Invasive carp in China's plateau lakes.

Abstract

Bighead and silver carp, which are native to eastern Asia ([1][1]), have been popular species for aquaculture and algal control ([2][2]), and since the 1960s, both fish have been introduced worldwide—silver carp into 34 countries and bighead carp into more than 20 countries. But, as J. H. Chick and M. A. Pegg discuss in their letter “Invasive carp in the Mississippi River Basin” (22 Jun., p. [2250][3]), these carp can be so successful as to pose a threat to aquatic ecosystems, a caution our studies in China certainly support. The natural range of silver carp is in the rivers and lakes of China, North Vietnam, and Siberia; that of bighead carp is smaller, extending only from the Yellow River in the north of China to the Pearl River in the south. In the Yangtze River, these carp migrate between river and lakes, and during the monsoon flood season they lay pelagic eggs, which, along with the hatched small fry, drift with the current ([3][4]). Successful reproduction of both carps requires a long river. In the early 1950s, bighead and silver carp were introduced into Lake Xingyun for the purpose of aquaculture ([4][5]). About 50% of the fish yield from this lake in the 1950s was from the endemic barbless carp, Cyprinus pellegrini Tchang. This carp is also a filter-feeder, feeding mainly on zooplankton, but its feeding apparatus is less developed and less powerful (filters less water) than those of bighead and silver carp because its filter-feeding apparatus experienced a relatively short period of differentiation during evolution ([5][6]). Since the introduction of bighead and silver carp, the proportion of barbless carp in the total fish yield declined to 20% in the 1960s, to 10% in the early 1970s, and now to less than 1% since the 1980s ([6][7]). In China, the disastrous impacts made by bighead and silver carp have been especially striking in many plateau lakes, where the continuous stocking of fingerlings has taken place on a wide scale since the late 1950s for increasing fish production. The invaders have suppressed and in some instances eliminated the native or endemic species ([7][8]). Such ecosystems may be especially vulnerable, because these lakes are usually isolated and the food webs are relatively simple. There are four major reasons why introduced bighead and silver carp can pose a threat to local fish communities: (i) They are powerful filter-feeders. (ii) These carp have an extremely wide food spectrum, including phytoplankton (usually >10 μm), zooplankton, and suspended detritus. They can cause significant decline in zooplankton abundance ([8][9]). (iii) They grow fast and reproduce quickly ([9][10]). (iv) Because all fishes forage on planktonic organisms during their early life-history stages, bighead and silver carp have the potential to compete for food with every species of fish, and some native fishes are filter-feeders as adults. Thus, the possible impacts of introduced bighead and silver carp on local fish communities urgently need to be assessed, especially in those waters (e.g., the Mississippi River) where the carp have successfully established reproducing populations. 1. [↵][11]1. S. Li 2. et al. 1. S. Li 2. et al. , in Comprehensive Genetic Study on Chinese Carps, S. Li et al., Eds. (Shanghai Scientific & Technical Publishers, Shanghai, 1990), p. 159. 2. [↵][12]1. R. L. Welcomme , FAO Fish. Tech. Pap. (Food and Agriculture Orgnization, Rome, 1988), vol. 294 P. Xie, J. Liu, TheScientificWorld 2001, 1, 337. 3. [↵][13]Ichthyological Department of Institute of Hydrobiology, Hubei Province, Fishes in the Yangtze River (Science Press, Beijing, 1976. 4. [↵][14]Lake Xingyun is located in the Yunnan-Guiyang Plateau, surface area 39 km2, mean depth 9 m, 1723 m above sea level, N24°17′ to 24°23′, E102°45′ to 102°48′. 5. [↵][15]1. J. K. Liu 2. et al. 1. W. X. Cao , in Cultivation of the Chinese Freshwater Fishes, J. K. Liu et al., Eds. (Science Press, Beijing, 1992), 3. p. 30. 6. [↵][16]1. K. Y. Huang , Sci. Fish Farm. 7, 40 (1997). 7. [↵][17]1. D. Song 1. J. Chen 2. et al. , in Evaluation on Animal Resources from Wuling Mountains Area Southwestern China, D. Song, Ed. (Science Press, Beijing, 1994), p. 399. 8. [↵][18]1. P. Xie, 2. Y. Yang , J. Plankton Res. 22, 1757 (2000); 1. P. Xie , Aquaculture 180, 295 (1999); 1. P. Xie , Aquaculture 195, 149 (2001). 9. [↵][19]In the Yangtze River, the weight of a 3-year-old fish reaches 3.6 kg for silver carp and 7.4 kg for bighead, the maximum size of bighead is 35 to 40 kg, and the mean egg number per adult female is 1.07 × 106 for silver carp and 2.0 × 106 for bighead carp (3). 10. This research was supported by the State Key Basic Research and Development Plan (G2000046800) and a key project of the Chinese Academy of Sciences (KZCX2-403). J. K. Liu, Y. F. Shen, and W. X. Cao gave useful suggestions on the draft of the letter. [1]: #ref-1 [2]: #ref-2 [3]: /lookup/doi/10.1126/science.292.5525.2250 [4]: #ref-3 [5]: #ref-4 [6]: #ref-5 [7]: #ref-6 [8]: #ref-7 [9]: #ref-8 [10]: #ref-9 [11]: #xref-ref-1-1 View reference 1 in text [12]: #xref-ref-2-1 View reference 2 in text [13]: #xref-ref-3-1 View reference 3 in text [14]: #xref-ref-4-1 View reference 4 in text [15]: #xref-ref-5-1 View reference 5 in text [16]: #xref-ref-6-1 View reference 6 in text [17]: #xref-ref-7-1 View reference 7 in text [18]: #xref-ref-8-1 View reference 8 in text [19]: #xref-ref-9-1 View reference 9 in text