title: Morphological abnormalities in gonads of the Baltic herring (Clupea harengus membras): Description of types and prevalence in the northern Baltic Sea.
abstract: Due to heavy anthropogenic influence and variation of the environmental conditions in the Baltic Sea, reproductive disorders are becoming a major environmental concern. We show here an increasing prevalence of gonadal malformations in the Baltic herring (Clupea harengus membras), a key species of the Baltic ecosystem and important in commercial fishery. During 1987-2014, the spawning herring population in the Archipelago Sea (AS) (North Baltic Sea, Finland) was monitored annually and analyzed for gross morphology of the gonads [total number (n) of analyzed fish = 38 284]. Four different types of malformations were repeatedly found and named as asymmetric, rudimentary, segmented, and branched gonads, but also hermaphroditic gonads and miscellaneous (unidentified) disorders were recorded. In 2013, additional samplings (n of fish analyzed = 541) showed similar malformations in herring from the Bothnian Sea. In some gonad types, histological examination revealed disintegration of seminiferous tubules and hyperplasia of the interstitial tissue. In 2014, the overall prevalence of malformations was still relatively low in the AS (frequency = 0-3.4 %; n = 750) and had apparently minimal effect on population recruitment. However, an increasing trend in the time-series (GLM; F = 32.65; p < 0.001) and a significantly higher prevalence in the Bothnian Sea (frequency = 0.7-5.0 %; n = 541; χ (2) = 6.24; p < 0.05) suggest that gonadal malformations may become a new threat for fish in the Baltic Sea. The observed gonad atrophies may be due to environmental endocrine disruption; however, also other explanations may exist and potential explanations are discussed.
authors.affiliation: Archipelago Research Institute, University of Turku, 20014, Turku, Finland. marjut.rajasilta@utu.fi.
authors.forename: Marjut
authors.initials: M
authors.lastname: Rajasilta
authors.affiliation: Archipelago Research Institute, University of Turku, 20014, Turku, Finland. hemiel@utu.fi.
authors.forename: Mikael
authors.initials: M
authors.lastname: Elfving
authors.affiliation: Archipelago Research Institute, University of Turku, 20014, Turku, Finland. jari.hanninen@utu.fi.
authors.forename: Jari
authors.initials: J
authors.lastname: Hänninen
authors.affiliation: Archipelago Research Institute, University of Turku, 20014, Turku, Finland. paivi.laine@utu.fi.
authors.forename: Päivi
authors.initials: P
authors.lastname: Laine
authors.affiliation: Centre for Environmental Research, University of Turku, 20014, Turku, Finland. ilppo.vuorinen@utu.fi.
authors.forename: Ilppo
authors.initials: I
authors.lastname: Vuorinen
authors.affiliation: Department of Cell Biology and Anatomy, Institute of Biomedicine, University of Turku, 20014, Turku, Finland. paranko@utu.fi.
authors.forename: Jorma
authors.initials: J
authors.lastname: Paranko
mesh_terms: D000818:Animals; D005260:Female; D005387:Finland / Q000453:epidemiology; D005393:Fish Diseases / Q000453:epidemiology* / Q000473:pathology; D005399:Fishes; D006058:Gonadal Disorders / Q000453:epidemiology* / Q000473:pathology; D006066:Gonads / Q000473:pathology*; D008297:Male; D015995:Prevalence
keywords: Baltic Sea; Gonads; Herring; Malformation; Reproduction