Mature Atlantic Salmon Research Articles

Marine post‐smolt growth and age at maturity of Atlantic salmon

The annual variation in sea‐age of maturation for a hatchery dependent stock of Atlantic salmon was compared to variation in post‐smolt growth as evidenced by circuli spacing patterns. The proportion of returns of 1‐seawinter (1 SW) and 2 SW salmon and the fraction of the smolt year class or cohort that maturated as 1 SW fish, were compared to seasonal growth indices determined from circuli spacing on the scales of smolt class survivors returning as 1 SW and 2 SW spawners. Using image processing techniques, we extracted inter‐circuli distances from scales from 2244 recaptured fish. Spacing data for the first year at sea were collected and then expressed as seasonal growth indices for the spring period, when post‐smolts first enter the ocean; the summer, when growth appears maximal; and winter, when growth appears to be at a minimum. In general, circuli spacings were wider for 1 SW than for the 2 SW returns of the same smolt cohort. The 1 SW fraction was significantly and positively correlated with late summer growth, suggesting that growth during this season is pivotal in determining the proportion of a smolt class that matures early.

Marine post-smolt growth and age at maturity of Atlantic salmon

Marine post-smolt growth and age at maturity of Atlantic salmon

Effects of aromatase inhibitors on sexual maturation in Atlantic salmon, Salmo salar, male parr

Atlantic salmon, Salmo salar, male parr were implanted with Silastic capsules filled with different aromatase inhibitors: 1,4,6-androstatriene-3,17-dione (ATD), 4-hydroxy-4-androstene-3,17-dione (4OH), and the non-steroidal CGS16949 A, 4-benzonitrile monohydrochloride (CGS). Aromatization in brain homogenates were lower in salmon implanted with CGS and ATD than in controls. This was not the case for 4OH, but administration of 4OH to brain homogenates reduced the aromatase activity. All three aromatase inhibitors had effected gonadal weights in fish sampled in the summer, but the effects were markedly different among inhibitors. Plasma levels of the androgen 11-ketotestosterone (11KT) and the progestin 17α, 20β-dihydroxy-4-pregnen-3-one (17,20P) were measured by means of radioimmunoassay. CGS and ATD, but not 4OH, significantly decreased the plasma 17,20P levels in the autumn. Plasma levels of 11 KT were not influenced by ATD or CGS treatment, but 4OH had a lowering effect in one autumn sampling. ATD and 4OH (CGS not tested) increased the proportion of maturing males.These findings suggest that aromatization is of physiological importance in different mechanisms controlling reproduction in salmon.

Phenotypic Divergence of Sea-ranched, Farmed, and Wild Salmon

We quantified divergence in phenotype of sea-ranched, farmed, and wild Atlantic salmon (Salmo salar) of a common genetic stock (River Imsa, Norway). These first-generation fish were also contrasted with a fifth-generation farmed population (Norwegian commercial strain) and with wild and multigeneration sea-ranched populations of coho salmon (Oncorhynchus kisutch). In comparisons using mature Atlantic salmon male parr, cultured juveniles had smaller heads and fins and narrower caudal peduncles and could be distinguished from wild juveniles with 100% accuracy. When juveniles were reared to adulthood in the natural marine environment, some environmentally induced differences due to juvenile hatchery rearing persisted but many disappeared. This was particularly true for head and trunk morphology. Greater adult divergence from the wild state was observed in multigeneration sea-ranched coho salmon, suggesting that evolutionary changes may accumulate with time. Continued farming of salmon juveniles through adulthood increased environmentally induced phenotypic divergence considerably. Both rayed-fin sizes and body streamlining decreased. Fifth-generation Norwegian farmed salmon showed the greatest morphological differences. Both the proportion of a fish's life history and number of generations spent in culture are thus probably important determinants of phenotypic divergence of cultured fish from their wild state.

Estimates of genetic and phenotypic parameters for body weight, growth rate and sexual maturity in Atlantic salmon

Body weights were recorded at tagging on 1704 one year old presmolts (offspring of 26 males and 115 females) and again after 4, 12, 16, 24 and 27 months in seawater. After 16 months in seawater the fish were classified, based on secondary sex characters, into early maturing fish and early immatures and after 27 months into normal maturing fish and non-matures. Sexually maturing fish were significantly heavier than early immatures and non-matures several months before secondary sex characters reduced their market quality. Estimated heritabilities were 0.10 to 0.32 for the six weight traits; 0.04 to 0.26 for specific growth rate (% day −1) in the periods between each weight recording and 0.09 and 0.15 for early and normal sexual maturity when estimated on the observed binary scale (0.34 and 0.24, respectively, transformed to the underlying liability scale). Genetic correlations between the weights were medium to high (0.48 to 0.98), while the results indicated a negative genetic as well as phenotypic correlation between specific growth rate in adjacent periods. Genetic correlations of early sexual maturity with weights until 16 months in seawater were all positive (0.11 to 0.49).

Photoperiod affects timing of parr-smolt transformation, subsequent growth and incidence of sexual maturation of Atlantic salmon ( Salmo salar)

Photoperiod affects timing of parr-smolt transformation, subsequent growth and incidence of sexual maturation of Atlantic salmon ( Salmo salar)

Relationships among Smolt Size, Marine Growth, and Sea Age at Maturity of Atlantic Salmon (Salmo salar) in Northern Spain

Scale analysis indicated that two-sea-winter (2SW) Atlantic salmon (Salmo salar) had a greater growth increment during the first year at sea than 1SW of the same smolt year in the Rivers Narcea and Esva, but no differences were found between sea age-classes in the River Cares. Interannual variation in marine growth was synchronized among rivers. Variation among years was greater than variation between sea age-classes, suggesting that marine growth per se does not determine age at maturity. In the River Narcea, 2SW salmon were larger than 1SW at the end of the first marine period, but differences between sea age-groups were not significant in the other two rivers. Some of this variability could be attributed to differences in size at smolting; for two rivers (Esva and Cares), 1SW salmon had been larger as smolts than 2SW salmon. Length increment during the first marine growth period was inversely correlated with smolt size (age-1 smolts); in spite of that compensatory effect, large smolts tended to maintain their size advantage at the time of formation of the first marine annulus, as indicated by positive correlations between smolt size and length at the first sea winter.

Smolt size in relation to age at first maturity of Atlantic salmon (Salmo salar): the role of lacustrine habitat

Back-calculated growth and size of Atlantic salmon smolts were compared in two groups of river systems in Newfoundland. One group consisted of rivers dominated by lacustrine habitats while the other had rivers characterized by fluvial habitats. Back-calculated length at each age and smolt size was significantly higher for the rivers dominated by lacustrine habitats. Associated with this was a lower proportion of maiden large salmon in adult returns. These findings are discussed in relation to density in fresh water, environmental conditions at sea, and life-history strategy.

Smolt size in relation to age at first maturity of Atlantic salmon (Salmo salar): the role of lacustrine habitat

Back‐calculated growth and size of Atlantic salmon smolts were compared in two groups of river systems in Newfoundland. One group consisted of rivers dominated by lacustrine habitats while the other had rivers characterized by fluvial habitats. Back‐calculated length at each age and smolt size was significantly higher for the rivers dominated by lacustrine habitats. Associated with this was a lower proportion of maiden large salmon in adult returns. These findings are discussed in relation to density in fresh water, environmental conditions at sea, and life‐history strategy.

Influence of size, winter duration and density on sexual maturation of Atlantic salmon (Salmo salar) juveniles in Little Codroy River (southwest Newfoundland)

Factors affecting sexual maturation of Atlantic salmon (Salmo salar L.) juveniles in fresh water were analysed under wild conditions in Little Codroy River (southwest Newfoundland). Large size after the first year of life and short winters favoured maturation of age 1 + male parr. Incidence of maturing 1+ males was greater where high densities of parr (>0.2 individuals m 2; fish >6cm fork length) were recorded in the second season of growth. These results were discussed according to current knowledge on early maturation in Atlantic salmon.

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.

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.

Growth and sexual maturation in Atlantic salmon, Salmon, salar L., reared in sea cages at two different light regimes

Abstract. Immature 1-sea-winter (ISW) Atlantic salmon, Salmo salar L. were reared in sea cages under natural light or constant additional light from 15 October 1987 to 24 June 1988 when the fish were fin clipped according to photoperiod and reared in a common cage under natural photoperiod until maturation. The group subjected to constant additional light (LL) had an overall increase in growth rate, which indicates a seasonal growth pattern influenced by photoperiod. An advanced ovulation time in the LL group gives further support to the hypothesis that endogenous rhythms controlling growth rate have been influenced. Incidence of maturation was lowest in the LL group.

Progression of Coronary Arterial Lesions in Atlantic Salmon (Salmo salar) as a Function of Growth Rate

Development of coronary arteriosclerosis has been studied in all life stages of both wild and cultured Atlantic salmon (Salmo salar). Lesions accumulate slowly during juvenile growth in freshwater in both wild and cultured populations and increase sharply during early marine life; much of the progression occurs well before the onset of sexual maturity. Fewer than 5% of sexually mature Atlantic salmon (wild or fast-growing cultivated) were free of coronary lesions. Lesions were distributed over 45–85% of the length of the coronary artery. Lesions were less abundant and less advanced in a cultured strain of salmon that grew more slowly than another cultured, fast-growing strain. We conclude that prevalence and severity of lesions in Atlantic salmon accelerate in parallel with, and possibly in response to, those factors responsible for rapid growth in the sea. We discuss diet, endocrine changes associated with sexual maturation, metabolic aspects of parr–smolt transformation, and physiological stress as factors possibly influencing progression of lesions associated with rapid growth during the marine stage.

Effects of winter temperature and feeding regime on the rate of early maturation in Atlantic salmon ( Salmo salar) male parr

Individually identified Atlantic salmon parr were submitted to different combinations of temperature and feeding regime during their first winter. These treatments were designed to test for causal relationships between winter growth, body lipid level in spring as measured by the condition factor, and subsequent maturation. Maturation was observed almost exclusively in the lower modal group (presumptive 2-year-old smolts). Large and significant differences in winter growth performance and condition factor in spring were observed among treatments. Some variation in the rate of male parr maturation was observed among treatments as well, but the differences were not significant. The pattern of growth and change in condition factor before male parr maturation were different from that which had been observed before grilse and post-smolt maturation. The results of this study suggest that the threshold for lipid storage which initiates male parr maturation might be very low, and male parr maturation is thus not very dependent upon winter growth and spring lipid storage level.

Serum prolactin and sex steroids in Atlantic salmon ( Salmo salar) during sexual maturation

Serum prolactin (PRL), total estrogen and androgen levels were measured monthly from May to September in adult Atlantic salmon. The fish were kept in sea water with no significant osmotic changes throughout the sampling period. Serum PRL in sexually maturing males and females, which spawned in November, and three immature females reached maximum levels (mean 10.6 ng/ml) at the end of June and declined thereafter. A significant increase in total androgen and estrogen levels in the maturing fish was not found until August–September. The results did not indicate any primary role for PRL in the regulation of sexual maturation in Atlantic salmon. However, a permissive action of PRL should not be excluded. The possible participation of PRL in the preadaptation for fresh water migration is discussed.

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.

Responses of juvenile and sexually mature two-summer-old salmon ( Salmo salar L.) to prolonged swimming

Two-summer-old juvenile and sexually mature Atlantic salmon were forced to swim for 0.5, 1, 2, 4, 8 or 12 h at 50 cm/s (ca. 2.5 body length/s). Collapsed fish and fish swimming the whole test time were sampled for physiological analyses. Both the juvenile and mature fish exhibited an initial stress response to increased flow, as shown by the elevated plasma cortisol and lactate concentrations and by the changes in erythrocytic ATP and chloride concentrations. The physiological state of the mature males recovered well within 2–4 h of swimming. In contrast, the juveniles had continuously high plasma cortisol and lactate values with a large individual variation, indicating that the energy production for swimming was partially anaerobic. The collapsed fish showed clear signs of anaerobic metabolism. The results indicate that the aerobic capacity for prolonged swimming is lowered in juvenile salmon also beyond the time of smolt migration, whereas the mature males have a swimming capacity similar to wild parr. However, the responses of juvenile salmon to swimming in autumn are not similar to those observed on migrating smolt.

Chemical Composition of Maturing and Spawning Atlantic Salmon from Different Locations

Abstract We examined the relation between the environmental or nutritional background and the chemical composition of body tissues and reproductive success in wild (sea-run, river-captured, ocean-captured, landlocked) and hatchery-reared Atlantic salmon (Salmo salar). More essential fatty acids of the linolenic acid family (n-3 acids, also called ω-3 acids) occurred in eggs of wild Atlantic salmon that had the highest percentages of eyed eggs and were highest in ocean-caught Atlantic salmon. A marked decrease in zinc concentration occurred in eggs and semen of hatchery-reared fish fed one experimental diet; these fish yielded a lower percentage of eyed eggs than other first-time spawners. The correlation between zinc levels and spermatocrit in semen of males from five locations was highly significant (P ≤ 0.01). Ovaries of ocean-captured fish contained 2.5–5 times as much zinc, 5–7 times as much iron, and 4–62 times as much copper as did eggs from sexually mature Atlantic salmon from other sources. An app...

Aromatase activity in brain and pituitary of immature and mature atlantic salmon ( Salmo salar L.) parr

Brain homogenates from Atlantic salmon parr converted tritiated androstenedione to testosterone, estrone, and 17β-estradiol. The formation of estrogens was markedly higher in homogenates of whole brains from mature parr males than from immature parr males. The highest estrogen synthesis was found in the telencephalon and diencephalon. In both of these parts the estrogen production was higher in mature males than in immature males. There was no difference in estrogen formation by pituitaries from immature female and immature male parr, whereas the formation of estrogens and testosterone was higher in the mature male parr.