Fishy breath isn’t always from seafood: A mouth that smells fishy, urine-like, or similar to ammonia may indicate kidney failure.
The kidneys are responsible for removing toxic chemicals from the blood by creating urine. In kidney failure, also known as end-stage renal disease, the kidneys become so damaged that they are no longer able to filter waste products and toxic chemicals from the blood. When this happens, the dangerous toxins and waste not discharged from the body accumulate and affect nearly every part of the body. The fishy breath odor can occur when kidney failure affects the respiratory system and causes breathing problems.