Astyanax fish and cavefish. Cave environments are characterized by

Astyanax mexicanus is a fish species that lived in freshwater and are divided into two forms, surface fish and cavefish. Cave environments are characterized by darkness and low food supply. During the evolution cavefish have lost some traits, they became eyeless and depigment and have acquired some traits to help them survive.  Cavefish depends on sporadic food supply during rainy season and also the food introduced by bats living in caves. However, to survive in this extreme environments, cavefish have developed diverse adaptations, including  starvation resistance, lowered metabolism, and increased fat storage when food become abundant. Although cavefish have slow metabolic rate, they are more active. Beale et al. suggested that cavefish exposed to continuous light instead of perpetual darkness. And the difference in metabolic rates between surface and cavefish leads to reveal the genetic basis of metabolic variation in vertebrates and how cave animals can adapt to nutrient-poor conditions.This study focused on the metabolic adaptations to sporadic low food supply.  – Fig.1. Cavefish adaptation to starvation. A)  After 2 month of fasting cavefish populations have lost greater weight than surface fish. B) Triglyceride composition was high in frequent fed adult Pachon and higher in Tinaja cavefish in comparison with surface fish.C) photomicrograph of livers. D) Stained livers indicates the presence of lipids. Tinaja cavefish stores lipid in greatly enlarge liver. CONCLUSIONThe adaptation strategies vary between independent cave fish populations. There are significant differences in appetite regulation between populations.MC4R is important for modulating weight. Mutation in MC4R have been identified to be reason in increasing appetite, growth, and starvation resistance. This genetic mutations in MC4R is also associated with obesity in humans which as a result lead to insatiableappetite. However, this mutation have no obvious effects on the lifespan and the health of the cavefish. Understanding metabolism variation of these cavefish might be beneficial for treating human diseases.