Male Atlantic Salmon Parr Research Articles

Effects of gonadectomy and androgen treatments on pituitary and plasma levels of gonadotropins in mature male Atlantic salmon, Salmo salar, parr--positive feedback control of both gonadotropins.

The aim of the present study was to clarify the role of feedback control on the (brain)-pituitary-gonadal axis in regulating FSH (gonadotropic hormone, GTH I) and LH (GTH II) in natural maturation in salmonids. In two experiments, 2-yr-old previously mature Atlantic salmon male parr were castrated or sham operated in the spring following their first reproductive season. In one of the experiments, castrated fish were also implanted with silicone elastomer capsules containing testosterone (T) or 11-ketoandrostenedione (11KA). The fish were sampled in July, September, and November (spawning period). Pituitary and plasma LH and FSH levels were measured using RIA and were lower in castrated than in sham-operated fish, indicating positive feedback on both FSH and LH. T, and to a lesser extent 11KA, increased pituitary LH content in castrated fish. The 11KA increased plasma and pituitary FSH levels, whereas T suppressed FSH in July and stimulated it in November. Plasma FSH levels peak earlier than LH, and it is suggested that if one or more feedback effects are involved in controlling the "all-or-nothing response," i.e., whether a fish will mature or not, a feedback effect on FSH is the most likely candidate.

Effects of Gonadectomy and Steroids on Plasma and Pituitary Levels of Somatolactin in Atlantic Salmon,Salmo salar

Somatolactin (SL) is a hormone recently isolated and characterized from fish pituitaries. Although the functions of SL are still largely unknown, it has been implicated in reproduction. In this study, the effects of gonadal steroids on SL secretion were investigated in Atlantic salmon male parr in two experiments. In both, mature males were gonadectomized in the autumn and implanted with Silastic capsules containing testosterone (T), 11-ketoandrostenedione (11kA), or 17α,20β-dihydroxy-4-pregnene-3-one (20-P), gonadectomized alone, or sham-operated. In addition, immature males were implanted with T or 11kA in experiment 1. After 4–5 weeks pituitaries and plasma were sampled and SL levels measured by radioimmunoassay (RIA). Plasma levels of T, 11-ketotestosterone, and 20-P were also measured by RIA. In experiment 1, initial immature males had lower (0.7±0.4 ng/ml) plasma SL levels than initial mature males (3.3±0.4 ng/ml), whereas pituitary content was not influenced. Gonadectomy significantly reduced both plasma SL levels (experiment 1, sham controls 5.6±0.5 ng/ml, castrated 1.6±0.5 ng/ml; experiment 2, sham controls 6.5±1.1 ng/ml, castrated 3.3±0.4 ng/ml) and the pituitary content of SL (experiment 1, sham controls 1206±187 ng/pituitary, castrated 663±104 ng/pituitary; experiment 2, sham controls 1043±199 ng/pituitary, castrated 629±70 ng/pituitary), suggesting that the testes stimulated the synthesis and release of pituitary SL. Overall, the effects of steroid replacement were inconsistent between the experiments, although in experiment 2 castrated males receiving the highest dose of T had significantly higher plasma SL levels (8.2±1.2 ng/ml) than all other castrated groups (1.8–4.3 ng/ml).

Alternative reproductive tactics in atlantic salmon: factors affecting mature parr success

In Atlantic salmon, as in most salmonids, males can mature early in the life cycle, as small freshwater fish, termed parr, and/or undergo a sea migration before maturing as full–size adults. The alternative life histories are contingent on environmental and social circumstances, such as growth rate, territory quality or any other factor that affects the individual9s state. In order to model the choice of life history in this group of commercially valuable species, it is necessary to understand not only the relative contribution of the different male types to subsequent generations, but also to know the factors that affect reproductive success in each type. In this paper we present the results of a study designed to investigate the factors that affect the reproductive success of mature parr. We used highly polymorphic minisatellite DNA markers to analyse paternity in a series of mating experiments where the number and body size of parr were manipulated. The fraction of eggs fertilized by mature parr ranged from 26 to 40 per cent, with individual parr fertilizing up to 26 per cent of the eggs. A strong positive correlation was found between parr size and reproductive success. The relative success of parr decreased with increasing parr number. Data from this and other studies on variation in the timing and degree of parr reproductive success are discussed in relation to the evolution of male mating strategies and life history in salmonids.

Sublethal effects of a carbamate pesticide on pheromonal mediated endocrine function in mature male Atlantic salmon (Salmo salar L.) parr

The sublethal effect of the carbamate pesticide carbofuran on the priming pheromonal system of Atlantic salmon (Salmo salar L.) was investigated. Previous studies have demonstrated that ovulated female salmon release a priming pheromone in their urine (considered to be an F-type prostaglandin) which is subsequently detected by mature male salmon and results in increased levels of plasma sex steroids and expressible milt. In the present study, electrophysiological recordings from the olfactory epithelium of mature male salmon parr indicated that the responses to prostaglandin F2α (PGF2α) were significantly reduced at nominal concentrations of carbofuran as low as 1.0 µg l-1, and the threshold of detection was reduced 10-fold. A 5 day exposure to carbofuran significantly reduced the ability of male parr to respond to PGF2α stimulation. The priming effect of PGF2α on milt and plasma 17,20β-dihydroxy-4-pregnen-3-one levels were abolished at water concentrations at and above 2.7 µg l-1. In addition, the priming effect of PGF2α on plasma testosterone and 11-ketotestosterone concentrations was abolished at water carbofuran concentrations above 6.5 µg l-1. Exposure to similar concentrations of carbofuran also resulted in a reduction in the levels of free and glucuronidated steroids in the bile of PGF2α primed male parr. The effect of carbofuran on the priming response did not appear to be due to a direct effect on the testes, since the ability of testes to respond to pituitary extract stimulation in vitro was not impaired in carbofuran-exposed males. Carbofuran appeared to reduce significantly or abolish the priming pheromonal system in mature male parr by directly affecting the ability of the olfactory system to detect PGF2α, although the toxicological mechanism involved is as yet unknown. The results are therefore discussed in relation to the possible sublethal effects of carbofuran on reproduction in the Atlantic salmon.

Sublethal effects of the pesticide Diazinon on olfactory function in mature male Atlantic salmon parr

Diazinon, an organophosphate pesticide, had a sublethal effect on the olfactory system of mature male Atlantic salmon parr. The olfactory responses of the parr to prostaglandin F2a (PGF2a) were studied after exposure of the epithelium to different concentrations of Diazinon in water. Electrophysiological recordings from the epithelium indicated that the responses to this prostaglandin were significantly reduced at nominal concentrations as low as 1.0μg l−1 and the threshold of detection was reduced 10‐fold at 2.0 μg 1−1 . Mature male salmon parr exposed for a period of 120 h to Diazinon (nominal concentrations 0.3, 0.8, 1.7, 2.7, 5.6, 13, 28 and 45 μg 1 −1) also had significantly reduced levels of the reproductive steroids, 17,20β‐dihydroxy‐4‐pregnen‐3‐one, testosterone and gonadotrophin II in the blood plasma after priming with ovulated female salmon urine. Both prostaglandin F2a and ovulated female urine are known to have important roles in synchronizing reproductive physiology and behaviour in salmonids as well as other fish species. The results are therefore discussed in relation to the possible sublethal effects of Diazinon on reproduction in the Atlantic salmon and possible effects on populations of salmonids.

Sublethal effects of the pesticide Diazinon on olfactory function in mature male Atlantic salmon parr

Sublethal effects of the pesticide Diazinon on olfactory function in mature male Atlantic salmon parr

Stimulatory and inhibitory effects of testosterone on testes in Atlantic salmon male parr

Stimulatory and inhibitory effects of testosterone on testes in Atlantic salmon male parr

Stimulatory and inhibitory effects of testosterone on testes in Atlantic salmon male parr

Immature 1‐year‐old Atlantic salmon Salmo salar parr were implanted with Silastic capsules of different sizes filled with testosterone (T). Testosterone had both positive and negative effects on testicular weights, spermatogenesis and steroidogenesis. The positive effects: higher incidence of males with enlarged gonads, spermiation, and high plasma levels of 11‐ketotestosterone (11‐KT) and 17,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P), were most pronounced in males treated with small T capsules. The negative effects: suppression of gonadal development and depressed plasma levels of 11‐KT and 17,20β‐P compared with mature controls, were most evident in fish treated with large T capsules.

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.

An electrophysiological study on the effects of pH on olfaction in mature male Atlantic salmon (Salmo salar) parr

The olfactory responses of mature male Atlantic salmon (Salmo salar L.) parr to known odorants were studied after exposure of the olfactory epithelia to water of varying pH. Electrophysiological recordings from the olfactory epithelia indicated that the responses of fish to both testosterone and urine from ovulated female Atlantic salmon were significantly reduced at pH 5·5 and 4·5 and abolished at pH 3·5. Concentration response studies indicated that at pH 5·5 and 6·5 significantly higher concentrations of testosterone and urine were required to produce the same amplitude responses as controls. Both testosterone and urine have previously been shown to be important chemical cues eliciting behavioural and physiological responses in Atlantic salmon. The results are therefore discussed in relation to the possible sublethal effects of acidification on reproduction and behaviour of Atlantic salmon and the effects on salmonid stocks.

An electrophysiological study on the effects of pH on olfaction in mature male Atlantic salmon (Salmo salar) parr

The olfactory responses of mature male Atlantic salmon (Salmo salar L.) parr to known odorants were studied after exposure of the olfactory epithelia to water of varying pH. Electrophysiological recordings from the olfactory epithelia indicated that the responses of fish to both testosterone and urine from ovulated female Atlantic salmon were significantly reduced at pH 5·5 and 4·5 and abolished at pH 3·5. Concentration response studies indicated that at pH 5·5 and 6·5 significantly higher concentrations of testosterone and urine were required to produce the same amplitude responses as controls. Both testosterone and urine have previously been shown to be important chemical cues eliciting behavioural and physiological responses in Atlantic salmon. The results are therefore discussed in relation to the possible sublethal effects of acidification on reproduction and behaviour of Atlantic salmon and the effects on salmonid stocks.

The role of urine in sibling recognition in Atlantic salmon Salmo salar (L.) parr

The ability of Atlantic salmon ( Salmo salar L.) parr to discriminate between the urine from sibling and non-sibling fish was studied by using electrophysiological and behavioural techniques. Urine was collected from four sibling groups of Atlantic salmon parr which had been reared separately. Urine from all four groups were potent odorants in the Atlantic salmon parr, eliciting responses that were recordable from the olfactory epithelium. However, the mean recorded responses were significantly greater in Atlantic salmon parr that were stimulated with the urine from sibling than from non-sibling fish. Urine from all four groups elicited display behaviour in the Atlantic salmon parr which often occurs during aggressive interactions between parr when defending territories. Atlantic salmon parr also moved towards the source of sibling urine but moved away from non-sibling urine. The results are discussed in relation to the role of urine and the adaptive significance of sibling recognition in the Atlantic salmon.

The use of genetic marking to assess the reproductive success of mature male Atlantic salmon parr (Salmo salar, L.) under natural spawning conditions

The reproductive success of mature male Atlantic salmon parr (Salmo salar) under natural spawning conditions was estimated using the polymorphism at the MEP‐2* locus as a genetic marker. The percentage of eggs per redd fertilized by parr varied considerably over the five redds examined (0·9–27.7%, mean 10·8%), but a gametic contribution from mature parr was detected in each case. Parr reproductive success has important implications for the population structure and evolution of the Atlantic salmon through its effect on gene flow.

17 alpha,20 beta-dihydroxy-4-pregnen-3-one 20-sulphate is a potent odorant in precocious male Atlantic salmon (Salmo salar L.) parr which have been pre-exposed to the urine of ovulated females.

Electrophysiological recordings from the olfactory epithelium have shown that 17 alpha,20 beta-dihydroxy-4-pregnen-3-one 20-sulphate (17,20 beta-P-sulphate; a conjugate of the oocyte-maturation-inducing steroid in teleosts) is a potent odorant in precocious male Atlantic salmon (Salmo salar L.) parr. However, the olfactory epithelium of these fish only appeared to be responsive to the steroid after stimulation with the urine of ovulated female Atlantic salmon. Immature fish did not respond at any time. Stimulation with urine from immature and precocious male Atlantic salmon parr did not make the olfactory epithelium of precocious male salmon parr responsive to the steroid. 17,20 beta-P-sulphate was found in the urines of ovulated females, precocious male parr and mature male Atlantic salmon. The findings are discussed in relation to the possible role of 17,20 beta-P-sulphate in the physiology of Atlantic salmon.

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.

Effects of Elevated Winter Temperature on Seawater Adaptability, Sexual Rematuration, and Downstream Migratory Behaviour in Mature Male Atlantic Salmon Parr (Salmo salar)

In experiments with two different salmon (Salmo salar) stocks, elevated winter temperatures (Celsius) 4–9° above the ambient increased the degree of testicular resorption in previously mature male Atlantic salmon parr. Two-summer-old mature male parr maintained at a temperature 9° over the ambient for 5 mo (January–May) showed an increase in hypoosmoregulatory ability when challenged in seawater at the time of smoltification whereas parr kept at elevated temperature for various 2-mo periods (January–February, February–March, or March–April) failed to show this improvement. Furthermore, previously mature males kept at an elevated winter water temperature for either 2 or 5 mo showed a lower incidence of sexual rematuration, and consequently a higher mean growth rate, after one summer in sea pens. A river release experiment showed that rearing previously mature males at 4–7° above the ambient water temperature from December to April increased the number of downstream migrating fish to a level similar to that of immature smolts. We suggest the use of a simple method for enhancing the potential yield of ranched and cultured salmon from early maturing males by removing them from the stock population and rearing them over winter in heated water.

Effects of castration and androgen treatment on aromatase activity in the brain of mature male Atlantic salmon ( Salmo salar L.) parr

Brain homogenates from male Atlantic salmon parr aromatized tritiated androstenedione to estrogens. The aromatase activity in homogenates of whole brains from castrated male parr was lower than that in homogenates from sham-operated male parr in autumn. This was also found in homogenates of the telencephalon and diencephalon, but not in homogenates of the tectum opticum. Treatment of castrated males with testosterone (T) and 11-ketoandrostenedione (OA) increased the aromatase activity in whole brains. T, but not OA, also significantly increased aromatase activity in all brain parts. In spring, half a year after the peak breeding period, mature pan males had a lower aromatase activity in telencephalon, diencephalon and tectum than that found in castrated males in autumn, whereas immature males displayed an even lower level of activity.

Role of Fat Stores in the Maturation of Male Atlantic Salmon (Salmo salar) Parr

We provide evidence that in male Atlantic salmon (Salmo salar) parr, maturation is suppressed when mesenteric fat fails to exceed an undefined level by May. In nonmaturing parr the postwinter increase in total lipids began in May, while the mesenteric store started filling in June. However, in male parr which would have matured, total lipids started increasing a month earlier, in April, and the mesenteric store started filling in May. Consequently, maturing male parr had significantly more mesenteric fat than nonmaturing fish by June. Mesenteric fat is needed for maturation. Levels continued to increase in nonmaturing parr during autumn months, but had declined in maturing parr by September. This depletion of mesenteric fat in maturing males coincided with increases in the gonadosomatic index from 0.05 to 10% and with reductions in both feeding and growth. Fasting during spring months delayed increases in total lipids and fat accumulation into the mesenteric store until June and suppressed maturation rates of male parr. The internal decision to suppress maturation is therefore dependent on mesenteric fat levels increasing in May. However, this requires the prior replenishment of other stores in April. A model is proposed to explain the physiological link between fat accumulation during spring and the initiation of maturation.

Differences in growth between maturing and non‐maturing male Atlantic salmon, Salmo salar L., parr

Sibling male Atlantic salmon parr that matured tended to be the larger fish in January, but their monthly specific growth rates between January and July did not differ from those of non‐maturing fish. Maturing fish had lower condition factors in March, but greater increases in condition factor during April, exceeding those of non‐maturing males by May. In maturing males, feeding rates between July and September, and specific growth rates in August and September, were lower than those of immature fish. Consequently, the mean size of immatures equalled or exceeded that of maturing males by October. Maturation rates were strongly correlated with increases in mean condition factor only during April.

Suppression of maturation in male Atlantic salmon ( Salmo salar L.) parr by reduction in feeding and growth during spring months

Four sibling populations of Atlantic salmon parr were subjected to seasonal variations in feeding opportunity, from February to September. Growth was restricted relative to a control population by increased density. During 2-month periods growth was increased by reducing density. Consequently different populations grew faster than controls at different times of year. In September the mean size of fish did not differ between populations, but percentage maturation did. Populations growing relatively fast during spring had high percentages of mature males, similar to the control population, while those growing relatively fast in winter and summer, but slowly in spring, had fewer mature males. In experiments where growth was suppressed by fasting fish in alternate weeks during different 2-month periods, maturation was suppressed by fasting in the spring. It is concluded that if spring growth is inadequate, maturation is switched off physiologically. This growth-related suppression of maturation may contribute to the correlation between growth and maturation rates in salmonids. We suggest it is adaptive, preventing maturation when the growing season starts late, and is too short for fish to acquire sufficient reserves for spawning.