Phagocytosis by B-cells and neutrophils in Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.)

Phagocytosis by fish cells has mostly been studied using adherent leucocytes, excluding suspended cells such as the majority of B-cells and neutrophils, but a recent study describes professional phagocytosis of latex beads and bacteria by B-cells from rainbow trout. In the present study, phagocytosis by B-cells and neutrophils from salmon and cod was studied. Leucocytes were isolated from peripheral blood (PBL) and head kidney (HKL). By flow cytometry analyses, proportions of MAb labelled cell populations with internalized fluorescent beads, as well as the number of beads within each cell, could be determined. Phagocytic capacity and ability were demonstrated in B-cells and neutrophils from salmon and cod. In salmon, B-cells had higher phagocytic ability than neutrophils in HKL, but not in PBL. For cod the phagocytic ability of B-cells were lower than for neutrophils in both HKL and PBL, but the phagocytic capacity of cod B-cells were higher than for neutrophils in both HKL and PBL. For salmon B-cells the phagocytic capacity was lower than or similar to neutrophils in HKL and PBL. The total phagocytic ability of leucocytes was different in the species studied. The highest phagocytic ability was observed in cod, showing similar values for PBL and HKL. Salmon PBL displayed about twice the phagocytic ability of cod PBL. There seemed to be some major differences between the two fish species concerning phagocytosis. In salmon, a rather large proportion of phagocytic leucocytes were phagocytic B-cells, indicating that B-cells may have an important function in particle clearance in this species. In cod, phagocytic leucocytes in HKL and PBL were mostly neutrophils, and only a small proportion of B-cells were phagocytic, supporting the more prominent role of innate immune functions in cod neutrophils.     

Net ground speed of downstream migrating radio-tagged Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) smolts in relation to environmental factors

The downstream migration of Atlantic salmon (Salmo salarL.) and sea trout smolt (S. trutta L.) was investigated using radio telemetry in the spring of 1999 and 2000. Forty wild sea trout smolts, 20 F1 sea trout smolts, 20 hatchery salmon smolts and 20 salmon smolts from river stockings were radio tagged and released in the Danish River Lilleaa. The downstream migration of the different groups of fish was monitored by manual tracking and by three automatic listening stations. The downstream migration of radio tagged smolts of both species occurred concurrently with their untagged counterparts. The diel migration pattern of the radio tagged smolts was predominantly nocturnal in both species. Wild sea trout smolt migrated significantly faster than both the F1 trout and the introduced salmon. There was no correlation between net ground speed, gill Na⁺,K⁺-ATPase activity or fish length in any of the different groups. The migration speed of wild sea trout smolts was positively correlated with water discharge in both years. In F1 sea trout smolts, migration speed was positively correlated with temperature in 1999. The migration speed of salmon smolts did not correlate to any of the investigated parameters.     

Sperm motility characteristics of wild Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta m. trutta L.) as a basis for milt selection

The aim of the study was to determine the sperm motility parameters in wild Atlantic salmon and sea trout to define criteria important for selection of milt for controlled fertilisation. Parameters for these species were determined in the fish migrating into north‐western rivers of Poland at spawning time. Eight motility parameters percentage of motile sperm (MOT), curvilinear velocity (VCL), average path velocity (VAP), straight line velocity (VSL), linearity (LIN), straightness (STR), amplitude of lateral head displacement (ALH), beat cross frequency (BCF) and motility duration were subjected to computer‐assisted sperm analysis (CASA). Milt of most individuals studied representing both salmon and trout showed spermatozoa density of 12–22 × 10⁹ ml^?1 and a high percentage of motile sperm (>70%). In general, spermatozoa swim progressively with slightly curved trajectories (mean STR = 70%, LIN = 65%) and velocity VCL of 180 μm s^?1 (salmon) and 190 μm s^?1 (trout), at 10 s post‐activation. Such sperm is easily accessible in the wild populations of salmon and sea trout and is recommended for use in reproduction trials. The spermatozoa of sea trout seem to show a greater tendency to follow curvilinear trajectories than those of salmon, both in the beginning and the final phase of motion. In the first phase of motility, the values and time dependencies of the motility parameters were similar in both species. In the end phase of movement differences in LIN and BCF time dependencies were found in the samples representing the two species. In salmon the linearity and beat cross frequency remained stable in this phase, contrary to the patterns in sea trout for which LIN decreased while BCF increased in the end period of movement. Durations of movement were similar in both species (ranges of 20–40 s).     

Astaxanthin binding to solubilized muscle proteins of Atlantic salmon (Salmo salar L.), haddock (Melanogrammus aeglefinus L.) and Atlantic halibut (Hippoglossus hippoglossus L.)

A study was conducted to compare astaxanthin binding ability of solubilized muscle proteins of Atlantic salmon (Salmo salar L.), haddock (Melanogrammus aeglefinus L.) and Atlantic halibut (Hippoglossus hippoglossus L.). Muscle proteins of juvenile Atlantic salmon, haddock and halibut were solubilized by sequential extraction of muscle tissue using low ionic strength solutions. Electrophoretic protein profiles of the six solubilized fractions from these species were similar. Each solubilized fraction from the three species was examined for its relative astaxanthin binding capacity. The amount of bound astaxanthin was significantly different (P < 0.05) among the six fractions of each species. Significant differences in astaxanthin binding were only found for fractions A and E among the species. The amount of bound astaxanthin in various fractions of each species showed a good correlation (R² = 0.80–0.92) with the ANS (8-anilino-1-naphthalenesulfonate) fluorescence intensity of those fractions. The pattern and extent of astaxanthin binding to the muscle proteins of juvenile salmon, haddock and halibut is comparable to that reported previously for adult Atlantic salmon [Saha, M.R., Ross, N.W., Gill, T.A., Olsen, R.E., Lall, S.P., 2005. Development of a method to assess binding of astaxanthin to Atlantic salmon S. salar L. muscle proteins. Aquacult. Res. 36, 336–343.]. These combined observations suggest that the carotenoid binding capacity of the muscle proteins of salmon is not the limiting factor in the deposition of carotenoid in their flesh.     

Physiological stress responses to confinement in diploid and triploid Atlantic salmon

Confinement of juvenile Atlantic salmon Salmo salar from four different populations (all–female diploids, all–female triploids, mixed sex diploids and mixed sex triploids) either before (FW parr) or after (SW smolts) transfer to sea elevated plasma cortisol and plasma lactate from control levels irrespective of ploidy status. Both before and after confinement, plasma cortisol levels in SW smolts (6–174 ng ml^–1) were higher than those in FW parr (4–58 ng ml^–1), which possibly reflected the physiological challenge of acclimation to SW. Mixed sex populations of SW smolts had higher cortisol levels than all–female populations. The duration of confinement (1, 3 or 6 h) affected the magnitude of the plasma cortisol and lactate responses in SW smolts. Plasma cortisol levels in diploid and triploid SW smolts subjected to 2 h of confinement decreased to pre–stress levels within 6 h post–confinement. Plasma lactate levels were not significantly different from pre–stress levels 48 h after confinement. As no difference exists in primary and secondary stress responses of Atlantic salmon of differing ploidy status, it is unlikely that differences in mortality rates between diploid and triploid populations under commercial conditions can be attributed to differences in their physiological responses to periods of stress lasting up to 6 h.     

Kinetics of Mx expression in rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar L.) parr in response to VHS-DNA vaccination

The duration of the Mx mRNA response to an intramuscular injection of the viral haemorrhagic septicaemia virus (VHSV) glycoprotein (G) gene DNA vaccine as well as to the control plasmid was determined in rainbow trout at 14 degrees C over a period of 11 weeks. The Mx response was detectable on day 7, peaked on day 14 and returned to pretreatment levels on day 21 and thereafter. No increase in Mx expression was detectable to the control plasmid. In further experiments, the kinetics of the Mx response were compared in rainbow trout and Atlantic salmon parr kept at 10 degrees C and injected with the DNA vaccine or the synthetic double-stranded RNA, poly I:C. In both species there was a rapid response to poly I:C detectable from day 1, reaching maximum from days 3 to 9 and decreasing to background level by day 12. The peak level and return to background was reached slightly later in salmon. In both species the response to the VHS/DNA vaccine was slower to begin, not being detectable on days 1 and 3, but elevated levels were found on day 6. However, in the salmon parr, the peak level was on day 6 and the signal disappeared by day 12, while in the rainbow trout, the response peaked at day 12 and lasted until day 21. The kinetics of the Mx response to the VHS/DNA vaccine in rainbow trout correlate with the early non-specific protection against VHS in this species following vaccination. It is speculated that the more transient Mx response in Atlantic salmon parr to the DNA vaccine may be related to the innate resistance of salmon to VHS.     

Population changes after two years of salmon (Salmo salar L.) stocking in upland trout (Salmo tmtta L.) streams

The survival of salmon stocked in upland trout streams in the presence of salmon parr was found to be only about half the value recorded when trout alone made up the resident stock. Changes in the trout population were also recorded following the two years of salmon stocking, and these suggested that the presence of salmon parr may also influence trout fry survival. The findings are discussed in the context of habitat competition and total stream holding capacity.     

Carbon distribution and nitrogen partitioning in a soil-plant system with barley (Hordeum vulgare L.), ryegrass (Lolium perenne) and rape (Brassica napus L.) grown in a14CO2-atmosphere

To examine the influence of plant-microorganism interactions on soil-N transformations (e.g. net mineralization, net immobilization) a pot experiment was conducted in a¹⁴C-labelled atmosphere by using different (two annuals, one perennial) plants species. It was assumed that variation in below-ground, microorganism-available C would influence N transformations in soil. Plant species were fertilized (low rate) with¹⁵N-labelled nitrogen and grown, during days 13 and 62 after germination, in a growth chamber with a¹⁴C-labelled atmosphere. Nitrification was inhibited by using nitrapyrin (N-Serve). During the chamber period, shoots were harvested, and associated roots and soil were collected on two sampling occasionm, e.g. after 4 and 7 weeks in the growth chamber.The distribution of net (%) assimilated¹⁴C was significantly affected by both plant and time factors, and there was a significant plant × time interaction. There were significant differences between plants in all plant-soil compartments examined as well as in the degree of the plant × time interaction.Differences in the¹⁴C distribution between plants were due to both interspecific and developmental variation. In general, when comparing¹⁵N and¹⁴C quantities between species, many of the differences found between plants can be explained by the differences determined in the weight of shoot or root parts. Despite the fact that amounts of C released were greater in ryegrass than in the other plant-treatments no unequivocal evidence was found to show that the effects of plant-microorganism interactions on soil-N mineralization were greater under ryegrass. Possible mechanisms accounting for the partitioning of N found among plant biomass, soil biomass and soil residues are discussed.     

Depression of Photosynthesis, Growth, and Yield in Field-Grown Green Pepper (Capsicum annuum L.) Exposed to Acidic Fog and Ambient Ozone

The relationship among physiological, injury, growth, and yield responses was examined in field-grown green pepper (Capsicum annuum L. `California Wonder') subjected to two airborne environmental stresses. The primary objectives were to determine if the stresses could cause alterations in the plant responses, and to determine if any stress induced alterations in physiological or injury responses were correlated with effects on growth or yield. Responses were monitored in green pepper exposed to simulated acidic fog alone, or in combination with ambient concentrations of ozone in open-top field chambers. Both highly acidic fog and ambient ozone depressed green pepper growth and yield responses via the inhibition of photosynthesis. Applications of highly acidic fog (i.e. two exposures of pH 1.68 fog per week for 11 weeks) caused a significant depression of net photosynthesis, reduction in leaf buffering capacity, and an extensive amount of leaf injury. These alterations closely paralleled decreases in growth and yield on a percentage basis. In contrast, ambient ozone had similar impacts on net photosynthesis, growth and yield, but enhanced leaf buffering capacity, and caused no visible injury. The pollutant-specific differences in plant response are discussed with respect to whole-plant carbon metabolism and physiological compensation.     

Genetic variation in haemolytic activity in Atlantic salmon (Salmo salar L.)

Spontaneous and antibody-dependent haemolytic activity against sheep red blood cells (SRBC) has been studied in serum from Atlantic salmon, Salmo salar L. Considerable increase in haemolytic activity was detected when SRBC were sensitized with haemolysin produced in Atlantic salmon. Haemolytic activity was sensitive both to divalent cations and to heat treatment. Significant reduction in haemolytic activity was detected after absorption with SRBC, indicating the presence of natural antibody against SRBC in Atlantic salmon serum. Persistent haemolytic activity of unsensitized SRBC in serum absorbed to remove natural antibodies was found, which suggests the activation of the alternative complement pathway, while the observed increased haemolytic activity in the presence of specific antibody against SRBC suggests activation of the classical complement pathway. Spontaneous and antibody-dependent haemolytic activity were both analysed in absorbed and non-absorbed sera in a family material of Atlantic salmon. The material consisted of 574 fish belonging to 57 fullsib groups within 20 paternal halfsib groups. Fish with signs of sexual maturity generally showed reduced haemolytic activity. Statistically significant effect of sire on the spontaneous haemolytic activity of both absorbed and nonabsorbed serum, and on antibody-dependent activity, provides evidence of significant additive genetic variation in both the alternative and the classical complement activation in Atlantic salmon. Neither on a phenotypical nor on a family basis were the two traits statistically correlated. The estimated heritabilities were 0.2–0.3 with a standard error of approximately 0.1.     

Effects of a high plant protein diet on the somatotropic system and cholecystokinin in Atlantic salmon (Salmo salar L.)

To investigate the endocrine signalling from dietary plant protein on somatotropic system and gastrointestinal hormone cholecystokinin (CCK), two iso-amino acid diets based on either high plant or high fish meal protein were fed to Atlantic salmon. Salmon with an average starting weight of 641 ± 23 g (N = 180), were fed a fish meal (FM) based diet (containing 40% FM) or diets mainly consisting of blended plant proteins (PP) containing only 13% marine protein, of which only 5% was FM for 3 months. mRNA levels of target genes GH, GH-R, IGF-I, IGF-II, IGFBP-1, IGF-IR in addition to CCK-L, were studied in brain, hepatic tissue and fast muscle, and circulating levels of IGF-I in plasma of Atlantic salmon were measured. We detected reduced feed intake resulting in lower growth, weight gain and muscle protein accretion in salmon fed plant protein compared to a diet based on fish meal. There were no significant effects on the regulation of the target genes in brain or in hepatic tissues, but a trend of down-regulation of IGF-I was detected in fast muscle. Lower feed intake, and therefore lower intake of the indispensable amino acids, may have resulted in lower pituitary GH and lower IGF-I mRNA levels in muscle tissues. This, together with higher protein catabolism, may be the main cause of the reduced growth of salmon fed plant protein diet. There were no signalling effects detected either by the minor differences of the diets on mRNA levels of GH, GH-R, IGF-IR, IGF-II, IGFBP-1, CCK or plasma protein IGF-I.     

Cardiovascular responses of three salmonid species affected with amoebic gill disease (AGD)

The cardiovascular effects of amoebic gill disease (AGD) were investigated immediately following surgery in three salmonid species; Atlantic salmon (Salmo salar L.), brown trout (Salmo trutta L.) and rainbow trout (Oncorhynchus mykiss Walbaum). Fish, both naïve (control) and infected (AGD-affected) of each species, were fitted with dorsal aorta catheters and cardiac flow probes. Cardiac output and dorsal aortic pressures were then continuously measured over a 6-h period following surgery. Results showed that Atlantic salmon, brown trout and rainbow trout displayed similar dorsal aortic pressure, cardiac output, and systemic vascular resistance (mean dorsal aotic pressure divided by cardiac output) values. However, the only significant differences relating to disease status i.e. infected or control, were found in Atlantic salmon. Although no significant differences were seen in dorsal aortic pressure values, AGD-affected salmon displayed significantly elevated systemic vascular resistance at 4 and 6 h post surgery. Cardiac output was also approximately 35% lower in AGD-affected salmon compared to the non-affected control counterparts. These results comparatively examine cardiac function in response to AGD across three salmonid species and highlight species-specific cardiovascular responses that occur in association with disease. It is suggested that the apparent cardiac dysfunction seen in AGD-affected Atlantic salmon could, under stressful conditions, become exacerbated. Cardiac failure is therefore suggested to be a possible physiological mechanism by which AGD causes or contributes to mortality in Atlantic salmon.     

Effects of aquaculture related stressors and nutritional restriction on circulating growth factors (GH, IGF-I and IGF-II) in Atlantic salmon and rainbow trout

The effects of aquaculture related stressors on circulating levels of GH, IGF-I and for the first time, IGF-II in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) were investigated. Specifically, circulating growth factor levels were measured in four different experiments. Two 24 h confinement stressor procedures, (one with Atlantic salmon, the other with rainbow trout); following a hypo-osmotic stressor (freshwater bath) in salt water acclimated, adult, Atlantic salmon; and during a 22 day starvation and re-feeding protocol with juvenile Atlantic salmon. Handling and confinement resulted in significant decreases in circulating levels of all three growth factors in Atlantic salmon, and IGF-I and IGF-II (but not GH) in rainbow trout. A 2-3 h freshwater bath to remove gill parasites on a commercial Atlantic salmon aquaculture operation caused a significant decrease in circulating GH and IGF-I concentrations, but no significant change in IGF-II concentration, 2 days post bathing. Starvation for a period of 15 days in Atlantic salmon resulted in a significant increase in circulating GH levels and a significant decrease in circulating IGF-I and IGF-II. Re-feeding of starved fish for 7 days resulted in a significant decrease in GH to the concentration measured in continually fed fish, however re-feeding did not change plasma levels of IGF-I and IGF-II relative to continually starved fish. The results presented here confirm previously observed handling and confinement stressor induced effects on GH and IGF-I and, for the first time, on IGF-II in salmonids. Furthermore this study confirms the nutritional regulation of GH, IGF-I and IGF-II in juvenile Atlantic salmon.     

A preliminary investigation into the vulnerability of young trout (Salmo trutta L.) and Atlantic salmon (S. salar L.) to downstream displacement by high water velocities

The downstream movement of young trout and salmon in relation to water velocity was studied in simulated river channels. The results are interpreted as showing that these young salmonids pass through a short period when they are very vulnerable to downstream displacement by flow. Behavioural differences between the two species are considered with the influence on fish movement of changing rate of water velocity, light and temperature.     

Genetic protein variation and natural selection in Atlantic salmon (Salmo salav, L.) parr

The principal focus of this study was an examination of the relationship between diallelic variation at the MEP-2 * locus and growth and survival in Atlantic salmon parr. In addition, patterns of growth and survival among genotypes at the AAT-I *, IDDH-I * and ZDHP-2 * loci were also examined. Significant differences in growth were found among MEP-2 * genotypes, with * 100/ 100 homozygotes largest in one of two independent comparisons and the * 125/I25 homozygotes largest in the other. No growth differences were observed among genotypes at any other locus. Although no significant differences were found in survival among genotypes at any locus, results of joint analysis of the patterns of growth and survival among MEP-2 * genotypes were consistent with a model of positive size-selective mortality. The demonstration of growth differences among MEP-2 * genotypes in parr and smolts may indicate an association between selection on this locus in fresh water and previously reported differences in sea-age at maturity among MEP-2 * genotypes in Atlantic salmon.