Going with the Flow: Spatial Distributions of Juvenile Coho Salmon Track an Annually Shifting Mosaic of Water Temperature

A critical challenge for ecologists is to understand the functional significance of habitat heterogeneity and connectivity for mobile animals. Here, we explore how a thermo-regulating fish responds to annual variation in the spatial patterning of thermal and trophic resources. In a third-order stream in coastal Alaska, juvenile coho salmon forage on sockeye salmon eggs at night in cold water and then move to warmer water to increase their digestive capacity. We mapped the spatial distributions of water temperature, juvenile coho salmon, and spawning sockeye salmon across a 5-year period during which summer discharge varied by greater than fivefold. In low flow years, warm water (9–12°C) was only available in thalweg (that is, main-channel) habitat at least approximately 400 m upstream of the cooler habitat (3–7°C) where sockeye salmon spawned. In high flow years, the entire stream thalweg was isothermal at 7–8°C, but inundated off-channel areas generated warm habitats (9–12°C) laterally adjacent to the downstream regions where sockeye salmon spawned. The daytime spatial distribution of juvenile coho salmon shifted from headwater thalweg habitats in low flow years, to downstream off-channel habitats in high flow years. In all years, the majority of juvenile coho salmon sampled during the daytime were found in warm habitat units without sockeye salmon present, yet they exhibited diet contents comprised virtually entirely of sockeye salmon eggs. Thus, thermoregulatory movements by coho salmon were able to track an annually shifting mosaic of water temperature. Our results demonstrate how the spatial habitat heterogeneity and connectivity of intact floodplains can in turn buffer aquatic organisms from high levels of temporal variation in habitat conditions and resource abundance.     

The immune response of tilapia Oreochromis mossambicus and its susceptibility to Streptococcus iniae under stress in low and high temperatures

Mozambique tilapia Oreochromis mossambicus acclimated to 27 degrees C were then held at 19, 23, 27 (control), 31 and 35 degrees C, and were examined for non-specific cellular and humoral responses after 12-96 h. Total leucocyte count decreased significantly when fish were transferred to 19 and 23 degrees C after 48 and 96 h, and when transferred to 35 degrees C over 12-96 h, respectively. Respiratory burst decreased significantly when fish were transferred to 19, 31 and 35 degrees C over 24-96 h, whereas phagocytic activity and phagocytic index decreased significantly when fish were transferred to low temperatures (19 and 23 degrees C) and high temperatures (31 and 35 degrees C) over 12-96 h. Lysozyme activity decreased significantly when fish were transferred to 19 degrees C after 12-96 h, but increased significantly when transferred to 31 and 35 degrees C over 48-96 h. Alternative complement pathway (ACH(50)) also decreased significantly when transferred to 19 and 23 degrees C after 12h, but increased significantly when transferred to 31 and 35 degrees C after 24h. In another experiment, tilapia reared at 27 degrees C were injected intraperitoneally with Streptococcus iniae at a dose of 1 x 10(7)colony-forming units (cfu)fish(-1), and then reared onward at water temperatures of 19, 23, 27 (control), 31 and 35 degrees C. Over 48-168 h, the cumulative mortality of S. iniae-injected fish held in 19 and 35 degrees C was significantly higher than that of injected-fish held in 23, 27 and 31 degrees C. It is concluded that transfer of tilapia O. mossambicus from 27 degrees C to low temperatures (19 and 23 degrees C) after 12h, and transfer of fish from 27 degrees C to high temperatures (31 and 35 degrees C) reduced their immune capability. Moreover, tilapia under temperature stress at 19 and 35 degrees C from 27 degrees C decreased its resistance against S. iniae.     

Development of an antibody ELISA for potency testing of furunculosis (Aeromonas salmonicida subsp salmonicida) vaccines in Atlantic salmon (Salmo salar L)

The study was conducted in Atlantic salmon to establish the initial and basic scientific documentation for an alternative batch potency test for salmon furuculosis vaccines. We assessed the antibody response development for Aeromonas salmonicida vaccines at different immunisation temperatures (3, 12 and 18 °C), by an enzyme-linked-immunosorbent assay (ELISA) 3, 6, 9 and 12 weeks post vaccination, and the correlation between antibody response and protection in cohabitation challenge experiments performed 6 and 12 weeks post vaccination. Fish immunised with a vaccine containing full antigen dose had a significant increase in antibody response after 252 day degrees and the measured values correlated well with protection after 500 day degrees. Fish vaccinated with a reduced antigen dose showed a significant lower antibody response than fish vaccinated with the full dose vaccine at all samplings, and showed a similar low relative percent survival (RPS) in the challenges. The results from this study indicate that an antibody ELISA can discriminate between vaccines of different antigen content and the method may replace challenge tests in batch potency testing of furunculosis vaccines in Atlantic salmon. An immunisation temperature of 12 °C and sampling after 6-9 weeks, seemed to be the most appropriate time for using antibody responses to confirm batch potency.     

Methemoglobin reductase activity in fish erythrocytes

NADH-methemoglobin reductase activity of erythrocytes from the coho salmon, Oncorhynchus kisutch, sockeye salmon, Oncorhynchus nerka, and the rainbow trout, Salmo gairdneri exhibited a major band of activity that resembled the human enzyme in electrophoretic mobility. No polymorphism was found in 35 samples from rainbow trout, 4 samples from Dolly Varden, 29 samples from sockeye salmon, and 24 samples from coho salmon. All samples differed from the human enzyme in that they appeared to be membrane-bound and required the presence of a detergent, Triton X-100, for solubilization. Rainbow trout and coho salmon enzymatic activity is greater than the human enzyme activity at 15 degrees C.     

Clove oil as an anaesthetic for adult sockeye salmon: field trials

Wild migrating sockeye salmon Oncorhynchus nerka exposed to 20, 50 and 80 mg 1⁻¹ of clove oil could be handled within 3 min, recovered within 10 min, and survived 15 min exposure trials. Fish tested at 110 mg 1⁻¹ did not recover from 15 min exposure trials. Response curves developed for induction and recovery time considered the following predictors: clove oil concentration, sex, fish length and depth. A significant positive dependence was observed between induction time and fish length for 20, 50 and 80 mg 1⁻¹ test concentrations; no dependence was observed between induction time and length at 110 and 140 mg 1⁻¹. Recovery time differed as a function of clove oil concentration, but not fish size. A concentration of 50 mg 1⁻¹ is recommended for anaesthetizing sockeye salmon ranging in length from 400 to 550 mm at water temperatures averaging 9–10° C.     

Ephemeral floodplain habitats provide best growth conditions for juvenile Chinook salmon in a California river

We reared juvenile Chinook salmon for two consecutive flood seasons within various habitats of the Cosumnes River and its floodplain to compare fish growth in river and floodplain habitats. Fish were placed in enclosures during times when wild salmon would naturally be rearing in floodplain habitats. We found significant differences in growth rates between salmon reared in floodplain and river enclosures. Salmon reared in seasonally inundated habitats with annual terrestrial vegetation experienced higher growth rates than those reared in a perennial pond on the floodplain. Growth of fish in the non-tidal river upstream of the floodplain varied with flow in the river. When flows were high, there was little growth and high mortality, but when the flows were low and clear, the fish grew rapidly. Fish displayed very poor growth in tidally influenced river habitat below the floodplain, a habitat type to which juveniles are commonly displaced during high flow events due to a lack of channel complexity in the main-stem river. Overall, ephemeral floodplain habitats supported higher growth rates for juvenile Chinook salmon than more permanent habitats in either the floodplain or river. Variable responses in both growth and mortality, however, indicate the importance of providing habitat complexity for juvenile salmon in floodplain reaches of streams, so fish can find optimal places for rearing under different flow conditions.     

Humoral immune responses of channel catfish (Ictalurus punctatus) fry and fingerlings exposed toEdwardsiella ictaluri

The ability of channel catfish to develop antibody responses to Edwardsiella ictaluri was evaluated. Fish were produced and reared under specific pathogen free (SPF) conditions. At the ages of 1, 2, 3 and 4 weeks and 2, 3, 4, 5, and 6 months post-hatch, a group of these naive fish were given a primary immersion exposure to E. ictaluri (mean doses of 6·4×10⁴ cfu ml⁻¹of tank water). Each group received a secondary immersion exposure 4 weeks after the primary exposure and were sampled 2 weeks after each exposure. Control groups were exposed to sterile culture medium. Specific antibody titres were first detected in fish exposed at 4 weeks post-hatch at an average weight of 85 mg. A secondary response was first demonstrated by fry that received a primary exposure at 4 weeks post-hatch and a secondary exposure at 8 weeks post-hatch. However, a true boosting effect was first demonstrated in fish that received their primary exposure at 2 months of age. Fish given a primary exposure before 4 weeks of age and a secondary exposure failed to produce a significant antibody response, even though they were the same age at secondary exposure as fish that produced strong antibody responses upon primary exposure. This phenomenon suggests that immunological tolerance was induced and indicates that channel catfish may not be capable of generating a humoral immune response before four weeks of age.     

Differences in host selection of actinospores of two myxosporeans, Myxobolus arcticus and Thelohanellus hovorkai

We investigated the host selection mechanism of actinospore stages of 2 myxosporeans, Myxobolus arcticus and Thelohanellus hovorkai, infecting masu salmon (Oncorhynchus masou) and common carp (Cyprinus carpio), respectively. Discharge of the polar filaments and sporoplasm release by M. arcticus actinospores occurred within the first 5 min of exposure to skin mucus of masu salmon. The actinospores also reacted to the mucus of nonsusceptible fish, i.e., sockeye salmon (Oncorhynchus nerka) and goldfish (Carassius auratus), although the reactivity was comparatively lower. After exposure of masu, and sockeye and chum salmon (Oncorhynchus keta) to M. arcticus actinospores, the penetration of sporoplasms was observed in the fins and gills of masu and sockeye salmon to a similar extent and to a lesser extent in chum salmon. Thelohanellus hovorkai actinospores exhibited a slow response of sporoplasm release to common carp mucus as well as penetration into the gills of common carp. Neither chemoresponse to mucus of nonsusceptible fish (goldfish and sockeye salmon) nor sporoplasm invasion in goldfish was observed for T. hovorkai actinospores. These results indicate notable differences in the host selection at the time of entry between M. arcticus and T. hovorkai; the former responds quickly to fish mucus with low host specificity, whereas the latter was highly host specific in a dilatory reaction.     

Partial amino acid sequences of several globin chains from the sockeye salmon, Oncorhynchus nerka

1. Partial amino acid sequences for several sockeye salmon hemoglobin beta-chains have been determined and compared to several other fish beta-chain sequences. 2. A 90% homology exists between the sockeye cathodal (C1) beta-chain and the trout Hb I beta-chain for residues 1-19. 3. The sockeye salmon anodal (A1-3) beta-chain is virtually identical to the trout HB IV beta-chain for the first 55 amino acid residues. 4. The alpha-chains of the sockeye salmon appear to be acetylated at the N-terminal position and about 0.6% of the sockeye hemoglobin is glycosylated.     

Effects of photoperiod on pituitary gonadotropin levels in masu salmon

We examined the effects of photoperiod on pituitary levels of two types of gonadotropin (GTH), GTH I and GTH II, in masu salmon Oncorhynchus masou to study their mechanism of synthesis. In Experiment 1, the effects of long or short photoperiod combined with castration were examined using 8-month-old precocious males. Castration was carried out in early August and then the fish were reared under a short (8L16D) or long (16L8D) photoperiod for 60 days. In Experiment 2, the effects of photoperiod combined with testosterone treatment were examined using 12-month-old immature females. Silastic tubes containing testosterone (500 microg /fish) or vehicle were implanted intra-peritoneally in early October. Fish were reared under 16L8D for 60 days, and then half of the fish were transferred to 8L16D, while the remaining fish were kept under 16L8D until Day 90. In Experiment 1, GTH I contents were higher under 16L8D than under 8L16D in the castrated group on Day 30. Moreover, GTH I contents were higher in the castrated group than the control group under 16L8D on Day 30. GTH II contents increased with testicular maturation in the control groups, whereas they remained at low levels in the castrated groups regardless of photoperiodic treatment. In Experiment 2, GTH I contents did not change remarkably in all the groups, while GTH II contents were remarkably increased by testosterone treatment regardless of photoperiodic treatment. These results indicate that the synthesis of GTH I and GTH II are differently regulated by photoperiod and testosterone in masu salmon.     

Disturbance of the intestinal mucosal immune system of farmed Atlantic salmon (Salmo salar), in response to long-term hypoxic conditions

The gastrointestinal (GI) tract has many important biological functions. One is to serve as a barrier between the fish and the external environment. A decreased physical barrier function of the intestine may lead to increased inflow of luminal content and subsequent activation of the intestinal mucosal immune system. This activation is governed by the ability of various compounds to induce cytokine release and immune cell activity, leading to an immune response. In mammals, the impact of stress on the intestinal barrier is well documented and results in increased intestinal permeability and thus increased stimulation of the mucosal immune system. Fish reared in sea cages may at times be exposed to unfavourable environmental conditions leading to chronic stress and disturbed intestinal integrity. This change in permeability may increase the exposure of the mucosal immune system to activating compounds. In the present study, the effect of a prolonged stress on the intestinal mucosal immune system of fish is therefore addressed. Atlantic salmon were exposed to low levels (50%) of dissolved oxygen (DO) for 6-7 weeks in consecutive experiments performed at 8 and 16 °C. Immune parameters were assessed in terms of mRNA expression of the key cytokines, interleukin-1β (IL-1β), IL-8, IL-10, interferon-γ (IFNγ) and transforming growth factor-β (TGFβ) as well as the immune regulatory inhibitor of nuclear factor κB (IκB). In the experiment at 8 °C also mucosal neutrophil infiltration was monitored. Subjecting the fish to low DO levels at 8 °C resulted in an increased mucosal neutrophil infiltration together with a down-regulation of IκB. At the higher temperature, 16 °C, low DO levels created decreased expression of the pro-inflammatory cytokine IL-1β in both intestinal regions as well as an increased expression of IL-10 in the proximal intestine. These results suggest that husbandry conditions in sea cages with DO levels as low as 50% clearly affects the intestinal mucosal immune system and results in a chronic inflammation. Moreover, the effects of low DO levels on the immune factors examined were more pronounced in the 16 °C experiment suggesting additive effects of high temperatures.     

Sex and proximity to reproductive maturity influence the survival, final maturation, and blood physiology of Pacific salmon when exposed to high temperature during a simulated migration

Some Pacific salmon populations have been experiencing increasingly warmer river temperatures during their once-in-a-lifetime spawning migration, which has been associated with en route and prespawn mortality. The mechanisms underlying such temperature-mediated mortality are poorly understood. Wild adult pink (Oncorhynchus gorbuscha) and sockeye (Oncorhynchus nerka) salmon were used in this study. The objectives were to investigate the effects of elevated water temperature on mortality, final maturation, and blood properties under controlled conditions that simulated a "cool" (13°C) and "warm" (19°C) freshwater spawning migration. After 10 d at 13°C, observed mortality was 50%-80% in all groups, which suggested that there was likely some mortality associated with handling and confinement. Observed mortality after 10 d at 19°C was higher, reaching ≥98% in male pink salmon and female pink and sockeye salmon. Thus, male sockeye salmon were the most thermally tolerant (54% observed mortality). Model selection supported the temperature- and sex-specific mortality patterns. The pink salmon were closer to reproductive maturation and farther along the senescence trajectory than sockeye salmon, which likely influenced their survival and physiological responses throughout the experiment. Females of both species held at 19°C had reduced plasma sex steroids compared with those held at 13°C, and female pink salmon were less likely to become fully mature at 19° than at 13°C. Male and female sockeye salmon held at 19°C had higher plasma chloride and osmolality than those held at 13°C, indicative of a thermally related stress response. These findings suggest that sex differences and proximity to reproductive maturity must be considered when predicting thermal tolerance and the magnitude of en route and prespawn mortality for Pacific salmon.     

Low temperature limits photoperiod control of smolting in atlantic salmon through endocrine mechanisms

We have examined the interaction of photoperiod and temperature in regulating the parr-smolt transformation and its endocrine control. Atlantic salmon juveniles were reared at a constant temperature of 10 degrees C or ambient temperature (2 degrees C from January to April followed by seasonal increase) under simulated natural day length. At 10 degrees C, an increase in day length [16 h of light and 8 h of darkness (LD 16:8)] in February accelerated increases in gill Na(+)-K(+)-ATPase activity, whereas fish at ambient temperature did not respond to increased day length. Increases in gill Na(+)-K(+)-ATPase activity under both photoperiods occurred later at ambient temperature than at 10 degrees C. Plasma growth hormone (GH), insulin-like growth factor, and thyroxine increased within 7 days of increased day length at 10 degrees C and remained elevated for 5-9 wk; the same photoperiod treatment at 2 degrees C resulted in much smaller increases of shorter duration. Plasma cortisol increased transiently 3 and 5 wk after LD 16:8 at 10 degrees C and ambient temperature, respectively. Plasma thyroxine was consistently higher at ambient temperature than at 10 degrees C. Plasma triiodothyronine was initially higher at 10 degrees C than at ambient temperature, and there was no response to LD 16:8 under either temperature regimen. There was a strong correlation between gill Na(+)-K(+)-ATPase activity and plasma GH; correlations were weaker with other hormones. The results provide evidence that low temperature limits the physiological response to increased day length and that GH, insulin-like growth factor I, cortisol, and thyroid hormones mediate the environmental control of the parr-smolt transformation.     

Effects of immunostimulants on ranched southern bluefin tuna Thunnus maccoyii: immune response, health and performance

Ranched southern bluefin tuna Thunnus maccoyii were fed baitfishes supplemented with vitamins (predominantly E and C) or vitamins and immunostimulants, nucleotides and β-glucans, over 12 weeks after transfer and monitored for enhancement in immune response, health and performance through their 19 week grow-out period. Fish from two different tows were sampled separately at three different sampling points: at transfer to grow-out pontoons, at 8 weeks post-transfer and at harvest, 19 weeks post-transfer. Lysozyme activity was enhanced during vitamin supplementation compared to control fish. Performance (i.e. survival, condition index and crude fat), health (i.e. blood plasma variables including pH, osmolality, cortisol, lactate and glucose) and alternative complement activity were not commonly improved through diet supplementation. There were some tow-specific improvements in performance through vitamin supplementation including survival, selected parasite prevalence and intensity, and alternative complement activity. Immunostimulant supplementation also showed a tow-specific improvement in plasma cortisol level. Tow-specific responses may suggest that life history, previous health condition and husbandry can affect the success of vitamin and immunostimulant enhancement of immune response, health and performance of ranched T. maccoyii.     

Prevalence of larval Anisakis simplex in pen-reared and wild-caught salmon (Salmonidae) from Puget Sound, Washington

The abundance of parasites of public health significance in pen-reared salmon and wild-caught salmon was compared. Two hundred eighty-seven salmon from Puget Sound, Washington, were examined for third-stage larvae of Anisakis simplex. Of these fish, 237 Atlantic salmon (Salmo salar), coho salmon (Oncorhynchus kisutch) and chinook salmon (O. tshawytscha) were reared in commercial salmon pens and 50 sockeye salmon (O. nerka) were caught during their spawning migration. All wild-caught salmon were found to be infected with larval A. simplex; conversely, all pen-reared fishes lacked such infections. Edible musculature of wild salmon were infected with 581 (87%) nematode larvae. Of other salmon parasites known to infect humans, one Diphyllobothrium sp. plerocercoid was collected from each of three of the 50 wild-caught salmon. The study showed that farmed salmon may increase the margin of safety for consumers of raw seafood.     

Olfactory Imprinting of Amino Acids in Lacustrine Sockeye Salmon

Juvenile salmon have an olfactory ability to imprint their natal stream odors, but neither the odor properties of natal stream water nor the imprinting timing and duration have been clarified as yet. Here we show, using electrophysiological and behavioral experiments, that one-year-old lacustrine sockeye salmon (Oncorhynchus nerka) can be imprinted around the stage of parr-smolt transformation (PST) by a single amino acid, 1 µM L-proline (Pro), or L-glutamic acid (Glu). We also show by real-time PCR that changes occur in mRNA levels of the salmon olfactory imprinting-related gene (SOIG) around PST. The electro-olfactogram (EOG) responses of test fish exposed to Pro in March (before PST) and April–June (during PST) for 2 weeks were significantly (1.7-fold) greater than those of non-exposed control fish, but not those of test fish exposed in July (after PST). When Pro and control water were added to the water inlets of a two-choice test tank during the spawning season 2 years after the test water exposure, 80% of maturing and matured test fish exposed before and during PST showed a preference for Pro, whereas those exposed after PST did not. The EOG response of test fish exposed to Pro or Glu for 1 hour, 6 hours, 1 day, 7 days, or 14 days in May revealed that only the response after 14 days of exposure was significantly (1.8-fold) greater than the control. The expression levels of SOIG mRNA increased before and during PST, and decreased after PST. We conclude that one-year-old lacustrine sockeye salmon can be imprinted by a single amino acid before and during PST, and that imprinting requires exposure for at least 14 days.     

Distribution,prevalence and severity of Parvicapsula minibicornis infections among anadromous salmonids in the Fraser River,British Columbia,Canada

Polymerase chain reaction (PCR) and microscopic examination of stained kidney sections were used to diagnose infections with the myxozoan parasite Parvicapsula minibicornis in maturing Fraser River salmon. In 2 series of collections, the parasite was detected in 109 of 406 migrating sockeye salmon Oncorhynchus nerka belonging to Early Stuart, Early Summer and Summer run-timing groups, mainly upper Fraser River stocks. However, the parasite was detected neither in fish at sea nor once they had migrated several 100 km upstream. Prevalence then increased to 95% or greater at the spawning grounds. Histological examination of kidney was less sensitive than PCR in detecting the parasite in salmon collected from the earliest sites in both collections found positive by PCR. Severity of infection was greatest at the spawning grounds. Development of infection in sockeye, measured by prevalence, severity or by the rate of false-negative histological diagnoses, appeared to be a useful estimate of in-river residence time. Prevalence and severity of infections in sequential samples of Harrison River and Weaver Creek sockeye stocks collected from the Harrison River indicated that more time had elapsed since parasite transmission than would be predicted based on migration distance alone. Pink salmon Oncorhynchus gorbuscha, coho salmon O. kisutch and chinook salmon O. tshawytscha were found to be infected with the parasite. Development of P. minibicornis in pink salmon was most similar to that in sockeye. Pink and coho salmon may be at risk to the pathological consequences of P. minibicornis infection.     

MOLECULAR GENETIC EVIDENCE FOR PARALLEL LIFE-HISTORY EVOLUTION WITHIN A PACIFIC SALMON (SOCKEYE SALMON AND KOKANEE,ONCORHYNCHUS NERKA)

The Pacific salmon Oncorhynchus nerka typically occurs as a sea-run form (sockeye salmon) or may reside permanently in lakes (kokanee) thoughout its native North Pacific. We tested whether such geographically extensive ecotypic variation resulted from parallel evolutionary divergence thoughout the North Pacific or whether the two forms are monophyletic groups by examining allelic variation between sockeye salmon and kokanee at two minisatellite DNA repeat loci and in mitochondrial DNA (mtDNA) Bgl II restriction sites. Our examination of over 750 fish from 24 populations, ranging from Kamchatka to the Columbia River, identified two major genetic groups of North Pacific O. nerka: a “northwestern” group consisting of fish from Kamchatka, western Alaska, and northwestern British Columbia, and a “southern” group consisting of sockeye salmon and kokanee populations from the Fraser and Columbia River systems. Maximum-likelihood analysis accompanied by bootstrapping provided strong support for these two genetic groups of O. nerka; the populations did not cluster by migratory form, but genetic affinities were organized more strongly by geographic proximity. The two major genetic groups resolved in our study probably stem from historical isolation and dispersal of O. nerka from two major Wisconsinan glacial refugia in the North Pacific. There were significant minisatellite DNA allele frequency differences between sockeye salmon and kokanee populations from different parts of the same watershed, between populations spawning in different tributaries of the same lake, and also between sympatric populations spawning in the same stream at the same time. MtDNA Bgl II restriction site variation was significant between sockeye salmon and kokanee spawning in different parts of the same major watershed but not between forms spawning in closer degrees of reproductive sympatry. Patterns of genetic affinity and allele sharing suggested that kokanee have arisen from sea-run sockeye salmon several times independently in the North Pacific. We conclude that sockeye salmon and kokanee are para- and polyphyletic, respectively, and that the present geographic distribution of the ecotypes results from parallel evolutionary origins of kokanee from sockeye (divergences between them) thoughout the North Pacific.