Territory size and distribution of newly-emerged Atlantic salmon (Salmo salar)

Newly emerged Atlantic salmon (Salmo salar) were observed from May to August 1981 at six isolated redds in Washington County, Maine, USA. Territorial size and distribution were measured. At the end of the emergence period (12 to 28 May), fish maintained positions (stations) at redds where water velocity did not exceed 52 cm s^–1 By 12 June, most salmon (80–96%) had moved off the redds of origin and had established territories 1 to 5 m from the redd. The area defended increased substantially after mid-June, but territorial aggression diminished by 15 July, and the fry dispersed downstream. All fish observed were territorial, and the percentage of time during which stations were held decreased from 89 in mid-May to as low as 40% in mid-June.Cooperators are the Maine Department of Inland Fisheries and Wildlife, University of Maine, U.S. Fish and Wildlife Service, and the Wildlife Management Institute     

Swimbladder Leiomyosarcoma in Atlantic salmon (Salmo salar) in North America

Leiomyosarcoma with associated retrovirus were found in North America for the first time in adult Atlantic salmon (Salmo salar) held in a quarantine facility at the North Attleboro National Fish Hatchery (NANFH), Massachusetts, USA. The fish had been collected as age 1-2 yr animals from the Pleasant River, Maine, and were to be used as brood stock in a population augmentation program for that river. Neoplastic disease was observed at NANFH initially in older (age 4 yr) fish, followed by age 3 yr fish. Disease was not observed in age 2 yr fish. The mortality pattern was chronic.     

Seasonal absence of fishes in tidepools of a boreal environment (Maine,USA)

Tidepool fishes of a rocky, boreal community in Maine (USA) were sampled periodically from September 1979 to September 1988. Unlike tidepool fish communities in many other areas of the world, those in Maine included no year-round residents. Several of the 22 species among the 1,135 fishes collected occupied tidepools seasonally as nursery areas. In particular, juvenile lumpfish,Cyclopterus lumpus, used tidepools from June to December during their first two years of life. Disappearance of these species from tidepools in winter appeared to be primarily a result of low water temperatures and reduced algal cover in pools.Cooperators are the University of Maine, Maine Department of Inland Fisheries and Wildlife, U.S. Fish and Wildlife Service, and Wildlife Management Institute.     

Ecological model of interactions between escaped and wild Atlantic salmon Salmo salar

Atlantic salmon in Maine were once abundant but have become depleted, and are listed as endangered under the federal Endangered Species Act. Historically, salmon numbers in Maine may have been as high as 100 000 adults, but habitat loss, pollution and overfishing have contributed to the decline of the species. In 2000, only 110 adults returned to spawn in Maine rivers. Maine produces c. 15 000 metric tons/year of aquacultured Atlantic salmon from a total of nearly 600 coastal net pens. Escapees from these pens may interact with the wild salmon. The dynamics of salmon populations under such conditions are poorly understood. In order to illuminate the role aquaculture may play in such a system, we have developed a model for simulating population trajectories for both wild salmon and competing populations derived from aquaculture escapes. The model simulates a small population of wild salmon based in a stream/estuary system, into which an aquaculture facility is losing fish to escapes. Biological parameters in the model were estimated as much as possible from data in the USFWS report on Maine salmon. We used the model to investigate the consequences of a variety of ecological interactions between the wild and cultured fish including competitive, genetic and disease effects. Initial results indicate that many of these effects allow the aquaculture‐derived population to supplant the wild fish, but that wild populations may still persist under some conditions.     

Why do some fish do it younger than others? learning from experiments

Atlantic salmon in Maine were once abundant but have become depleted, and are listed as endangered under the federal Endangered Species Act. Historically, salmon numbers in Maine may have been as high as 100 000 adults, but habitat loss, pollution and overfishing have contributed to the decline of the species. In 2000, only 110 adults returned to spawn in Maine rivers. Maine produces c. 15 000 metric tons/year of aquacultured Atlantic salmon from a total of nearly 600 coastal net pens. Escapees from these pens may interact with the wild salmon. The dynamics of salmon populations under such conditions are poorly understood. In order to illuminate the role aquaculture may play in such a system, we have developed a model for simulating population trajectories for both wild salmon and competing populations derived from aquaculture escapes. The model simulates a small population of wild salmon based in a stream/estuary system, into which an aquaculture facility is losing fish to escapes. Biological parameters in the model were estimated as much as possible from data in the USFWS report on Maine salmon. We used the model to investigate the consequences of a variety of ecological interactions between the wild and cultured fish including competitive, genetic and disease effects. Initial results indicate that many of these effects allow the aquaculture‐derived population to supplant the wild fish, but that wild populations may still persist under some conditions.     

The effect of ultrasonic tags on the growth rates of Atlantic salmon, Salmo salar L., parr of varying size just prior to smolting

The attachment of dummy, ultrasonic, acoustic tags, of the Stirling Mk. VI design, to pre-smolt Atlantic salmon parr significantly affected fish growth rates. Fish less than 160 mm in length lost weight and showed no change in length. Fish over 160 mm in length put on weight, though at a rate significantly lower than that of untagged controls. For fish between 160 and 180mm in length, the increase in length was significantly smaller in tagged fish than in untagged controls. Over 180 mm in length, no difference could be detected in the length gains of tagged and untagged fish.
Smaller tagged fish gave up maintaining station and showed signs of distress at an earlier stage in the experiment than larger tagged fish. Tag-related mortality was inversely related to fish size. All but two of the control fish survived the experiment and continued to maintain station throughout.
The results suggest that the minimum length of Atlantic salmon parr on which this design of acoustic tag could be employed is 160 mm, and that caution is needed in the interpretation of track lengths longer than l0 daysof parr in the size range 160–180 mm.     

Naked DNA vaccination of Atlantic salmon Salmo salar against IHNV

A naked plasmid DNA encoding the glycoprotein (pCMV4-G) of a 1976 isolate of infectious hematopoietic necrosis virus (IHNV) obtained from steelhead Oncorhynchus mykiss was used to vaccinate Atlantic salmon Salmo salar against IHNV. Eight weeks post-vaccination the fish were challenged with a strain of IHNV originally isolated from farmed Atlantic salmon undergoing an epizootic. Fish injected with the glycoprotein-encoding plasmid were significantly (p < 0.05) protected against IHNV by both immersion and cohabitation challenge. Survivors of the first challenges were pooled and re-challenged by immersion 12 wk after the initial challenge. Significant (p < 0.05) protection was observed in all of the previously challenged groups including those receiving the complete vaccine. Fish injected with the glycoprotein-encoding plasmid produced low levels of virus-neutralizing antibodies prior to the first challenge. Neutralizing antibodies increased in all groups after exposure to the IHNV. Passive transfer of pooled sera from pCMV4-G vaccinates and IHN survivors provided relative survivals of 40 to 100% compared to fish injected with sera collected from fish immunized with control vaccines or left unhandled. In this study, DNA vaccination effectively protected Atlantic salmon smolts against challenges with IHNV.     

Relative production of Atlantic salmon from fluvial and lacustrine habitats estimated from analyses of scale characteristics

Empirical and back-calculated growth of Atlantic salmon parr were compared between fish reared in fluvial and lacustrine habitats of Conne River, Newfoundland. Length at age was significantly higher for lacustrine parr. Various classification and maximum likelihood estimators indicated that 75% or more of the fish used lakes for rearing. Lacustrine use is another aspect of the inherent variability and plasticity of Atlantic salmon life-history traits. As most Newfoundland river systems include lakes, estimates of regional spawning targets and potential smolt production will need to take lake habitat into account.     

Age-specific aggregation of wild juvenile Atlantic salmon Salmo salar at cool water sources during high temperature events

This study quantified the use of cool water sources by wild 0+, 1+ and 2+ year Atlantic salmon Salmo salar during high water temperatures ( i.e. >23° C) in summer 1995 and 2004. During these events, 0+ year Atlantic salmon did not aggregate or increase in abundance in cool water sites. Interestingly, 1+ and 2+ year Atlantic salmon numbers increased in cool water sites. In addition, these older juveniles formed numerous, discrete aggregations along the plume created by a tributary with aggregation locations being similar between years. Aged 2+ year fish aggregations were at the coolest sources whereas 1+ year aggregations were in locations cooler than the main river. Fish in aggregations on average used deeper sections (average depth: 380 mm) compared with the coolest available habitat in the thermal plume (average depth: 230 mm). Hence, during high temperature events, older juvenile Atlantic salmon moved to cooler water sites and then aggregated in deeper microhabitats.     

Short-term changes in tidepools following two hurricanes

Three tidepools in the rocky intertidal zone of coastal Maine, USA, were examined before and after the passing of two hurricanes: Gloria, in 1985, and Bob, in 1991. Surface area was little changed in one pool, and reduced in a second pool that were formed from rock. Surface area increased significantly in a third pool that had a nonpermanent border. Sand deposition on the bottom of tidepools increased in three of the five pairs of observations, and sand was not present before or after storms in the other two instances. Algal cover was generally reduced, and beds of blue mussel (Mytilus edulis) were significantly reduced or were extirpated. Fish numbers were generally lower after the storms, but numbers returned to pre-event levels in the following season. Physical and biological alterations to tidepools were often severe for the short term, but systems were resilient for the long term.Cooperators are the University of Maine, Maine Department of Inland Fisheries and Wildlife, National Biological Service, and the Wildlife Management Institute     

Enzymes released from Lepeophtheirus salmonis in response to mucus from different salmonids

Adult and mobile preadult sea lice Lepophtheirus salmonis were incubated with mucus samples from rainbow trout (Oncorhynchus mykiss), coho salmon (O. kisutch), Atlantic salmon (Salmo salar), and winter flounder (Pseudopleuronectes americanus) to determine the response of L. salmonis to fish skin mucus as assessed by the release of proteases and alkaline phosphatase. There was variation in the release of respective enzymes by sea lice in response to different fish. As well, sealice collected from British Columbia responded differently than New Brunswick sea lice to coho salmon mucus. Fish mucus and seawater samples were also analyzed using protease gel zymography to observe changes in the presence of low molecular weight (LMW) proteases after L. salmonis incubation. Significantly higher proportions of sea lice secreted multiple bands of L. salmonis-derived LMW proteases after incubation with rainbow trout or Atlantic salmon mucus in comparison with seawater, coho salmon, or winter flounder mucus. Susceptibility to L. salmonis infections may be related to the stimulation of LMW proteases from L. salmonis by fish mucus. The resistance of coho salmon to L. salmonis infection may be due to agents in their mucus that block the secretion of these LMW proteases or factors may exist in the mucus of susceptible species that stimulate their release.     

The accumulation of 137-caesium from fresh water by alevins and fry of Atlantic salmon and brown trout

The accumulation of 137-caesium from water by alevins and fry of Atlantic salmon and brown trout was studied, At 'normal' pH (∼7.4), input rates (k_WF) and equilibrium concentration factors (CF_eq) of 137-caesium were four to five times greater in both species of alevins than those in the fry. Input rates and equilibrium concentration factors were consistently greater in brown trout than in Atlantic salmon. The input rate of 137-caesium was most rapid in kidney, gill and gut of fry. The majority of the radiocaesium was, however, deposited in muscle tissue which had consistently the longest biological half-life of 50–90 days. 137-Caesium input was significantly reduced at low pH (∼5.0) but output rates (k_FW) were little affected. It is concluded that juvenile fish are more susceptible than adults to radiocaesium accumulation from freshwater but that food is the major source of 137-caesium in freshwater fish. The behaviour of 137-caesium is discussed with respect to potassium.     

An epidemiological study of cataracts in seawater farmed Atlantic salmon Salmo salar

Cataracts in farmed Atlantic salmon have been known for many years, but the aetiology and importance of the disease have not been clarified. A cross-sectional field study of 51 cages of Atlantic salmon at 49 randomly selected sea sites was performed during the summer of 1998. The target population was spring and autumn entry groups of the 1997 generation salmon. Approximately 15 fish from each cage, altogether 777 fish, were autopsied by the same person. Each eye of the fish was scored for cataracts on a scale from 0 to 4 using an otoscope lamp with magnification. The weight and length of each fish were measured. The prevalence of cataracts was 83 % and 79% in spring entry groups and autumn entry groups, respectively. The overall mean cataract index (mean score of both eyes) was 1.23, being significantly higher in the spring entry groups (1.36) than the autumn entry groups (0.85). The final results in the spring entry groups showed that the fish groups with higher weight at sea transfer also had a higher cataract index at inspection. The risk of development of cataracts varied significantly among the offspring from the 5 strains represented in the study. Fish from sites located in 2 counties in the southern part of Norway had a significantly higher cataract index than fish farmed in the northernmost county in the study. For the autumn entry groups none of the explanatory variables was significant. In the spring entry groups a significant negative relationship was observed between the cataract score and the weight of the fish at the time of inspection (Pearson's r = -0.17), while the corresponding correlation for the autumn released groups was r = -0.10. Among the spring entry groups the average weight of the fish with the highest cataract score was estimated to about a third of the weight of the fish with no visible cataracts.     

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.     

Alkaline preserved herring by-products in feed for Atlantic salmon (Salmo salar L.)

The aim of the present study was to investigate the digestibility, growth and slaughter quality in Atlantic salmon (Salmo salar L.) fed a novel type of moist feed. The moist feed was prepared from alkaline preserved (pH 11.2) herring (Clupea harengus) filleting by-products, mixed with a crude binder based on seaweed before the feed was shaped in a pelleting process and the final structure was set immersing the pellets in an acidic bath. The feeding experiment was carried out with seawater-adapted salmon with an average initial weight of 1.7 kg. The moist feed and a control feed were fed to three groups of salmon with 190 fish per group. The coefficient of total tract apparent digestibility of fat, protein and energy in fish fed the moist feed was 0.96, 0.81 and 0.87, respectively. The weight gain for fish fed moist feed was significantly higher compared to salmon fed commercially extruded control feed. Carcass quality data showed that fish fed the moist feed had significantly higher dressing out percentage and less visceral fat compared to fish fed the control feed. It is concluded that alkaline preserved fish by-products can be efficiently utilized in a novel moist feed technology, yielding good growth and digestibility in Atlantic salmon.     

Replacement of fish oil with thraustochytrid Schizochytrium sp. L oil in Atlantic salmon parr (Salmo salar L) diets

Replacing fish oil with that from a docosahexaenoic acid (22:6omega3, DHA) rich single cell micro-organism, thraustochytrid Schizochytrium sp. L, in diets for Atlantic salmon (Salmo salar) was investigated. Four experimental diets containing 100% thraustochytrid oil (TO), 100% palm oil (PO) and a 4:1 palm and thraustochytrid oil mixture (MX) were compared to a fish oil (FO) diet over 9 weeks. A saltwater transfer challenge occurred at the end of the trial for 14 days to test the diet treatments on the ability of salmon to smolt. There were no significant differences in the feed consumption of the diets or the digestibility of the omega3 or omega6 PUFA, indicating no differences in the digestibility of fatty acids between diets. No significant differences were noted between the growth of fish on the four diet treatments. Significant differences were noted in the fatty acid profiles of the fish muscle tissues between all diets. Fish on the TO diet had a significantly greater percentage of DHA in muscle tissue compared with fish on all other diets. Blood osmolarity, which is inversely related to the ability of salmon to smolt, from the TO and FO fed fish was significantly lower than that of fish on the PO diet. This study showed that thraustochytrid oil can be used to replace fish oil in Atlantic salmon diets without detriment to the growth of parr. Including thraustochytrid oil in fish diets significantly increases the amount of DHA in Atlantic salmon muscle and therefore is a candidate for use in oil blends for salmon diets. Thraustochytrid oil provides a renewable source of essential fatty acids, in particular DHA, for aquafeeds.     

Infectious pancreatic necrosis virus infection in Atlantic salmon Salmo salar post-smolts affects the outcome of secondary infections with infectious salmon anaemia virus or Vibrio salmonicida.

Infectious pancreatic necrosis (IPN) virus (IPNV) infection in Atlantic salmon Salmo salar L. post-smolts and its influence on the outcome of secondary infections with infectious salmon anaemia (ISA) virus (ISAV) or Vibrio salmonicida were studied. The infections with ISAV or V salmonicida were performed both in a period of acute IPN and in the following IPNV carrier stage, 3 and 6 to 8 wk after experimental IPNV challenge, respectively. An IPNV carrier condition at low virus titre did not influence the mortality rates after secondary infections. Neither the ISAV infection nor the V. salmonicida infection in experimentally induced IPNV carriers resulted in mortalities different from those observed after challenge of IPNV-free fish. At higher IPNV titres in Atlantic salmon with acute IPN, the outcome of secondary infections was quite different from that observed in IPNV-free fish and in IPNV carriers. In 2 different experiments significantly more fish died when fish with acute IPN were infected with V salmonicida than when fish were infected with V salmonicida alone. Mortality also started earlier in the double-infected group than in the group challenged with V. salmonicida alone, 3 to 4 and 8 d after V salmonicida infection, respectively. Similar results were observed independent of whether mortalities due to IPN alone were registered in the experiments. When Atlantic salmon with acute IPN were infected with ISAV, significantly fewer fish died than when fish were infected with ISAV alone. The ongoing IPNV infection seemed to provide some protection against development of ISA.     

Effects of vegetable feed ingredients on bone health in Atlantic salmon

The aim of the present study was to examine if dietary inclusion of vegetable lipids (VL) and proteins (VP) influenced markers of bone health in Atlantic salmon. Triplicate groups were fed one of four different diets; 100% fish protein (FP) and fish lipids (FL) (FPFL), 80% VP and 35% VL (80VP35VL), 40% VP and 70% VL (40VP70VL), or 80% VP and 70% VL (80VP70VL) for 12 months on‐growth in sea water. Fish were analyzed for vertebral bone mineralization (mineral content, as % of bone dry weight), vertebral deformities (radiology), vertebral bone mRNA expression of factors involved in mineralization (bone gla protein, bgp) and growth regulation (igf‐I and growth hormone receptor), as well as plasma vitamin D metabolites. The fish grew from 0.35 to 4 kg during the experimental period. At the end of the experiment, significantly lower prevalence of fish with one or more deformed vertebrae was observed in the 80VP70VL group (11%) compared to the other groups (33–43%). There was a significant higher relative expression of igf‐I mRNA in vertebral bone of fish fed the 80VP70VL diet compared to control fish (FPFL), while the other genes studied were unaffected. Elevated plasma 25‐hydroxyvitamin D₃ recorded in the marine feed group is discussed as a predictor for later development of bone deformities. In conclusion, the present study shows that high inclusion levels of vegetable lipids and proteins may have a positive effect on bone health in Atlantic salmon postsmolts.     

Relative ventricular weight of wild Atlantic salmon parr in relation to sex, gonad maturation and migratory activity

Relative ventricular weight (RVW, ventricular weight/body weight · 100) was measured for five groups of Atlantic salmon parr from the Girnock Burn in Scotland. The mean RVW was: mature males, 0.087; immature resident males, 0.054; immature resident females, 0.056; immature migrant males, 0.056; immature migrant females, 0.053. For a group of mature male parr from the R. Nith, Galloway, Scotland, the mean RVW was 0.108. There were no significant differences in the RVW between groups of immature fish. The RVW of each group of mature male parr was significantly greater than those of each, group of immature parr. Condition indices (weight/length³) were closely similar between all groups of parr. The functional significance of plasticity in ventricular weight is discussed in relation to life histories of Atlantic salmon.     

N-Terminal Sequence and Main Characteristics of Atlantic Salmon (Salmo salar) Albumin

Atlantic salmon (Salmo salar) serum albumin was purified from plasma and its N-terminal sequence determined. Atlantic salmon albumin is the predominant plasma protein, negatively charged, at pH 8.6. Albumin was purified to >95% purity which yielded a single band on SDS-PAGE and agarose gel electrophoresis. The molecular weight of the purified albumin was approximately 6,5 kDa. The N-terminal sequence of Atlantic chinook salmon albumin was consistent with that predicted from its previously determined cDNA sequence and was identical to that of salmon (Oncorhynchus tshawytscha) albumin through the first 15 residues. However, the fact that the actual N-terminus was different from that predicted from cDNA sequence indicates that Atlantic salmon albumin, like chinook salmon albumin, lacks a propeptide.