Diet of fishes and food web structure of Lake Langcuo assessed from Tibetan Plateau, southwest China

The diet of Gymnocypris species and the food web structure in Lake Langcuo (4300 m above sea level) of the southwest Tibetan Plateau of China were investigated by carbon (δC) and nitrogen (δN) stable isotope analyses. Ephemeropteran and chironomid larvae were the major components of the diet of Gymnocypris chui, making it an omnivore with animals as the majority component, while the Myriophyllum spicatum and ephemeropteran larvae was the most important for Gymnocypris scleracanthus, qualifying it as an omnivore with plants as the majority component. Ephemeropteran larvae also made up the most abundant constituent of the Triplophysa stoliczkae diet. Overall diet changed during development of G. chui, but the dominant food remained unaltered, whereas the major component of G. scleracanthus diet changed. An average trophic enrichment factor of 3.4‰ was used to calculate the trophic levels based on δN, with the results indicated that the food web has three trophic levels: primary producers and primary and secondary consumers. The primary consumer trophic level was represented by zooplankton, aquatic insect larvae, and gammarids, with a mean δN value of 7.79‰. The secondary consumer level included all fish, with a mean δN value of 10.68‰. The primary consumers were chiefly dependent on autochthonous carbon input. This is the first quantitative study of the food web in a lake of the Tibetan Plateau above 4000 m. The study provides information critical to lake management and conservation in the Tibetan Plateau.