does anyone know what this might be i have a red oscar that has not eat in 3days and has a white coming out his butt and swimming on his side but he looks good and if my other oscar go buy him he moves fast like he ok have any idea need help thanks tom

White stringy poo usually means parasites.
What do you feed him, for feeding mealworms can allso cause whiye poo.
here's an old thread , and Jenni explains what she did to cure the problem.

www.oscarfishlover.com/oscar-fish-advice...ith-white-poop#95729
Allthough the oter mods may have some more ideas!

btw welcome to OFL.

thanks for your help

Have you tested your water for ammonia, nitrite, nitrates and PH?

Yes, white stringy faeces can be an indication other parasitic infestation. Is the fish breathing heavily at all? Also, what have you been feeding your fish?