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1.
ABSTRACT:   In order to confirm the conditions required to produce underyearling smolts, juvenile sockeye salmon Oncorhynchus nerka were reared under different photoperiod and temperature conditions. The level of smoltification was assessed by plasma sodium concentration 24 h after transfer to sea water (plasma-Na), gill Na+,K+-ATPase activity (gill-ATPase), and plasma thyroxine (plasma-T4) and growth hormone (plasma-GH) concentrations. Mean fork length of all groups reached more than approximately 8.5 cm at the end of the experiment. The fish that experienced an alteration in photoperiod from short day (8:16 h light–dark cycle) to long day (16:8 h light–dark cycle) showed significant elevation in gill-ATPase from 9 to 16 µmol inorganic phosphate per milligram protein per hour (µmol Pi/mg pro/h) and reduction in plasma-Na from 194 to 154 mM. This group displayed distinct pigmentation on their fin margins. However, in groups reared under constant short day and constant long day, changes in gill-ATPase and plasma-Na occurred vaguely at each different time and pigmentation on fin margins were not observed. The observed photoperiod-induced changes were greater at 7°C than at 11°C. Further, the alteration of the photoperiod induced two–threefold increases in plasma-GH and plasma-T4. These results suggest that lengthening of photoperiod from short to long daylight at 7°C causes smoltification accompanied by active secretion of growth hormone and thyroxine in underyearling sockeye salmon when the fish are larger than 8.5 cm in fork length.  相似文献   

2.
The transmission of viral encephalopathy and retinopathy (VER) was investigated in juvenile sea bream, Sparus aurata L. Two different infection routes [intraperitoneal (i.p.) and intramuscular injection (i.m.)] were tested at two different temperatures (20 and 26 °C) using sea bream of mean weight 0.7, 2 and 4 g, as well as an immersion challenge performed at 26 °C with sea bream of 0.7 g. Successful transmission of the disease was only achieved by i.m. injection. Mortalities of 100% occurred in sea bream of 0.7 g at day 15 post-infection and 47% in sea bream of both 2 and 4 g at day 30 post-infection in all the experimental infections at 26 °C. No mortalities were ever observed with infections at 20 °C. When mortalities were observed, the virus was detected by immunoperoxidase staining in the SSN-1 cell line inoculated with tissues from infected fish. Histological examination of both normal and infected fish showed a vacuolization in the bipolar and granular layers of the retina of the infected sea bream. This is the first experimentally induced transmission of VER in sea bream. Differences were observed at the time of disease onset depending on water temperature, the route of infection and the age of the juvenile fish.  相似文献   

3.
In the last 9 years, epizootics of an icterus condition has affected coho salmon, Oncorhynchus kisutch (Walbaum), reared in seawater cages in southern regions of Chile. At necropsy, fish from field cases exhibited signs of jaundice accompanied by pale light-brown livers and dark spleens. Histopathological and haematological results indicated that these fish presented haemolytic anaemia. After microbiological examination no bacterial or viral agents could be identified as aetiological agents of this disease. In an infectivity trial, coho salmon, Atlantic salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), were inoculated intraperitoneally with a filtrate of an organ homogenate (0.45 microm) from a diseased coho salmon and held for 60 days in tanks supplied with fresh water. The disease was only reproduced in coho salmon in which mortalities, beginning at day 23 post-inoculation (p.i.), reached a cumulative value of 24% at day 27 p.i. This condition was transmitted to non-inoculated cohabiting coho salmon suggesting that it is a waterborne disease. Thus, this icteric condition is caused by an infectious form of haemolytic anaemia, probably of viral aetiology, and coho salmon are more susceptible than either Atlantic salmon or rainbow trout.  相似文献   

4.
The reproductive migration of anadromous salmonids through estuarine waters is one of the most challenging stages of their life cycle, yet little is known about the environmental and physiological conditions that influence migratory behaviour. We captured, sampled tissues, tagged and released 365 sockeye salmon (Oncorhynchus nerka) homing through inner coastal waters towards the Fraser River, British Columbia, Canada. Biotelemetry was used to assess the behaviour of individual sockeye salmon approaching estuarine waters and at river entry, which were related to both fish physiological condition at release and to prevailing environmental conditions. Sockeye salmon tended to stay close to the shore, migrated during the day, and movements were related to tide. Sockeye salmon migration rate was linked to wind‐induced currents, salinity and an individual's physiological state, but these factors were specific to location and stock. We propose that wind‐induced currents exposed sockeye salmon entering the estuary to stronger olfactory cues associated with Fraser River water, which in turn resulted in faster migration rates presumably due to either an increased ability for olfactory navigation and/or advanced reproductive schedule through a neuroendocrine response to olfactory cues. However, once the migration had progressed further into more concentrated freshwater of the river plume, sockeye salmon presumably used wind‐induced currents to aid in movements towards the river, which may be associated with energy conservation. Results from this study improve our biological understanding of the movements of Fraser River sockeye salmon and are also broadly relevant to other anadromous salmonids homing in marine environments.  相似文献   

5.
We examined spatial correlations for three coastal variables [upwelling index, sea surface temperature (SST), and sea surface salinity (SSS)] that might affect juvenile salmon ( Oncorhynchus spp.) during their early marine life. Observed correlation patterns in environmental variables were compared with those in survival rates of pink ( O. gorbuscha ), chum ( O. keta ), and sockeye ( O. nerka ) salmon stocks to help identify appropriate variables to include in models of salmon productivity. Both the upwelling index and coastal SST were characterized by strong positive correlations at short distances, which declined slowly with distance in the winter months, but much more rapidly in the summer. The SSS had much weaker and more variable correlations at all distances throughout the year. The distance at which stations were no longer correlated (spatial decorrelation scale) was largest for the upwelling index (> 1000 km), intermediate for SST (400–800 km in summer), and shortest for SSS (< 400 km). Survival rate indices of salmon showed moderate positive correlations among adjacent stocks that decreased to zero at larger distances. Spatial decorrelation scales ranged from approximately 500 km for sockeye salmon to approximately 1000 km for chum salmon. We conclude that variability in the coastal marine environment during summer, as well as variability in salmon survival rates, are dominated by regional scale variability of several hundred to 1000 km. The correlation scale for SST in the summer most closely matched the observed correlation scales for survival rates of salmon, suggesting that regional-scale variations in coastal SST can help explain the observed regional-scale covariation in survival rates among salmon stocks.  相似文献   

6.
Abstract Snakeheads, Channa striatus (Bloch), were inoculated with a spore suspension of the specific pathogenic Aphanomyces , isolated from fish affected by epizootic ulcerative syndrome (EUS), in South East Asia. Fish were held at three different temperatures: 19, 26 and 31 °C. Histological changes induced by the infection are described. In the early stages of the disease, degenerative changes were observed in all samples, but inflammatory infiltrate was much more marked in fish kept at 26 and 31 °C. By 8 days post-injection, extensive mycotic granulomatosis was observed in the samples kept at 26 and 31 °C. The fish kept at 19 °C developed a severe invasive myonecrosis with limited macrophage response. From 14 to 28 days post-injection, healing became well established at 26 and 31 °C and surviving fish kept at these temperatures recovered completely by 28 days. The lesion was still progressing at 21 days post-injection in fish kept at 19 °C, and all such fish succumbed by this time. Thus, mortalities in the fish kept at 19 °C were considerably higher than in the groups of fish kept at 26 and 31 °C. The findings help to explain why mortalities from EUS occur when water temperatures are low.  相似文献   

7.
Abstract. Trophonts of Cryptocaryon irritans Brown from infected three-spot damselfish, Dascyllus trimaculatus Ruppell, were kept at temperatures ranging from 7 to 37°C to observe encystment and development of the tomites. At 30, 25 and 20°C, the percentage of trophonts that had encysted in 16 h were 70, 77 and 64% respectively; at 37°C, 44% encysted and at 7°C only 10% had encysted.
The optimum temperature for excystment was 30°C; 50% excysted in 5 days and 100% in 7 days. At 25°C, 60% of the tomites started to excyst on the eighth day, and 70% on the ninth day. At 20°C, 10% started to excyst on the ninth day, reaching 40% on the tenth day. No excystment occurred at 37 and 7°C.
Newly encysted tomonts were placed in various dilutions of sea water (31 %0) and kept at temperatures ranging from 7 to 37°C. Low salinities, i.e. 16%0 and lower caused tomonts to rupture. At 37, 20 and 7°C, 35% of the tomonts started to rupture immediately in 50% sea water, while at 30 and 25 C, 30% of the tomonts ruptured in 25% seawater. However, none of the cysts developed normally at these dilutions. The percentage rupturing increased with decreasing salinity.  相似文献   

8.
Abstract. In a study of the possible role of waterborne infectious haematopoietic necrosis virus in transmission of the disease among spawning sockeye salmon, Oncorhynchus nerka (Walbaum), both infection rates and virus titres were higher in fish held at high density in a side channel than in fish in the adjacent river. Virus was never isolated from river water, but was found in water from the side channel at levels ranging from 32.5 to 1600 plaque-forming units (p.f.u.)/ml. Uninfected yearling sockeye salmon held in a box in the side channel developed localized gill infections with IHN virus. The disease did not progress to the viscera until a threshold titre of about 105 p.f.u./g was reached in the gill. The effectiveness of the gill as a barrier limiting development of systemic infections means that waterborne IHN virus probably does not greatly increase the infection rate in a sockeye salmon population during spawning.  相似文献   

9.
Piscirickettsia salmonis, the aetiological agent of salmonid rickettsial septicaemia (SRS), is a global pathogen of wild and cultured marine salmonids. Here, we describe the development and application of a reproducible, standardized immersion challenge model to induce clinical SRS in juvenile pink (Oncorhynchus gorbuscha), Atlantic (Salmo salar) and sockeye salmon (O. nerka). Following a 1‐hr immersion in 105 colony‐forming units/ml, cumulative mortality in Atlantic salmon was 63.2% while mortality in sockeye salmon was 10%. Prevalence and levels of the bacterium in kidney prior to onset of mortality were lower in sockeye compared with Atlantic or pink salmon. The timing and magnitude of bacterial shedding were estimated from water samples collected during the exposure trials. Shedding was estimated to be 82‐fold higher in Atlantic salmon as compared to sockeye salmon and peaked in the Atlantic salmon trial at 36 d post‐immersion. These data suggest sockeye salmon are less susceptible to P. salmonis than Atlantic or pink salmon. Finally, skin lesions were observed on infected fish during all trials, often in the absence of detectable infection in kidney. As a result, we hypothesize that skin is the primary point of entry for P. salmonis during the immersion challenge.  相似文献   

10.
Abstract  Conservation efforts for endangered Snake River sockeye salmon ( Oncorhynchus nerka ) have been hindered by high en route adult mortality during their ∼1450 km freshwater spawning migration. Identifying causal factors for this mortality has been difficult given very small (often <10 fish) annual returns in recent decades. However, several hundred hatchery-bred fish returned in 2000 and we intercepted and radio-tagged 31 in mid-migration to monitor behaviours and survival. All fish initially migrated at similar rates, but later-timed fish eventually slowed migration and were far more likely to be unsuccessful. Late-season mortality was strongly associated with water temperatures near tolerance thresholds (21–24 °C). The data also suggest increased risk for fish in poor initial condition (i.e., with injuries or parasites) and probable recent selection against late-timed salmon. Results parallel temperature- and condition-related adult mortality in Columbia and Fraser River sockeye salmon populations and demonstrate the potential vulnerability of marginal southern populations to regional climate warming.  相似文献   

11.
Eight temperature-recording data storage tags were recovered from three salmonids in Alaska (pink and coho salmon and steelhead trout) and five chum salmon in Japan after 21–117 days, containing the first long-term records of ambient temperature from Pacific salmonids migrating at sea. Temperature data imply diel patterns of descents to deeper, cooler water and ascents to the surface. Fish were found at higher average temperatures at night, with narrower temperature ranges and fewer descents than during the day. Fish tagged in the Gulf of Alaska were at higher temperatures on average (10–12°C) than chum salmon tagged in the Bering Sea (8–10°C). Chum salmon were also found at a wider range of temperatures (−1–22°C vs 5–15°C). This is probably related both to the different oceanographic regions through which the fish migrated, as well as species differences in thermal range and vertical movements. Proportions of time that individual fish spent at different temperatures seemed to vary among oceanographic regions. Steelhead trout may descend to moderate depths (50 m) and not be limited to the top few metres, as had been believed. Japanese chum salmon may seek deep, cold waters as they encounter warm surface temperatures on their homeward migrations. Temperature data from all fish showed an initial period (4–21 days) of day and night temperatures near those of sea surface temperatures, suggesting a period of recuperation from tagging trauma. A period of tagging recuperation suggests that vertical movement data from short-term ultrasonic telemetry studies may not represent normal behaviour of fish. The considerable diurnal and shorter-term variation in ambient temperatures suggests that offshore ocean distribution may be linked more to prey distribution and foraging than to sea surface temperatures.  相似文献   

12.
Gram-positive cocci recovered from diseased rainbow trout from a farm in England were characterized by different methods, including pulsed field gel electrophoresis, as virulent Lactococcus garvieae serogroup 2 (pulsotype A1). Groups of rainbow trout were kept at a range of temperatures and injected intraperitoneally (i.p.) with one of the UK isolates, L. garvieae 00021. The 18 °C and 16 °C groups showed 67% and 28% mortality, respectively, by day 27 post-injection. Fish kept at 14 °C or lower were less susceptible (≤3% mortality). Raising the temperature of all groups to 18 °C at day 27 post-injection did not result in recurrence of the disease, even though viable bacteria were recovered from all groups 42 days later. Grayling were highly susceptible, with 65% mortalities when challenged with 200 colony forming unit fish−1 by i.p. injection and 37% mortalities when exposed to effluent water from tanks containing affected rainbow trout. Other fish species tested, Atlantic salmon, brown trout and seven cyprinid species, were less susceptible. Viable L. garvieae was isolated from the internal organs of all species tested at the end of the trials, suggesting that they may pose a threat as possible carriers to susceptible farmed and wild fish.  相似文献   

13.
In August 2008 the Kasatoshi volcano in the Aleutian archipelago erupted. Prevailing winds carried volcanic ash to the Gulf of Alaska, where its soluble iron dissolved and initiated a widespread phytoplankton bloom. Two years later, the abundance of sockeye salmon (Oncorhynchus nerka) returning to spawn in the Fraser River was larger than any observed since 1913. Kasatoshi's influence on growth and survival has been proposed as the ultimate cause of the abundant return. However, when relevant data are brought to bear on the hypothesis, it shows that: (1) survival of the abundant sockeye salmon cohort was unremarkable when compared with the historical record; (2) without an accompanying volcano, survival of the returns in 2011 was about the same as in 2010; (3) parental abundance that spawned the abundant return in 2010 was the sixth largest since 1948; (4) during their first summer at sea, sockeye salmon are not known to migrate in the offshore region where the anomalous chlorophyll bloom occurred; (5) an older cohort that was likely exposed to the chlorophyll bloom had the second lowest productivity on record when it returned in 2009; (6) immature sockeye salmon do not feed on diatoms, so any trophodynamic benefit derived from excess chlorophyll in mid‐to late August 2008 would have to have found a rapid trophic pathway to sockeye salmon on the continental shelf; and (7) no other populations of sockeye salmon or other species of salmon that are known to rear in the same region had unexpectedly high returns.  相似文献   

14.
Late-spawning Fraser River sockeye salmon, Oncorhynchus nerka , stocks have suffered significant prespawn mortality associated with an unusually early freshwater migration pattern and the myxosporean parasite Parvicapsula minibicornis . Surveys of migrating adult salmon from several spawning populations were conducted in 1999 and 2000 to determine the extent of infection with P. minibicornis , when and where the parasite first becomes detectable during migration, and whether early migrating stocks might be used as sentinels to assess risk of infection in late-spawning stocks. Posterior kidney, preserved in 95% ethanol, was examined for P. minibicornis in stained histological sections and using a polymerase chain reaction (PCR) test. The prevalence of this parasite in all Fraser River sockeye salmon stocks examined was high (range 47–100% infected). In contrast, P. minibicornis was not detected in the fish tested from the two sockeye salmon stocks outside the Fraser River drainage in either 1999 or 2000. The parasite was also not detected histologically or by PCR in the kidney tissue of the fish from the Fraser River that were sampled in salt water or early during their freshwater migration up the river. These findings and the progression in the prevalence and intensity of infection as the fish from three stocks (early Stuart, Weaver Creek and Cultus Lake) were monitored over time, suggest salmon acquired the parasite either in the lower Strait of Georgia or in the lower Fraser River before the confluence of the Harrison River. In both 1999 and 2000 the parasite was present in all Fraser River sockeye salmon stocks sampled, which suggests that early Stuart salmon may be valuable as a sentinel stock for the presence of the parasite in later-spawning stocks.  相似文献   

15.
Previous research has documented two main migratory routes of juvenile sockeye salmon (Oncorhynchus nerka) through the Strait of Georgia, British Columbia, Canada, and large interannual variability in marine survival rates of the Chilko Lake stock. Simulation models were used to explore the influence of surface currents on the migratory route of juvenile sockeye salmon (smolts) through the Strait of Georgia. We used a model of downstream migration to generate daily numbers of Chilko Lake sockeye salmon smolts entering the Strait of Georgia, based on daily counts of smolts leaving the rearing lake. A numerical hydrodynamic model (driven by surface wind, tide, and Fraser River discharge) hindcasted surface currents in the Strait of Georgia on a 2 km × 2 km grid. A smolt migration model simulated fish moving through the Strait with different compass-oriented migratory behaviours (i.e. swimming speed and directional orientation) within the time-varying surface advection field. Results showed that surface currents within the Strait of Georgia can affect the migratory route of sockeye salmon smolts in spite of their large size (8 cm). Wind is the forcing mechanism primarily responsible for determining which migratory route would be used. Under prevailing wind conditions (i.e. toward the north-west), most sockeye salmon smolts would use the eastern migratory route; however, relatively brief south-eastward wind events (lasting about 2 days) would force most smolts into the western migratory route. Given the heterogeneity of food for salmon within the Strait, we hypothesize that wind-driven variability in the annual proportion of smolts that use the western and eastern migratory routes in the Strait of Georgia affects early marine survival rates of Fraser River sockeye salmon.  相似文献   

16.
The survival of two Atlantic salmon stocks that inhabit rivers confluent with the North Sea was examined in respect to historical distributions of sea surface water temperatures. The rivers Figgjo and North Esk are relatively small salmon rivers in southern Norway and eastern Scotland, respectively. Wild salmon smolts have been tagged in these rivers since 1965. Tag returns were used to evaluate the survival of salmon in the North Sea. Survival rates of one-sea-winter (1SW) and 2SW fish were correlated within stocks, as well as between stocks. Survival rates were compared with the areal extent of thermal habitat in the north-eastern Atlantic Ocean. A positive correlation was found between the area of 8–10°C water in May and the survival of salmon. A reciprocal negative correlation was also found between survival and 5–7°C water in the same month. An analysis of sea surface temperature distributions for periods of good vs. poor salmon survival showed that when cool surface waters dominate the Norwegian coast and North Sea during May, salmon survival has been poor. Conversely, when the 8°C isotherm has extended northward along the Norwegian coast during May, survival has been good. The effect of water temperature distributions on the growth of postsmolts and other survival factors are discussed.  相似文献   

17.
ABSTRACT:   Feeding activity was examined at high temperatures by using a demand feeder for thermally selected and normal rainbow trout Oncorhynchus mykiss strains. When the water temperature was raised in experiment 1 from 17.5 to 25.7°C at 0.3°C/day in 21 days, the average daily food consumption rate in the thermally selected strain rose to 7.1%, which was significantly higher than that of the normal strain (4.1%, P  < 0.05). The corresponding rate was also significantly higher in the thermally selected (0.8%) than in the normal strain (0.2%, P  < 0.05) of fish in experiment 2 where water temperature was raised to 24.1°C in 0.5°C/day increments. When water temperature was raised rapidly in experiment 3 from 16.7 to 21.7°C in one day and gradually to 24.4°C in 28 days at 0.1°C/day, the average daily food consumption rates were 1.0 and 0.1% for the thermally selected and normal strains, respectively, with significant difference ( P  < 0.01). These results suggest that the thermally selected strain has acquired thermal tolerance as a result of artificial selection.  相似文献   

18.
Abstract. Infectivity experiments were undertaken by water-borne inoculation of kuruma shrimp, Penaeus japonicus Bate, larvae with BMN virus. Mysis stage larvae were inoculated with the virus by exposure for 2h in sea water containing a homogenized and filtered preparation (450nm) of naturally BMN virus-infected shrimp stored for about 7 weeks at −80°C. Inoculated shrimp stocked in rearing jars were examined to determine whether nuclear hypertrophy of the mid-gut gland epithelial cells characteristic for BMN virus infection could be observed in fresh squash preparations under dark field illumination equipped with a wet-type condenser. Four days post-inoculation at 25–30°C incubation temperature were considered to be satisfactory for the experimental trial.  相似文献   

19.
The effects of temperature and salinity on the settlement, subsequent survival and development of the copepodids of Lepeophtheirus salmonis on Atlantic salmon were investigated experimentally. There was a significantly greater settlement and survival of copepodids at 10 days post-infection (dpi) at 12 °C compared with at 7 °C at a constant salinity of 34‰. Development of L. salmonis was also more rapid at 12 °C. Settlement was significantly greater at a salinity of 34‰ than at 24‰. In one experiment, survival at 10 dpi was significantly greater at 34‰; however, a second experiment found that there was no significant difference between the two saline levels. This may have been because of a rise in water temperature for 2 dpi, which appears to have overridden the effect of low salinity. Development of L. salmonis was more rapid at 34‰. Copepodids settled on all of the external surfaces of the salmon, although the proportion on different surfaces varied between experiments. The gills, particularly at low temperatures, the body surface, and the pectoral and dorsal fins were especially favoured.  相似文献   

20.
The length and weight of Russian sockeye ( Oncorhynchus nerka ) returning to the Ozernaya River (Kamchatka) was substantially reduced in years when the ocean abundances of Kamchatkan pink ( O. gorbuscha ) and sockeye salmon were high. We found that the density-dependent reduction in sockeye growth on a per-capita basis was greater for sockeye than for pink salmon. However, the overall effect of pink salmon abundance on sockeye growth was greater because of the higher numerical abundance of pink salmon. The strongest statistical relationships were found for sockeye from separate age groups; pooled data combining all age classes were statistically insignificant. We estimate that, if pink salmon were absent, the most strongly affected age group of sockeye salmon (2.1 males) would weigh twice as much at maturity than if pink salmon populations from eastern and western Kamchatka were both simultaneously at peak observed abundances. Trophic competition in the ocean between pink and sockeye salmon can therefore have a significant influence on the productivity of sockeye populations for the most strongly affected age groups. These effects are large enough that they should be explicitly considered in the management of salmon populations.  相似文献   

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