Who is Fish Lamb from Cloudstreet and what is their importance?

Samson "Fish" Lamb is the Lamb's second son. He suffers an accident early in the novel while fishing..... an accident that results in brain damage. After the accident, Samson has the mind of a small, joyful child. He is also, however, subject to fits of fear and rage, as well as the loss of bodily functions. In the end, he falls into the river and drowns.