Hormones, Metamorphosis, and Smolting

Dickhoff, Walton W.

doi:10.1016/b978-0-12-629055-4.50025-8

Cited by 21 publications

(15 citation statements)

References 144 publications

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“…Plisetskaya et al (1988) found that plasma insulin peaked (from about 2 to about 7-8 ng ml-1) in coho salmon at the parrtransitional stage, during the very beginning of smoltification. This insulin surge preceded the surges of all the other hormones, such as thyroxine, GH, prolactin and cortisol (Dickhoff 1993), and occurred in late February-late March, about two months before smoltification was completed in May. This is in close agreement with results from the present study, although in both studies insulin peaks between different years showed slight temporal differences.…”

Section: Discussionsupporting

confidence: 82%

Plasma levels of insulin and liver glycogen contents in one- and two-year old Atlantic salmon (Salmo salar L.) during the period of parr-smolt transformation

Mayer

Borg

Plisetskaya

1994

Fish Physiol Biochem

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Plasma levels of insulin were measured by specific radioimmunoassay in 1-year and 2-year old Atlantic salmon (Salmo salar) parr during the period of parr-smolt transformation. The two-year old fish were of two different categories; silvering pre-smolts and previously mature male parr. If insulin plays an important role in parr-smolt transformation and/or subsequent osmoregulatory changes it was expected that the pre-smolts would show a different insulin profile compared to the mature male parr and one-year old parr, both of which show impaired hypoosmoregulatory ability compared to smolts. Measurements were taken during two separate years. Between January and April both categories of two-year old fish had generally higher plasma levels of insulin compared to the non-smolting one-year old parr. In the pre-smolts insulin levels ranged from 4.0 to 7.9 ng ml(-1), and from 7.8 to 16.7 ng ml(-1) in 1990 and 1992 respectively, while in the previously mature males the same respective values were from 4.3 to 10.0 ng ml(-1), and from 6.6 to 24.1 ng ml(-1). In the two-year old fish, whether pre-smolts or mature males, plasma insulin levels peaked between 1-2 months before final smoltification, after which insulin titers declined sharply. In 1990, the 1-year old parr showed a dual peak in plasma insulin. Insulin first peaked in February (7.8 ng ml(-1)), and then again in April-May (7.7 ng ml(-1)), while in 1992 the 1-year old parr showed a number of smaller transient peaks (5-7 ng ml(-1)) between March-May, followed by sharp elevation of insulin levels in June. Liver glycogen contents were at their highest (3.5-5.0 g 100 g(-1) I liver wet weight) in March in both 1-year and 2-year old fish. Glycogen levels were low during the later stages of parr-smolt transformation, before rising again in June in both the 1-year old and precociously mature parr, but not in the smolts.

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Section: Discussionsupporting

confidence: 82%

Plasma levels of insulin and liver glycogen contents in one- and two-year old Atlantic salmon (Salmo salar L.) during the period of parr-smolt transformation

Mayer

Borg

Plisetskaya

1994

Fish Physiol Biochem

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“…The distribution of dio2b expression seen in the smolt brain is far more extensive than that observed in adult mammals and birds, in which effects are confined to the pituitary and basal diencephalon. This probably reflects the widespread reorganization of brain function entailed in smoltification [18,26], which involves profound, quasi-metamorphic [27][28][29] changes in behavior and physiology. At the same time, it forces us to reconsider the regulatory pathways leading to photoperiodic dio2 induction.…”

Section: Discussionmentioning

confidence: 99%

Functional Divergence of Type 2 Deiodinase Paralogs in the Atlantic Salmon

et al. 2015

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Thyroid hormone (TH) is an ancestral signal linked to seasonal life history transitions throughout vertebrates. TH action depends upon tissue-localized regulation of levels of active TH (triiodothyronine, T3), through spatiotemporal expression of thyroid hormone deiodinase (dio) genes. We investigated the dio gene family in juvenile Atlantic salmon (Salmo salar) parr, which prepare for seaward migration in the spring (smoltification) through TH-dependent changes in physiology. We identified two type 2 deiodinase paralogs, dio2a and dio2b, responsible for conversion of thyroxine (T4) to T3. During smoltification, dio2b was induced in the brain and gills in zones of cell proliferation following increasing day length. Contrastingly, dio2a expression was induced in the gills by transfer to salt water (SW), with the magnitude of the response proportional to the plasma chloride level. This response reflected a selective enrichment for osmotic response elements (OREs) in the dio2a promoter region. Transcriptomic profiling of gill tissue from fish transferred to SW plus or minus the deiodinase inhibitor, iopanoic acid, revealed SW-induced increases in cellular respiration as the principal consequence of gill dio2 activity. Divergent evolution of dio2 paralogs supports organ-specific timing of the TH-dependent events governing the phenotypic plasticity required for migration to sea.

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“…The preacclimation process involves physiological and morphological changes that improve salinity tolerance of developing/migrating salmonids (16,31,48). These physiological changes, such as salinity tolerance, are driven by changes in circulating hormones such as growth hormone (GH), prolactin (PRL), somatolactin (SL), insulin-like growth factor-I (IGF-I), and cortisol (8,24,45).…”

mentioning

confidence: 99%

Salinity acclimation affects the somatotropic axis in rainbow trout

Shepherd¹,

Drennon²,

Johnson³

et al. 2005

American Journal of Physiology-Regulatory, Integrative and Comp

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In this study, we set out to examine the role of the somatotropic axis in the ion-regulation process in rainbow trout. Specifically, our objective was to examine whether plasma insulin-like growth factor-binding proteins (IGFBPs) are modulated by gradual salinity exposure. To this end, freshwater (FW)-adapted rainbow trout were subjected to gradual salinity increases, up to 66% seawater, over a period of 5 days. During this acclimation process, minimal elevations in plasma Ca 2ϩ and Cl Ϫ were seen in the salinity-acclimated groups compared with FW controls. There were no changes in plasma Na ϩ levels, and only a minor transient change in plasma cortisol levels was seen with salinity exposure. The salinity challenged animals responded with elevations in plasma growth hormone (GH) and IGF-I levels and gill Na ϩ -K ϩ -ATPase activity. We identified IGFBPs of 21, 32, 42, and 50 kDa in size in the plasma of these animals, and they were consistently higher with salinity. Despite the overall increase in IGFBPs with salinity, transient changes in individual BPs over the 5-day period were noted in the FW and salinity-exposed fish. Specifically, the transient changes in plasma levels of the 21-, 42-, and 50-kDa IGFBPs were different between the FW and salinity groups, while the 32-kDa IGFBP showed a similar trend (increases with sampling time) in both groups. Considered together, the elevated plasma IGFBPs suggest a key role for these binding proteins in the regulation of IGF-I during salinity acclimation in salmonids.insulin-like growth factor binding-proteins; insulin-like growth factor-I; growth hormone; rainbow trout; salinity EURYHALINE TELEOSTS, such as killifish, tilapia, and eels, survive abrupt full-strength seawater (SW) transfer without prior physiological preparation (14,42,92), whereas salmonids undergo a preacclimation process that is essential to SW survival (46). The preacclimation process involves physiological and morphological changes that improve salinity tolerance of developing/migrating salmonids (16,31,48). These physiological changes, such as salinity tolerance, are driven by changes in circulating hormones such as growth hormone (GH), prolactin (PRL), somatolactin (SL), insulin-like growth factor-I (IGF-I), and cortisol (8,24,45).Efforts to separate the endocrine and physiological response to salinity exposure, from the acquisition of salinity tolerance by migrating salmonids, have been made difficult by species differences (48) and aspects of the preacclimation process such as developmental and sex-specific differences (8,10,30,48,50,55), changes in temperature and photoperiod (5, 8, 9, 27), diet and rearing conditions (64, 97), growth, genetic lineage and domestication (24,27,57), and the method and duration used for salinity challenge (9,72,73,75,93).Aside from the aforementioned factors that influence salinity tolerance and hormone levels in salmonids, there is good evidence to show that the preacclimation process, SW tolerance, and enhanced growth of SW-acclimated salmonids are controlled by ...

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Hormones, Metamorphosis, and Smolting

Cited by 21 publications

References 144 publications

Plasma levels of insulin and liver glycogen contents in one- and two-year old Atlantic salmon (Salmo salar L.) during the period of parr-smolt transformation

Plasma levels of insulin and liver glycogen contents in one- and two-year old Atlantic salmon (Salmo salar L.) during the period of parr-smolt transformation

Functional Divergence of Type 2 Deiodinase Paralogs in the Atlantic Salmon

Salinity acclimation affects the somatotropic axis in rainbow trout

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