Dose-dependent effect of un-ionized ammonia on hatching success of fertilized eggs of silver carp Hypophthalmichthys molitrix and bighead carp Hypophthalmichthys nobilis

Abstract

Ammonia is one of the most common pollutants in aquaculture systems and its elevated concentration in surface water is a critical concern in fish larvae production. The purpose of this study was to assess the effects of un-ionized ammonia (NH₃) on hatch success of fertilized eggs of silver carp Hypophthalmichthys molitrix and bighead carp Hypophthalmichthys nobilis, two ecologically and commercially important species in freshwater ecosystems. The results showed total hatch rates and viability of newly hatched larvae 24 h post-hatch decreased significantly with increasing NH₃–N concentration for both silver carp and bighead carp, whereas abnormal rate increased significantly with increasing NH₃–N concentration. When fitted to the data of total hatch rates and viability of newly hatched larvae 24 h post-hatch, it is clear that the logistic model with three parameters can be fitted to ecotoxicological data well and can describe dose-dependent effects of un-ionized ammonia on hatching success of fertilized eggs of both silver carp and bighead carp. According to the model, the EC₅₀ for the hatch rates of silver carp and bighead carp was 0.98 and 0.86 mg L⁻¹, respectively. Our results should be useful to hatchery managers and fingerling producers in establishing acceptable water quality parameters for the hatchery and nursery ponds.

Keywords:

• ammonia
• silver carp
• bighead carp
• embryonic development
• fertilized eggs

Acknowledgements

The authors thank Hanjiang Fish Breeding Farm for providing fertilized eggs. This study was supported by the State Key Fundamental Research and Development Program (2008CB418102).