Complex sentence: They are also one of the oldest trout races to colonise Ireland, perhaps as old as 50,000 yrs. Ferox canabalise brown trout (which returned to many of the same lakes when geological processes and climatic conditions allowed) and also prey on other fish species.
Split into simpler sentences: They are also one of the oldest trout races to colonise Ireland, perhaps as old as 50,000 years. Ferox cannibalise brown trout (which returned to many of the same lakes when geological processes and climatic conditions allowed) and also prey on other fish species.