Ammonia is toxic to fish in natural and artificial waters.We evaluated the acute(96 h) and chronic(21 d) toxicity of un-ionized ammonia to GH transgenic common carp(Cyprinus carpio L.) and non-transgenic common carp using a static-renewal bioassay.The 24,48,72 and 96 h median lethal concentrations(LC50) of un-ionized ammonia were slightly lower in transgenic carp(2.64,2.44,2.28 and 2.16 mg N/L,respectively) than in non-transgenic carp(2.70,2.64,2.52 and 2.33 mg N/L,respectively).Similarly,the median lethal time(LT50) was significantly shorter for transgenic carp(1.41,7.91 and 117.42 h) than for non-transgenic common carp(2.53,14.06 and 150.44 h) following exposure to 3.86,3.29,or 2.09 mg N/L,respectively.Moreover,the mortality of transgenic carp was significantly higher than that of non-transgenic carp at all un-ionized ammonia concentrations((0.91 ± 0.12),(0.48 ± 0.06) and(0.12 ± 0.01) mg N/L) during the 21 d chronic toxicity test.Our results suggest that GH transgenic carp are less tolerant of unionized ammonia than non-transgenic carp.Our data are useful for evaluating potential environmental risk,optimizing stocking density in intensive aquaculture and establishing water quality criteria for ammonia in aquaculture.
