Mature Salmon Research Articles

Changes in plasma somatolactin levels during spawning migration of chum salmon (Oncorhynchus keta)

Plasma somatolactin (SL) concentrations were examined in chum salmon in relation to gonadal maturation; immature salmon in the Bering Sea at various stages of maturation, and mature salmon during upstream migration caught at the ocean, bay and river. Plasma SL concentrations as well as plasma prolactin (PRL) and growth hormone (GH) levels in the immature fish caught in the Bering Sea were maintained essentially at similar levels. Plasma SL in mature salmon increased significantly from the fish in the ocean to the fish in the river in both sexes. Although all the fish had fully developed gonads, females completed ovulation while still in the bay, whereas final spermeation in males was achieved after entry into the river. Thus, no clear correlation was seen between plasma SL levels and final gonadal maturation. On the other hand, plasma PRL concentrations in both male and female fish were higher in the fish in the river than those in the ocean and bay, and plasma GH levels were higher in both sexes in the fish in the bay and river than those in the ocean. Plasma levels of triglycerides, glucose, free fatty acids and ionized sodium and calcium were also examined. Significant-negative correlations were seen between plasma SL and plasma ionized calcium in mature male salmon, and between plasma SL and plasma triglycerides in mature female salmon. Although our findings do not rule out the possibility of the involvement of SL in final maturation, the results indicate that SL seems to be involved at least in energy and/or calcium metabolism during the spawning migration.

Differential recruitment of steroid hormone response elements may dictate the expression of the pituitary gonadotropin II beta subunit gene during salmon maturation

Differential recruitment of steroid hormone response elements may dictate the expression of the pituitary gonadotropin II beta subunit gene during salmon maturation

Differential recruitment of steroid hormone response elements may dictate the expression of the pituitary gonadotropin II beta subunit gene during salmon maturation.

The role of testosterone (T) and 17 beta-estradiol (E2) in the control of chinook salmon gonadotropin II beta subunit (sGTHII beta) gene was examined. Both E2 and T specifically stimulated GTHII beta gene expression in cultured juvenile rainbow trout pituitary cells. 5'-Flanking regions of the sGTHII beta gene linked to the chloramphenicol acetyltransferase (CAT) expression vector were transfected into these pituitary cells, and cultures were treated with steroid hormones. Estrogen-stimulated CAT activity occurred with constructs containing a 13-base pair estrogen responsive element (ERE) sequence [proximal ERE (pERE)] located at -273 to -260 upstream of its transcriptional start site. Binding specificity of pERE was confirmed by mobility shift and DNA methylation interference assays using the DNA binding domain of the human estrogen receptor. Interestingly, the pERE functioned to derepress the activity of the proximal silencer (pSil) only in the pituitary cells of juvenile trout but not in cells derived from maturing and sexually matured fish. Another potential ERE sequence comprised of three tandemly linked half-ERE palindromes was located from -2736 to -2659 [distal ERE (dERE)] of the sGTHII beta gene. Distal ERE might be responsible for the steroid responsiveness of the longest sGTHII beta/CAT construct (-3500CAT) observed in the pituitary cells of maturing fish. The function of pERE and dERE were further examined in the heterologous HeLa cells by mutagenesis and cotransfection with a rainbow trout estrogen receptor expression vector. Disruption of the palindromic structure of pERE severely impaired its function. When the sequences between pERE and dERE were deleted, a 200-fold increase in CAT activity was observed in response to E2. A model is proposed to describe the regulation of GTHII beta gene expression at different reproductive stages.

Life History Forms of Male Masu Salmon (Oncorhynchus masou) in South Primor'e, Russia

In South Primor'e (Russia), mature male masu salmon (Oncorhynchus masou) parr are found at age 0 + to 3 + (9–22 cm). After first maturation, some male parr die, while others survive and mature the following year. Immature males become smolts after one or two winters in rivers and migrate to the sea in spring–early summer. After one winter in the sea, they return as sea-run normal-sized (40–70 cm) males at age R.1 +. Besides mature male parr and normal-sized sea-run males, jacks (28–33 cm) at age R.0 + were found. Such males return to rivers after some months of marine life and do not overwinter in the sea. Some jacks previously spawned as parr, while others did not. All jacks and normal-sized sea-run males die after spawning. Thus, male masu salmon mature as one of four life history forms: (1) male parr, (2) jacks that matured previously as parr, (3) jacks that did not mature previously as parr, and (4) ordinary sea-run males. While mature male parr and sea-run males are ordinary life history forms, both forms of jack are rare.

Structural and chemical changes in the muscle of chum salmon ( Oncorhynchus keta) during spawning migration

The white muscle of migrating chum salmon ( Oncorhynchus keta) becomes increasingly soft and watery as the fish matures and progresses towards its spawning grounds. Flesh colour, measured by HunterLab parameters a and a L , was a better indicator of maturity grade than muscle fat, protein or moisture. In the transition from grade 1, silver-bright, to grade 4, spawning, chum muscle protein decreased from 17·9% to 15·8%, fat decreased from 4·9% to 1·0% and moisture increased from 74·2% to 79·5%. Compositional changes and concurrent textural degradation of the flesh may be attributed to the physical stress of migration, starvation, and hormonal changes during the development of the reproductive system. The structural basis for loss of firm texture was investigated with light and transmission electron microscopy (TEM) by comparing the immature (silver-bright) and mature (spawning) salmon. Light micrographs revealed an apparent loss in myofibrillar material within muscle cells as the salmon matured. With TEM, local or focal areas of degeneration were visible in both the spawning and silver-bright fish, but changes were more severe in the mature fish. Given a series of micrographs of muscle, judges could distinguish between the two groups using a scoring system based on defined criteria of myofibril ‘splitting’, ‘smearing’, ‘thinning’, and ‘inter-myofibril spaces’.

Unidirectional Natural Hybridization between Brown Trout (Salmo trutta) and Atlantic Salmon (S.salar) in Newfoundland

Protein electrophoresis and mitochondrial DNA analysis were used to detect the frequency and direction of natural hybridization between brown trout (Salmo trutta) and Atlantic salmon (S. salar) in nine Newfoundland rivers. In total, 37 hybrids were discovered in a sample of 792 juvenile fish for a regional frequency of 4.67%. Local frequencies ranged from 0.00 to 18.75% and were significantly heterogeneous. All of the hybrids sampled were produced from matings between female brown trout and male Atlantic salmon. Possible reasons for the breakdown of prereproductive isolating mechanisms between these species are considered. Reproductive characteristics of the populations involved appear to have a major influence on the dynamics of hybridization between these species in Newfoundland. It is proposed that an abundance of sexually mature Atlantic salmon parr in Newfoundland streams is responsible for both the frequency and direction of hybridization observed in this study.

Artificial hybridization of Newfoundland brown trout and Atlantic salmon: hatchability, survival and growth to first feeding

The relative viability of hybrids produced using anadromous brown trout, Atlantic salmon grilse and sexually mature Atlantic salmon parr from a Newfoundland river was investigated. The sperm of sexually mature salmon performed equally well compared to anadromous salmon sperm when fertilizing both salmon and trout eggs. Hatching success was high in all crosses and controls. By first feeding, hybrids produced using brown trout eggs had suffered higher mortality and were smaller in size than the reciprocal hybrid and both parental controls. Hybrids produced using salmon eggs exhibited high viability and by first feeding were greater in size than both parental controls. A comparison of hatching time and length of hatching period suggests a paternal influence in embryo development. Possible reasons for the differences between reciprocal hybrids and the significance of results with respect to aquaculture are discussed.

Effect of stripping on the length, condition and gonadal state of mature male Atlantic salmon, Salmo salar L., parr during autumn and winter

Hatchery-reared mature male Atlantic salmon parr were shorter than immature parr of the same age through the winter period and this difference increased prior to smolting in spring. Stripping had no effect on growth. In autumn mature male parr had a higher condition factor (CF) than immature parr, but from early January no difference was observed between unstripped mature males and immature parr. Stripping reduced the CF of male parr but the difference had disappeared by the time of smolting when the CFs of both mature groups were lower than that of immature fish. The quantity of expressible milt in stripped males decreased from c. 3% body weight in November and December to <0.05% by 2 March, after which no further milt expression was recorded. Milt expression in previously unstripped males was about 1% of body weight on 2 March, similar to that of stripped males 1 month earlier.

The Atlantic salmon prepro-gonadotropin releasing hormone gene and mRNA

Screening for the gene encoding salmon gonadotropin releasing hormone (sGnRH) in an Atlantic salmon ( Salmo salar) genomic library resulted in isolation of a positive clone designated λsGnRH-1. An anchor polymerase chain reaction (PCR) technique was used to amplify GnRH cDNA derived from salmon hypothalamic mRNA. The cDNA sequence was aligned to the 7607 base pair genomic sequence which was shown to encode the entire prepro-GnRH gene. The cDNA proved that the cloned gene is expressed in the hypothalamus of mature salmon. The coding domain of sGnRH differs from the mammalian GnRH by six nucleotide changes which allow the two amino acid differences between the two GnRH variants. Salmon GnRH associated peptide (GAP) differs extensively in sequence and size from the mammalian counterpart. Compared to the GnRH cDNA of a cichlid species the similarity is 69.3% in the protein coding sequence.

産卵回帰シロサケの加熱処理筋肉の保水性

産卵回帰シロサケの加熱処理筋肉の保水性

The cytochrome P450 system of atlantic salmon (Salmo salar): I. Basal properties and induction of P450 1A1 in liver of immature and mature fish

The major components of the cytochrome P450 (P450) system in liver microsomes of Atlantic salmon were studied using spectrophotometric, catalytic and immunochemical techniques. In juvenile fish sampled during the winter season, high basal activities of 7-ethoxyresorufin O-deethylase (EROD) were found. The Km for 7-ethoxyresorufin was 0.4 µM, and Vmax 1.23 nmol/min/mg protein in juvenile fish. In mature fish sampled from the same group of fish in December, EROD activity was barely detectable (20-30 pmol/min/mg protein). Treatment with the P450 1A1 inducer β-naphthoflavone (BNF) resulted in almost 2-fold induction of total P450, and 30-40-fold induction of EROD activity in immature fish. A similar fold increase was seen in mature fish. The differences in EROD activity between untreated and BNF-treated fish, was accompanied by similar differences in a P450 1A1 cross-reacting protein (Mr=58,000 D) in immunochemical studies using rabbit anti-cod P450 1A1 IgG. However, judging from these studies, the levels of P450 1A1-protein in mature salmon far exceeded those accounted for by the measured EROD activity in comparison to immature fish (both before and after BNF-treatment), indicating inhibiting effects of sex steroids on the measured activity. This effect was not seen on 7-ethoxycoumarin O-deethylase activity. A long-term storage experiment indicated that Atlantic salmon liver microsomes can be stored for 2 years at -80°C in 20% glycerol without losing more than 20-40% of its catalytic activity.

Immunohistochemical localization of cathepsin B and L in the white muscle of chum salmon (Oncorhynchus keta) in spawning migration: probable participation of phagocytes rich in cathepsins in extensive muscle softening of the mature salmon

The study was undertaken to elucidate the cause of the enhancement of catheptic activity in the white muscle of chum salmon during spawing migration The study may provide a new concept that makes clear the mechanisms of protein turnover taking place in the muscle of the salmon and the extensive muscle softening, i.e., the muscle tissue degradation occurring after the death of the fish

Extragonadal 17β-hydroxysteroid dehydrogenase activity in rainbow trout

Blood cells of male and female rainbow trout showed 17(3-hydroxysteroid dehydrogenase (17(βHSD) activity in vitro, reducing 11β-hydroxyandrostenedione and 11-ketoandro-stenedione (OA) to 11β-hydroxytestosterone and 11-ketotestosterone (OT), respectively. Enzyme activity did not vary with gonadal development in either sex. The conversion of tritiated precursors was partly inhibited in the presence of steroid-free serum or radioinert steroid, but inhibition was less strong when radioinert androgens were added to steroid-free serum or when the serum contained endogenous steroids. Treatment of male trout with salmon gonadotropin in vivo and/or incubation with a pituitary extract of mature salmon in vitro did not affect OA conversion when blood cells were incubated in the absence of serum, whereas it was slightly but significantly higher when they were incubated in the presence of serum and pituitary extract. In addition to blood cells and steroidogenic tissues, spleen, intestine, brain, liver, excretory kidney, and skin tissue also produced an OA metabolite isopolar to OT in vitro, so that 17βHSD appears to be present in a variety of trout issues. With respect to the biological significance of extragonadal steroid metabolism in vivo, the ligand binding characteristics of circulating steroid binding proteins may be of primary relevance in regulating substrate availability.

Large-Scale Escapes of Farmed Atlantic Salmon (Salmo salar) into Norwegian Rivers Threaten Natural Populations

We present data on Atlantic salmon (Salmo salar) which show that escaped farmed salmon enter Norwegian rivers in great numbers. Escaped farmed salmon comprised a substantial proportion of the mature salmon present on the spawning grounds in autumn. A potential for large-scale genetic introgression thus exists. The sex ratios, length distributions, and times of ascent of wild and farmed salmon differed significantly, reflecting major variations in biology and behavior. High proportions of farmed salmon (&gt; 20%) were found only in rivers having fish farms situated closer than 20 km from the outlet.

Steroid secretion of rainbow trout testis in vitro: Variation during the reproductive cycle

Testicular tissue collected at different stages of gonadal development was incubated with a pituitary extract (PE) from mature salmon. Three androgens (11-ketotestosterone, OT; 11β-hydroxytestosterone, OHT; and testosterone, T) and 17α,20β-dihydroxyprogesterone (17–20βP) were quantified by radioimmunoassay in incubation media. OHT and OT were secreted in larger quantities than T and 17–20βP. The PE dose that evoked a half-maximal response (ED 50), the ratios of maximum stimulated vs baseline secretion, and total testicular steroid output all changed during the reproductive cycle. Androgen secretion in response to PE was low in immature and spent fish, both in terms of ED 50 and the ratio of maximum stimulated vs baseline secretion. This ratio increased in testes showing the first signs of maturation and remained elevated during rapid testicular growth, before reaching maximum values at full maturity. The lowest ED 50 values were found at the end of spermatogenesis and during the peak spawning period. 17–20βP secretion could not be stimulated noticeably until the fish had entered the spawning period and, as opposed to androgens, remained stimulable in spent fish. ED 50 values for 17–20βP ranged, without showing clear-cut variations, above those calculated for androgens. The changes in PE reactivity and steroid secretion capacity during the reproductive cycle are likely to contribute to the changes in circulating steroid concentrations and may allow modulations of testicular steroid production without large changes in circulating GTH levels.

Plasma growth hormone levels increase during seawater exposure of sexually mature Atlantic salmon parr (Salmo salar L.)

At the time of smoltification in May, smolts and sexually mature male parr were transferred to seawater (25% salinity) and sampled after 6 and 24 hr. Plasma levels of growth hormone (GH) were measured by radioimmunoassay. There was no difference in GH levels between smolts and mature parr in fresh water. GH levels did not change during exposure of smolts to seawater. In the mature male parr, plasma GH levels increased after 24 hr, when the levels were almost five times those of the freshwater controls. In the mature male parr, there was an increase in plasma osmolality, sodium, and magnesium after 24 hr in seawater; magnesium also increased after 6 hr. The levels of potassium and calcium did not change in either immature parr or mature male parr. The increase in plasma GH levels in the mature parr in seawater may be part of a mechanism to increase hypoosmoregulatory ability in fish not ready for seawater entry.

Changes in plasma hormone levels during loss of hypoosmoregulatory capacity in mature chum salmon ( Oncorhynchus keta) kept in seawater

Returning chum salmon ( Oncorhynchus keta) in northern Honshu Island, Japan, complete gonadal maturation while in the bay. Mature fish caught in the bay failed to survive in seawater for more than a week, whereas they adapted to fresh water efficiently. Mortality in seawater seems to be due primarily to an increased plasma osmolality. Maladaptation to seawater was more pronounced in the fish caught deep in the bay than those caught outside the bay, and also greater in females than in males. In close correlation with the increased plasma osmolality and electrolyte concentrations, plasma levels of cortisol and growth hormone increased in the fish kept in seawater. Cortisol and growth hormone may be secreted in response to the increased plasma osmolality and would not be the direct cause of the maladaptation to seawater. Plasma prolactin remained low in the seawater fish, indicating that the increased secretion of prolactin, a freshwater-adapting hormone, is not the cause of maladaptation to seawater either. On the other hand, when the fish caught in the river were kept in fresh water, an increase in plasma prolactin concentrations was seen, particularly in females, whereas no significant change was seen in plasma cortisol and growth hormone. Concentrations of 17α,20β-dihydroxy-4-pregnen-3-one in the female and of testosterone in both the male and female were extremely high in the bay fish and decreased slightly but significantly after 7 days in fresh water. The gonadal steroids may have inhibitory effects on osmoregulation in the mature salmon in seawater.

The effects of hypoxia, alkalinity and neurochemicals on hatching of Atlantic salmon ( Salmo salar) eggs

The hatching process of eggs from Atlantic salmon was investigated. Salmon eggs were subjected to hypoxia under different alkaline conditions in the laboratory using different buffers in the test systems. Hypoxia was a highly effective inducer of hatching in mature salmon eggs (2 days before natural hatching at 5–7°C), causing 100% hatching within 2 h of application at physiological pH. Salmon eggs were also induced to hatch by hypoxia 2–3 weeks ahead of normal hatching, but hatching occurred more slowly and asynchronously than in mature eggs and was not complete (86%). However, in this situation the induction of salmon egg hatching by hypoxia was greatly facilitated at alkaline pH. Hypoxia induced hatching only when applied less than 1 month prior to normal hatching, i.e. after ca. 300 day degrees (dC) of development. Under normoxic and physiological pH conditions hatching of mature salmon eggs was induced by dopaminergic antagonists and delayed by dopaminergic agonists. Noradrenergic and serotonergic agents also induced hatching, but they apparently act through a terminal dopaminergic mechanism. The data suggest that hypoxia is involved in the natural hatching process, and that physiological signals for hatching in mature salmon eggs may involve specific neural monitors of oxygen tension.

Plasma levels of five androgens and 17α-hydroxy-20β-dihydroprogesterone in immature and mature male Baltic salmon (Salmo salar) parr, and the effects of castration and androgen replacement in mature parr

During the spawning period, the plasma levels of the androgens 11-ketotestosterone, testosterone, 11β-hydroxytestosterone, 11β-hydroxyandrostenedione, 11-ketoandrostenedione, and of the progestin 17α-hydroxy-20β-dihydroprogesterone were higher in mature compared with immature male Baltic salmon parr. 11-Ketotestosterone was always found to be the predominant androgen in the plasma of mature male parr and mature anadromous males. Mature male parr and large mature anadromous males had similar androgen profiles during the main spawning period, although 11-ketotestosterone tended to be higher in the mature anadromous males and testosterone was always higher in the mature male parr. At the time of the main spawning period, plasma levels of 17α-hydroxy-20β-dihydroprogesterone rose sharply in mature male parr, these levels being similar to those found in the plasma of large mature anadromous males. All measured androgens were low or nondetectable in castrated parr. Treatment of castrated parr with Silastic capsules containing 11-ketoandrostenedione resulted in high plasma 11-ketoandrostenedione levels and even higher levels of 11-ketotestosterone, indicating an extratesticular site of androgen conversion.

Abundance of Spawning Pacific Salmon in Two Lake Superior Streams, 1981–1987

We examined, by mark and recapture procedures, the abundance of Pacific salmon entering two Lake Superior tributaries to spawn between 1981 and 1987. In 1987, abundance of pink salmon in the Carp and Pancake rivers declined to 50 and 25%, respectively, of that observed in 1981. In contrast, abundance estimates and catch records indicated that coho and chinook salmon had increased since 1981. The construction of a lowhead barrier dam on the Carp River in 1983/84 allowed passage of coho and chinook but precluded passage by pink salmon. Construction of the barrier dam did not appear to be the major cause for changes in abundance of pink salmon. Most mature pink salmon (>50% of total abundance) entered the spawning streams during a 2-week period following either onshore wind or a heavy rainfall. We submit that it is premature to suggest a lake-wide decline in pink salmon abundance.