This is actually a hard question to answer. They are a very slow growing animal and it is thought that they can live for 80 years or more. The exact age of a crayfish is difficult to know because they moult regularly (once or twice a year), each time growing a new exoskeleton. So you can’t tag and release an individual and follow it over a long period. Scientists have been trying for many years to work out a direct way to determine the age of crustaceans and some recent Australian research holds promise in this area. Unfortunately, this technique requires the animal to be sacrificed and would have to be calibrated on each species. Currently, the age of live crayfish can only be estimated based on size. This is routinely done by measuring the length of their carapace -the part of their exoskeleton that extends backwards from their head and protects their upper body.