Mature Atlantic Salmon Research Articles

Steroid release from separated theca and granulosa layers of Atlantic salmon (Salmo salar) ovarian follicles: the effects of a purified salmon gonadotrophin preparation

Theca and granulosa layers were removed from ovarian follicles of mature Atlantic salmon (Salmo salar) and were separately incubated under sterile conditions with and without a partially purified salmon gonadotrophin preparation (GTH). Aliquots of the incubation media were removed at intervals and analysed for the steroids 17α, 20β-dihydroxy-4-pregnen-3-one (17α20βP), 17α-hydroxyprogesterone, progesterone, androstenedione, testosterone and oestradiol. The biosynthesis of C19 and C21 steroids was very largely restricted to the thecal tissue and was markedly stimulated in the presence of GTH. Androstenedione (max 65 ng/ml) and testosterone (max 14 ng/ml) were released from the earliest stages of incubation whereas the release of 17α-hydroxyprogesterone (max 51 ng/ml) and progesterone (max 5.5 ng/ml) commenced only after a lengthy induction period. A trace (1.0 ng/ml) of 17α20βP was produced by the theca in the presence of GTH but oestradiol was not detected. The granulosa preparations released levels of 17α-hydroxyprogesterone and androstenedione only marginally above the detection limits (ca 0.7 ng/ml) and there was little stimulation of output with GTH. Oestradiol (max 4 ng/ml) was released only in the presence of GTH. 17α20βP, progesterone and testosterone were not detected as products of this tissue. These results, together with those derived earlier from incubations of complete follicles support the view that the synthesis of 17α20βP is essentially a two-cell process in which 17α-hydroxyprogesterone produced in the theca is subject to the action of steroid 20β-hydroxysteroid dehydrogenase in the granulosa. The temporal pattern of release of steroids in these and earlier experiments is considered in relation to mechanisms of steroid biosynthesis and to their possible roles in oocyte final maturation.

In vitro biosynthesis of 17α,20β-dihydroxy-4-pregnen-3-one by the ovaries, testes, and head kidneys of the Atlantic salmon Salmo salar

Ovaries, testes, and head kidneys of sexually mature Atlantic salmon, Salmo salar, biosynthesized 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHP) from equimolar amounts of [ 3H]pregnenolone plus [4- 14C]progesterone in vitro. The 3H: 14C isotope ratios of steroid metabolites indicated that the biosynthetic pathways to 17α,20β-diOHP in the testes differed from those observed in the ovaries and head kidneys. [4- 14C]Progesterone appeared to be the principal precursor of 17α,20β-diOHP in the testes, whereas both precursors were efficiently biotransformed to 17α,20β-diOHP in the ovaries and head kidneys. 17α-Hydroxy-4-pregnen-3-one (17α-OHP) was the immediate precursor to 17α,20β-diOHP in all tissues. However, appreciable amounts of 17α,20β-diOHP accumulated in vitro in the testes only in the presence of exogenous [ 14C]progesterone. Incubation of the testes, ovaries, and head kidneys with [ 14C]pregnenolone resulted in high yields of 17α,20β-diOHP in the ovaries and head kidneys but no detectable amounts of the steroid in the testes. The results confirm that progesterone is the favored precursor to 17α,20β-diOHP in the testes. The results also suggest that the head kidneys may be an excellent cellular source of 17α,20β-diOHP in both male and female Atlantic salmon and may play an important role in the sexual maturation process in this fish. It is suggested that biosynthetic control mechanisms affecting 17α,20β-diOHP synthesis and/or spermiation and ovulation may differ in male and female Atlantic salmon.

Selection against parr maturation in Atlantic salmon

The feasibility of using scale characteristics to detect maturation as parr of anadromous male Atlantic salmon was examined. Smolt age and growth rate were found to be reliable indicators of prior maturation, whereas scale morphology did not differ between maturation phenotypes. Although determination of prior maturation was not 100% efficient, the resulting selection intensities would allow for effective artificial selection against anadromous males which had matured as parr.

Protease activities and carotenoid levels during the sexual maturation of Atlantic salmon ( Salmo salar)

Protease activities in the digestive tract and carotenoid levels in flesh, ovaries and plasma were determined in Atlantic salmon ( Salmo salar) in their third sea year during the period from early March until December. Protease activities in the digestive tissues changed significantly during the maturation process: the fish have higher enzyme activities in early maturation and lower in the later stages until maturity. The trypsin-like isozymes were studied by IEF electrophoresis during maturation, and variations observed were possibly genetic. The level of astaxanthin in flesh and ovaries decreased significantly during sexual maturation, but the total amount in the ovaries continued to increase. The covariance between astaxanthin in the plasma and trypsin-like activities in the digestive tissues was significant, and the level of astaxanthin in the plasma was also influenced by time and stage of sexual maturation.

Observations on Renibacterium salmoninarum and the salmonid egg

Renibacterium salmoninanun cells were located entering the developing oogonia of experimentally infected juvenile rainbow trout Salmo gairdneri. These cells appeared to be viable. R. salmoninanun was cultured from the surface and contents of eggs from a mature Atlantic salmon Salmo salar even though the eggs had been bathed during water-hardening in erythromycin phosphate, penicillin or proflavin. No bacteria were detected in the fry hatched from these infected eggs.

Response to individual selection for age at sexual maturity in Atlantic salmon

Atlantic salmon ( Salmo salar) that mature sexually at 1 year of age (as parr or precocious males), at 4 years of age (after two winters in the sea) and at 5 years of age (after three winters in the sea) were used to study response to individual selection for age at sexual maturity. Six mating groups were made: between fish of the same age (4 × 4 and 5 × 5); reciprocal matings between 4- and 5-year-old fish (4 × 5 and 5 × 4); and matings between 1-year-old precocious males and 4- and 5-year-old females (1 × 4 and 1 × 5). Parental age at sexual maturity was found to influence markedly the offspring age at sexual maturity. The heritability for age at maturity in the sea was estimated at 0.48 ± 0.20 from the offspring—dam regression. It is concluded that there is considerable opportunity to alter the age at sexual maturity in Atlantic salmon through selection. Evidence was found that maturation of parr is a heritable trait and that it is independently inherited from maturation in the sea.

Inheritance of developmental rates in Atlantic salmon, Salmo salar L.

Alm (1959) demonstrated that rapid sexual maturation in salmonids accompanied rapid growth. In experiments at Almondbank, the inference that maturation and growth rates were aspects of a common developmental tempo was tested by comparing rates of growth, smolting and sexual maturation among 12 batches of progeny of three female Atlantic salmon and four males of differing age at first maturity. The present paper demonstrates that the incidence of maturation of males at age 1+, as parr, was significantly higher ( P < 0.01) among progeny of male parr than among progeny of males of total age 2+ and 3+ years (1.1+ and 2.1+). Further, the incidence of maturity as parr was increased 5.4 times (1.4–14.7 times) and a further 1.7 times (1.6–1.7) over two and three generations respectively, in selection experiments using mature parr as sires. It is suggested that selection for rapid growth and late maturation in Atlantic salmon may be incompatible objectives, but that these objectives may be achieved best by a combination of selection for rapid development combined with environmental suppression of maturation.

The downstream migration of precociously mature Atlantic salmon, Salmo salar L, parr in autumn; its relation to the spawning migration of mature adult fish

The autumn emigration of juvenile Atlantic salmon, Sulmo salur L. from the Girnock Burn, Aberdeenshire, is shown to be comprised of two components. Precociously mature males and sexually immature fish differ in their dependence on seasonal and biological cues for the release of migratory behaviour. The emigration of ripe mature male parr is shown to follow the entry of mature adult salmon to the stream; when adult fish are prevented from entering the stream, the emigration is induced by seasonal factors. Spent male parr tend not to participate in the autumn emigration. The emigration is considered to be principally an appetitive phenomenon which maximizes the number of precociously mature males attaining sexual contact with adults.

A note on the significance of the olfactory sense upon sexual maturation in Atlantic salmon ( Salmo salar L.)

The significance of the olfactory sense upon sexual maturation in Atlantic salmon was studied. Eighty-one salmon in the salt-water stage were rendered anosmic by cauterizing the olfactory mucosa, a further 81 fishes served as a reference group. All fishes were raised in the same floating net cage. The olfactory mucosa was destroyed once more during the experimental period in the already anosmicized group in order to avoid regeneration. After 5 months, the sexual maturation in both groups was determined by visual inspection of the gonads, and ranged on a six-step scale. The results indicate that the olfactory sense is not mandatory to late development of sexual maturity. No difference was found between the two groups with regard to growth during the experimental period. This finding indicates that the olfactory sense is of little importance to salmonids in the competition for food in a fish-farming environment.

Identification and distribution of the Leydig cell homolog in the testis of sexually mature Atlantic salmon ( Salmo salar)

Identification and distribution of the Leydig cell homolog in the testis of sexually mature Atlantic salmon ( Salmo salar)