Juvenile pink salmon ( Oncorhynchus gorbuscha (Walbaum, 1792)) enter seawater (SW) shortly following emergence. Little is known about growth and development during this life-history stage when sensitivity to sea louse exposure may be high, an issue that is of current concern in British Columbia. We tested the hypothesis that growth and ionoregulatory development were similar in hatchery-raised (Quinsam) and wild (Glendale and One’s Point) juvenile pink salmon (measured over 22 weeks) following SW entry. Fish body mass increased from 0.20 ± 0.01 to 6.47 ± 0.37 g, with mean specific growth rates of 2.74% to 3.05% body mass·day–1 among the three groups. In all three groups, gill Na+–K+-ATPase (NKA) activity peaked at 12 µmol ADP·mg protein–1·h–1 following 8 weeks post-transfer to SW. Whole body Na+ and Cl– concentrations, which again did not differ among groups, were highest upon initial exposure to SW (~70 mmol·kg wet mass–1) and declined over time as gill NKA activity increased, indicating that the hypo-osmoregulatory capacity was not fully developed following emergence and initial entry into SW. Thus, consistent with our hypothesis, few differences were observed between hatchery-raised and wild juvenile pink salmon reared under laboratory conditions. These baseline data may be important for future studies in determining the effects of sea lice on wild juvenile pink salmon.

Swimming performance was assessed in juvenile pink salmon Oncorhynchus gorbuscha (body mass<5.0 g) using five different protocols: four constant acceleration tests each with a different acceleration profile (rates of 0.005, 0.011, 0.021 and 0.053 cm s(-2)) and a repeated ramped-critical swimming speed test. Regardless of the swim protocol, the final swimming speeds did not differ significantly (P>0.05) among swim tests and ranged from 4.54 to 5.20 body lengths s(-1). This result supports the hypothesis that at an early life stage, O. gorbuscha display the same fatigue speeds independent of the swimming test utilized. Whole body and plasma [Na+] and [Cl-] measured at the conclusion of these tests were significantly elevated when compared with control values (P<0.05) and appear to be predominantly associated with dehydration rather than net ion gain. Given this finding for a small salmonid, estimates of swim performance can be accurately measured with acceleration tests lasting<10 min, allowing a more rapid processing than is possible with a longer critical swim speed test.

Marine mammals are repeatedly exposed to elevated extra-thoracic pressure and alveolar collapse during diving and readily experience alveolar expansion upon inhalation – a unique capability as compared to terrestrial mammals. How marine mammal lungs overcome the challenges of frequent alveolar collapse and recruitment remains unknown. Recent studies indicate that pinniped lung surfactant has more anti-adhesive components compared to terrestrial mammals, which would aid in alveolar opening. However, pulmonary surfactant composition has not yet been investigated in odontocetes, whose physiology and diving behavior differ from pinnipeds. The aim of this study was to investigate the phosphatidylcholine (PC) composition of lung surfactants from various marine mammals and compare these to a terrestrial mammal. We found an increase in anti-adhesive PC species in harp seal (Pagophilus groenlandicus) and California sea lion (Zalophus californianus) compared to dog (Canus lupus familiaris), as well as an increase in the fluidizing PCs 16:0/14:0 and 16:0/16:1 in pinnipeds compared to odontocetes. The harbor porpoise (a representative of the odontocetes) did not have higher levels of fluidizing PCs compared to dog. Our preliminary results support previous findings that pinnipeds may have adapted unique surfactant compositions that allow them to dive at high pressures for extended periods without adverse effects. Future studies will need to investigate the differences in other surfactant components to fully assess the surfactant composition in odontocetes.

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Salinity tolerance in wild (Glendale) and hatchery (Quinsam) pink salmon Oncorhynchus gorbuscha (average mass 0·2 g) was assessed by measuring whole body [Na(+)] and [Cl⁻] after 24 or 72 h exposures to fresh water (FW) and 33, 66 or 100% sea water (SW). Gill Na(+), K(+)-ATPase activity was measured following exposure to FW and 100% SW and increased significantly in both populations after a 24 h exposure to 100% SW. Whole body [Na(+)] and whole body [Cl⁻] increased significantly in both populations after 24 h in 33, 66 and 100% SW, where whole body [Cl⁻] differed significantly between Quinsam and Glendale populations. Extending the seawater exposure to 72 h resulted in no further increases in whole body [Na(+)] and whole body [Cl⁻] at any salinity, but there was more variability among the responses of the two populations. Per cent whole body water (c. 81%) was maintained in all groups of fish regardless of salinity exposure or population, indicating that the increase in whole body ion levels may have been related to maintaining water balance as no mortality was observed in this study. Thus, both wild and hatchery juvenile O. gorbuscha tolerated abrupt salinity changes, which triggered an increase in gill Na(+), K(+)-ATPase within 24 h. These results are discussed in terms of the preparedness of emerging O. gorbuscha for the marine phase of their life cycle.