Bisexual fish in the Urdaibai estuary

Chemical compounds contaminating water can alter the sexual development of aquatic organisms, giving rise to hermaphrodite creatures with both masculine and feminine gametes.

In March 2004, a team of researchers from the University of the Basque Country (UPV/EHU), while studying the reproductive apparatus of mussels, found something surprising in the Urdaibai estuary (Bizkaia): a high proportion of these bivalve molluscs were hermaphrodite, much higher than what could be considered normal. However, this find did not catch the scientists totally unawares – studies carried out in the 90s had already proved that environmental contaminants could have an influence on the reproduction of aquatic organisms.

The Cellular Biology in Environmental Toxicology team led by Professor Miren P. Cajaraville deduced that numerous chemical compounds in water influence the growth, behaviour, reproduction and the immune function of organisms, due to interference with the endocrine system. This is why these compounds are known as ‘endocrine disruptors’. Basically they are alkylphenols (amongst others, breakdown derivatives of domestic detergents and cosmetics), pesticides, plastifiers, petroleum derivatives and synthetic hormones. On occasions, they influence the organisms themselves; otherwise the consequences may appear in the second or third generation.

Bisexual organisms

This proportion of hermaphrodite mussels and the changes found in the development of their gametes gave rise to the DERBIUR project, which will terminate in December 2008. The aim of this research was to determine the possible presence of endocrine disruptors in Urdaibai and analyse the alterations that these substances can cause in bivalve molluscs (mussels, oysters, etc.) and in fish.

Significant results were also found on this occasion. On the one hand, the alterations in the development of the gametes (the masculine or feminine cells necessary for reproduction) have been confirmed and, on the other, a high prevalence of intersex (specifically in the grey mullet) was observed. As regards the purification plant treating waste water in Gernika, a third of the male grey mullet in this area had feminine sex gametes.

Biomarkers, clues to alterations

To arrive at these conclusions, apart from microscopic analyses, the UPV/EHU researchers used various biomarkers. For example, they studied the changes in the levels of vitellogenin in the fish. La vitellogenin is a protein specific to females and which is used as a biomarker for feminisation. In fact, Ms Miren P. Cajaraville’s team observed that some male grey mullet also had this protein.

How the levels of expression of the gene known as aromatase changed was also analysed. This is the gene responsible for the synthesis of the estrogenic hormones (feminine sexual hormones). The enzymes that code this gene are capable of converting masculine hormones to feminine ones. They found that the intersex grey mullet have a greater expression of the aromatase gene than either the male or female fish.

What is more, thanks to the chemical analyses undertaken by CID/CSIC in Barcelona, high levels of alkylphenol metabolites were found in the vesicle of the grey mullet. Thus, the alkylphenols could be responsible for the alterations found in the grey mullet.

The research team had the use of a mobile laboratory to carry out dissections on taking the organisms out of the water. Some of the samples obtained from these dissections are registered here “in situ” prior to their analysis with the microscope, and the remains are frozen to undertake analyses of proteins and genetic expressivity at the University’s Cellular Biology and Histology laboratory.

The results obtained by the UPV/EHU researchers coincide with those from international researchs. Also, CID/CSIC in Barcelona has found similar results to the Urdaibai findings amongst fish in the river Ebro.