Biogeography is the study of patterns in distribution of fish (or other) species.  Biogeography provides an understanding of where populations are currently present and can help infer evolutionary relationships at a broad scale, including historic population isolation and colonization events.  Geologically, many species patterns can be tracked with plate tectonics. 

Phylogeny and biogeography of liverbearers (genus Brachyrhaphis; figure credit: Ingley et al. 2015).

 The study of biogeography can also complement understanding of current ecological processes to explain distribution of populations at a local scale.

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