Remediation of ammonia accumulation during live transport of juvenile cod, Gadus morhua L., and the effects of fast period on ammonia levels and water quality

The stress and trauma associated with handling and movement of fish may have welfare implications and may also increase susceptibility to disease post-transfer. Juvenile salmonids have been transported live from hatchery to production grow out units for some time but little information is available on the live transport of marine finfish species such as Atlantic cod, Gadus morhua L. The present study examines the accumulation of un-ionised ammonia (UIA-N) in live transport of juvenile cod and examines the effectiveness of aeration, an ammonia absorbing agent and duration of fast period in controlling the level of UIA-N. UIA-N increased significantly with higher stocking densities in simulated transports of 24 h duration, from 0.08 μg l−1 at 10 kg m−3 to 0.43 μg l−1 at 30 kg m−3, and also with duration of the simulated transports, rising from 1.14 μg l−1 after 3 h to 6.01 μg l−1 at 24 h in a second trial. Average UIA-N was significantly higher when diffuse aeration with air as well as oxygenation was used, 9.03 μg l−1 compared with 1.54 μg l−1 with oxygenation only. Air diffusion had the effect of maintaining a higher pH which consequently increased the potential for ammonia toxicity. Mean ammonia level was significantly less at 3.17 μg l−1 in a simulated 24 h transport when an ammonia absorbing product was used compared with 6.01 μg l−1 l UIA-N in control tanks. This additive would be beneficial during transports of marine finfish for the regulation of ammonia. The effects of varying fast periods and related duration of gut evacuation in juvenile cod on water chemistry including ammonia levels were also assessed. From this an optimum fast period of 36 h for live transport of cod at 12 °C is recommended. Stocking densities of up to 30 kg m−3 did not give rise to toxic levels of ammonia. Aeration in addition to oxygenation, while increasing pH, leads to elevated ammonia, but ammonia accumulation can be reduced by using an absorbing agent.