Routes of water loss in South African abalone (Haliotis midae) during aerial exposure

South African abalone, Haliotis midae, were exposed to air at 12 °C for 36 h to simulate the extent and rate mass loss experienced by animals during long distance live exports. Animals lost 15.1 ± 0.94% of their mass during the 36 h air exposure, an approximation of the highest mass losses sustained by industry.The total mass loss was attributed to water loss, as the contribution of dry mass to the total mass remained constant under all conditions. Water content decreased from 64.8% of the body mass (Mb) under control conditions to 58.8% Mb after 36 h in air. In real terms, however, animals had lost 22% of the body water pool.Abalone exhibited a typically high water turnover rate when in water (125 μL g− 1 h− 1), which decreased markedly during air exposure (2.2 μL g− 1 h− 1). Haemolymph volume decreased from 43% Mb in water to 14% Mb in air. The concomitant decrease in haemolymph pressure probably limited the first step in urine formation (ultra-filtration through the pericardium). Thus we observed that while urine flow represented about 26% of the total water loss when the animals were in water, urine flow ceased during air exposure.The decrease in haemolymph volume in air represents a redistribution of water to the tissues and not a bulk loss of haemolymph. This is supported by the concentration of haemolymph ions by a factor of 1.2 during aerial exposure, which was predicted based on the 22% decrease in water content. Under the same conditions, evaporation from water containers with similar surface to volume dimensions as abalone, accounted for only an 8.25% mass loss. As all other water loss routes were accounted for, we measured pedal mucus production rates of abalone in water and air. During 36 h aerial exposure, the pedal mucus production represented a loss of 6.8% Mb. We conclude that water loss during 36 h air exposure is attributable to evaporation (8.25% Mb) and pedal mucus production (6.8% Mb). This paves the way for directed research into mitigating water loss during the live export process.