In order to go even further with his research, Joseph Schnitzler has begun collaboration with the Universiteit Antwerpen (Prof. Ronny Blust), where he has had the possibility to work with farmed sea bass as opposed to those from an estuary. This is a way to limit the heterogeneity of the fish studied. In the fishing net, the researcher does not know what he has caught: was the fish diseased? Was it properly nourished? These are factors that can cause the results of the studies to be biased. In an experimental aquarium, the sea bass are subjected to the same life conditions: stress, food, temperature, etc., much like laboratory mice. The researchers have also been able to dose the quantity of pollutants imposed on the fish: in the first aquarium, no pollutant; in the second, third and fourth, an increasing dose corresponding more or less to what we find in the estuaries already studied (0,3 – 1 ppm); and in the fifth, a very high dose (10 ppm).

The electron microscope made it possible to study the thyroid cells with great precision. Joseph Schnitzler explains. “The more polluted the aquarium, the more the follicles are of different shapes and sizes. But only the fish of the fifth aquarium show a drop in hormone production. In all the other aquariums, we do not really measure any difference, without doubt due to the compensation effect described above” (5) We also measure an increase in enzyme activity transforming T4 into T3 hormones, which corroborates the idea that the organism which is exposed to pollutants attempts to compensate. As for the quantity of thyroid hormones in the muscles, we do not see a difference except in aquarium number 5, which is the most contaminated.

Joseph Schnitzler confides: “I won’t deny that I was expecting these hormonal disruptions linked to pollution to have a more spectacular effect on the animals. Like, for example, a size difference between the fish from the non-polluted aquarium and the others. But there is no difference. Having said that, I think it would be different for the fish living in the sea because they, unlike our laboratory sea bass, cannot allow themselves to use up as much energy to compensate for the damage caused by pollution. In a natural environment, there are other needs which need to be permanently satisfied: finding food, escaping from predators, etc.”

Joseph Schnitzler now plans to study the effects of these organic pollutants on fish larvae (an FRFC project has just been launched with the University of Namur (6)), because the larval stage is a key moment for the functioning of the thyroid hormone. We can hypothesize that the fish developing from these polluted larvae will show a series of abnormalities. Let’s not get too far ahead of ourselves though, we’ll meet again in two or three years’ time.