Walleye fillet

I fish local bass tournaments and catch alot of walleye this time of year and I usually give them away or put them back. This year I decided to keep them to eat. I caught 4 nice ones yesterday. I bleed them out on the boat about 45 minutes before heading to the ramp. I had a cooler of ice in my truck for the ride home. I cleaned them when I got home and some of the fillets had black lines or what looked like veins. Is this normal and safe to eat?
Thanks