Impact of clay particles on the cutaneous exchange of oxygen across the chorion of Atlantic salmon eggs

Rates of oxygen consumption for Atlantic salmon Salmo salar embryos approaching hatching were determined. Values were recorded using a 'closed system' experimental set-tip. A magnetic stirrer was used to ensure that zones of oxygen depletion did not develop in the microenvironment surrounding the respiring eggs. Recorded values of oxygen consumption ranged from 0.0024 to 0.0038 mg O-2 egg(-1) h(-1), with a mean consumption rate of 0.0032 mg 0, egg(-1) h-1. The values of oxygen consumption were similar to those reported in other studies using a closed system experimental set-up, however, they were lower than those reported in a study adopting a flow-through system. The introduction of clay-sized sediment to the incubation chamber created a thin film (<1 mm) of sediment on the egg surface, and resulted in reduced rates of oxygen consumption. The additional 0.3 g of clay sediment reduced oxygen consumption by an average of 41 % and the addition of a further 0.2 g of clay sediment reduced consumption by an average of 98%. Two explanations for the recorded reduction in consumption were proposed: (i) the creation of a low permeability seal around the eggs restricted the availability of oxygen to the incubating embryos and (ii) the clay-sized fine sediment physically blocked the micro-pore canals in the egg membrane, thereby restricting oxygen uptake