Mitigation of ammonia concentrations for improving wet, live fish and crab transport conditions

The transport of live aquaculture species, both throughout the culture period and during marketing as live products, is far from optimized. In wet transports, the bottleneck is the total ammonia nitrogen (TAN) concentration that develops in the transport water. The effect of actively removing TAN from the water on the survival of fish and crabs during wet transport is herein reported. The TAN concentration was controlled by exchanging NH₄⁺ with Na⁺ using self-synthesized polymer-coated zinc-hexa-cyanoferrate (Zn-HCF) cation-exchange material. Theoretical simulation followed by empirical experiments were carried out to mimic the transports of Gilthead seabream and European Brown crab, in the presence and absence of Zn-HCF. The Zn-HCF proved very efficient: while the TAN concentration in the seabream test tanks did not exceed the predetermined 5 mgN/L value (throughout the work), the control tanks showed much higher values. In the Brown Crab experiment the control had to be stopped after 2.3 days to avoid animal welfare issues, while the test completed the full 4.8 d. Yet, the crabs from the Test tanks exhibited much higher survival rates following 24 and 48 h dry packing. The results show unequivocally that the addition of Zn-HCF to wet transfer tanks can improve the vitality of the shipped animals, allow to extend the transfer periods and/or increase the shipment density.