That's typical of minnows that have had their slime coat removed by being caught in a net. Where the circle is was where they got stuck in the net. Golden Shiners are very fragile fish, and holding them in warmer water is hard on them. Ideally you want the water temp to be in the mid 60's.
. Test your water for abnormalities in ammonia, nitrate, nitrite, pH and correct if necessary. Fungus and Finrot are often secondary infections of wounds on the fins or skin caused by : poor water quality and/or poor fish handling techniques. The frayed fins are bacteria infections the white marks are fungus.
They have chemicals to treat that in aquarium fish. but also test the water. High levels of ammonia, and other poor water quality issues will stress the fish, and any slilme removal can allow basically open wounds for the bacteria/fungus to get a foothold. If the fish aren't in tip top shape, they cannot fight off the infection.
Finer Shiner, Better Bait https://pentairaes.com/bait-holding-formulas.html
and other chemicals like this help you with holding the fish longer.