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The Antarctic notothenioid Pagothenia borchgrevinki was collected from the stenothermal waters of McMurdo Sound in the summers of 2004, 2005 and 2006. Acclimation ability at 4°C was tested in healthy P. borchgrevinki and in individuals infected with x-cell gill disease. All healthy fish successfully acclimated to 4°C, establishing compensatory changes in resting oxygen consumption rate (R rest ) and critical swimming speed (U crit ) during a 1 month acclimation period, which were maintained during a longer, 6 month acclimation period. In contrast, individuals infected with xcell disease were unable to acclimate to 4°C, demonstrating significantly reduced survival rates compared with healthy individuals at 4°C. Measurements of R rest suggest that limitations in the ability of x-cell fish to uptake oxygen from the external milieu may have a negative effect on their survival at 4°C.

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No abstract

We investigated the effect of environmental hypoxia on vision in snapper (Pagrus auratus). Juvenile snapper inhabit estuarine environments where oxygen conditions fluctuate on a seasonal basis. Optomotor experiments demonstrated that visual acuity is impaired by environmental hypoxia, but not until levels approach the critical oxygen tension (P crit) of this species (around 25% air-saturated seawater). In 100, 80, and 60% air-saturated seawater, a positive optomotor response was present at a minimum separable angle (M SA) of 1°. In 40% air-saturated seawater, vision was partially impaired with positive responses at M SAs of 2° and above. However, in 25% air-saturated seawater, visual acuity was seriously impaired, with positive responses only present at M SAs of 6° and above. Snapper were found to possess a choroid rete, facilitating the maintenance of high ocular oxygen partial pressures (PO2) during normoxia and moderate hypoxia (PO2, between 269 and 290 mmHg). However, at 40 and 25% water oxygen saturation, ocular PO2 was reduced to below 175 mmHg, which is perhaps linked to impairment of visual acuity in these conditions. The ability to preserve visual function during moderate hypoxia is beneficial for the maintenance of a visual lifestyle in the fluctuating oxygen environments of estuaries.