Biologisches Effektmonitoring mit Aalmuttern aus Nord- und Ostsee
Institut für Angewandte Ökologie Forschungsgesellschaft mbH (2007), FKZ 30102023
Eelpout (Zoarces viviparus), also known as viviparous blenny has been proposed by HELCOM and OSPARCOM as a favourite sentinal species for monitoring of the impacts of marine environmental pollution. It has also been selected by the German Environmental Specimen Bank (ESB) as a bioindicator for the presence of potential hazardous substances in coastal waters.
The present study investigated the prevalenve of gonadal disorders in eelpout, e.g. intersex and atresia. All gonad samples originated from specimens collected in spring 2006 at sampling areas of the German ESB routine contaminant monitoring. Two samples were taken in May from the German Wadden Sea National Parks (Varel, Büsum), the third sample was collected in June from the Bodden National Park of Western Pomerania at the German Baltic Sea (Darss). Muscle and liver tissue of fish selected for gonad analysis were pooled for future chemical analysis.
The testes of male eelpout were examined by light microscopy. Gonads from sampling sites Varel and Büsum showed a less developed gonadal stage than those from the station Darss. The observed difference is in agreement with sampling time, i.e. gonads sampled in May are less developed. Intersex (ovotestis) was recorded in samples from all stations. The prevalence was 15% at Varel (n=47) and 24% at Büsum (n=33). The highest prevalence (43%) was observed at the Baltic station Darss. However, because of the low sample size (n=7) this result should be treated with caution. In general, the degree of intersexuality was low with only few single primary oocytes dispersed in normally developed testis tissue of all fish sampled. There was no substantial difference in severity of intersex between the sampling sites. No other pathological condition was observed in testes.
Ovaries from female eelpout were examined using macroscopical and histological methods. The degree of gonadal development did not vary between the North Sea stations but was slightly increased in females from the Darss station sampled at a later date. In all samples the most mature oocytes where in an advanced vitellogenic stage. It was easy to notice by binocular observation that almost all of the ovaries showed signs of follicular and oocyte degeneration. Histological examination revealed typical characteristics of follicular atresia. Most commonly late stages of atresia resulted in severe degeneration/ resorption of the follicle and oocyte. In samples from Varel (n=27) and Büsum (n=22) 100% of the female eelpout were affected by atresia. No minor form of atresia was observed, the degree of atresia was either moderate or severe. The prevalence of atresia at the Baltic sampling site (n=27) was 93% with a slightly lower intensity of degeneration in comparison with the sampling sites in the Wadden Sea.
This study is the first evidence of the presence of gonadal disorders in eelpout from the German North Sea. Furthermore, the results are in good agreement with previous field work of the Institute of Applied Ecology Ltd. and confirm the presence of intersex and atresia in male and female eelpout from the German Baltic. Additional monitoring and research are needed to investigate possible causes of the unexpectedly high prevalence of atresia in developing ovaries of female eelpout.
Keywords: Germany, Wadden Sea, Baltic Sea, eelpout, intersex, atresia, biological effects monitoring