Fish transport in the aquaculture sector: An overview of the road transport of Atlantic salmon in Tasmania

Abstract

Although species-specific aquaculture production systems typically operate over reduced geographical ranges relative to many other terrestrial animal production systems, it is nonetheless often necessary to transport live fish between facilities by road to permit on-growing or finishing. Road transport is therefore common in Australian salmonid (trout and salmon) production and is a particularly significant feature of Atlantic salmon (Salmo salar) culture in Tasmania, where it is necessary to transport juvenile fish (smolts) from inland freshwater hatchery facilities to coastal marine farms for grow-out to slaughter. The most obvious respect in which road transport of live fish differs from that of terrestrial livestock is the requirement to provide a life-support system for the duration of the process. Aside from an inherent requirement for water, it is essential to provide oxygenation to support basic respiration. Thereafter, water quality must be managed to limit the accumulation of potentially toxic metabolites. Among these, carbon dioxide (CO2) is of particular concern. Without appropriate management, CO2 can rapidly accumulate to levels as high as 80 mg/L-1 and result in hypercapnia, respiratory dysfunction, narcosis, and ultimately death. Current life-support systems typically function to maintain CO2 at acceptable levels of 20-30 mg/L-1. Water temperature changes during and at the end of the transport process may also be an issue but are typically only a relatively minor consideration. In common with other livestock transport systems, the loading process and associated handling can evoke a physiological stress response which, though intended to be adaptive, may interact synergistically with aspects of the life-support system. Increased rates of oxygen consumption and CO2 excretion place additional demands on the life-support system while, from the fish's perspective, the changes in gill perfusion and circulation that facilitate such alterations in gas exchange can also operate to increase solute loss and result in diuresis and ionoregulatory dysfunction. As a consequence, once a suitable life-support system has been provided, the efforts of salmon farmers are focused on the need to minimize handling stress. The majority operate sophisticated pumping and counting systems that are intended to minimize aerial exposure of fish and, in a manner consistent with the natural behavior of the animal, mimic as far as is practicable the process of being washed downstream.