Some 15 years or so ago, an eel expert has done some studies on the effects on wastewater pollution on eels. For the findings revealed structural and functional alterations of the gills, hence an influence on osmoregulation. Lemaire Gony reported that these injuries are to be reversible, but the liver lesions however is irreversible. This was writing by Lemaire Gony in around the year of 1993, in which I myself for many decades before viewing this writers/experts findings, I been telling others for many decades before.
Cadmium was administered with an water produced perivascular fibroses, where as a one time injection of benzo(a)pyren has led to a decrease in glycogen and a accumulationof the lipid globules. The liver of eels exposed to both cadmium and benz(a)pyren showed complete disorganisation of the parenchyma and nuclear degeneration.
Test as well on the japanese eel (Anguilla japonica) (Freshwater), with various heavy metals disrupted the eels growth. Within eels, even relativety low concentrations caused vertibral malformations.
Now note, all of my background on eels are from both, researched facts and by having any number of various eels through the decades in studying at home on these species. Both or a proven fact for ones success in maintaining and if any medical problems should arise. At some point, you can be a success at it or fail all due to the complexity of making the correct or incorrect diagnoses from the start.
I hope and pray, that from posting something in which is as imporant as this, other members would do far better for their eels then just admiring them in their tanks