why does semen smell the way it does?

i have noticed semen has two scents.

the first scent is the ocean breeze scent that you smell when you first ejaculate. sometimes it smells like bleach too

the second is when its been sitting around for a while.. when it begins to smell like squid or rotting seafood.

i have no problem with the first kind, but the second one is truly annoying.
why does semen start to smell like that, and how can i prevent it or reduce the stench?

My husbands cum is strong, has the chlorine smell and is bitter and nasty...  However my boyfriend's cum is virtually tasteless, almost sweet.  He eats pineapple and cottage cheese regularly, exercises a ton and takes great care of himself.  So yes, your diet and lifestyle will 100% effect the thickness, smell, and taste.  Your body does use many ways to detox itself.  If you eat bad and don't take care of yourself, all that bad stuff gets out of you through your fluids.  My husbands cum also is very salty and makes my vagina feel itchy for a few hours after.  While my boyfriends is thinner, and I can't get enough of it!