Some reasons why your boyfriend has a fishy smell include urinary tract infections, Trimethylaminuria and sexually transmitted infections.
Trimethylaminuria which is also known as fish odor syndrome is a genetic disorder in which the body cannot break down trimethylamine, which leads to a fish odor in various bodily fluids including semen, sweat and urine.
Trimethylaminuria is a rare condition that causes a buildup of the chemical trimethylamine in the body.
The body releases the excess trimethylamine through sweat, urine, breath, and reproductive fluids, giving off a strong fishy odor.
And some sexually transmitted infections such as gonorrhea and chlamydia can cause a fish odor in semen or discharge.
Certain foods can also cause a fishy odor in males and even females such as garlic, meats and asparagus which can temporarily alter the smell of semen.
Smegma and prostatitis can also cause a fishy odor in males and females.
Smegma is the natural secretion under the foreskin and can become stale and have a pungent odor.
Prostatitis is inflammation of the prostate which can also cause a fishy smell in semen.
If your boyfriend continues to have a fishy smell and it does not go away within a few days to a week your boyfriend should see a doctor to be safe and to find out exactly the cause of the fishy smell.