Przewalski’s Naked Carp (Gymnocypris przewalskii): An Endangered Species Taking a Metabolic Holiday in Lake Qinghai, China

Abstract

The naked carp is an endangered cyprinid that migrates annually between freshwater rivers, where it spawns, and Lake Qinghai, where it feeds and grows. Lake Qinghai is a high-altitude lake (3,200 m) in western China that currently exhibits the following composition (in mmol L(-1): [Na(+)] 200, [Cl(-)] 173, [Mg(2+)] 36, [Ca(2+)] 0.23, [K(+)] 5.3, total CO(2) 21, titration alkalinity 29; osmolality 375 mOsm kg(-1); pH 9.3), but concentrations are increasing because of water diversion and climate change. We studied the physiology of river water to lake water transfer. When river fish are transferred to lake water, there is a transitory metabolic acidosis followed by a slight respiratory alkalosis, and hemoconcentration occurs. All plasma electrolytes rise over the initial 48 h, and final levels in lake water-acclimated fish are very close to lake water concentrations for [Na(+)], [Cl(-)], [K(+)], and osmolality, whereas [Ca(2+)] continues to be regulated well above ambient levels. However, [Mg(2+)] rises to a much greater extent (fourfold in 48 h); final plasma levels in lake fish may reach 12 mmol L(-1) but are still much lower than in lake water (36 mmol L(-1)). At the same time, urine flow rate decreases drastically to <5% of river water values; only the renal excretion of Mg(2+) is maintained. Both gill and kidney Na(+),K(+)-ATPase rapidly decline, with final levels in lake water fish only 30% and 70%, respectively, of those in river water fish. Metabolic rate also quickly decreases on exposure to lake water, with O(2) consumption and ammonia-N excretion rates eventually falling to only 60% and 30%, respectively, of those in river fish, while plasma ammonia rises fivefold. The fish appear to be benefiting from a metabolic holiday at present because of decreases in iono- and osmoregulatory costs while in lake water; elevated plasma [Mg(2+)] and ammonia may be additional factors depressing metabolic rate. If the lake continues to dehydrate, these benefits may change to pathology.

The effect of hypoxia on gill morphology and ionoregulatory status in the Lake Qinghai scaleless carp, Gymnocypris przewalskii

“…Mean annual air temperature is -0.6°C, and surface lake water temperatures rarely exceed 13°C in August (Walker et al, 1996). The scaleless carp, however, has an interesting life history relative to most carp species, in that it undergoes an annual spawning migration from the lake into freshwater rivers (Wang et al, 2003;Wood et al, 2006) when they swim 40-50·km over several weeks before reaching their spawning grounds (Walker et al, 1996). Thus, although this species inhabits moderately hypoxic, cool waters, like those of crucian carp or goldfish, it is dependent upon exercise to reach its spawning ground and its body form is superficially more salmonid-like than carplike.…”

Cloning and characterization of two subunits of calcineurin cDNA in naked carp (Gymnocypris przewalskii) from Lake Qinghai, China

“…In the past fifty years, the total amount reserves has decreased from 20 × 10 4 tons in 1960 to less than 0.5 × 10 4 tons now, especially because of decreasing water level and increasing salinity [2][3][4] www.fhc.viamedica.pl as the increasing salinity levels of the lake, which is mainly caused by continuously decreased water levels at a rate of 10-12 cm per year over the last 50 years [5]. The increase of salinity began since 1978 and its rate is currently accelerating [6,7]. Further, another challenge for the naked carp is the salinity changes during their annual migration from the saline lake to adjoining freshwater rivers including Quanjihe river, Shaliuhe river, Heimahe river and Buhahe river, where they spawn and then return to the lake [4].…”

Phylogeography and conservation genetics of scaleless carp (Gymnocypris przewalskii) of Lake Qinghai, China.

“…In response to management and conservation concerns for fish populations, an international collaborative project between Canada (Queen's University, University of Northern British Columbia, University of British Columbia, and McMaster University) and China (Zhejiang University) was initiated to study the evolution, ecology, and physiological adaptations of the scaleless carp and related species to the environments of the Tibetan Plateau. The results of the physiological studies have been reported elsewhere (Wood et al, 2007;Matey et al, 2008) and further publications are pending. This thesis analyzes genetic variation in order to examine the phylogeography and systematics of scaleless carp.…”

“…The lake has regressed to about one-third of its original size, becoming saline in the process. It is currently the largest saline lake in China (surface area 4600 km 2 ) with a high pH (9.4) and a salinity of 13.13 g/L (Wood et al, 2007). Several freshwater rivers drain into the lake, the largest of which is the Buha River, which, when combined with the Shaliu and Haerga…”

“…Remarkably, scaleless carp are currently able to tolerate the high salinity by allowing most plasma ions to equilibrate with the lake water, thereby reducing the energy demands required for ion regulation (Wood et al, 2007). This ability to thrive in saline waters has made scaleless carp a candidate for aquaculture expansion in other salt lakes of the plateau, which have few or no fish species (Walker et al, 1996).…”