Asymmetric production responses to biculture in recirculating aquaculture systems: Danube salmon (Hucho hucho) and rainbow trout (Oncorhynchus mykiss)

This study aimed to investigate the impact of bicultural rearing on the growth performance, feed efficiency, survival, somatic indices, and plasma biochemical parameters of Danube salmon (Hucho hucho) and rainbow trout (Oncorhynchus mykiss) in a recirculating aquaculture system (RAS) for 84 days. The fish were stocked at monoculture (HU100 for Danube salmon and HU0 for rainbow trout), and biculture (HU50) with equal total density. Rainbow trout had remarkably improved growth performance when reared in biculture, with significant differences in final weight, total length, Fulton's condition factor, specific growth rate, and feed efficiency, and a lower feed conversion ratio compared with monoculture. For Danube salmon, the fish had improved growth and feed efficiency when reared in monoculture, with significant differences in weight gain and specific growth rate compared with biculture, while somatic indices were unaffected by treatment. Survival rates were high ( ≥ 96% for Danube salmon and ≥ 98% for rainbow trout ) with no differences between treatments. The plasma biochemistry analysis showed species-specific responses, with increased glucose, albumin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and ammonia (NH₃) levels in the Danube salmon monoculture. This study shows that biculture in RAS is beneficial for rainbow trout but may be limited by some constraints for the Danube salmon. The study is also helpful in the practical implementation of the intensive culture of these species, especially regarding the balance between the conservation-oriented culture of Danube salmon and rainbow trout biculture.

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