Mature Male Atlantic Salmon Parr Research Articles

The impact of two pesticides on olfactory-mediated endocrine function in mature male Atlantic salmon (Salmo salar L.) parr

Short-term exposure of the olfactory epithelium of mature male Atlantic salmon parr to either the pesticide simazine (concentrations 1.0 and 2.0 μg l−1) or the pesticide atrazine (concentration 1.0 μg l−1) significantly reduced the olfactory response to the female priming pheromone, prostaglandin F2α. In addition, the reproductive priming effect of the pheromone on the levels of expressible milt was also reduced after exposure to the individual pesticides (simazine 0.1, 0.5, 1.0 and 2.0 μg l−1 and atrazine 0.5 and 2.0 μg l−1). When the olfactory epithelium was exposed to a mixture of simazine and atrazine, (concentrations of 0.5:0.5 and 1.0:1.0 μg l−1), there was no significant reduction in the olfactory response when compared to the single pesticides at equivalent concentrations. In addition, exposure to a mixture of simazine and atrazine had no synergistic effect on the priming response, and plasma levels of testosterone, 11-ketotestosterone and 17,20β-dihydroxy-4-pregnen-3-one were similar in the groups of male parr exposed to the individual pesticides. Although the levels of expressible milt were reduced in all groups, there were no significant differences between the different pesticide treatments. The results of the study suggest that the two s-triazine pesticides have an additive and not a synergistic impact on olfactory-mediated endocrine function in mature male salmon parr.

Evidence of Successful Natural Reproduction between Brown Trout and Mature Male Atlantic Salmon Parr

Abstract Hybridization between Atlantic salmon Salmo salar and brown trout S. trutta is frequently reported, and the role of mature male Atlantic salmon parr has been suspected but never proven. Salmon fry were stocked into a headwater tributary stream of the Connecticut River, where no adult salmon are present. The stream has a self-sustaining population of brown trout. Enzyme electrophoresis revealed the presence of one hybrid (0.81% of the sampled population). The maternal species was identified as brown trout; therefore, the only possibility for the male parent was that it was a mature male Atlantic salmon parr. This is the first direct evidence of parr producing hybrid offspring in a totally natural setting and in the absence of any sea-return salmon.

Reproductive priming in mature male Atlantic salmon parr exposed to the sound of redd cutting

The sounds of a wild female Atlantic salmon cutting a redd were associated with significant increases in the levels of plasma 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) and of expressible milt in mature male parr, comparable with levels of the steroid and milt produced in parr exposed to the priming pheromone, prostaglandin F2a. Hence auditory cues may have a significant role in synchronising reproductive physiology in Atlantic salmon.

Reproductive priming in mature male Atlantic salmon parr exposed to the sound of redd cutting

The sounds of a wild female Atlantic salmon cutting a redd were associated with significant increases in the levels of plasma 17,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20βP) and of expressible milt in mature male parr, comparable with levels of the steroid and milt produced in parr exposed to the priming pheromone, prostaglandin F2a. Hence auditory cues may have a significant role in synchronising reproductive physiology in 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

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.