Comment by croemer

The measured concentrations are on the order of 1-20 ng/mL in blood. Cmax in humans when taking those drugs are about 100-1000x higher.

I wouldn't put too much weight on the finding that those with detections had different urea/lactate etc. There might be something underlying explaining both drug and physiology, like age.

Could still be bad to have chronic exposure at such low levels - also fish physiology is different.