Safe management of Cyprinid herpesvirus 3-induced mortalities of common carp (Cyprinus carpio) by silaging process

Abstract

In open farming systems, fish losses are unfortunate daily finding, hence a simple, safe and highly adaptable method is needed to manage dead fish. The aim of this study was to develop three silaging methods of common carp (Cyprinus carpio) carcasses to identify cost-effective, eco-friendly, and efficient method to turn dead fish into organic fertiliser and to determine whether Cyprinid herpesvirus 3 (CyHV-3) can be inactivated during a 34-weeks trial. In our study, dead fish were chopped, minced and mixed with starter bacteria culture and wheat bran (Basic), water and wheat bran starter (Hydrated) or Bokashi commercial mix (Commercial), and placed in a 1 L jars (in quadruplicates). The CyHV-3 infectivity potential was assessed by two cell cultures and expression of the virus genes classified into three temporal kinetic classes. The feasibility of the silaging method and selection of the best method assessed by pH monitoring, characterisation of the odour profile, elemental analysis and calculating the cost of the in-farm silaging. Cell cultures and the subsequent gene expression analyses showed that the virus was successfully inactivated in the Basic, Hydrated and Commercial silages, confirming their safety. Among the three silaging methods, the Hydrated was the cost-effective one; however, concerning the other features (odour profile, feasibility and final pH level), the Basic was selected as the most promising for implementation. Additionally, elemental analysis showed that the level of nutrients in Basic silage was higher than in commonly used natural fertilisers, while the content of heavy metals (Pb, Cd, Zn) met the official recommendations for organic fertilisers. The study provides premise of an effective method of silaging of dead carp that offers pathogen inactivation (via combination of decreased pH and microbial activity), turns common by-stream into a valuable product and increases profitability of the farm in a sustainable and cost-effective way.