Hatchery-reared Atlantic Salmon Research Articles

Size of wild and hatchery-reared Atlantic salmon populations in the northern Baltic Sea estimated by a stratified mark-recapture method

Abstract We estimated the total size of the Atlantic salmon (Salmo salar) population complex (wild and cultured) in the Gulf of Bothnia, northern Baltic Sea, using a stratified mark-recapture method. In 2001 and 2002, 1970 salmon were captured by the commercial trapnet fishery and tagged with external arrow tags. A total of 349 tagged fish was later recaptured among 65 180 salmon screened for tags. Recoveries were gathered by the commercial trapnets and by screening fish entering counting facilities in rivers and broodstock fisheries at the river mouths. In addition, tags were recovered from recreational river catches. Our estimates suggest that the total size of the migrating population in both years was about 230 000 fish. Proportions of wild and cultured salmon differed between the two years. In 2001, the proportion of wild salmon was 37%; the corresponding figure for 2002 was 62%. Based on estimates of wild salmon smolt production and the number of released smolts, the estimated proportion of cultured smolts that survived the feeding migration and returned to the Gulf of Bothnia (2–4%) was approximately 2.5–4.5 times lower than that of wild smolts (9–10%).

Survival of reared and wild Atlantic salmon smolts: size matters more in bad years

Abstract We compared the marine survival of Carlin-tagged wild and hatchery-reared Atlantic salmon smolts of the Simojoki river, northern Baltic Sea. All the reared and released smolts were the offspring of native spawners returning to the river. Reared smolts were adipose-fin-clipped and released from the hatchery several weeks before tagging. The wild and reared smolts were simultaneously caught and tagged at a smolt trap located at the Simojoki river mouth. The study was conducted in two years, 1991 and 1993, when post-smolt survival in the Baltic Sea was different. Tags were returned by fishermen and return rates were used to estimate the survival of the smolt groups. We applied generalized linear models with survival as response variable and the year, origin, and smolt size as explanatory variables. On average, wild smolts had a 4.5 times higher survival rate than reared fish of the same smolt size. The difference in observed tag recovery rates as such was only about twofold or less, as the larger size of the reared smolts compared with the wild ones compensated for their lower survival rate. The better survival of wild than reared smolts was more pronounced in the low-survival year (1993 smolt year class) than in the high-survival year (1991 smolt year class).

A biochemical study of mucus lysozyme, proteins and plasma thyroxine of Atlantic salmon (Salmo salar) during smoltification

Abstract Smoltification is a complex developmental phase encompassing hormonal, metabolic and osmoregulatory changes, enabling the Atlantic salmon to migrate from fresh water to sea water. The biological interface between fish and their aqueous environment is a mucus coat composed of biochemically diverse secretions, which have been implicated in respiration, disease resistance and osmoregulation. In this study mucus and blood were sampled from hatchery-reared Atlantic salmon over the period of smoltification. Our aim was to investigate changes in mucus proteins and enzymes and to monitor plasma thyroxine during smoltification. Mucus protein analysis was carried out by sodium dodecyl sulphate (SDS)-PAGE and banding patterns were observed and compared over smoltification. The protein profile results revealed that mucus profiles for individual fish within sample groups were very similar. There were differences in protein profiles between groups sampled on different dates. Significant and consistent changes were observed in the 30- and 14.5-kDa regions of the protein profiles. The intensity of protein bands in the 30-kDa region decreased during the 12-week period. The 14.5-kDa band increased in intensity over time and co-migrated with the lysozyme standard (Hen Egg White Lysozyme, HEWL), which has a molecular mass of 14.2 kDa. Lysozyme, protease and carbonic anhydrase activities were investigated in mucus samples. Lysozyme activity (60–264 IU/ml) was detected in all mucus samples assayed over the period of March to May. There was a significant increase in this activity (264 IU/ml, p p Visual assessment of the salmon showed full smolt characteristics by mid-May. There was an overall increase in plasma thyroxine during the smoltification period. A significant surge in plasma thyroxine (21–36.3 nmol/l, p

Stress-reducing methods for releases of Atlantic salmon (Salmo salar) smolts in Norway

One-year-old, hatchery-reared Atlantic salmon ( Salmo salar ) smolts were Carlin-tagged to test the effects of light sedation and salt water addition during transporting as well as releasing methods on migratory behavior and marine survival in northern Norway. A total of 1600 salmon were tagged for the migratory behavior study in the Halselva River. The fish were transported in water containing either 1 g l −1 metomidate or 11 g l −1 balanced sea salt (Instant Ocean), or a combination of the two. The groups were then allowed to recover for 2 days in net pens in the river, after which they were permitted to migrate freely from the net pens located 1 km upstream from the fish trap. These groups were compared to the untreated groups, which were released directly into the river at the same releasing site at the same time. The results showed that brackish water with metomidate as transport medium, and/or recovery after transport led to improved recaptures of smolts compared to untreated controls. In addition, two groups of approximately 3000 Carlin-tagged Atlantic salmon were transported in 1998 by helicopter from the research station to the nearby Alta River (1-h transport time, including loading) and either released directly into the river or kept in a net pen in the river for 7 days before release. The same releases were performed in 1999. Recaptures of adult salmon in the Alta River were 0.43% and 1.43% (1998 releases) and 1.23% and 1.89% (1999 releases) for smolts released either directly or allowed 7 days to recover in the river before release, respectively. These results shows that the use of stress-reducing methods, especially recovery after transport, can improve both the migratory behavior and marine survival of smolt releases.

Fin development in stream- and hatchery-reared Atlantic salmon

To determine the effect of development and environment on fin growth, we measured fin lengths of juvenile Atlantic salmon (Salmo salar) from two hatcheries (August, October and April–May), stream-reared fish (July and October) stocked as fry into two tributaries, and smolts from the main stem of the Connecticut River (May). For stream-reared parr, there was a linear relationship between the dorsal, caudal and anal fins with fork length, while the pectoral, pelvic and adipose fins exhibited a curvilinear relationship with fork length. Parr from a high gradient stream had larger caudal fins than fish from a low gradient stream, but other fins did not differ. Regression lines for the fins of stream-reared smolts were all linear when fin length was regressed against fork length. Stream-reared parr had larger pectoral, pelvic and anal fins than smolts of similar size while dorsal and caudal fin lengths did not differ. Regression equations formulated using the fins of stream-reared parr were used to calculate the percent difference (100observed fin length/expected) in fin lengths between stream- and hatchery-reared parr. The pelvic, adipose, caudal and anal fins of hatchery-reared parr showed no signs of degeneration by the first sampling period 7 months after hatching, whereas degeneration in the pectoral (13–20%) and dorsal (15–18%) fins was evident at this time. By the end of the study, degeneration was present in every fin except the adipose, with the pectoral (35– 65%) and dorsal (32–58%) fins exhibiting the greatest amount of fin loss. All fins of hatchery-reared parr became shorter with time. There were minor differences in fin degeneration among parr from the two hatcheries, but the overall pattern of decreasing fin size was similar, indicating a common cause of fin degeneration. Comparison of stream- and hatchery-reared fish is a valuable means of determining the impact of captive environments on fin growth. Published by Elsevier Science B.V.

Seasonal changes in androgen levels in stream- and hatchery-reared Atlantic salmon parr and their relationship to smolting

Seasonal changes in androgen levels in stream- and hatchery-reared Atlantic salmon parr and their relationship to smolting

Social enhancement and social inhibition of foraging behaviour in hatchery-reared Atlantic salmon

Social enhancement and social inhibition of foraging behaviour in hatchery-reared Atlantic salmon

Metabolic enzyme activity during smolting in stream- and hatchery-reared Atlantic salmon (Salmo salar)

To evaluate the metabolic differences between Atlantic salmon (Salmo salar) parr and smolts and the effect of rearing environment, we examined metabolic enzyme activity in white muscle, liver, and heart in stream- and hatchery-reared juveniles. Spring increases in gill Na+,K+-ATPase (3.5-fold) and cardiosomatic index (37–69%) and decreases in condition factor (~17%) occurred in smolts, but not in parr. White muscle phosphofructokinase (PFK) increased during spring and was 3.6-fold higher in smolts than in parr by late spring. There were seasonal increases in liver citrate synthase (CS) (~42%), liver β-hydroxyacyl-coenzyme A dehydrogenase (HOAD) (~60%), and heart CS (~23%) and decreases in liver lactate dehydrogenase (LDH) (~28%) in parr and smolts. Activity of liver HOAD was greater in stream-reared smolts (~18%) than in parr or hatchery smolts. Heart PFK activity increased during spring in wild-reared parr and smolts, while it decreased in hatchery-reared smolts. White muscle LDH and PFK increased earlier in spring in hatchery- than in stream-reared smolts. Our results suggest that increased heart size and high white muscle PFK occur during smolting and may be adaptive for downstream and ocean migration. Hatchery- and stream-reared Atlantic salmon differ in the timing of metabolic changes during smolting, which may impact their long-term survival.

Metabolic enzyme activity during smolting in stream- and hatchery-reared Atlantic salmon (<i>Salmo salar</i>)

Metabolic enzyme activity during smolting in stream- and hatchery-reared Atlantic salmon (<i>Salmo salar</i>)

Can Atlantic salmon smolt twice? Endocrine and biochemical changes during smolting

Smolting is characterized by morphological and physiological changes, some of which are reversible if fish remain in freshwater. Whether fish that smolt in the first year will repeat physiological changes associated with smolting a second time is not known. To assess whether Atlantic salmon (Salmo salar) can smolt more than once, we sampled hatchery-reared Atlantic salmon at monthly intervals for 2 years beginning the fall after hatching. Fish showed differences in rate of growth and were easily differentiated by size into upper mode (UM) and lower mode (LM) by the first fall. In the first spring, gill Na+,K+-ATPase activity of UM and LM fish increased six- and three-fold, respectively. Plasma growth hormone levels in spring were significantly elevated in UM fish but not in LM. Plasma cortisol levels changed little and gill corticosteroid receptor concentration did not differ between the groups. During the summer, gill Na+,K+-ATPase activity declined in both groups and remained low until the next spring. The second spring, growth hormone levels did not increase significantly and cortisol levels increased. The increase in gill Na+,K+-ATPase activity and cortisol and high saltwater tolerance indicate that UM Atlantic salmon can smolt in two consecutive years.

Development of Kudoa thyrsites (Myxozoa: Myxosporea) in netpen-reared Atlantic salmon determined by light microscopy and a polymerase chain reaction test.

The intramuscular phase of development of Kudoa thyrsites, the myxosporean associated with post-mortem myoliquefaction, or 'soft flesh syndrome', is described using histological preparations of the musculature of seawater netpen-reared Atlantic salmon Salmo salar. Hatchery-reared Atlantic salmon were naturally exposed to the infective stage while held in the experimental seawater netpens of the Pacific Biological Station in Nanaimo, British Columbia, Canada. In fish exposed during the summer of 1995, K. thyrsites infections were first detected in the somatic musculature at 13 wk post-exposure (p.e.) using only light microscopy. In the 1997 exposure, infections were first detected at 6 wk p.e. using a PCR test and at 9 wk p.e. using light microscopy. The earliest stage detected by histology was a small plasmodium containing 4 nuclei. No host response was observed that was directly related to the presence of intact plasmodia within muscle fibers. However, a response was associated with ruptured plasmodia, which was characterized by chronic, multifocal inflammation between the muscle fibers.

Recovery from loading and transport stress in Atlantic salmon ( Salmosalar L.) smolts

The main objective of this study was to analyse the recovery from loading and transport stress of hatchery-reared Atlantic salmon smolts. The experiment was carried out during the regular transport of fish from Eidfjord to Bondhus river (4.5 h), from Lundamo to Surna river (2.5 h) and from Eikesdal to Eira river (0.5 h). Blood samples were obtained from the smolts before transport (control), 30 min after loading and 1, 24 and 48 h after transport. Additionally, blood samples were obtained after a 24 h seawater challenge test before and after transport. Blood samples were analysed for haematocrit, plasma cortisol, lactate, glucose, chloride and sodium. Plasma cortisol concentrations increased up to 15 times from resting values, with a peak 1 h after transport. A severe discrepancy in both fresh- and seawater osmoregulatory ability was observed 24 and 48 h after transport. It is suspected that the low recapture rates and survival of the hatchery-reared salmon smolts were, in part, caused by the handling and transport of the smolts prior to the release.

Condition and performance of juvenile Atlantic salmon (Salmo salar): effects of rearing practices on hatchery fish and comparison with wild fish

This study examined the effects of various modifications of rearing practices on hatchery-reared Atlantic salmon (Salmo salar) fingerlings and compared condition and performance of hatchery fingerlings (age 0+) and yearlings (age 1+) with those of wild-reared Atlantic salmon. Reduced fish density (and increased ration) in rearing tanks promoted increased growth and condition factor and significant changes in muscle composition, including increased muscle lipid content and glycolytic enzyme activity, specfically phosphofructokinase and lactate dehydrogenase. However, these changes had no effect on anaerobic capacity. Moreover, swimming performance was poorer in fingerlings reared at low compared with normal density. Raising the water velocity from 0 to 4 cm ·s-1(~0.7 body length ·s-1) had overall beneficial effects, most notably increased endurance in fixed velocity sprint tests and a reduction of ion loss in an epinephrine challenge test. Increasing velocity to 9 cm ·s-1had no further effects. Wild fingerlings were larger with better fin quality and superior anaerobic capacity and swim performance. Even larger differences were seen between hatchery-reared and wild yearlings. It is concluded that significant changes in morphology, physiology, and muscle biochemistry of juvenile Atlantic salmon can be brought about by changing hatchery rearing conditions, but these changes are of limited effectiveness in reducing the difference between hatchery-reared and wild fish.

Influence of Transmitter Attachment Procedures on Swimming Performance of Wild and Hatchery-Reared Atlantic Salmon Smolts

Effects of transmitter attachment procedures on smolts of Atlantic salmon Salmo salar have primarily been examined in the laboratory with hatchery-reared fish. Biotelemetry researchers must extrapolate findings of tagging studies to wild, migrating smolts. Because hatchery rearing can affect salmonid development and because field tagging procedures and environmental conditions can differ from those in the laboratory, we measured critical swimming speed of hatchery-reared Atlantic salmon smolts equipped with internal, external, or gastric dummy radio transmitters in the laboratory. We then repeated the experiment with wild, migrating fish in ambient environmental conditions. Swimming ability of hatchery smolts was not significantly affected by any attachment procedure, and no significant differences were found between fish tested 1 or 16 h after tagging. Similarly, wild smolts were not impaired by gastric transmitters; however, performance of wild fish tested 1 or 16 h after internal or external attachment was significantly lower than that of wild controls. Thus, reaction of hatchery-reared Atlantic salmon smolts to attachment procedures can differ from that of wild migrants. Biotelemetry researchers should exercise caution in interpreting data obtained from wild Atlantic salmon smolts equipped with internal or external radio transmitters during the first 16 h after tagging.

Migratory behaviour of post-smolt Atlantic salmon during initial stages of seaward migration

The movements of 24 hatchery-reared Atlantic salmon Salmo salar smolts, with miniature acoustic transmitters (pingers) implanted surgically, were determined after release in the coastal waters of Passamaquoddy Bay (mean tide range 6 m), New Brunswick, Canada, to describe the first stages of seaward migration. Automated pinger detection at fixed sites, and pinger location and tracking by boat were used. Post-smolts left the release area rapidly, and the majority moved to open waters of the bay within several tidal cycles. Initially, post-smolts moved with a seaward orientation on ebb tides and held positions on flood tides. Their movements into open waters were diurnal, and the timing corresponded with the state of the tide during which they moved through a narrow channel. Post-smolts moved preferentially through this passageway with the aid of the tidal stream. Successful movements out through the channel occurred during ebb tides and any movements back in were during flood tides. Ground speed of fish moving through the channel was 4·2 body lengths s−1 and faster than the tidal stream velocities in the channel. The relative velocity of fish swimming through the channel was 2 body lengths s−1. Post-smolt movement was indicative of active, directed swimming with a reliance on ebb-tide transport for migration through a coastal area with strong tidal currents. Some post-smolts moved seaward directly with no apparent period of acclimation for the transfer to the marine environment, whereas others delayed their departure. These differences in behaviour were probably related to asynchrony in smolting when fish were released.

Detection of Aeromonas salmonicida, causal agent of furunculosis in salmonid fish, from the tank effluent of hatchery-reared Atlantic salmon smolts

The fish pathogen, Aeromonas salmonicida, could be detected only by bacteriological culture from the kidney of dead or moribund fish in one tank in a hatchery rearing Atlantic salmon (Salmo salar L.) smolts. However, by using a DNA probe specific for this species, allied to a PCR assay, the pathogen could be detected in water, feces and effluent samples taken from this fish tank. Also, the presence of the pathogen was found in effluent samples from two fish tanks containing apparently healthy fish. Subsequently, the presence of pathogen in these tanks was confirmed by an increase in the daily mortality rate and by a plate culture from moribund fish.

Sources of variation in age at smolting in hatchery-reared Atlantic salmon (Salmo salar)

Length-frequency distributions of Atlantic salmon parr are bimodal during the first November post-hatch and the proportion of presumptive 1 + smolts (S1) can be estimated by integrating the area under the upper modal curve. Such proportions were found for a total of 179 full-sib families of approximately 1000 fish per family. Variance between families suggested genetic effects although an unbiased estimate of heritability was not obtainable because of the experimental design. Correlations between length measurements in July and November were significantly (P < 0.01) greater than zero and families, with a mean length advantage in the lower size mode, also tended to produce larger fish in the upper mode. There was a negative correlation (P < 0.07) between mean length in July and the proportion of presumptive 1 + smolts. Thus, while selection for increased size during July would be expected to produce a positive, correlated growth response in both modes in November, a decrease in the number of 1 + smolts would be expected. Key words: Salmon, smolting age, Salmo salar, hatchery

Muscle ornithine decarboxylase activity as an indication of recent growth in pre-smolt Atlantic salmon, Salmo salar

Ornithine decarboxylase (ODC) is a key regulatory enzyme in the growth process of higher vertebrates. Epaxial muscle ODC activity was correlated to specific growth rate for weight (r 2=0.70) in 55 juvenile Atlantic salmon subjected to four different photoperiods during their first autumn of growth, the period of time when hatchery-reared Atlantic salmon typically develop a bimodal length-frequency distribution. The correlation was strongest for fish which developed such a bimodality, which was the case for those exposed to a natural photoperiod or to a 12 h light: 12 h dark (LD 12:12) photoperiod ( r 2=0.77 in both cases). Larger (upper mode) fish had significantly higher muscle ODC activity than smaller (lower mode) fish ( P<0.001 and P<0.05, respectively, for the two photoperiods), by greater than an order of magnitude. Weaker correlations were found for fish exposed to LD 16:8 and LD 8:16 photoperiods ( r 2=0.53 and 0.47, respectively). In these cases, clear bimodality was not observed for fork length, and larger fish did not have significantly higher muscle ODC activity than smaller fish. These results suggest that epaxial muscle ODC activity is a good indication of short-term changes in growth rate in fish, such as are seen during the recruitment of fish into the upper mode of the bimodal length-frequency distribution typically observed in juvenile hatchery-reared Atlantic salmon.

Glochidium morphology of the freshwater pearl mussel (Margaritifera margaritifera) and glochidiosis of Atlantic salmon (Salmo salar): a study by scanning electron microscopy

The morphology of glochidia of the freshwater pearl mussel Margaritifera margaritifera L. and the development of the cyst for 50 days after glochidial infection of wild and hatchery-reared Atlantic salmon (Salmo salar L.) parr were studied using scanning electron microscopy. The microvillar surface of the inner epithelium of the glochidium, which may function in nutrition, respiration, and osmoregulation, is described. Glochidia were found to have five sensory tufts as well as marginal ciliary bands which are believed to function in directing water currents. After artificial infection of salmon parr, cyst formation was the result of shape change and migration of gill epithelial cells, but not hyperplasia. The process of cyst formation lasted from 9 to 12 h. No mortality of salmon parr occurred during the experiment. Based on our study, glochidia appear to have a negligible effect on the gills of Atlantic salmon, its preferred fish host. These results are discussed in the context of the possibility of a mutually beneficial coexistence of Atlantic salmon and pearl mussels in northern European rivers such as the Varzuga River in Russia.

Homing and straying of hatchery-reared Atlantic salmon, Salmo salar L., released in three rivers in Norway

Releases of hatchery-reared smolts of Atlantic salmon, Salmo salar L., in the Rivers Orkla, Gaula and Alta, Norway yielded large percentages of strays (194, 13.7 and 13.8% respectively), based on recaptures from anglers. Homing precision to the rivers of release was independent of the release site on the river. Distribution of recaptured adult salmon within the rivers was dependent on the release site; upstream releases yielded more upstream recaptures than did downstream releases.