Female Sockeye Salmon Research Articles

Factors affecting the duration of nest defense and reproductive lifespan of female sockeye salmon, Oncorhynchus nerka

Reproductive success of female animals is often affected by a combination of fecundity and parental care. In female salmonid fishes, acquisition of nest (redd) sites and prevention of their use by other females are critical to reproductive success. These factors are particularly important for stocks that spawn at high densities. Body size is positively correlated with fecundity and egg size, and has been hypothesized to control the outcome of intrasexual competition and longevity. We tested this hypothesis by evaluating the influences of body size, intrasexual aggression and arrival date on duration and success of redd guarding by female sockeye salmon, Oncorhynchus nerka, in a small Alaskan creek. Contrary to the hypothesis, larger females guarded their redds no longer than smaller females, and did not live as long in the stream. Aggression was not related to body size or overall longevity but was positively correlated with residence period on the redd. Females that entered the creek earlier lived longer, spent longer on their redds, and spent more time guarding their redds after spawning than females that entered the creek later. However, despite their longevity, early-arriving fish were more likely to have their redds reused by another female because they died before all the females had selected redd sites. The small average body size in this stock is consistent with weak selection for large size, and with our evidence that size provided little if any advantage in nest guarding.

Effects of senescence and density on the aggression of adult female sockeye salmon

Aggression of individual female sockeye salmon Oncorhynchus nerka in Hansen Creek, Alaska, was unrelated to body size or density but it decreased over the last 7 days of life from an average of 8·89–1·47 counts 15 min−1. In addition, as females neared death they tended to use less violent forms of aggression.

Effects of senescence and density on the aggression of adult female sockeye salmon

Aggression of individual female sockeye salmon Oncorhynchus nerka in Hansen Creek, Alaska, was unrelated to body size or density but it decreased over the last 7 days of life from an average of 8·89–1·47 counts 15 min−1. In addition, as females neared death they tended to use less violent forms of aggression.

Low GnRH Levels in the Brain and the Pituitary in Triploid Female Sockeye Salmon

Low GnRH Levels in the Brain and the Pituitary in Triploid Female Sockeye Salmon

Plasma nonesterified fatty acid profiles in male and female sockeye salmon, (Oncorhynchus nerka), during the spawning migration

To establish if there are sex-specific differences in the utilization of specific fatty acids in salmon during migration, we monitored plasma nonesterified fatty acids (NEFA) in male and female early-run Stuart sockeye salmon, Oncorhynchus nerka, during their spawning migration in the Fraser River. Total plasma NEFA concentrations declined in both males and females to 60 and 40% of their respective initial levels. Palmitic (C16:0), oleic (C18:1), docosahexaenoic (C22:6n3), and eicosapentaenoic (C20:5n3) acids consistently represented between 66 and 77% of the total plasma NEFAs throughout the migration. These fatty acids are probably utilized as a source of energy to sustain swimming during the migration. A difference in monoene levels between sexes suggest that females utilized monoenes, particularly oleic acid, for yolk production. Fatty acid concentrations of the n6) series remained constant in both sexes; however, a sudden increase of C20 polyunsaturate proportions of both the n3 and n6 series was observed at the time of gonadal maturation in both sexes. While plasma NEFAs are important as energy sources for migrating sockeye salmon, there is also a selective utilization of plasma NEFAs for gonadal development and reproduction that is reflected in altered NEFA profiles of male and female fish, respectively.

Plasma nonesterified fatty acid profiles in male and female sockeye salmon, (<I>Oncorhynchus nerka</I>), during the spawning migration

Plasma nonesterified fatty acid profiles in male and female sockeye salmon, (<I>Oncorhynchus nerka</I>), during the spawning migration

Sequential Tests for Infectious Hematopoietic Necrosis Virus in Individuals and Populations of Sockeye Salmon (Oncorhynchus nerka)

The incidence and titer distribution of infectious hematopoietic necrosis virus in cavity fluid from spent female sockeye salmon (Oncorhynchus nerka) varied little when fish from a naturally spawning population were sampled three times on alternate days. However, when prespawning female sockeye salmon from a second population were individually tagged, penned, and sampled daily, the incidence and proportion of fish with high virus titer rose over a 6-d period. In 10 instances, consecutive cavity fluid samples from the same fish reverted from virus-positive to virus-negative. We suggest that spent fish should be sampled when accurate and quantitative data on the incidence and level of the virus are required.

Fecundity and Egg Retention of Some Sockeye Salmon (Oncorhynchus nerka) Stocks in British Columbia

The fecundity and egg retention of anadromous female sockeye salmon (Oncorhynchus nerka) collected during 1971–82 from several stocks in British Columbia undergoing controlled fertilization to enhance adult sockeye production were examined. The relationship between egg number and postorbital–hypural length based on 863 females representing 14 stocks was not consistent between all age-types, stocks, and years, probably because of inadequate sample size in some instances. Combined samples, however, revealed a significant positive relationship between postorbital–hypural length and egg number for age 1.2, 1.3, and 2.2 females. Mean absolute fecundity for the respective age-types was 3218, 4125, and 3544 eggs. For samples of 10 or more females, significant stock and annual differences were detected when individual mean absolute fecundity was adjusted to a postorbital–hypural length of 447 mm, but not for females of different age. A comparison of mean fecundities for coastal stocks with historical data for interior British Columbia stocks suggests that coastal stocks are 18% more fecund than interior stocks. Possible causal mechanisms for this regional difference are hypothesized. Examination of 796 carcasses (representing five stocks) for egg retention revealed a range from totally spawned to totally unspawned females, with 56% of the carcasses containing 20 eggs or less and 68% containing 50 eggs or less. The mean egg retention based on all samples combined was estimated to be 6.5% of the mean individual fecundity. This value was reduced to 3.9% when stock means were averaged.

Appearance and quantification of infectious hematopoietic necrosis virus in female sockeye salmon (Oncorhynchus nerka) during their spawning migration.

The incidence and amount of infectious hematopoietic necrosis (IHN) virus was determined in 10 organs and body fluids from each of 100 female sockeye salmon (Oncorhynchus nerka) before, during, and after their spawning migration into freshwater. Virus was found in high concentrations only in fish sampled during and after spawning. Infection rates increased from nil to 100 percent within 2 weeks. In spawning fish, incidences of IHN virus were high in all organs and fluids except brain and serum, and the highest concentrations were in the pyloric caeca and lower gut. Immediately before spawning, IHN virus was found most frequently in the gills, less frequently in the pyloric caeca and spleen, and rarely in other organs.

Metabolic organization of liver during spawning migration of sockeye salmon.

Although earlier studies have established broad outlines of biochemical changes during salmon spawning migration, the metabolic organization of specific organs has hitherto remained unknown. In this study, we assessed the performance of isolated liver cells from anorexic female sockeye salmon (Oncorhynchus nerka) at four sampling sites along their 1,150-km spawning migration. Isolated hepatocytes maintain high rates of gluconeogenesis and CO2 release from amino acids and lactate throughout the migration. Alanine, derived from proteolysis of white muscle, constitutes the single most important source for de novo synthesis of glucose. Just before spawning, when glycogen reserves reach a maximum, gluconeogenesis from alanine is specifically inhibited, whereas its conversion to CO2 and the utilization of other substrates are relatively unchanged. Spawning, apparently supported by carbohydrate catabolism, is accompanied by depletion of glycogen reserves from muscle as well as liver and a stimulation of gluconeogenesis from amino acids. At the onset of migration, palmitate oxidation accounts for about half the CO2 released by liver cells; its contribution decreases during the migration and is negligible after spawning.

Variation in the susceptibility of sockeye salmon Oncorhynchus nerka to infectious haemopoietic necrosis virus

Each of 16 mature female sockeye salmon Oncorhynchus nerka from two river drainages were spawned with individual males, and the progeny from each pair were later challenged with virulent infectious haematopoietic necrosis (IHN) virus. At each of 4 monthly challenges, distinct differences were detected in the susceptibility of the fish to IHN from each family. Average percentage mortality was 98 or more in highly susceptible families, in families of intermediate susceptibility, 85 and in resistant families, 52. Furthermore, the mean time to death was only 9.8 days for fish from the susceptible families but 17.9 days for fish from the more resistant families. These results were similar at each monthly challenge. Challenging the fish at various virus‐dosage levels did not change total mortality, but high dosages hastened the onset of mortality. A genetic basis for resistance is proposed to explain these results.

Effects of Androgens, Estrogens, and Cortisol on the Skin, Stomach, Liver, Pancreas, and Kidney in Gonadectomized Adult Sockeye Salmon (Oncorhynchus nerka)

A study was made of the histological changes occurring in the skin, stomach, liver, pancreas and kidney of adult gonadectomized male and female sockeye salmon in response to hormone treatments. The males received 11-ketotestosterone, 17α-methyltestosterone or cortisol for 4 or 7 weeks, and the females received estradiol, estradiol cypionate, or cortisol for 8 weeks.In the males, androgen injection evoked a highly significant increase in the thickness of the epidermis, a marked atrophy of the stomach, and a degeneration in the liver and kidney. In the pancreas, the exocrine portion showed characteristics of cytolysis in the acini, whereas the islets of Langerhans were hypertrophied. These changes were generally more pronounced after 7 weeks than after 4 but, in the skin, no further increase in the thickening of the epidermis was noted after the 4th week of treatment. No differences between responses of these tissues to 11-ketotestosterone and 17α-methyltestosterosne were detected.Estrogen administration in the females evoked similar, albeit weaker, responses in the skin, stomach, pancreas, and kidney than those recorded in the androgen-treated males. The liver of the females exhibited the characteristics of a hyperactive organ, which probably reflects estrogen-induced vitellogenesis.The effects of cortisol were similar in both sexes: little, if any, change was noted in the skin; atrophy or degeneration was observed in the stomach, liver, kidney, and in the exocrine portion of the pancreas, and the islets of Langerhans were hypertrophied. The cortisol-induced alterations were not, however, as pronounced as those noted in either the androgen- or estrogen-treated fish.These changes are discussed in relation to the changes observed in normal sexually maturing and reproducing Pacific salmon.

Effect of Sexual Maturation and Gonadectomy at Sexual Maturity on Cortisol Secretion Rate in Sockeye Salmon (Oncorhynchus nerka)

Changes in cortisol dynamics in male and female sockeye salmon (Oncorhynchus nerka) have been investigated at various stages during sexual maturation, after spawning, and after gonadectomy just prior to their reaching sexual maturity. The metabolic clearance rate of cortisol was determined by the single injection technique and calculated using the formula for a two-pool system. The volume of distribution of cortisol in the inner pool and the outer pool, metabolic clearance rate, and cortisol secretion rate increased in both male and female salmon during sexual maturation. These changes were reversed in fish that were gonadectomized just before reaching functional maturity and allowed to recuperate for 2 or 8 weeks.There was a decrease in the amount of red carotenoid pigment in the flesh of salmon held in the laboratory during sexual maturation. This loss of pigment was reversed in salmon that were gonadectomized and fed marine zooplankton for 8 weeks.

Cortisol Secretion Rate in Gonadectomized Female Sockeye Salmon (Oncorhynchus nerka): Effects of Estrogen and Cortisol Treatment

Gonadectomized female sockeye salmon (Oncorhynchus nerka) were injected intramuscularly with cortisol, estradiol, estradiol cypionate, or peanut oil for 8 weeks. The metabolic clearance rate of cortisol was determined by the single injection technique and calculated from the formula for a two pool system. The cortisol secretion rate was determined from the metabolic clearance rate and the plasma cortisol concentration.The volume of distribution of cortisol in the inner compartment (V1) and the outer compartment (V2), the metabolic clearance rate (MCR), the resting secretion rate (S), and the resting plasma cortisol concentration were all significantly higher in the estradiol-injected group than in the peanut oil-injected control group, and the plasma cortisol concentration at the end of the experiment was lower. V1, MCR, and S were also significantly higher in the estradiol cypionate-injected group. There were no significant differences between the cortisol-injected group and the peanut oil-injected control group or in the biological half life of cortisol between any groups.There were no significant changes in the red colour of the flesh or in body weight during the experiment. However, the cortisol-injected group did show the largest weight loss.

TESTOSTERONE, CONJUGATED AND "FREE", IN THE BLOOD OF SPAWNED FRASER RIVER SOCKEYE SALMON (ONCORHYNCHUS NERKA)

Testosterone was isolated from both the "free" and conjugated steroid fractions obtained from the plasma of spawned female sockeye salmon. The structure of the steroid was confirmed by several criteria including a sulphuric acid chromogen and infrared spectra. Evidence is presented for the presence of testosterone in the conjugated steroid fraction prepared from spawned male sockeye. Several unsuccessful attempts were made to detect dehydroepiandrosterone and androsterone.

Biochemical Studies on Sockeye Salmon During Spawning Migration.: IX. Fat, Protein and Water in the Major Internal Organs and Cholesterol in the Liver and Gonads of the Standard Fish

Absolute changes in fat, protein and water of all major internal organs and free and esterified cholesterol of the liver and gonads of standard male and female sockeye salmon (Oncorhynchus nerka) during the 1957 Fraser River spawning migration to Stuart Lake are discussed. The alimentary tract is the major source of fat and protein from the internal organs and the greater part of this reserve is expended in the first 250 miles (403 km) of the river migration. The testes consumed only 0.5% of the energy expended from the body of the standard male while the ovaries consumed 8% of the energy expended from the body of the standard female.

Biochemical Studies on Sockeye Salmon During Spawning Migration. V. Cholesterol, Fat, Protein and Water in the Body of the Standard Fish

The absolute changes in fat, protein, water and free and esterified cholesterol for the entire body of standard male and female sockeye salmon (Oncorhynchus nerka) during the Fraser River spawning migration are discussed.The data were obtained for twelve groups of males and twelve groups of females, totalling 216 fish. The fish were caught at three locations: before entering the river, 250 miles up the river, and at one of the spawning grounds 715 miles from the first sampling station.