Juvenile Atlantic Salmon Research Articles

The effects of initial length and body curvature on shrinkage of juvenile Atlantic salmon during freezing

The effects of initial length and body curvature on shrinkage of juvenile Atlantic salmon during freezing

The effects of initial length and body curvature on shrinkage of juvenile Atlantic salmon during freezing

Fork length was measured in two groups of salmon parr (32–139 mm, frozen in a straight posture and frozen in a curved posture) before (L1) and after (L2) freezing and thawing. All the fish shrank. The decrease in length was significantly greater in the curved fish than the straight fish. The absolute reduction in length (L1–L2) was related directly to L1, whereas the percentage reduction in length [(L1–L2)/L1× 100] was related inversely to L1.

Does one result trump all others? A response to Magurran, Irving and Henderson

Magurran, Irving and Henderson (1997) have reported that a population of European minnows, Phoxinus phoxinus, did not show an obvious behavioural fright reaction when they were presented with conspecific skin extract in a wild situation. Fish from the same population show a strong response when tested in aquaria. From these data the authors conclude that the fright reaction may be contingent on such factors as assessed risk and hunger. From this reasonable hypothesis they progress to the assertion that the Schreckstoff of ostariophysan fishes should not be considered an alarm pheromone. Much of their paper is devoted to arguments supporting their hypothesis that Schreckstoff cannot operate as an alarm pheromone. I argue that it is appropriate and adaptive to respond to alarm signals in a contingent manner, and attempt to answer the various arguments regarding the validity of terming Schreckstoff an alarm pheromone.

Dietary phosphorus requirement of juvenile Atlantic salmon, Salmo salar L.

The objective of this study was to determine the dietary phosphorus (P) requirement of juvenile Atlantic salmon, Salmon salar L. Triplicate groups of fish (mean initial weight 1.4 g) were fed semipurified, casein-gelatine-based diets containing one of five levels of P (4, 8, 10, 15 and 25 g kg−1) from Ca(H2PO4)2·H2O, or a commercial feed (17 g kg−1 P) for 9 weeks. Weight gains did not differ significantly among treatment groups fed the experimental diets but were slightly less than gains in fish fed the commercial feed. Feed efficiency (wet weight gain/dry feed consumed) was similar in all groups, averaging 1.45. Availability of dietary P, estimated from apparent retention and apparent digestibility, was 86%. Whole-body P concentrations declined in fish fed diets containing less than 10 g kg−1 P. Fitting a logistic curve to dietary P vs. whole-body P concentrations indicated that a minimum of 11 g kg−1 dietary P (9 g kg−1 digestible P) was required by juvenile Atlantic salmon to maintain whole-body P concentrations at initial levels. Calculation of a dietary requirement using a simple factorial model which incorporated measurements of P availability, feed efficiency and normal whole-body P concentration indicated that the dietary requirement was approximately 10 g kg−1. The dietary requirement established in this study (10–11 g kg−1) is higher than previously reported for Atlantic salmon or other fishes. Possible reasons for the wide range of reported dietary P requirements in fishes are discussed.

Effects of piperonyl butoxide and β‐naphthoflavone on cytochrome P4501A expression and activity in Atlantic salmon (Salmo salar L.)

AbstractThe effects of piperonyl butoxide (PBO) and β‐naphthoflavone (BNF) on cytochrome P4501A (CYP1A) expression and activity in juvenile Atlantic salmon (Salmo salar L.) with regard to time and temperature was investigated. The time exposure study was performed at 8 °C, and the results show that PBO, although acutely functioning as a CYP1A inhibitor, is able to induce CYP1A expression in salmon liver. Both PBO and BNF give highest induction of CYP1A mRNA 48 h after intraperitoneal injection (five‐ and 14‐fold, respectively). The mRNA levels induced by PBO and BNF were sustained during the 8 d of the experiment (four‐ and 11‐fold, respectively). The CYP1A protein content measured by enzyme‐linked immunosorbent assay demonstrated the highest induction by PBO 8 d after exposure (eightfold) and by BNF 4 d after exposure (11‐fold). Activity of CYP1A measured by ethoxyresorufin‐O‐deethylase (EROD) demonstrated inhibition after PBO treatment the first 24 h after exposure, followed by threefold induction from 48 h and to the end of the experiment (8 d). β‐Naphthoflavone strongly induced EROD activity, with the highest levels occurring 4 d after treatment (56‐fold) and 8 d after treatment (22‐fold). In the temperature study, the results demonstrated temperature compensation, as salmon acclimated to 7°C for 3 weeks had a significantly higher EROD activity than those acclimated to 11 and 15°C. This was not reflected in significantly higher levels of reduced nicotinamide adenine dinucleotide phosphate cytochrome c reductase activity or CYP1A protein. The inductive properties of PBO and BNF on CYP1A expression was also demonstrated in primary cultures of salmon hepatocytes.

Regulation of hyperphagia in response to varying energy deficits in overwintering juvenile Atlantic salmon

Resident juvenile Atlantic salmon responded to a period of winter food restriction by subsequently increasing appetite when food again became available. This hyperphagy contributed to the restoration of an energy deficit (derived from a biometric estimation of body lipid reserves) incurred during the period of food restriction. The extent of this deficit influenced the duration of the hyperphagic response: those fish incurring the greatest fat losses maintained appetite longer than those with a smaller energy deficit. The initial feeding intensity of fish incurring a wide range of fat losses was found to be similar, indicating that fish were regulating the length as opposed to the intensity of the hyperphagic response in order to restore losses. The ecological implications of the results are discussed in relation to juvenile salmon overwintering strategies.

Regulation of hyperphagia in response to varying energy deficits in overwintering juvenile Atlantic salmon

Resident juvenile Atlantic salmon responded to a period of winter food restriction by subsequently increasing appetite when food again became available. This hyperphagy contributed to the restoration of an energy deficit (derived from a biometric estimation of body lipid reserves) incurred during the period of food restriction. The extent of this deficit influenced the duration of the hyperphagic response: those fish incurring the greatest fat losses maintained appetite longer than those with a smaller energy deficit. The initial feeding intensity of fish incurring a wide range of fat losses was found to be similar, indicating that fish were regulating the length as opposed to the intensity of the hyperphagic response in order to restore losses. The ecological implications of the results are discussed in relation to juvenile salmon overwintering strategies.

Use of soy protein concentrates and lecithin products in diets fed to coho and atlantic salmon

AbstractAquacultural production is increasing in most parts of the world, establishing new and rapidly growing markets for various oil products. One of the more interesting nutritional requirements for aquatic animals is lecithin or phosphatidylcholine. In this paper, lecithin in aquaculture is reviewed with emphasis on freshwater fish and crayfish. Further, new data on use of lecithin and two soy protein concentrates in diets fed to coho and Atlantic salmon are presented. Juvenile coho and Atlantic salmon were fed either solvent‐extracted soybean meal (SBM) or Promocalf® at 30% of the diet, Promoveal® at 10, 20 or 30% of the diet, or one of three new lecithin products at a constant level of 3% of the diet. Juvenile coho salmon fed SBM, Promocalf®, or Promoveal® at 30% of the diet exhibited depressed weight gain and an elevated feed conversion ratio (FCR) compared to fish fed a positive control diet. Fish fed 10 or 20% Promoveal® had similar weight gain and FCR compared to fish fed the control diet. Coho salmon fed either of the three lecithin products (Aqualipid®, Blendmax®, or Centrol®) had similar weight gains and FCR values compared to fish fed the control diet. Whole‐body proximate components were not as responsive to dietary treatments as weight gain and FCR data. Juvenile Atlantic salmon exhibited depressed weight gain only when fed 30% Promocalf® and all three lecithin products. Further, whole‐body crude protein concentrations in fish fed the three lecithin products were depressed.

Effects of l-thyroxine on brain monoamines during parr-smolt transformation of Atlantic salmon ( Salmo Salar L.)

During spring, seaward migrating juvenile Atlantic salmon ( Salmo salar) undergo parr-smolt transformation (PST) which involves changes in physiology, including one or two peaks in plasma thyroxine (T 4). To investigate if changes in plasma T 4 influence neural function, we measured levels of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and also measured serotonin (5-hydroxytryptamine, 5-HT) and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) in brain regions of two groups of Atlantic salmon parr on an 8:16 h light/dark photoperiod. One group was treated with ambient T 4 to simulate the natural smolt peak in plasma T 4. T 4 treatment depressed DOPAC levels as well as DOPAC/DA and 5-HIAA/5-HT ratios in the olfactory system but with no changes in the optic tectum. We conclude that during PST monoaminergic functions in specific brain regions of juvenile Atlantic salmon are affected by T 4 treatment.

Alternative reproductive tactics in atlantic salmon: factors affecting mature parr success

In Atlantic salmon, as in most salmonids, males can mature early in the life cycle, as small freshwater fish, termed parr, and/or undergo a sea migration before maturing as full–size adults. The alternative life histories are contingent on environmental and social circumstances, such as growth rate, territory quality or any other factor that affects the individual9s state. In order to model the choice of life history in this group of commercially valuable species, it is necessary to understand not only the relative contribution of the different male types to subsequent generations, but also to know the factors that affect reproductive success in each type. In this paper we present the results of a study designed to investigate the factors that affect the reproductive success of mature parr. We used highly polymorphic minisatellite DNA markers to analyse paternity in a series of mating experiments where the number and body size of parr were manipulated. The fraction of eggs fertilized by mature parr ranged from 26 to 40 per cent, with individual parr fertilizing up to 26 per cent of the eggs. A strong positive correlation was found between parr size and reproductive success. The relative success of parr decreased with increasing parr number. Data from this and other studies on variation in the timing and degree of parr reproductive success are discussed in relation to the evolution of male mating strategies and life history in salmonids.

Vitamins C and E interact in juvenile Atlantic salmon ( Salmo salar, L.)

A two way regression study was performed to investigate the interactions between vitamins C and E, and the influence of dietary vitamin C on the development of vitamin E deficiency in first feeding Atlantic salmon. The fish were fed three levels of all-rac- α-tocopheryl acetate (0, 150, and 300 mg/kg), each with six levels of ascorbate monophosphate (0, 7.5, 15, 30, 45, and 60 mg/kg ascorbic acid equivalents). Vitamin C protected the fish against vitamin E deficiency in a dose dependent manner, as seen from the data on growth, mortality, hematology, and lipid oxidation in the liver, indicated by the concentration of malondialdehyde. Vitamin C did not influence the tissue levels of vitamin E, except in vitamin C deficiency, which induced a large drop in liver vitamin E concentration. The liver level of vitamin C increased in response to supplementation of both vitamins. The results indicate two different interaction mechanisms: a synergistic effect of simultaneous protection of the water and lipid phases against oxidation, and regeneration of vitamin E from the vitamin E radical by ascorbic acid. Copyright © 1996 Elsevier Science Inc.

Effects of decreases in photoperiod on growth and bimodality in Atlantic salmon Salmo salar L.

Two experiments were performed to study the relative significance of the absolute daylength and the change in photoperiod on the growth and development of bimodality in juvenile Atlantic salmon Salmo salar L. In Experiment A juveniles were reared on 24 h daily light until they were seven months old (65–82 mm in length after size grading). They were then divided into six groups and subjected to six photoperiods (6, 9, 12, 15, 18 and 24 h of light). In Experiment B the decrease in photoperiod was made in two steps. First, the day length was reduced to 18 and 21 hours, three months after first feeding when the weight of the juveniles averaged 2.5 g and one group was kept under 24 hour daily light. Two months later, each of these treatment groups was subdivided to produce new groups of juveniles (65–82 mm in length) under 6, 9 and 12 h of daily light. Irrespective of whether the photoperiods were reduced in one or two steps, groups held under short-day photoperiods, 6–12 h, grew significantly slower (Exp. A) and showed higher proportions of lower modal group fish (Exp. B) than groups treated with long-day photoperiods, greater than 12 h. There were low proportions of lower modal group fish among juveniles larger than 75 mm at the dates of decreases in daylength irrespective of photoperiod (Exp. B, 0–16%), and high or variable proportions among fish smaller than 75 mm, depending on photoperiod (Exp B. 32–71%). It is concluded that the growth response of juvenile Atlantic salmon changes in the range of 12–15 hours of daily light. This mechanism is probably linked to the size of the parr and is one important reason for the development of bimodal length-frequency distributions.

Nocturnal activity of juvenile Atlantic salmon (Salmo salar) in late summer: evidence of diel activity partitioning

Nocturnal activity of juvenile Atlantic salmon (Salmo salar) in late summer: evidence of diel activity partitioning

A comparative study of automatic feeding and self-feeding in juvenile Atlantic salmon ( Salmo salar) fed diets of different energy levels

The growth performances of juvenile Atlantic salmon fed diets differing in energy content, either using self-feeders or in excess with automatic feeders, were compared. In addition, the pattern of feeding activity is described for fish fed with self-feeders. In fish fed using self-feeders, growth was intermediate between the performance of fish fed with low and high energy diets by means of automatic feeders. Fish groups tended to become more homogeneous in size with the passage of time, this being more pronounced in groups fed using self-feeders than in those fed using automatic feeders. Dietary energy content influenced growth and digestible energy intake of salmon fed by means of automatic feeders, but this was not seen in self-fed salmon. These results indicate that regulation of feed intake is influenced by the feeding strategy, probably because pellets are only available on demand for fish fed with self-feeders, whereas in groups fed by means of automatic feeders, pellets are freely available in excess. In fish fed with self-feeders, all feed distributed appeared to have been eaten. Feeding activity showed a main peak during the first hours of light and a second, smaller, peak at the end of the light phase. It is concluded that Atlantic salmon feeds preferentially during the photophase and can be fed efficiently with self-feeders.

Effect of temporary reductions in feeding on protein synthesis and energy storage of juvenile Atlantic salmon

Biochemical and tissue‐composition indices were used to determine the impacts of temporary feeding reductions on juvenile Atlantic salmon (4.2g initial weight). Three levels of food reduction (fasting, 20% of control, 50% of control) lasting for 2, 4 or 8 days were compared to a control group (constant feeding at 2.75% of body weight day−1). Ornithine decarboxylase (ODC) activity and RNA concentrations were used to measure changes in protein synthesis; condition factor (K), liver‐somatic index (LSI), visceral‐somatic index (VSI), and gut index (GI)were used to provide information on stored energy levels. Results showed that physiological adjustments to decreases or increases in feeding occur very quickly. The most rapid responses were changes in ODC activity (within 2 days) and LSI (2–4 days). Changes in RNA concentrations and K required 4–8 days. There was no apparent effect of the treatments on VSI or GI. Temporary reductions of feeding lasting 2 days or less would not be detected by any index except ODC activity. Changes in the indices are discussed with respect to short‐term changes in rates of protein synthesis and energy storage.

Effect of temporary reductions in feeding on protein synthesis and energy storage of juvenile Atlantic salmon

Effect of temporary reductions in feeding on protein synthesis and energy storage of juvenile Atlantic salmon

Food acquisition and growth of juvenile Atlantic salmon ( Salmo salar) in relation to spatial distribution of food

Triplicate groups of juvenile Atlantic salmon ( Salmo salar) were exposed to either standing or flowing water (currents corresponding to a swimming speed of approximately 1.5 Bl s −1) for 79 days (17.06–04.09). Food was relatively evenly distributed throughout the entire water body in the 1.3 m 3 tanks with circumferential water currents, but food availability was limited to only a small part of the tanks with standing water. Most of the males (85%) were maturing at the end of the experiment. There were no significant differences in the frequencies of maturing males between treatments. Fish exposed to water currents grew significantly better than those held in standing water. On average, the immature exercised fish grew 14% faster than their unexercised counterparts, whereas differences in growth rates between exercised and unexercised fish were 24% for maturing fish. Amongst immature fish there was greater inter-individual variability in food intake in groups (CV g ) held in standing water than in those exposed to water currents. Day-to-day variations in food intake of individual fish (CV i ) were also found to be significantly greater for the salmon held in standing water. Differences in CV i and CV g between treatment groups, were expected to lead to corresponding differences in the variability of growth rates (CV SGR). The observed differences in CV SGR were, however, small, but there was a negative correlation between CV i and group average SGR. This may suggest that feeding behaviour was characterised by interference and scrambling conditions, rather than clear-cut hierarchies. The trends in the variabilities of food intake and growth of the maturing fish were similar to those seen in the immature fish, but overall variability was greater due to the fact that the maturing fish displayed reduced feeding and growth towards the end of the experiment. The results of this investigation clearly show that an adequate spatial distribution of food is essential in order to ensure rapid and homogeneous growth of farmed salmonids. The employment of water currents in rearing tanks would seem to be a useful measure for ensuring an even spread of food.

Monitoring for Early Detection ofAeromonas salmonicidato Enhance Antibiotic Therapy and Control Furunculosis in Atlantic Salmon

Abstract Juvenile Atlantic salmon Salmo salar at the White River National Fish Hatchery were monitored quarterly for Aeromonas salmonicida, the etiologic agent of furunculosis. Samples were obtained in August, November, January, and March, within an 8-month smolt production cycle during 1992–1993. Aeromonas salmonicida was isolated in August from external mucus and kidneys of fish within six production pools, each containing about 7,500 fish. Topical disinfection with a 60-min bath of Chloramine-T at 15 mg/L on three consecutive days did not control the prevalence of infection. Atlantic salmon were then fed 77.0 mg of oxytetracycline per kilogram of fish for 10 d. Mortality subsided in all tanks within 4 d after initiation of oral antibiotic therapy. Further examination failed to isolate the pathogen 21 d after cessation of treatment. In November, A. salmonicida was detected in the mucus of one fish from a single tank; treatment was not prescribed. Pathogens were not detected shortly after fish were marke...

Can juvenile Atlantic salmon use multiple cue systems in spatial learning?

An ability to form a map or spatial representation of a home range should facilitate efficient foraging and promote the use of effective escape routes to shelter. Although a few experiments have shown some species of fish are capable of simple spatial behaviour, little is known about the behavioural mechanisms they use to orient as they forage. Whether juvenile Atlantic salmon, Salmo salar, have the capacity to use conspicuous visual landmarks to help them track a moving resource was investigated. The experiment was then modified to determine whether the salmon could continue to track the resource in the absence of conspicuous visual cues. The salmon followed a moveable food source in the presence and, after retraining, in the absence of distinct coloured landmarks. It is suggested that juvenile salmon may be capable of using multiple forms of cue to help them solve spatial tasks such as tracking a moving resource.

Lake‐use by juvenile Atlantic salmon (Salmo salarL.) and other salmonids in northern Norway

Abstract–The utilization of lakes, and inlet and outlet streams by juvenile Atlantic salmon (Salmo salarL.), brown trout (Salmo truttaL.) and Arctic charr (Salvelinus alpinus(L.), were investigated in 16 watercourses northern Norway, all known to inhabit salmon stocks. In lakes, fish were caught by small mesh size gill nets, while in rivers fish were caught electrofishing. In the shallow littoral (0‐3 m depth) there were juvenile salmon in 15 of 19 investigated lakes, juvenile trout in 17 and juvenile charr in seven. Trout dominated significantly in numbers in the shallow littoral of seven lakes, while salmon and charr dominated in three lakes each. When trout and salmon were frequent in the shallow littoral, charr was usually not present in this habitat, but were found in the profundal zone in most of the lakes. Atlantic salmon parr utilized both shallow and deep lakes, and used both stones and macrophytic vegetation as shelter. The utilization of lakes by salmon parr seemed to be closely related to utilization of small inlet streams for spawning. In most inlet and outlet streams salmon dominated over trout in numbers, while charr were absent. This is the first documentation of lake‐use by naturally occurring salmon parr in Scandinavia.