This study tested whether methylene blue added to fish feed could protect tilapia from nitrite poisoning, which causes dangerous oxygen transport problems. Fish fed methylene blue for 5 days before nitrite exposure had no deaths and better blood oxygen levels compared to control fish that experienced deaths and organ damage. The methylene blue worked by preventing the conversion of healthy hemoglobin to dysfunctional methemoglobin. This suggests oral methylene blue could be an effective way to protect against oxygen transport disruption.
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Oral MB preloading in tilapia prevented methemoglobin accumulation and mortality under nitrite stress, supporting dietary MB as a proactive hemoglobin-protective strategy.