How Omnivorous Fish Keep Mountain Lakes Thriving
An interesting sidestory
In the intricate world of mountain lake ecosystems, the eating habits of fish reveal fascinating insights into how species coexist and maintain balance. Our study explored the diets of three fish species in a mountain lake on the Iberian Peninsula: two cyprinids—the northern Iberian chub (Squalius carolitertii) and the northern straight-mouth nase (Pseudochondrostoma duriense)—and one salmonid, the brown trout (Salmo trutta).
The northern Iberian chub displayed remarkable dietary flexibility, consuming everything from detritus and aquatic insects to micromammals and small fish. In contrast, the straight-mouth nase stuck mainly to detritus, showing little dietary variation. Interestingly, as chub grew larger, they consumed less zooplankton, while the nase exhibited no such changes in diet as they aged. Meanwhile, brown trout acted as top predators, feeding exclusively on the cyprinids.
This study highlights how omnivory—a species’ ability to feed at multiple trophic levels—supports coexistence. The chub’s adaptable feeding habits reduce competition by exploiting diverse food sources, including rare items like micromammals and terrestrial insects. Such adaptability can stabilize food webs, allowing fish to tap into alternative energy pathways, even during sudden changes in the ecosystem.
Our findings underline the critical role of omnivorous fish in mountain lakes and suggest exciting avenues for future research into how these ecosystems are fueled by energy inputs from unexpected sources, such as land-dwelling creatures swept into aquatic environments.