For 3 years now, the residents and visitors of the Aposelemis area have been facing an eerie sight: dead fish everywhere or fish that desperately seem to be looking for some oxygen outside the water!
Every year, the scientists of the Hellenic Center for Marine Research (ELKETHE) – although they are not responsible for monitoring the waters in Aposelemik – are called upon to answer what is ultimately behind the mass killing of fish, something that even today is an unsolved puzzle.
And why do we say “unsolved”? While in the previous 2 years, scientists reached – up to a point – a conclusion, this year the facts have changed.
THE Dr. Pantelis Katharios, Director of Research at the Aquaculture Microbiology Laboratory at ELKETHE he tells Cretalive that it is a phenomenon that we have been encountering for the last 3 years, every spring. This year, due to the weather conditions with the high temperatures, we saw it happen earlier than other times. However, we have dead fish in Aposelemis sometime from April to June.
What changed this year? The ELKETHE scientist explains that in 2022 and 2023, he was called to the site to take samples some 24 hours after the phenomenon had occurred. This year, however, he was in Aposelemis at the birth of the phenomenon, on Monday, April 22. In previous years, therefore, he found that the oxygen in Aposelemis was at normal levels and therefore did not justify the mass killing of fish since it is usually the main reason for a similar phenomenon. We come to 2024, however, and when Dr. P. Katharios rushed to the scene, after he was contacted by the Municipality of Hersonissos, he saw dead fish on the banks and many alive ones trying to get their heads out of the water to breathe. It is a behavior of fish that indicates that there is a lack of oxygen in the water. Immediately, with an oximeter it was found that the oxygen levels were almost at zero!
He therefore believes that the picture would have been similar in the previous 2 years, however, when the measurements were made, the oxygen had returned to normal levels. Also, the fish arrived at the ELKETHE laboratories when they had already rotted and it was more difficult to proceed with the analysis process.
“We are sure that the anoxia killed the fish“, he says. But what is being looked at now is what caused the anoxia. Dr. P. Katharios considers that the most probable cause is the bloom of phytoplankton. They are probably not toxic organisms, as originally thought, and the fish mortality is due to environmental reasons. Usually the sudden and excessive growth of phytoplankton organisms is followed by a sudden drop in dissolved oxygen in the water leading to suffocation of fish that cannot escape from these waters. In short, it is a natural phenomenon that if not fully analyzed and explained we will encounter it every Spring. That is, we will see every year fish die in Aposelemis without being able to do anything about it, it will just happen!
The ELKETHE scientist states that if there is no renewal of the water or some other type of intervention, such as aeration of the water with technical means when a sharp drop in oxygen is observed, the phenomenon will be uncontrollable.
In previous years, laboratories and scientists from various disciplines collaborated at ELKETHE, they proceeded to study the environmental DNA, i.e. all the organisms that “participated” in the phenomenon. A series of tests were carried out that never came to the conclusion that there is a pathogenic agent in this particular phenomenon. Once again, there does not appear to be sewage due to the absence of odor but also due to the repeatability of the phenomenon on a seasonal basis.
Corresponding efforts to explain the phenomenon are made, at the same time, by the agency responsible for the dam.
In order to identify the… root of the evil, which organism – even a non-toxic/pathogenic one – is responsible for the lack of oxygen and the killing of the fish, a systematic monitoring should be done, not trying to find solutions after the fact and with piecemeal way.
This is a decision that needs to be made at a central level.
source: cretalive.gr
