GENETIC VARIABILITY IN DEMERSAL FISHES: DEPTH DISTRIBUTION VERSUS PHYLOGENETIC CONSTRAINS.- Microevolutionaryprocesses in deep sea environment has been the most difficult to deal with. There are hypothesis that considerthose environment as paradigm of stability. Another hypothesis postulate periodicals disturbations where the species reactsaccording with the plasticity of the genetic information and restricting phylogenetics. In this context genetic variability hasbeen studied in three species that inhabit deep sea of the Chilean coast, two macrourids and a morid: Macrourus holotrachys,Caeloiynchus fasciatus and Antimora rostrata. 29 loci were studied and three of them are polymorphic coincident for thethree species. The genetic variability is very low, 0.03; 0.026 and 0.05 respectively. Apparently these values fit with Smithand Fujio hypothesis that relates low variability and habitat generalist. On the other hand every species develops differentbehaviour with different capacities to explore the environment. The Gadiform group shows as a characteristics low variability(Smith and Fujio, 1982). In comparing against other groups the low variability could be the result of phylogenetic constrainin the group.