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Fish on the roof of the world: Densities, habitats and trophic position of stone loaches (Triplophysa) in Tibetan streams

Abstract:

The fast increase in temperature on the Tibetan Plateau, with anticipated future changes in aquatic ecosystems and biodiversity, highlights the urgent need for ecological data on the sparsely studied Tibetan running waters. In the present study we surveyed eight Tibetan streams to obtain data on densities, feeding selectivity and trophic position of the stone loach Triplophysa. Benthic algae, detritus, macroinvertebrates and fish were quantified and collected for stable isotope and stomach content analysis. Triplophysa density (mean 0.70 individuals m-2, maximum 1.6 individuals m-2) decreased with altitude and increased with the percentage cover of fine substratum. Glacier-fed sites tended to have the lowest fish densities, whereas the highest densities were found near lakes. Mean fish length (4.1-9.6cm) was positively related to the percentage cover of coarse substratum. Triplophysa was omnivorous, but the composition of the stomach contents varied greatly between sites and among individuals. Algal matter was ingested at most sites, but macroinvertebrates (Chironomidae, Baetidae and Simuliidae) dominated the ingestion (average 50-100%). The trophic position of Triplophysa, identified from δ15N (‰) of the biota, varied between 2.6 and 4.2 among localities (mean 3.6) and was inversely related to the biomass of benthic algae, but unrelated to quantities of other potential food sources.