There are tons of videos circulating the internet which state that using Mountain Dew or other Cola can stop caught fish that are bleeding profusely and help them survive. While there is no disputing that the blood does seem to "disappear" do we really know what is happening here?
In 2019 Prof. Steven Cooke from Carleton University put this theory to the test. Can Mountain Dew stop fish from bleeding and save its life? Here's what he did and what he found out:
"We captured Northern Pike (Esox lucius) via hook and line, experimentally injured their gills in a standardized manner, and treated them with either Mountain Dew, Coca Cola, or carbonated lake water and observed the duration and intensity of bleeding, as well as overall blood loss (using gill colour as a proxy) while the fish was held in a lake water bath. As a control, we had a group of experimentally injured fish that did not have liquid poured over their gills before the observation period. All treatments and the control were conducted at two different water temperatures (11-18 °C and 24-27 °C) to determine if the effects of pouring carbonated beverages over injured gills is temperature dependent. When compared to the control, we found that the duration and intensity of bleeding increased regardless of the type of carbonated beverages used in this study, and there was no effect of water temperature. Use of chilled versus ambient temperature beverages similarly had no influence on outcomes. As such, there is no scientific evidence to support the use of carbonated beverages for reducing or stopping blood loss for fish that have had their gills injured during recreational angling based on the context studied here. This study reinforced the need to scientifically test angler anecdotes and theories when it comes to best practices for catch-and-release fishing."
The entire study can be found at the link below for those that are interested.