In the study of Central American convict cichlid fish, CBN scientists Ryan L. Earley, Ph.D. and Matthew Grober, Ph.D. of Georgia State University, and Lawrence Blumer, Ph.D. of Morehouse College, compared bile retention and gall bladder size in dominant and subordinate males that had eaten equal amounts of food.
The scientists discovered not only were the gall bladders in the subordinate fish much larger, they were filled with dark "bad bile," unlike the pale bile in the dominant fish. The difference in gall bladder function also likely contributed to subordinate fish growing more slowly than the dominant ones. Cichlids have rigid dominance hierarchies, providing excellent models for the study of social stress. Previous cichlid studies have determined that the chronic stress of social subordination has other physiological consequences, including changes in body weight and hormones.
CBN scientists believe the latest finding supports a link between social stress and digestive function and could have implications for understanding disorders such as gallstones, a product of excess bile accumulation, in humans.
"Because social stress activates the nervous system of humans in similar ways as it does in fishes," said Earley, "the study could hold clues to evaluating the risk factors that contribute to gallstone formation in people."
Added Grober, "This is the first compelling evidence that gall bladder disease in vertebrates could be induced by social stress."