Olfactory inhibition and recovery in chum salmon (Oncorhynchus keta) following copper exposure

Copper can be an effective hatchery treatment to control certain parasitic and fungal infections in salmonids, yet it is also highly toxic to the fish's olfactory system. Numerous reports have described the early inhibitory impacts of copper on fish olfaction, but very few have addressed processes of recovery. Here we show that the chum salmon (Oncorhynchus keta) olfactory system can recover from short-term (4 h) exposures to copper (3-58 µg·L^[-1]) within 1 day, as indicated by electro-olfactogram (EOG) recordings. Recovery followed initial EOG reductions of up to 88%. We also applied a novel cytophysiological approach to monitor changes in the olfactory receptor cells using a fluorescent styryl dye, AM1-43. Copper's influence on the number of receptor cells that labelled with the dye was biphasic, initially increasing the number at the two lowest copper concentrations (3 and 8 µg·L^[-1]) and decreasing the number at the two highest concentrations (24 and 58 µg·L^[-1]). Changes in the ability of olfactory receptor neurons to internalize the dye were monitored up to 10 days in fish recovering from copper exposure.Le cuivre peut servir de traitement efficace des piscicultures afin de contrôler certaines infections à parasites ou à champignons chez les salmonidés, bien qu'il soit très toxique pour le système olfactif des poissons. De nombreux travaux ont décrit les premiers effets inhibiteurs du cuivre sur l'olfaction des poissons, mais très peu se sont intéressés aux processus de récupération. Nous montrons ici que le système olfactif du saumon kéta (Oncorhynchus keta) peut récupérer après de courtes (4 h) expositions au cuivre (3–58 µg·L^[-1]) en moins d'une journée, d'après les enregistrements d'électro-olfactogrammes (EOG). La récupération fait suite à des réductions initiales de l'EOG pouvant atteindre 88 %. Une nouvelle méthode cytophysiologique utilisant un colorant styryle fluorescent, AM1-43, permet de suivre les changements dans les cellules olfactives réceptrices. L'effet du cuivre sur le nombre de cellules réceptrices marquées par le colorant se fait en deux phases, au départ une augmentation du nombre aux deux concentrations les plus faibles de cuivre (3 et 8 µg·L^[-1]) et une diminution aux deux concentrations les plus élevées (24 et 58 µg·L^[-1]. Nous avons suivi les changements de la capacité des neurones olfactifs récepteurs d'incorporer le colorant jusqu'à 10 jours chez des poissons en train de récupérer d'une exposition au cuivre

Effects of insulin-like growth factor I on GnRH-induced gonadotropin subunit gene expressions in masu salmon pituitary cells at different stages of sexual maturation.

Effects of insulin-like growth factor I (IGF-I) and salmon gonadotropin-releasing hormone (sGnRH) on expression of gonadotropin (GTH) subunit genes were examined using primary pituitary cell cultures of masu salmon (Oncorhynchus masou). Fishes were assessed at three reproductive stages, i.e., in April (early maturation), in June (maturing), and in September (spawning). Amounts of GTH subunit mRNAs in pituitary cells were determined using real-time PCR after incubation with IGF-I and/or sGnRH. IGF-I alone had almost no effects on three GTH subunit mRNAs in both sexes, except for decrease in follicle-stimulating hormone (FSH) β mRNA in males in June. sGnRH alone was effective in stimulation of FSHβ and luteinizing hormone (LH) β gene expression in males in April. Thereafter it had no significant effects on GTH subunit mRNAs, although in September it tended to increase FSHβ and LHβ mRNAs in females. Co-administered IGF-I counteracted the sGnRH-induced expression of FSHβ and LHβ genes in males in April, but not in females in September. These results suggest that IGF-I is involved in direct regulation of GTH subunit genes during sexual maturation. In particular, IGF-I differently modulates sGnRH-induced GTH subunit gene expression, depending on reproductive stages

Stimulatory effects of insulin-like growth factor 1 on expression of gonadotropin subunit genes and release of follicle-stimulating hormone and luteinizing hormone in masu salmon pituitary cells early in gametogenesis

Insulin-like growth factor-I (IGF-I) has been shown to be involved in pubertal activation of gonadotropin (GTH) secretion. The aim of this study was to determine if IGF-I directly stimulates synthesis and release of GTH at an early stage of gametogenesis. The effects of IGF-I on expression of genes encoding glycoprotein α (GPα), follicle-stimulating hormone (FSH) β, and luteinizing hormone (LH) β subunits and release of FSH and LH were examined using primary pituitary cells of masu salmon at three reproductive stages: early gametogenesis, maturing stage, and spawning. IGF-I alone or IGF-I + salmon GnRH (sGnRH) were added to the primary pituitary cell cultures. Amounts of GPα, FSHβ, and LHβ mRNAs were determined by real-time PCR. Plasma and medium levels of FSH and LH were determined by RIA. In males, IGF-I increased the amounts of all three subunit mRNAs early in gametogenesis in a dose-dependent manner, but not in the later stages. In females, IGF-I stimulated release of FSH and LH early in gametogenesis, whereas no stimulatory effects on the subunit mRNA levels were observed at any stage. IGF-I + sGnRH stimulated release of FSH and LH at all stages in both sexes, but had different effects on the subunit mRNA levels depending on subunit and stage. The present results suggest that IGF-I itself directly stimulates synthesis and release of GTH early in gametogenesis in masu salmon, possibly acting as a metabolic signal that triggers the onset of puberty

Changes in activity and transcript level of liver and gill metabolic enzymes during smoltification in wild and hatchery-reared masu salmon (Oncorhynchus masou)

It is important for success of the masu salmon, Oncorhynchus masou, stock enhancement program in Hokkaido (northern Japan) to demonstrate physiological problems in hatchery-reared (hatchery) smolt for artificial release. The present study examined changes in liver and gill metabolic parameters in wild and hatchery masu salmon during smoltification and elucidated differences in hepatic and gill metabolism between wild and hatchery fish. As reference to freshwater-adapted wild and hatchery smolt in this study, metabolic parameters of coastal smolt were studied. Yearling wild and hatchery smolting fish were collected from the Ken-ichi River and the Donan Research Branch, which used Ken-ichi river water for fish culture, at the same time every month from March through May, 2008. Coastal smolts were caught from Nemuro Bay of Hokkaido in June. Decreased hepatic glycogen content during smoltification, which was observed in wild fish and revealed activation of glycogenolysis, was not found in hatchery fish. Hatchery fish demonstrated a positive change in hepatic ATP content during smoltification, while wild fish showed negative change in the content, which reflected activated consumption of hepatic ATP stores during smoltification. Increases in gill pyruvate kinase activity during smoltification, which were found in wild fish and indicated activation of glycolysis, were not detected in hatchery fish. There was a difference in increased timing of hepatic citrate synthase activity during smoltification between hatchery and wild fish. Increased gill citrate synthase activity during smoltification, which was observed in wild fish and reflected enhancement of the citric acid cycle, was not found in hatchery fish. Hatchery smolt revealed lower liver cytochrome c oxidase activity and transcript levels of some respiratory chain enzymes compared to wild smolt in May, which suggested lower respiratory chain capacity in hatchery fish at mid-smolt stage. On the other hand, there were no remarkable differences in hepatic and gill 3-hydroxyacyl-coenzyme A dehydrogenase related to lipolysis and creatine kinase activities, which operate in resolution of creatine phosphate, during smoltification between hatchery and wild fish. These results suggested hatchery masu salmon had some metabolic problems with carbohydrate metabolism, the citric acid cycle, and the respiratory chain. Our study will give valuable information to improve physiological quality of hatchery smolt for artificial release