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

Abstract

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.

Water balance trumps ion balance for early marine survival of juvenile pink salmon (Oncorhynchus gorbuscha)

“…Gill NKA activity did not increase as seen in post-larval stages (Honma 1982;Grant et al 2009); levels remained low and comparable to those previously reported for FW pre-smolt salmonids (Richards et al 2003;Madsen et al 2009), and the proportion of NKCC IR cells in the branchial Wlament epithelium did not increase. A 35 % increase in body [Cl ¡ ] persisted 5 days post-SW entry, indicating a failure to maintain ion balance [the closely related chum regains [Cl ¡ ] balance 24 h post-transfer (Black 1951)], and the reduction in wet mass despite no change in dry mass clearly indicates a failure to maintain water balance.…”

“…In fact, pink salmon fry migrate seaward directly following yolk absorption and gravel emergence at a size of 0.2 g (Heard 1991;Grant et al 2009). This life history pattern represents an extreme within salmonids, as most others move to SW after at least 1 year in FW and at sizes between 2 and 30 g (Rounsefell 1958;Clarke 1982;Hoar 1988;Quinn and Myers 2004).…”

“…These results suggest larval hypo-osmoregulatory development, but extra-branchial mitochondrion rich cells (MRC's) as seen on the yolk sac of chum alevins (Kaneko et al 1995) could explain this eVect. Further confounding interpretation is the observation that fry experience a doubling of whole body Na + and Cl ¡ content that coincides with naturally timed SW entry post-yolk absorption (Grant et al 2009). The reported elevation in whole body ion levels persists until gill NKA activity peaks 2 months later.…”

“…This period of acclimatization greatly exceeds the hours to days reported for other salmonids (O. keta, O. mykiss, O. kisutch, S. salar;Black 1951;Miles and Smith 1968;Leray et al 1981;Prunet and Boeuf 1985) and suggests hypo-osmoregulatory capacity may be underdeveloped upon naturally timed ocean entry. Furthermore, the majority of the increase in gill NKA activity occurs after SW entry (Honma 1982;Grant et al 2009), also suggesting compensatory rather than preparatory changes. Evidently, when and how SW tolerance and hypo-osmoregulatory ability of juvenile pink salmon develops remains unclear.…”

Physiological consequences of the salmon louse (Lepeophtheirus salmonis) on juvenile pink salmon (Oncorhynchus gorbuscha): implications for wild salmon ecology and management, and for salmon aquaculture

“…In juvenile pink salmon transferred directly from FW to SW at the time of their out-migration, a 200 -300% increase in whole body ion levels was observed that gradually returned to pre-transfer values within 8 -10 weeks [23].…”