Atlantic Salmon Salmo Salar Parr Research Articles

Maturation of male age‐0 Atlantic salmon following a massive, localized flood

Maturation of male age‐0 Atlantic salmon Salmo salar parr in New England, U.S.A. streams is rare (˜5%), but age‐0 parr maturation was high (74%) by autumn in the Sawmill River following a massive, localized flood. Maturation was low in two other study streams (3, 7%) in the same year as the flood, and in the Sawmill River (6%) and the other rivers (5%) in the subsequent year, suggesting that high maturation rates were related to the flood. The high age‐0 maturation rates appear to have been the result of greater growth opportunity following the flood. Masses of fish in October were two‐fold greater in the Sawmill River (13·2 g) than in the other rivers (6·5, 6·9 g). Mechanisms contributing to the fast growth may include community reorganization following the flood and water temperature differences among rivers. The flood caused an age‐0 year‐class failure for brook trout Salvelinus fontinalis and brown trout Salmo trutta and a large reduction (69%) in the number of salmon compared to the other rivers, possibly reducing competition or agonistic interactions among remaining fish. Average water temperatures were slightly warmer in the Sawmill River (17·0° C) than in the other rivers (15·5, 14·9° C). By influencing community structure and growth of remaining fish, it appears that a strong environmental disturbance can also alter the direction and timing of life histories in Atlantic salmon.

Allozyme heterozygosity and development in Atlantic salmon, Salmo salar

The development of Atlantic salmon (Salmo salar) parr was monitored during the first year in a fresh-water hatchery environment to test whether multilocus heterozygosity (computed for six allozyme loci: s AAT-4*, IDDH-1*, IDDH-2*, IDPH-3*, s MDH-3,4* andm MEP-2*) is associated with growth (body mass, fork length) and maturity status (mature male parr). The length frequency distribution of population was unimodal in September, but was clearly bimodal by December. UMG fish tended to be more heterozygous and had higher growth rates than LMG fish. The heterozygosity of UMG fish and mature male parr (MMP) did not differ significantly but MMP showed lower growth rates than UMG. There were positive correlations between the number of heterozygotic loci and the fork length, weight or growth rates of individuals.

Social dominance, prior residence and the acquisition of profitable feeding sites in juvenile Atlantic salmon

Twelve groups of 10 Atlantic salmon Salmo salar parr were screened for dominance in small tanks with a single localized food source using a serial removal method and the top, middle and bottom two fish in each group were classified as high, medium and low social status, respectively. These 72 ranked fish were weighed and formed into four groups or waves, each consisting of six fish of each status category. The fish were given dye marks according to status and wave and were then introduced into an artificial stream in four waves over a 12‐day period. Patterns of settlement/emigration were recorded over a 2‐month period, at the end of which the fish were removed from the stream, identified and reweighed, and daily specific growth rates calculated. Fifty‐one fish established feeding stations in the flume, the remainder emigrating via a downstream trap. The average growth rate over the 2‐month period was 0·87% day−1. Probability of settlement and growth rates following settlement were significantly higher in fish from the earlier waves. In contrast, salmon that were dominant in the initial trial were less likely than subordinate fish to settle in the experimental stream and showed lower postsettlement growth rates. The possibility that fish have individually consistent behavioural profiles that promote success in different competitive environments is discussed with reference to published literature for other groups. A small‐scale trial at the end of the main experiment confirmed the prior residence effect and demonstrated that 1 day was sufficient for such an effect to be evident.

Daily feeding rhythms in Atlantic salmon I: feeding and aggression in parr under ambient environmental conditions

Daily feeding patterns of tank‐reared Atlantic salmon Salmo salar parr under ambient conditions and their relationship with patterns of aggression were investigated during spring and autumn. A single, early afternoon feeding peak was observed during spring but no consistent pattern emerged from the autumn trial (fish did tend to feed in synchrony, even though the population's feeding pattern varied between days). Aggression was highest at first light during both spring and autumn, reducing thereafter throughout the day. Feeding and aggression were out of phase during spring, with the level of feeding increasing as aggression decreased. It is suggested that the high levels of early morning aggression are associated with re‐establishment of the social order that breaks down after a period of darkness; in the spring this may have inhibited feeding.

Erratum: The relation between redd counts and Atlantic salmon (Salmo salar) parr populations in the Dennys River, Maine

Erratum: The relation between redd counts and Atlantic salmon (Salmo salar) parr populations in the Dennys River, Maine

Comparison between parr and smolt Atlantic salmon (Salmo salar) α subunit gene expression of Na+/K+ ATPase in gill tissue

Increases in branchial Na(+)/K(+) ATPase activity during seawater adaptation of euryhaline fish species, have been well documented. During the parr-smolt transformation of salmonids this activity increases two to five fold and is used as an indicator of the transformation. In order to improve the understanding of differences in enzyme activity found between Atlantic salmonSalmo salar parr and smolt fish, we investigated the gene expression of the Na(+)/K(+) ATPase α-subunit(s) in gill tissue. Gill mRNAs were analyzed and quantified at distinct time points using Northern and Dot blot techniques. We amplified by PCR, a conserved region of the cDNA encoding the Na(+)/K(+) ATPase α-subunit of the rainbow troutOncorhynchus mykiss. The PCR products (670 bp) were cloned and all independent clones showed a sequence corresponding to the α subunit of the Na(+)/K(+) ATPase. The fragments obtained appeared as a heterogenous population of three sequences showing, when compared between each other, 86 to 93% identity. This suggests that different allelic forms of the α-subunit are expressed in gill tissue. Hybridization studies performed with these PCR probes revealed two mRNA species, a major 3.7 kb transcript and a minor transcript of 1.8 kb. Enhanced 3.7 kb transcript levels are concurrent with elevated enzyme activity in smolts during the March and April parrsmolt transformation of Atlantic salmon. Interestingly, our study disclosed that smolt fish only displayed a two-fold increase in transcript levels when compared to parr whereas enzyme activity showed a 4 to 5 fold increase. This suggests that the increase in the 3.7 kb mRNA content of gill tissue is probably not the only mediator leading to the rise in enzyme activity during parr-smolt transformation.

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.

Plasma levels of insulin and liver glycogen contents in one- and two-year old Atlantic salmon (Salmo salar L.) during the period of parr-smolt transformation

Plasma levels of insulin were measured by specific radioimmunoassay in 1-year and 2-year old Atlantic salmon (Salmo salar) parr during the period of parr-smolt transformation. The two-year old fish were of two different categories; silvering pre-smolts and previously mature male parr. If insulin plays an important role in parr-smolt transformation and/or subsequent osmoregulatory changes it was expected that the pre-smolts would show a different insulin profile compared to the mature male parr and one-year old parr, both of which show impaired hypoosmoregulatory ability compared to smolts. Measurements were taken during two separate years. Between January and April both categories of two-year old fish had generally higher plasma levels of insulin compared to the non-smolting one-year old parr. In the pre-smolts insulin levels ranged from 4.0 to 7.9 ng ml(-1), and from 7.8 to 16.7 ng ml(-1) in 1990 and 1992 respectively, while in the previously mature males the same respective values were from 4.3 to 10.0 ng ml(-1), and from 6.6 to 24.1 ng ml(-1). In the two-year old fish, whether pre-smolts or mature males, plasma insulin levels peaked between 1-2 months before final smoltification, after which insulin titers declined sharply. In 1990, the 1-year old parr showed a dual peak in plasma insulin. Insulin first peaked in February (7.8 ng ml(-1)), and then again in April-May (7.7 ng ml(-1)), while in 1992 the 1-year old parr showed a number of smaller transient peaks (5-7 ng ml(-1)) between March-May, followed by sharp elevation of insulin levels in June. Liver glycogen contents were at their highest (3.5-5.0 g 100 g(-1) I liver wet weight) in March in both 1-year and 2-year old fish. Glycogen levels were low during the later stages of parr-smolt transformation, before rising again in June in both the 1-year old and precociously mature parr, but not in the smolts.

Effects of Dietary Iron Concentrations on the Cytochrome P450 System of Atlantic Salmon (Salmo salar)

Groups of Atlantic salmon (Salmo salar) parr were fed a basal diet containing 27 mg Fe∙kg feed−1 supplemented with different iron levels (0, 80, and 160 mg∙kg−1, respectively) for 8 wk. After this period, a subgroup of each iron regime was treated intraperitoneally with β-naphthoflavone (BNF), a potent inducer of cytochrome P450 1A1 in fish. Differences between the iron regimes were observed in hepatic iron content, which was higher in the high-iron group, and in P450 1A1 levels and monooxygenase activity, measured as 7-ethoxyresorufin O-deethylase (EROD), which were lower in the high-iron group. Differences were also observed in the induction response of P450 1A1 and EROD to BNF. Levels of a constitutive isozyme denoted P450con, belonging to the P450 3A subfamily, did not respond to the dietary iron in the same manner, demonstrating selective regulatory effects of iron on different P450 isozymes.

Acquired protection in Atlantic salmon Salmo salar parr and post-smolts against pancreas disease

Experimental infection of Atlantic salmon Salrno salar parr and post-smolts with pancreas disease infective kidney homogenate induced a highly significant protection against the disease following exposure to challenge infections at either 3 , 4 , 7 or 9 mo after the initial infection. Protection was maintamed in fish infected as parr and exposed to a challenge infection following smolting and sea water transfer. A carrier status was not demonstrated in immune fish since homogenates of kidneys taken 1 and 2 wk post-challenge were not infective, unlike homogenates of kidneys from non-immune fish.

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.

Cells with affinity for periodic acid – Schiff are present in the pars intermedia of Atlantic salmon

Examination of pituitaries from two populations of Atlantic salmon (Salmo salar) parr held under natural photoperiods revealed at least two histologically distinct cell types. One type has fine granules with affinity for lead hematoxylin (PIPbH). Another type, hitherto believed to be absent in salmonids, has larger granules which are Schiff-positive (PIPAS). These cells are significantly (P < 0.05) shorter and narrower and have significantly smaller nuclei (P < 0.05) than the PIPbH type. No evidence was found for ascribing to the PIPAS cells the functions assigned to them in other species: melanophore control and reproduction. However, PIPAS granules became evident only during fall-winter, when the smolting process begins. The incidence of these cells rose and then declined sharply during this period, suggesting a possible role in some aspect of smoltification. While the role of these PIPAS cells deserves further study, their presence is in itself important from an evolutionary point of view.

Response and Recovery of Brain Acetylcholinesterase Activity in Atlantic Salmon (Salmo salar) Exposed to Fenitrothion

Atlantic salmon (Salmo salar) parr were exposed to a number of concentrations of either technical grade fenitrothion or an operational formulation of the pesticide for 7 d or to the operational formulation for two, 24 h periods separated by 7 d. Brain acetylcholinesterase (AChE) activity decreased as concentration, of fenitrothion increased. Recovery period was directly related to amount of depression, with recovery of AChE from exposure to 0.004 μL/L fenitrothion taking less than 1 wk. Samples must be taken soon after spray operations to detect exposure to such low levels of fenitrothion through AChE monitoring.

Smolting Status of Downstream Migrating Atlantic Salmon (Salmo salar) Parr

Significant numbers of Atlantic salmon (Salmo salar) parr have been observed to accompany seaward migrating smolts in some rivers. Downstream migrating parr in Freshwater River Newfoundland, have lower salinity tolerance and branchial Na+–K+ ATPase activity than smolts. However, moisture content in downstream migrating parr was similar to that of smolts; both groups had higher mean moisture content than nonmigratory parr. Mean plasma sodium concentration was significantly higher than in smolts, but somewhat lower than in nonmigratory parr. Elevated moisture levels and slightly depressed plasma sodium concentrations are consistent with the view that seaward movement is associated with osmoregulatory imbalance in both parr and smolts. Brackish water found in estuaries appears important for gradual development of salinity tolerance in these migrants.

Plasma electrolytes, gill aluminum content, and gill morphology of juvenile Atlantic salmon (Salmo salar) and brook trout (Salvelinus fontinalis) indigenous to acidic streams of Nova Scotia

Plasma electrolytes and gill [Al] were determined and gill morphology and histology were examined in Atlantic salmon (Salmo salar) parr and brook trout (Salvelinus fontinalis) from feral populations in acidic streams of southwest Nova Scotia. Plasma [Na+] and [Cl−] were lowest in fish from streams with the lowest pH levels, but there were no correlations between plasma [Na+] or [Cl−] and exchangeable [Al] in streams for both species. Gill [Al] increased exponentially with increasing exchangeable [Al] in water, but was less than 100 μg/g dry weight in both species. There were no correlations between plasma [Na+] or [Cl−] and gill [Al] for both species, and plasma [Na+] and [Cl−] were ultimately linked to low pH. Scanning electron microscopy of gills showed normal primary and secondary lamellae, with few signs of fusion or hyperplasia, only a slight amount of mucus, regular chloride cell crypts, and epithelial cells with distinct microridges. Histology of gill sections showed few lesions in the primary lamellae but some focal histologic lesions in the secondary lamellae of greater than 50% of fish, regardless of ambient pH or [Al]. The histopathology included hypertrophy of individual epithelial, mucous, and chloride cells, clubbing of tips of secondary lamellae, and localized epithelial hyperplasia. These features were focal and not comparable to the extensive morphological changes or histologic lesions usually attributed to high [Al] at low pH. Dissolved organic carbon concentrations greater than 5 mg/L in the acidic streams apparently afforded protection against Al effects at concentrations of at least 360 μg total Al/L.

Patterns of Growth and Smolting of Atlantic Salmon (Salmo salar) Parr in a Southwestern Newfoundland River

A simple model of growth and smolting of Atlantic salmon (Salmo salar) parr, which can account for distributions of ages and lengths of random samples of sea-run smolts in Western Arm Brook, in northern Newfoundland, cannot account for distributions in Little Codroy River, in southwestern Newfoundland. Possible reasons for discrepancies include mortality dependent on growth rates, non-Gaussian growth rate distributions, and variability in individual growth rates. Smolt data do not allow us to reject any of these possibilities. Precocious maturation of male parr does not account for the discrepancies.

Spring migratory synchrony of salmonid, catostomid, and cyprinid fishes in Rivière à la Truite, Québec

During May–June 1980 and June–July 1982, six fish species exited Rivière à la Truite, a major tributary of the lower Moisie River, Quebec, in highly synchronized emigrations. Species included longnose sucker (Catostomus catostomus), white sucker (C. commersoni), lake chub (Couesius plumbeus), juvenile sea lamprey (Petromyzon marinus), Atlantic salmon (Salmo salar) parr and smolt, and anadromous brook trout (Salvelinus fontinalis). In 1980, emigration for all species except the lamprey began on 27 May and ended by 9–11 June; lamprey movements began on 4–5 June and peaked on 10 June. Similar but slightly later patterns occurred in 1982. Onset of the runs in each year coincided with declining water levels and discharge. Thus species of widely different habits exhibit similar and highly synchronized migratory patterns, possibly in response to strong changes in stream environment.

Studies on Precocious Maturity in Artificially-Reared 1+ Atlantic Salmon Parr Salmo salar L.

Studies on Precocious Maturity in Artificially-Reared 1+ Atlantic Salmon Parr Salmo salar L.

Feeding by Hatchery-Reared and Wild Atlantic Salmon (Salmo salar) Parr in Streams

Hatchery-reared Atlantic salmon (Salmo salar) parr were captured 1–3 mo after release in streams, along with wild parr from the same streams. Identification of their stomach contents showed total number of organisms and number of taxa per stomach were greater and there was a higher index of stomach fullness in wild than in hatchery parr resident ≤ 2 mo in a stream. Wild parr consumed more Brachycentridae, Hydroptilidae, Diptera, and Plecoptera than did hatchery parr, but sometimes less Odontoceridae and Heptageniidae. These differences may have arisen from size-dependent food selection, the effects of feeding experience, or possible microhabitat differences between wild and hatchery parr. Key words: salmon parr, hatchery-reared, wild, feeding

The effect of porcine somatotropin on growth, and survival in seawater of Atlantic salmon (Salmo salar) parr.

The effects of porcine growth hormone on growth and salinity tolerance were studied in Atlantic salmon (Salmo salar) parr. Fish were held in freshwater at 11.5 °C during June and July under a photoperiod with light to dark periods opposite to the prevailing natural conditions. Fish treated with 1.0 μg/g body weight of growth hormone preparation on alternate days were significantly longer (P <.05), after 4 weeks, than placebo-injected controls. All hormone-injected fish survived transfer to seawater, 30‰ salinity. But under the same conditions, placebo-injected control fish showed a high mortality rate. Growth-hormone treatment caused a darkening of fin margins and a yellowing of the operculae and fin surfaces. The silvering which normally accompanies smoltification was not observed. The role of growth hormone in eliciting these actions and its possible role in the parr–smolt transformation are discussed.