My guppy died because of this

Today one of my guppies died. He had a large lump on his belly. Does anyone know what this is?

 

Looks like prolapse sorry for your loss

 

Can you explain what a prolapse is? He has had this since birth and he is a year old.

 

Prolapse is when a fish strains too much, due to either constipation or eggs/pregnancy, and suffers a rectal prolapse through the anal pore. They basically push out part of their bowels.

Here is another guppy with it:

 

Could a prolapse effect his growth? because it has taken him a incredibly long time to grow. He still looked like fry after 3 months.

 

It could have, because his body was trying to heal despite the fact that it couldn't. It is probable that the energy he would have used to grow wouldhave gone to 'healing' and protecting the 'wound' from infections, therefore delaying his growth.