Optimisation of Safe Loading Density for Live Transportation of Rainbow Trout, Oncorhynchus mykiss (Walbaum, 1792), Yearlings in Plastic Bags

A field study evaluated the safe loading density for live transportation of rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), yearlings in plastic bags of super-oxygenated water. The experimental fish (197.5 ± 40 g) were starved for 72 h and mildly sedated with clove oil (40 µL.L-1 for 2–3 min) before packing. Three loading densities of live rainbow trout (120, 170, 230 g.L-1) were packed in plastic bags containing 6 L of stream water and 10–12 L of medical-grade oxygen gas. Six replicate bags per loading density were then subjected to 10 h of transportation by road at ~10 °C. On arrival at the destination, important water quality indicators and fish survival were recorded from each plastic bag. With increasing fish loading density, there was a corresponding increase in the concentrations of carbon dioxide (CO2), total ammonia nitrogen (TAN), free ammonia (NH3), total dissolved solids (TDS) concentrations and specific conductivity in the transport water, and a decrease in dissolved oxygen (DO, R2 = 0.91-0.99). These differences in vital water quality indicators were significantly more in the 230 g.L-1 group. However, there was no mortality even at the highest loading density, as the critical water quality parameters did not cross the acute lethal thresholds for rainbow trout. Based on the findings, it is recommended that a loading density of 230 g.L-1 is safe for live transportation of rainbow trout yearlings in plastic bags over a transport duration of 10 h at ~10 °C, following adequate starvation and mild sedation.