Sexual disruption in a second species of wild cyprinid fish (the Gudgeon, gobio gobio) in United Kingdom freshwaters

To establish whether the intersex condition seen in the roach (Rutilus ruti lus) in United Kingdom (UK) rivers was species specific or a more general p henomenon in fish, evidence for sexual disruption was sought in a second cy prinid species, the gudgeon (Gobio gobio). Gudgeon were collected from the Rivers Aire and Lea (at locations that receive high-volume discharges of se wage treatment works [STW] effluent and that contain intersex roach) and fr om two still waters, and their gonads were examined histologically for evid ence of intersexuality (the simultaneous presence of oocytes and testicular tissue). Intersex gonads were found at all sites, with the highest inciden ces occurring at one of the still waters (Lakeside Fisheries: 15%) and at s ites on the River Aire (Thwaite Weir, Silsden Bridge, and Knostrop: 14, 13, and 12%, respectively). In the River Lea and Longton Park Lake, the incide nce of intersexuality in gudgeon was 6%. In most cases, intersex gonads wer e characterized by a few primary oocytes/gonad section in an otherwise norm al testis. However, at some sites on the River Aire (Thwaite Weir and Knost rop), the intersex condition was more severe. At Thwaite Weir, for example, more than half of the gonad in 40% of the intersex fish was comprised of o varian tissue. Elevated concentrations of plasma vitellogenin both in male and in intersex fish indicated that fish had been exposed to estrogen(s). S ome of the gudgeon were found at sites several kilometers downstream of any point discharge of STW effluent; therefore, the results likely are represe ntative of this species in wild populations found in typical UK river ecosy stems. Together with the findings in the roach, these data on the gudgeon c onfirm that sexual disruption in fish in UK rivers is not species specific.