Slime you are seeing is actually oil produced from the shad. Shad has oil glands in their heads and produce more oil in warmer water. We all use a fine salt in our tanks to keep the shad healthier. Also use it with minnows / shiners. Bait stays a lot more active and healthier with salt added. I buy a fine stock salt in a 25 lb bag at our local Atwoods for around 4.00 that lasts a couple years.