Pineal response in the cichlid fish Oreochromis mossambicus to extreme osmolality, pH, and temperature.

Unusually large pineal glands have been observed in Oreochromis alcalicus grahami of Lake Magadi, Kenya. To test the hypothesis that this phenomenon could result from the extremes of osmolality, pH, and temperature found in the lake, Oreochromis mossambicus males were exposed to either high osmolality (564 mOsm/L), high pH (10.08), or high temperature (40 C); control groups were exposed to 7 mOsm/L at a pH of 7.89 and a temperature of 26 C. After 21 days in the adverse environments, fish in all the experimental groups had significantly higher pineal weights and serum melatonin levels than the control fish. It is concluded that pineal activity increases in response to these environmental stresses, as it has been shown to increase with certain other types of stress.