According to Executive Order 13112, signed by President Clinton in 1999, the U.S. definition for "invasive species" is "an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health."
Introducing a species of live bait can often affect the ecosystem that you are releasing the bait fish into. Ecological damage can include changes in the soil of surrounding forests or negative impact on native species of animals.
It can cost a lot to maintain invasive populations of bait fish. This money often comes from fishing licenses and the government. It costs money to keep populations from out-competing other species in the area, as well as to restock waters that have been negatively affected by the bait fish.
Effects on Fishing
Invasive species often affect sport fishing and the areas that fishermen use. Sport fish populations could shrink, or the fish themselves could shrink, putting new limits on what can be caught.
Rusty crayfish species, originally from the Ohio River Basin, was introduced to Wisconsin waters. These animals eat local insects, fish, and eggs, and destroy the plant life underwater that is home to native fish. Burbot, or Lota Lota, have infiltrated several rivers in Wyoming. Examples of this invasive activity are spreading quickly and impacting several species of fish in the areas.
Check with individual state laws for releasing bait, before attempting to fish with live bait. Some states may not even allow the use of live bait. In general, do not use or release any live bait while fishing, just to be safe. There is still much to learn in the area of impact of invasive species.