Background
Endocrine disruption is among the most discussed fields of ecotoxicologocal research. Most of
current research has its focus on chemical based endocrine disruption in aquatic animals such as
fish and amphibians. However, in wildlife fish such as roach (Rutilus rutilus) the appearance of
testicular oocytes are often reported as feminizing effects of endocrine disrupting chemicals but
such effects are also seen in areas lacking impact of anthropogenic pollution. Thus, it appears that
endocrine disruption might be due to other naturally occurring reasons. Some evidence exists that
it can be also the result of infections with parasites. Different parasite species of the phylum
microspora, such as Nosema granulosis, are known to cause feminization in crustaceans
(Rodgers-Gray et al., Int. J. Parasitol 2004). Similarly, fish such as roach are also commonly
infected with microsporidians of the genus Pleistophora. In a field study from the Finish coast an
increasing prevalence of infection with P. mirandellae of female and male roach was positively
associated with the occurrence of hermaphroditism (Wiklund et al., Dis. Aquatic Org. 1996). The
authors described infection of oocytes with this microsporidian, therefore feminization of the host
could possibly favour the establishment of P. mirandellae. In addition to protozoans also
helminths like the cestode Ligula intestinalis are known to affect growth and maturation of the
gonads (Schabuss et al., J. Helminthol 2005). L. intestinalis reduces levels of sex steroids in
infected fish such as roach and chub probably by suppressing the secretion of gonadotropins or
gonadotropin releasing hormones (Arme, J. Helminthol., 1997). However, the underlying
molecular and biochemical mechanisms are not known until yet, due to a paucity of experimental
studies addressing the impact of L. intestinalis on sex steroid regulation.
Objectives
- To investigate the potential and importance of naturally occurring endocrine disruption induced by parasites in fish (i.e. is it more important than endocrine disruption by chemicals?)
- Perform experimental infections of fish with parasites that may induce endocrine disruption.
- Study the underlying molecular and biochemical mechanisms of potential effects like feminization and/or suppression of gonadal growth.
- Comparing the presumed effects of parasites on hypothalamus-pituitary-gonad axis with those of established endocrine disrupters .
- Provide information on the abundance of parasites potentially inducing endocrine effects. Can a considerable contribution to endocrine disruption by parasites be expected in a broad regional context or is restriction to local ”hot spots” to be assumed?
Scope
- Initially, performance of a comprehensive literature search to provide an overview on what is the current status of knowledge with regard to potential endocrine-like effects due to parasite infection in fish. Subsequently, reconsideration of the project on that basis and - if necessary - adjustment of experimental work.
- Determination of effects of parasite infection during several life stages of fish with regard to the hormonal system and the gonadal tissue.
- Investigations on the mode of action in terms of molecular and biochemical analyses in comparison to the effects of natural hormones or substances known to mediate hormone-like effects. Comprehensive studies to cover several possibilities of potential interaction like hypothalamus, pituitary and gonads.
- Histology of gonadal tissue
- Preparation of an overview on the abundance of parasite species potentially relevant in that context.
- Assessment of findings in a comparative discussion including a view on non-fish species.
Outcome / deliverables
Sound scientific basis whether and how parasites are able to induce endocrine disruption in fish. First estimation to which extent parasite infections might contribute to endocrine disruption in fish.
Risk analysis of non execution of proposed research
Currently, endocrine disruption is commonly associated with the presence of chemicals. The proposed project concentrates on the degree of ”naturally” occurring endocrine disruption which is caused by parasites. It appears likely that the degree of chemical induced endocrine disruption in fish and amphibians is over-estimated due to the lack of studies on endocrine disruption by parasites.
