Growth and ionoregulatory ontogeny of wild and hatchery-raised juvenile pink salmon (Oncorhynchus gorbuscha)

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 mu mol 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 (similar to 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.