Oxytetracycline (OTC) has been a workhorse antibiotic in aquaculture for a long time. In South Korea, where olive flounder is the top finfish species, farmers use it regularly to manage bacterial outbreaks. Everyone knows OTC works against bacteria. But what it actually does to the fish itself, especially at higher doses, has not been nearly as well understood. A recent study took a closer look. Fish were exposed to OTC at 100, 200, and 400 ppm for just one hour. Then the researchers spent the next three days tracking what changed at the gene level and in the tissues. The results show that OTC does a lot more than kill…