Why is it that Red meat shouldnt be eaten on Good Friday???

We just had a work morning tea for a girls birthday & the topic came up & most people said they dont eat red meat on Friday, now I am Hindu, but love seafood so have asked DH to bring some home & asked if he can cook it all tomorrow.
Not for religious purposes but beacuse I get to eat seafood LOL...

Then someone asked the reason why & actually noone knew why?

So does anyone know the reason why????