Lake Zacapu and La Zarcita springs form a Protected Natural Area (PNA) in Michoacán State, México, which is a priority site for freshwater fish conservation. This area is home to a Critically Endangered endemic salamander and five Endangered endemic fish species, and another six fish species that are in other threat categories in the IUCN Red List, and the Official Mexican Standard (NORMA-059-SEMARNAT-2019). From 2019 to 2023, we studied the changes related to fish populations and made comparisons with the previous study that was undertaken in 1996. The reproductive biology and trophic ecology of the fish species in Lake Zacapu and the La Zarcita springs were studied. This information was distributed to state and municipal authorities, as well as to the fishermen's union, resulting in decisions being made about the fishing and supply rules for the PNA.