Mexican golden trout

Its range

This trout marks the southern limit of the genus on the American continent. It lives in the rivers of the Sierra Madre Occidental, in Mexico, at a latitude where no salmonid should be found at all: relief compensates for climate, and nothing else does.

A position like that has one immediate consequence. The southernmost populations of a cold-adapted group occupy, by definition, the habitats closest to their tolerance limit. The smallest warming reaches them before it reaches anything else, and there is no ground further south to fall back on.

Conservation

The international assessment made on 28 February 2019 rests on two observations and not on any count of fish: a very restricted geographic distribution, and a continuing decline in the quality of the habitat inside it. The second is what matters, because it needs neither overfishing nor a competing species to produce its effect.

A small commercial fishery is also on record, which implies regular local catches on a fish whose entire range fits into a handful of mountain basins.

Other names

Mexican golden trout, and the same name in every language of the catalogue. The scientific epithet says it more precisely: chrysogaster is built on the Greek words for gold and belly, and points at the underside rather than at the whole fish.

The common name collides with the California golden trout, a distinct and geographically separate species. Both circulate in English-language writing, where only the country adjective tells them apart.

A word on the documentation, since it conditions everything above. The greatest published length for the species is given in standard length and probably reflects the small number of specimens ever measured rather than a real ceiling. Neither the biology, nor the diet, nor the detail of the reproduction is documented in the reference bases: what is written here is close to everything available.