EFFECTS OF WATER TROPHIC STATUS ON GROWTH PERFORMANCES OF HEMICULTER LEUCISCULUS AND ANABARILIUS GRAHAMI

Eutrophication and invasion do seem often to go hand in hand.Experimental evidence to support the ability of eutroph-ication to facilitate either the incidence, speed, or impact of non-indigenous species invasion is conspicuously lacking.With the increase of water trophic status from oligotrophic to mesotrphic, great changes happened in the fish composit ion of Fuxian Lake located in Yunnan Plateau, China, at present. A lot of exotic fishes were introduced into Fuxian Lake and spread quickly, and the populations of many native fishes declined which even become extinct. Effects of water trophic status on growth, feeding utilization, body composition of Hemiculter leucisculus (exotic fish for Fuxian Lake) and Anabarilius grahami (native fish for Fuxian Lake) were studied in this experiment,with an attempt to compare their adaptive ability to eutrophication in the aspect of growth performances. Fishes were reared at the water temperature from 17 e to 20 e in three types of water (LTS, the low-trophic-status water;MTS, the moderate-trophic-status water; and HTS, the high-trophic-status water). The group reared in LTS also served as the control of the groups reared in MTS and HTS for each species. The experiment lasted for 40 days. Feeding rate (FR), specific growth rate (SGR), feed conversion efficiency (FCE) and protein retention efficiency (PRE) were insignificantly affected by water trophic status for both H. leucisculus and A. grahami. There were no significant differences in body protein, lipid, ash and energy contents among the groups reared in three waters with different trophic status for two experimental fishes1However, energy retention efficiencies (ERE) of H. leucisculus reared in HTS was significantly lower than those reared in LTS, and EREs of A. grahami reared in MTS and HTS were significantly higher than that reared in LTS; Water content of A. grahami reared in MTS was significantly lower than those reared in LTS and HTS. Though effects of water trophic status on the growth performances of each fish were not evident,markedly differences were showed between H. leucisculus and A. grahami in the growth response to the increase of water trophic status. SGR of A. grahami was slightly higher than H. leucisculus. FCE and PRE of A. grahami were both higher than those of H. leucisculus, but the differences were significant only in MTS and HTS. ERE of A. grahami was signif-icantly higher than that of H. leucisculus. Interspecific differences in SGR, FCE, PRE and ERE all increased with the enhancement of water trophic status. The percentages increased in FR, SGR, FCE, PRE and ERE over control of H. leucisculus reared in MTS and HTS which were lower than those of A. grahami reared in the same type of water. Those differences between H. leucisculus and A. grahami in the effects of water trophic status on growth performances indicate that high trophic status is more unfavorable to the growth of H. leucisculus than that of A. grahami. The results speculated that the exotic fish might not show higher adaptive ability to eutrophication than the nat ive fish in growth performances.