The Survival and Growth of Juvenile Silver Catfish, Rhamdia quelen, Exposed to Different NH3 and Hardness Levels

摘要

Ammonia is the main end product of nitrogen metabolism in fish (Ismino-Orbe et al. 2003; Kajimura et al. 2004) and exists in both ionized (NH.4+) and unionized (NH3) forms. The unionized form appears to be the most toxic (Russo and Thurston 1991; Miron et al. 2008). In fish, ammonia is primarily excreted through the gills. Ammonia production in fish depends primarily on protein intake and metabolic efficiency. These parameters are species specific and might be affected by increasing the levels of environmental ammonia (Dosdat et al. 2003). In intensive high-density systems, the ammonia concentration may increase to levels that can reduce growth or even cause death (Le Ruyet et al. 1997b). Human activities have also contributed to the increase in theamount of ammonia introduced into natural waters. This increase is a result of the generalized use of fertilizers and other industrial products and is also a consequence of the production of organic waste by agricultural activities (Randall and Tsui 2002).