The effect of various ambient ammonia concentrations on the nitrogen metabolism of carp fry (Cyprinus carpio L.)

1. Authors studied how 125, 375 and 625 μg/l amounts of NH4Cl added to the water influenced the ammonia excretion of carp fry with an average weight of 2.4 g, compared to the control. During the course of the experiments the NH4N concentration, the pH and the temperature were measured for three days, twice daily. 2. On the basis of our results the threshold concentration exerting harmful effects on the ammonia household of carp fry (disturbing the normal rate of metabolism in the fishes and decreasing their growth rate) is between 125 and 375 μg/l. NH4H (50–100 μg/ NH3). 3. The ammonia concentrations exceeding 375 μg/l NH+4 (and 100 μg/l NH3, respectively) can be regarded as undesirable and harmful in frybreeding fish ponds. 4. With regard to the ambient ammonia, a daily cycle developed in the excretion of ammonia: contrary to the control, a minimum in ammonia excretion was measured in the morning, while a maximum was measured in the afternoon