These strange little fishes live in caves of eastern Mexico. It’s strange because cave environment is entirely dark and there is no plant, therefore there is no food available for these fishes. Despite the famine environment tetra fished can survive, although there went to very complex changes when it compare to their relatives living in rivers. These fish lost their eyes and develop some strategies to survive in this harsh conditions.
Some group of researchers took the fishes into laboratory and compare to them genetically closest fishes. Researchers revealed that cave fishes have increased apatite which is a necessary behavior to gather some food when there are not much around. The increased appetite help fishes to gain more weight, they can store up to 10 times more fat. However, surface fishes have not this behavior when they exposure the large amount of food.
Another big difference is cave fish has fluctuating level of glucose in their blood. Blood glucose levels of Mexican cave fish after having meal is extremely high compare to surface fishes. On the other hand, during fasting period blood glucose level is going down. Basically, they can’t control their blood glucose level effectively.
In animals, blood glucose level is controlled by insulin hormone which is secreted by the pancreas. When insulin release it bind to surface of the cells and stimulate the cells to take glucose sugar into it. It has been found that these fishes have mutation on their insulin receptors. The mutation leads impaired insulin binding to receptors of the cells which eventually cause decreased glucose uptake into the cells.
Most interesting point in this study, if human has the same mutation it will cause an endocrine disorder known as type II diabetes. However, the Mexican fish which have identical mutation living perfectly. Also, the mutation giving some extra advantages to compare surface fishes.