https://phys.org/news/2018-07-dumping-fish-scraps-stingrays.html

"It might seem harmless, but feeding wildlife, whether on purpose or not, can change animals' behaviour, disrupt the food chain, and cause negative health impacts," said lead author of the study, Joni Pini-Fitzsimmons.

Associate Professor Culum Brown, head of the Fish Lab at Macquarie University said, "Despite the common practice of discarding fish waste into waterways, the effects of this behaviour have not been evaluated and are likely not being considered in fisheries management."