Reproductive events and associated reduction in the seawater adaptability of brook charr ( Salvelinus fontinalis): evaluation of gill metabolic adjustments

We tested the hypothesis that along with gill Na +K +ATPase activity reduction, branchial energetic metabolism of brook charr ( Salvelinus fontinalis) is altered during sexual maturation. Maturing and sterile fish were transferred from freshwater (FW) to seawater (SW). The activity of gill pyruvate kinase (PK), cytochrome C oxidase (COX), citrate synthase (CS) and lactate dehydrogenase (LDH) was measured at different intervals. Following 1 month in SW, twofold increases in Na +K +ATPase activity were recorded in all groups, while mean metabolic enzyme activities were sharply reduced (COX: 0.051 ± 0.029 to 0.036 ± 0.018; PK: 1.670 ± 0565 to 1.210 ± 0.340 LDH: 2.245 ± 0.690 to 1.642 ± 0.381 μmol mg –1 protein min –1). Interestingly, during this period, no mortality occurred. After 5 months, comparison of Na +K +ATPase:CS and Na +K +ATPase:LDH ratios of mature and sterile fish held either in FW or SW, indicated that the response of Na +K +ATPase largely exceeds the response of the metabolic enzyme apparatus in hyperosmotic conditions. Hence, the reduced iono-osmoregulatory capacity and higher mortality observed in SW-maturing fish during the reproductive season appears to be mainly attributable to Na +K +ATPase activity reduction rather than the alteration of gill metabolic capacity, since no concurrent increase of metabolic enzyme activity with Na +K +ATPase activity occurred. Réduction de la capacité d’adaptation à l’eau de mer de l’omble de fontaine ( Salvelinus fontinalis) en période de reproduction: évaluation des ajustements métaboliques du tissu branchial. Nous avons vérifié l’hypothèse selon laquelle la réduction de l’activité de la Na +K +ATPase branchiale observée en période de reproduction chez l’omble de fontaine ( Salvelinus fontinalis), est couplée à des ajustements métaboliques. Des poissons matures et stériles ont été transférés en eau douce (FW) et en eau salée (SW). L’activité de la pyruvate kinase (PK), de la cytochrome C oxydase (COX), de la citrate synthase (CS) et de la lactate deshydrogénase (LDH) a été mesurée à différents intervalles. L’activité de la Na +K +ATPase après un mois d’exposition à l’eau de mer a doublé chez tous les groupes alors que les activités moyennes de plusieurs enzymes métaboliques ont affiché une réduction marquée (COX: 0.051 ± 0.029 to 0.036 ± 0.018; PK: 1.670 ± 0565 to 1.210 ± 0.340 LDH: 2.245 ± 0.690 to 1.642 ± 0.381 μmol mg –1 protein min –1) sans qu’aucune mortalité ne soit observée. Après cinq mois en eau s