RAINBOW TROUT Oncorhynchus mykiss TRANSPORTATION – EFFECTS OF HANDLING PROCEDURES AND NEW TECHNOLOGICAL IMPROVEMENTS ON WATER QUALITY; STRESS MARKERS AND PRODUCT QUALITY

Rainbow trout is one of the most frequently live-transported fish species in Europe. The health and stress response of the fish during and after transport and final product quality depend to a large degree on handling before and during the transport. Starvation periods and water changes before transport lower ammonia and faecal load in the transport water, but cannot prevent water quality deterioration during transport. An increase in toxic ammonium and a rapid increase in carbon dioxide concentration occur in transport water. Additional filter technology can optimise water conditions during transport. In the current study airlift degassing technologies and ammonium absorber filters were tested as were starvation practises before transport. Welfare and stress responses were measured as effects on blood markers, water parameters and product quality under laboratory and real conditions.

In the first experiment trout were starved for 2 days before transport in replicates. In the next experiments treatment transport boxes were equipped with airlift technology and zeolite filter units (T) and tested against a control group (without airlift and zeolite). Trout were transported first at lab scale and later under real conditions at a standard fish density (180kg/m³) and at increased fish density (250kg/m³). Water parameters (T, pH, CO₂, O₂, NH₄⁺, NO₂^-) were measured hourly. At experimental completion, blood was taken and analysed for cortisol, glucose, lactate, NH₃, CO₂ and pH. Filet samples were collected and bacterial count, chemical composition and sensory data were determined.

Ammonium water content of starved fishes was significantly lower (4.6 ± 0.5 -N mg/l) than without starvation (6.2 ± 1.2 -N mg/l). In the commercial transport, the CO₂ concentration in the water was reduced significantly in using airlift treatments when compared with controls and positive effects on blood markers were detected (Tab.1). Zeolite filter units reduced NH₄⁺ accumulation in transport waters. The tested technologies significantly improve transport water quality and fish welfare status even under higher transport densities. No differences in sensory quality and in chemical composition were detected. There was a clear indication, that additional filter technology improves the microbiological product safety during storage.