Natural Convection: A Mechanism for Transporting Oxygen to Incubating Salmon Eggs

Respiratory exchange at the surface of developing fish eggs is influenced by two processes: diffusion and convection. The respiring egg acts as an oxygen sink, removing dissolved oxygen from the diffusion layer surrounding the outer surfaces of the egg capsule. To maintain the oxygen gradient in the diffusion layer, oxygen must be delivered to it by convection. This paper describes two components of convective transport: that provided by forced convection — the bulk transport of oxygenated water to the egg; and a newly recognized component, natural convection. Salmon normally spawn in gravel environments. Mass transfer of oxygen to incubating eggs, resulting from forced convection, is provided by subsurface water moving with a velocity related primarily to properties of the gravel and the hydraulic gradient. Egg-induced natural convection is seen as a component embedded in these relations. Acting as an emergency oxygen transport and metabolite disposal mechanism at low water velocities, natural convection...