinities, often exceeding 36.5 psu levels found in some shelf sectors;and (c) some fish from Paraiba do Sul River, GB and PEC exhibit Sr/Ca valuesbelow RVHSSr/Ca consistent with estuarine residence. These results suggestthat G. genidens is not strictly estuarine-dependent.