As one of the most primitive "They have an oral disc with several quite savage looking teeth inside and they use this to attach to larger fish out in the ocean, raft a hole then feed on blood and fluids and even chunks of flesh," SARDI research scientist Chris Bice said. "They only feed in the marine environment and as soon as they move into freshwater [from saltwater] and start their upstream migration, they stop feeding. "So, whilst they may look a bit savage, they are of no risk or danger to humans."