Modulation of cellular innate immunity by Lepeophtheirus salmonis secretory products

Lepeophtheirus salmonis produces pharmacologically active substances that have been shown to modify genetic expression of inflammatory mediators in SHK-1 cells and head kidney macrophages of salmon. Differences in genetic expression among genera of Oncorhynchus and Salmo reflect different susceptibilities to L. salmonis. This study was conducted to determine if the presence of L. salmonis secretory products (SEPs)(1) alters the cellular innate immune response (specifically macrophage function) among several salmonids. Phagocytic assays were performed using SHK-1 cells and macrophages isolated from pink (Oncorhynchus gorbuscha), chum (Oncorhynchus keta) and Atlantic (Salmo salar) salmon following incubation with SEPs and Aeromonas salmonicida. Respiratory burst assays were analyzed using pink, chum and Atlantic salmon macrophages after exposure to SEPs. For SHK-1 cells, incubation with SEPS led to dose-dependent increases in phagocytosis. Following incubation with SEPs, chum salmon macrophages had the highest phagocytic index (55.1%) followed by Atlantic (26.4%) and pink (15.8%) salmon. In contrast, respiratory burst response was greatest in pink salmon and minimal in the other two species. Our results suggest that the cellular innate immune response of salmon is modified in the presence of L. salmonis secretions and differences observed among species provide insight into species-specific consequences of sea lice infection.

Does river of origin influence the early marine migratory performance of Salmo salar?

The early marine migratory behaviour of two populations of hatchery-reared Atlantic salmon Salmo salar was compared in a common-garden experiment. Post-smolts from a river in a long fjord (Laerdal River, 144 km from the open coastline, n = 79) and a short fjord (Flekke River, 20 km from the open coastline, n = 80) in western Norway were tagged with acoustic transmitters and released during the spring of 2005 and 2006 in the inner part of the Hardangerfjord system (Opo River mouth, 179 km from the open coastline). The migratory behaviour of the tagged fish was monitored by acoustic listening stations in the fjord system up to 167 km from the release site. The Laerdal fish began migrating before the Flekke fish and had higher progression rates in the middle part of the fjord system. A greater number of Laerdal fish was detected along the most direct migratory route and in the outermost part of the Hardangerfjord system, which is indicative of a higher survival. The results from this study demonstrate differences in early marine migratory behaviour between S. salar from two different stocks and suggest that the distance a S. salar population travels to reach the open coastline may influence its early marine migratory behaviour and performance. The selective pressures of marine predation and arrival time at feeding areas in the ocean may be stronger for stocks with a longer inshore migration, creating more efficient migrants over time.

Metabolic adaptations of oxidative muscle during spawning migration in the Atlantic salmon Salmo salar L

The adaptability/plasticity of the highly oxidative red muscle in Atlantic salmon was demonstrated during spawning migration. Substrate concentrations and the enzymatic pathways of ATP production were examined in red muscle obtained from Atlantic salmon at different sites along their migratory route in the Exploits River, Newfoundland, Canada. Individuals were chronologically sampled from a seawater site, two sites upstream, and at spawning. The 20% decrease in salmon body weight during the later stages of migration was accompanied by large decreases (mg dry weight(-1)) in both glycogen (P < 0.01) and total muscle lipid (P < 0.01). In contrast, water content and protein concentration (mg dry weight(-1)) of the red muscle increased by 25 and 34%, respectively, at spawning. Enzymes of the glycolytic pathways demonstrated a significant (P < 0.001) decrease in maximal activity as migration proceeded whereas enzymes of the oxidative phosphorylation pathways, specifically the citric acid cycle enzymes, exhibited an increase (P < 0.001) in maximal activity at spawning. The antioxidant enzyme superoxide dismutase also demonstrated an increase (P < 0.001) in maximal activity during the latter stages of migration. These adaptations imply that the red epaxial muscle of Atlantic salmon has a more efficient means of oxidizing lipids, while minimizing free radical damage, during the later stages of migration and spawning, thereby potentially increasing post spawning survival.

Recent salmon declines: a result of lost feeding opportunities due to bad timing?

As the timing of spring productivity blooms in near-shore areas advances due to warming trends in global climate, the selection pressures on out-migrating salmon smolts are shifting. Species and stocks that leave natal streams earlier may be favoured over later-migrating fish. The low post-release survival of hatchery fish during recent years may be in part due to static release times that do not take the timing of plankton blooms into account. This study examined the effects of release time on the migratory behaviour and survival of wild and hatchery-reared coho salmon (Oncorhynchus kisutch) using acoustic and coded-wire telemetry. Plankton monitoring and near-shore seining were also conducted to determine which habitat and food sources were favoured. Acoustic tags (n = 140) and coded-wire tags (n = 266,692) were implanted into coho salmon smolts at the Seymour and Quinsam Rivers, in British Columbia, Canada. Differences between wild and hatchery fish, and early and late releases were examined during the entire lifecycle. Physiological sampling was also carried out on 30 fish from each release group. The smolt-to-adult survival of coho salmon released during periods of high marine productivity was 1.5- to 3-fold greater than those released both before and after, and the fish's degree of smoltification affected their downstream migration time and duration of stay in the estuary. Therefore, hatchery managers should consider having smolts fully developed and ready for release during the peak of the near-shore plankton blooms. Monitoring chlorophyll a levels and water temperature early in the spring could provide a forecast of the timing of these blooms, giving hatcheries time to adjust their release schedule.

Genetic versus rearing-environment effects on phenotype: hatchery and natural rearing effects on hatchery- and wild-born coho salmon

With the current trends in climate and fisheries, well-designed mitigative strategies for conserving fish stocks may become increasingly necessary. The poor post-release survival of hatchery-reared Pacific salmon indicates that salmon enhancement programs require assessment. The objective of this study was to determine the relative roles that genotype and rearing environment play in the phenotypic expression of young salmon, including their survival, growth, physiology, swimming endurance, predator avoidance and migratory behaviour. Wild- and hatchery-born coho salmon adults (Oncorhynchus kisutch) returning to the Chehalis River in British Columbia, Canada, were crossed to create pure hatchery, pure wild, and hybrid offspring. A proportion of the progeny from each cross was reared in a traditional hatchery environment, whereas the remaining fry were reared naturally in a contained side channel. The resulting phenotypic differences between replicates, between rearing environments, and between cross types were compared. While there were few phenotypic differences noted between genetic groups reared in the same habitat, rearing environment played a significant role in smolt size, survival, swimming endurance, predator avoidance and migratory behaviour. The lack of any observed genetic differences between wild- and hatchery-born salmon may be due to the long-term mixing of these genotypes from hatchery introgression into wild populations, or conversely, due to strong selection in nature--capable of maintaining highly fit genotypes whether or not fish have experienced part of their life history under cultured conditions.

Effects of the sea louse Lepeophtheirus salmonis on temporal changes in cortisol, sex steroids, growth and reproductive investment in Arctic charr Salvelinus alpinus

Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for 34 days to either a high (mean +/-s.e. 0.15 +/- 0.01 sea lice Lepeophtheirus salmonis g(-1) fish mass) (HI), medium (0.07 +/- 0.00 sea lice g(-1) fish mass) (MI) or no [control (C)] sea-lice infection during early stages of gonad development (June to July). Infection with sea lice resulted in increased plasma cortisol concentrations and this was related to intensity of infection; females tended to have higher cortisol concentrations than males at high infection intensities (HI group: female c. 130 ng ml(-1); male c. 80 ng ml(-1)). Plasma osmolality (C c. 330, MI c. 350 and HI c. 415 mOsm) and chloride concentrations (C c. 135, MI c. 155 and HI c. 190 mM) increased significantly with infection intensity, indicating osmoregulatory problems in infected fish. A strong positive relationship between plasma osmolality and cortisol concentration was recorded. Plasma sex-steroid concentrations were influenced negatively by sea-lice infection, particularly in the HI group, and were inversely related to plasma cortisol concentrations. The most heavily infected fish postponed the initiation of reproductive development until exposed to fresh water and timing of ovulation tended to be delayed in these fish. Growth rate and condition were negatively influenced by sea-lice infection and growth rate was inversely related to plasma cortisol concentrations. Sea-lice infection resulted in mortality among females in the HI group, and the proportion of maturing females was lower in the MI group (46%) than in the controls (85%). Egg production in the MI and HI groups was c. 50 and 30% of the C group. Egg size, embryonic survival and fry mass did not differ across groups. Sea lice influence reproductive development and egg production in S. alpinus, and consequently these parasites may influence populations via sublethal effects on broodfish, affecting growth and condition, and their reproductive output.

An investigation into the poor survival of an endangered Coho salmon population

To investigate reasons for the decline of an endangered population of coho salmon (O. kisutch), 190 smolts were acoustically tagged during three consecutive years and their movements and survival were estimated using the Pacific Ocean Shelf Tracking project (POST) array. Median travel times of the Thompson River coho salmon smolts to the lower Fraser River sub-array were 16, 12 and 10 days during 2004, 2005 and 2006, respectively. Few smolts were recorded on marine arrays. Freshwater survival rates of the tagged smolts during their downstream migration were 0.0-5.6% (0.0-9.0% s.e.) in 2004, 7.0% (6.2% s.e.) in 2005, and 50.9% (18.6% s.e.) in 2006. Overall smolt-to-adult return rates exhibited a similar pattern, which suggests that low freshwater survival rates of out-migrating smolts may be a primary reason for the poor conservation status of this endangered coho salmon population.

Concurrent injection of a rhabdovirus-specific DNA vaccine with a polyvalent, oil-adjuvanted vaccine delays the specific anti-viral immune response in Atlantic salmon, Salmo salar L

Vaccines are commonly used in salmonid aquaculture as a method of disease prevention. Although there is a substantial amount of published research regarding the immunological and physiological effects following the injection of different polyvalent vaccines and DNA vaccines, there are no published reports examining the physiological and immunological effects of concurrent vaccine injection, which is the situation encountered in aquaculture. Using key immunological parameters such as lysozyme activity and specific antibody titres we examined the short-term activation of the immune response of cultured Atlantic salmon (Salmo salar L.) following concurrent injection with a traditional, polyvalent, oil-adjuvanted vaccine (AV) and an IHNV-specific DNA vaccine (DV). Our results indicate that different aspects of the innate and adaptive immune responses are influenced in either a positive or negative manner. While concurrent vaccine injection elicited an increase in lysozyme activity, changes in antibody titre (Ab) were antigen specific. The production of anti-Aeromonas salmonicida Abs was significantly greater in the combined vaccine group at 296 degree days post-vaccine injection (dd pvi), while the production of anti-Listonella anguillarum Abs was significantly greater at 106 dd pvi in the combined vaccine group. Of even greater interest was the apparent delay in production of IHNV-specific neutralizing antibodies (NAb) when the DV was injected concurrently with the polyvalent AV. The results indicated that concurrent injection of a polyvalent oil-AV and a DV can be beneficial to the production of antibodies; however, the specific anti-viral response may be delayed.

The association between metabolic rate, immune parameters, and growth performance of rainbow trout, Oncorhynchus mykiss (Walbaum), following the injection of a DNA vaccine alone and concurrently with a polyvalent, oil-adjuvanted vaccine

This research demonstrates a significant increase in routine metabolic rate (RMR) following injection of a DNA vaccine concurrently with a polyvalent, oil-adjuvanted vaccine. The increase in RMR was transient and associated with increased activity of both the non-specific and specific immune responses. Rainbow trout (Oncorhynchus mykiss) were injected with a DNA vaccine (DV), a commercially available polyvalent, oil-adjuvanted vaccine (AV), or the two vaccines in combination and sampled at 203, 305, and 406 days (dd) post-vaccine injection (pvi) for RMR and key immune parameters (serum lysozyme activity, serum neutralization antibody titres). The RMR of fish that received both the DV and the AV was significantly higher at 203 dd pvi, compared to fish from all other treatment groups which included the control, the AV, and the DV groups. The increased RMR corresponded to elevated levels of serum lysozyme activity and an earlier seroconversion of virus-specific neutralizing antibodies. To determine if growth performance was affected by the transient increase in RMR, specific growth rate (SGR), percent daily weight gain (WG), and feed conversion ratio (FCR) were determined at 798, 1204, and 1610 dd pvi. Although fish in all three vaccine groups showed significant increases in SGR and WG at 798 and 1610 dd pvi compared to the control group, the overall weight of the fish was not different at the end of the experiment. In summary, this study shows that concurrent injection of a DV and an AV transiently increases the RMR of rainbow trout and changes the manner in which the immune response occurs, but does not affect the overall growth performance of the fish.

Survival of migrating salmon smolts in large rivers with and without dams

The mortality of salmon smolts during their migration out of freshwater and into the ocean has been difficult to measure. In the Columbia River, which has an extensive network of hydroelectric dams, the decline in abundance of adult salmon returning from the ocean since the late 1970s has been ascribed in large measure to the presence of the dams, although the completion of the hydropower system occurred at the same time as large-scale shifts in ocean climate, as measured by climate indices such as the Pacific Decadal Oscillation. We measured the survival of salmon smolts during their migration to sea using elements of the large-scale acoustic telemetry system, the Pacific Ocean Shelf Tracking (POST) array. Survival measurements using acoustic tags were comparable to those obtained independently using the Passive Integrated Transponder (PIT) tag system, which is operational at Columbia and Snake River dams. Because the technology underlying the POST array works in both freshwater and the ocean, it is therefore possible to extend the measurement of survival to large rivers lacking dams, such as the Fraser, and to also extend the measurement of survival to the lower Columbia River and estuary, where there are no dams. Of particular note, survival during the downstream migration of at least some endangered Columbia and Snake River Chinook and steelhead stocks appears to be as high or higher than that of the same species migrating out of the Fraser River in Canada, which lacks dams. Equally surprising, smolt survival during migration through the hydrosystem, when scaled by either the time or distance migrated, is higher than in the lower Columbia River and estuary where dams are absent. Our results raise important questions regarding the factors that are preventing the recovery of salmon stocks in the Columbia and the future health of stocks in the Fraser River.

Miniature electronic technologies now allow researchers to track a salmon's migration from its birthplace in a river's headwaters in the Rocky Mountains to the North Pacific, opening a window on the mysteries of migration and survival. Surprisingly, outward migrating salmon (smolts) have similar survival during migration down dammed and undammed rivers, challenging widely held notions about factors affecting salmon abundance. Elements of the large-scale POST (Pacific Ocean Shelf Tracking) acoustic telemetry array revealed the migrations. Although salmon smolt survival to the Pacific Ocean was comparable in both the dammed Columbia and undammed Fraser rivers, it was higher in the Columbia once distance or travel time was taken into account—and higher within the hydropower system than below the dammed section. There is not yet enough evidence to determine whether (1) the Fraser has a problem that reduces salmon survival to that of a heavily dammed river or (2) factors other than dams play a larger, unsuspected role in salmon survival. Wherever future research leads on those questions, the new fish tagging technology has demonstrated itself as a useful tool for obtaining objective scientific data with important value in a number of public policy arenas.

Electronic tagging of two species of salmon smolts reveals similar survival rates during migration down the dammed Columbia and undammed Fraser Rivers, challenging popular notions about factors affecting salmon abundance.

Effects of soft-water acclimation on the physiology, swimming performance, and cardiac parameters of the rainbow trout, Oncorhynchus mykiss

Rainbow trout acclimated to soft water were submitted to an incremental velocity trial, and exhibited a 14% decrease in critical swimming speed (U(crit) * 1.37 +/- 0.055 vs. 1.54 +/- 0.044 m s(-1)) compared to fish kept in hard water. After a standardized swimming protocol, soft-water-acclimated fish had higher blood lactate concentrations (6.5 +/- 0.66 and 6.0 +/- 0.64 mmol L(-1) (soft water) vs. 5.0 +/- 0.46 and 3.9 +/- 0.32 mmol L(-1) (hard water)), revealing a greater use of anaerobic metabolism for the same exercise. Cardiovascular parameters were investigated while fish were swimming at increasing water velocities, revealing that soft-water-acclimated fish had lower increases in heart rate (105% vs. 118% of pre-exercise values), due to higher heart rates observed during acclimation and during the first 10 min of the swimming trial. This was also reflected by the plateau in heart rate and stroke volume observed during the swimming protocol, which can be attributed to increased cardiovascular function in response to soft-water acclimation. These results are in accord with previously reported increases in blood-to-water diffusion distance, due to proliferation of chloride cells at the gills in response to soft-water conditions, and underscore the costs and limitations of soft-water acclimation.

Growth and performance of Atlantic salmon, Salmo salar L., following administration of a rhabdovirus DNA vaccine alone or concurrently with an oil-adjuvanted, polyvalent vaccine

This research demonstrates for the first time an absence of growth-related side effects in Atlantic salmon, Salmo salar L., following the injection of a DNA vaccine alone or concurrently with a commercially available, polyvalent, oil-adjuvanted vaccine. Using weight and specific growth rate measurements, individually tagged Atlantic salmon were monitored for 2028 degree days (dd) post-vaccination. During this time, DNA-vaccinated fish did not differ in weight, length, condition factor or specific growth rate compared to unvaccinated control fish. While differences in weight were observed between unvaccinated control and concurrently vaccinated fish, there were no significant differences in weight, length, condition factor or specific growth rate between concurrently vaccinated fish and adjuvant-vaccinated fish, suggesting that only adjuvant vaccination affected growth. To further determine if concurrent injection of a DNA vaccine and a polyvalent, oil-adjuvanted vaccine had a physiological impact on the Atlantic salmon, swimming performance tests were performed at 106 dd post-vaccination with U(crit,1), U(crit,2), the U(crit) recovery ratio (RR) and the normalized RR being similar to values obtained from unvaccinated control fish. In summary, this study shows that concurrent injection of a DNA vaccine and a polyvalent, oil-adjuvanted vaccine does not negatively influence the growth or swimming performance of Atlantic salmon compared to adjuvant vaccination alone.

Physiological effects of thermomechanical newsprint mill effluent on Atlantic salmon (Salmo salar L.)

Anadramous Atlantic salmon (Salmo salar L.) returning to Exploits River, Newfoundland, Canada, to spawn encounter low concentrations of thermomechanical pulp (TMP) effluent as they migrate upstream past an integrated newsprint mill. Various physiological responses of adult Atlantic salmon from the Exploits River were studied under laboratory conditions. The effects of a 6-h exposure to 0%, 6%, 12%, or 25% (v/v) TMP effluent or an increasing concentration gradient of effluent (0-25%) on cardiac output (Q ), critical swimming performance (U(crit)), hematocrit, and blood glucose, cortisol, lactate, and osmolality were examined. Relative to other treatment groups, Q during routine and low-level activity was 7-10% higher in fish exposed to at least 12% effluent. The 25% exposure group had a distinctly lower U(crit) and scope for increase in Q than the other treatment groups. These findings suggest that effluent exposure elevates physiological maintenance and repair costs, resulting in a reallocation of energetic resources.

Changes in ventilation, metabolism, and behaviour, but not bradycardia, contribute to hypoxia survival in two species of Amazonian armoured catfish

Amazonian armoured catfishes exhibit substantial cardiac hypoxia tolerance, but little is known concerning organismal cardiorespiratory, metabolic, and behavioural responses to low oxygen levels. This study assessed the general mechanisms used by two species of armoured catfish, Glyptoperichthyes gibbceps and Liposarcus pardalis, to survive the frequent periods of hypoxia encountered in the Amazon River. The gill ventilation rate (fv) and heart rate (fh) were studied under controlled hypoxia in aquaria and under natural hypoxia in a simulated pond. Glyptoperichthyes gibbceps were fitted with radiotelemetry tags and held in field cages to study their habits of depth selection and air breathing. When denied aerial respiration under hypoxia in aquaria, G. gibbceps increased fv, but neither they nor L. pardalis exhibited alterations in fh. An increase in fvwas initially observed in G. gibbceps during pond hypoxia before aerial respiration was initiated and fvdeclined. Glyptoperichthyes gibbceps were hyperglycaemic under normoxia, and extremely large increases in plasma glucose and lactate concentrations were observed under hypoxia. Field studies confirmed their nocturnal behaviour and showed that air breathing increased at night, regardless of dissolved oxygen concentration. Our results show that armoured catfishes preferentially up-regulate fvand anaerobic metabolism and exhibit no bradycardia during hypoxia.

Inhibition of oxygen consumption by pentachlorophenol and tetrachloroguaiacol in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) were exposed for 24 h to concentrations representing 100, 50 and 25% of the 96 h-LC50 of pentachlorophenol (PCP) or tetrachloroguaiacol (TCG), and their oxygen consumption, cardiac output, heart rate and stroke volume were measured at regular intervals. Oxygen consumption either remained stable at basal levels (PCP), or increased to 130% of basal levels (TCG) when fish were exposed to the 96 h-LC50 of each chemical. However, oxygen consumption decreased to about 50-60% of basal levels when fish were exposed to concentrations of PCP or TCG representing 50 and 25% of the 96 h-LC50. This decrease in oxygen consumption did not appear to affect cardiac function since cardiac output, heart rate and stroke volume remained stable. PCP is best known for its capacity to uncouple oxidative phosphorylation and increase oxygen consumption. However, this study showed that it can also decrease oxygen consumption, and that the effects of PCP and TCG on fish metabolism are similar.

Swimming performance of walleye (Stizostedion vitreum)

Swimming performance of walleye (Stizostedion vitreum) from a wild population was measured relative to fork length (0.18-0.67 m) and water temperature (5.8-20.5°C), to provide models for setting water velocities in fishways and culverts. Ucrit60 (the highest speed maintainable for 60 min) values ranged from 0.30 to 0.73 m/s and increased significantly with length and temperature. Ucrit10 (the highest speed maintainable for 10 min) values ranged from 0.43 to 1.14 m/s and also increased significantly with fish length and water temperature. When startled, walleye were able to attain higher speeds (1.60-2.60 m/s) during short (temperature-independent) bursts of swimming activity. The relatively low Ucrit60 values suggest that walleye possess a narrow scope for aerobic activity compared with other species, which may account for their poor performance in fishways. However, the small differences between Ucrit60 and Ucrit10 values and the large differences between Ucrit10 and fast-start performance suggest that low passage efficiency may be caused by a behavioural disinclination to switch from low to high intensity activity.