Aging changes in the optic tectum of the guppy Poecilia (Lebistes) reticulatus

Histological surveys of the brains of guppies throughout their lifespan showed no overall loss of tissue with advancing age. Brain and body increased in size at a similar rate throughout adult life in male fish. In old females after the age of two years, brain growth apparently ceased, although body growth continued at a low rate. In both sexes there was a loss of neurones from the stratum griseum periventriculare in the midbrain roof in old age; the decrease in size was significant. The midbrain is a major correlative center concerned with spatial orientation. How far neuronal loss may contribute to functional behavioral disorder in old age is unknown, but a loss of orientation could render the older fish more susceptible to predation.