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Branchial osmoregulatory response to salinity in the gilthead sea bream,Sparus auratus
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Abstract(s)
The branchial osmoregulatory response of gilthead sea bream (Sparus auratus L.)
to short-term (2–192 hr) and long-term (2 weeks) exposure to different environmental salinities (5%,
15%, 25%, 38% and 60%) was investigated. A ‘‘U-shaped’’ relationship was observed between
environmental salinity and gill Naþ,Kþ-ATPase activity in both long- and short-term exposure to
altered salinity, with the increase in activity occurring between 24 and 96 hr after the onset of
exposure. Plasma osmolality and plasma ions (sodium, chloride, calcium and potassium) showed a
tendency to increase in parallel with salinity. These variables only differed significantly (Po0.05) in
fish adapted to 60% salinity with respect to fish adapted to full-strength sea-water (SW). Plasma
glucose remained unchanged whereas plasma lactate was elevated at 5% and 60%. Muscle water
content (MWC) was significantly lower in fish adapted to 60%. Chloride cells (CC) were only present
on the surface of the gill filaments and absent from the secondary lamellae. CC distribution was not
altered by external salinity. However, the number and size of CC were significantly increased at
salinity extremes (5% and 60%), whereas fish exposed to intermediate salinities (15% and 25%) had
fewer and smaller cells. Furthermore, the CC of fish exposed to diluted SW became rounder whereas
they were more elongated in fish in full-strength and hypersaline SW. This is consistent with
previous reports indicating the existence of two CC types in euryhaline fish. At likely environmental
salinities, gilthead sea bream show minor changes in plasma variables and the effective regulation of
gill Naþ,Kþ-ATPase. However, at very low salinities both haemodilution and up-regulation of gill
Naþ,Kþ-ATPase predict a poor adaptation most likely related to deficiency or absence of specific
components of the CC important for ion uptake.
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Citation
Laiz-Carrión, Raúl; Guerreiro, Pedro M.; Fuentes, Juan; Canario, Adelino V.M.; Martín Del Río, María P.; Mancera, Juan M.Branchial osmoregulatory response to salinity in the gilthead sea bream,Sparus auratus, Journal of Experimental Zoology Part A: Comparative Experimental Biology, 303A, 7, 563-576, 2005