Sometime in the mid 1900s the lake was stocked with zander, and in late 1990s the population started growing. Back then the average weight was high and fish around 6-8 kilos was not uncommon. Today the population has shifted. There are still big fish in the lake, but there are also Alot of smaller ones. The big perch declined around the same time as the rise of the zander population, but recently the perch population has exploded and today you can have a great time catching loads of medium size perch, with the chance to get a biggin. Pikefishing in Mjörn is hard and not like in most other lakes. Big pike in the lake mostly hunt in the pelagic, meaning they can be just about anywhere in the lake as long as there are baitfish around.
Popular species to fish for in Mjörn are e.g. zander, perch, pike, burbot, trout, bream and ide. But there are more species such as smelt, bleak, roach, ruffe, tench, eel and a very small population of crucian carp and common carp.