Mature Sockeye Salmon Research Articles

Declines in body size of sockeye salmon associated with increased competition in the ocean

Declining body sizes have been documented for several species of Pacific salmon; however, whether size declines are caused mainly by ocean warming or other ecological factors, and whether they result primarily from trends in age at maturation or changing growth rates remain poorly understood. We quantified changes in mean body size and contributions from shifting size-at-age and age structure of mature sockeye salmon returning to Bristol Bay, Alaska, over the past 60 years. Mean length declined by 3%, corresponding to a 10% decline in mean body mass, since the early 1960s, though much of this decline occurred since the early 2000s. Changes in size-at-age were the dominant cause of body size declines and were more consistent than trends in age structure among the major rivers that flow into Bristol Bay. Annual variation in size-at-age was largely explained by competition among Bristol Bay sockeye salmon and interspecific competition with other salmon in the North Pacific Ocean. Warm winters were associated with better growth of sockeye salmon, whereas warm summers were associated with reduced growth. Our findings point to competition at sea as the main driver of sockeye salmon size declines, and emphasize the trade-off between fish abundance and body size.

Long-term changes of abundance and population structure for sockeye salmon in Lake Dalneye (southeastern Kamchatka)

Effects of interannual fluctuations of sockeye salmon escapement to the spawning grounds on dynamics of sexual, age and length-weight structure of the population are demonstrated on generalized data of long-term observations in Lake Dalneye in 1939–2020. Mature sockeye specimens were caught in the Dalnaya River during their anadromous migration to the lake and analyzed by the authors, personally; archive and earlier published data were used, as well. The escapement was evaluated by visual assessment of the sockeye migrants entered to Lake Dalneye and confirmed by counting of mature individuals on the littoral spawning grounds in the lake. Number of dwarf sockeye salmon was estimated using the earlier found correlation between their stock and forage zooplankton biomass (Kurenkov, 1991; Pogodaev, Kurenkov, 2012). The zooplankton biomass was assessed on samples of zooplankton collected monthly at a stationary station in the central part of the lake (once a month during the ice period and up to three times per month during the ice-free period) from the layer 0–50/55 m by vertical towing of Juday plankton net (mouth diameter 18 cm). The numbers of anadromous sockeye males and females had ratio 1 : 1 in years with the maximum spawning stock, but < 1 : 1 when their returns to the lake decreased. Besides, the males were smaller in such years and the dwarfs (matured without migration to the sea) and jacks (matured with short marine period) were able to escape commercial fishing gears. Age of the spawners had a tendency to increase with decreasing of spawning runs and, conversely, more abundant runs were formed by younger spawners. Long-term pressure from fishery and selection of larger individuals caused the body length and weight decreasing for mature sockeye salmon, shortening of their period of marine feeding, and increasing of the smallsized males portion in the population.

Using stable isotopes to infer stock-specific high-seas distribution of maturing sockeye salmon in the North Pacific.

The stock‐specific distribution of maturing salmon in the North Pacific has been a persistent information gap that has prevented us from determining the ocean conditions experienced by individual stocks. This continues to impede understanding of the role of ocean conditions in stock‐specific population dynamics. We assessed scale archives for 17 sockeye salmon (Oncorhynchus nerka) stocks covering the entire North Pacific, from the Columbia River (Washington State and British Columbia) to Kamchatka Peninsula (Russia), to infer salmon locations during their last growing season before returning to their spawning grounds. The approach used, first pioneered in salmon stocks in the Atlantic, relies on the relationship between temporal changes in δ13C in salmon scales and sea surface temperature to estimate salmon distribution based on correlation strength. An advantage of this approach is that it does not require fish sampling at sea, but relies on existing fishery agency collections of salmon scales. Significant correlations were found for 7 of the stocks allowing us to propose plausible feeding grounds. Complementary information from δ15N, historical tagging studies, and connectivity analysis were used to further refine distribution estimates. This study is a first step toward estimating stock‐specific distributions of salmon in the North Pacific and provides a basis for the application of the approach to other salmon scale archives. This information has the potential to improve our ability to relate stock dynamics to ocean conditions, ultimately enabling improved stock management. For example, our estimated distributions of Bristol Bay and NE Pacific stocks demonstrated that they occupy different areas with a number of the former being distributed in the high productivity shelf waters of the Aleutian Islands and Bering Sea. This may explain why these stocks seem to have responded differently to changes in ocean conditions, and the long‐term trend of increased productivity of Bristol Bay sockeye.

ON BIOLOGY OF SOCKEYE SALMON ONCORHYNCHGUS NERKA FROM THE ZHUPANOVA RIVER (EAST KAMCHATKA)

Runs and escapements of sockeye salmon to the Zhupanova River have increased since 1985 with the run of 10.63 . 103 ind. instead of 1.45 . 103 ind. in 1960–1984, on average. The increasing was reasoned by change of the pink salmon odd year-classes domination in West Kamchatka to domination of even year-classes after the extremely high escapement in 1983. In 2005–2006, the sockeye salmon stock in the Zhupanova River became even more higher that continues till nowadays (runs of 68.20 . 103 ind. in 2005–2017, on average). This growth corresponds with general increasing of the pacific salmons abundance in the Russian Far East as the result of favorable environmental and feeding conditions in the North Pacific. General biological indices (age, body length and weight, maturity, fecundity) of mature sockeye salmon originated from the Zhupanova River are presented on the data of commercial catches in the sea in 1999–2017. The sockeye salmon population from this river has 11 age groups. The age group 1.3 is the most abundant and associated with the age groups 1.2 and 1.4. Majority of sockeye in the catches from the Zhupanova has the age 1.3 (on average 66.2 % in 1999–2017). Besides, returns of underyearlings with age 0.2, 0.3, and 0.4, and the fish with age 2.2, 2.3, 2.4, 3.2, and 3.3 are detected. The body length and weight are similar for all age groups of sockeye salmon: for males/females the mean length is 57.56/57.70 cm, mean weight is 2.69/2.62 kg. The mean males:females ratio is 44.7 : 55.3. The mean absolute fecundity is 4121 eggs. In opposite of sockeye salmon in some rivers of East Kamchatka, the population of the Zhupanova has no negative year-to-year trend of the body length or weight.

Sex-specific differences in cardiac control and hematology of sockeye salmon (Oncorhynchus nerka) approaching their spawning grounds

Some male salmonids (e.g., rainbow trout) display profound cardiovascular adjustments during sexual maturation, including cardiac growth and hypertension, and tachycardia has been observed in free-ranging male salmonids near their spawning grounds. In the present study, we investigated cardiac control, dorsal aortic blood pressure, cardiac morphometrics, and hematological variables in wild, sexually maturing sockeye salmon (Oncorhynchus nerka) with a particular aim to decipher any sex-specific differences. Routine heart rate (f(H)) was significantly higher in females (52 vs. 43 beats/min), which was due to significantly lower cholinergic tone (28 vs. 46%), because there were no differences in adrenergic tone or intrinsic heart rate between sexes. No differences in blood pressure were observed despite males possessing an 11% greater relative ventricular mass. Concomitant with higher routine heart rates, female sockeye had significantly higher levels of cortisol, testosterone, and 17beta-estradiol, whereas the level of 11-ketotestosterone was higher in males. There were no differences in hematocrit or hemoglobin concentration between the sexes. The findings of this study highlight the importance of considering sex as a variable in research fields such as conservation biology and when modeling the consequences of local and global climate change. Indeed, this study helps to provide a mechanistic basis for the significantly higher rates of female mortality observed in previous studies of wild-caught sockeye salmon.

Experimental evidence of homing to site of incubation by mature sockeye salmon, Oncorhynchus nerka

Fish of the family Salmonidae (salmon, trout and charr) are famous for their ability to learn (‘imprint’) olfactory information as juveniles and to use those odour memories as adults to home to their natal site for reproduction years later. However, the spatial scale at which salmonids home has not been determined, and this is important not only for an understanding of the imprinting and homing processes but also because homing determines the spatial scale at which salmon populations are structured. To test the hypothesis that salmon home to specific habitat units within a single small creek, we induced banding patterns on the otoliths (ear bones) of pre-hatch sockeye salmon embryos by altering the temperatures at which they were incubated. Thermally marked embryos were buried in a small pond associated with Hansen Creek, in southwestern Alaska, and allowed to complete development and migrate. In the year when the salmon were expected to return to the creek, examination of otoliths from carcasses revealed that 12 of 324 salmon in the pond were marked, whereas all 138 salmon examined in the creek were unmarked. This distribution of marked fish indicates that more of the experimental salmon returned to the pond than would have occurred by chance, although we cannot be certain that all surviving salmon did so. These results contribute to the growing literature indicating the capacity for very fine-scale populations structure in salmon.

Tooth size and skin thickness in mature sockeye salmon: evidence for habitat constraints and variable investment between the sexes

Abstract – Pacific salmon develop many sexually dimorphic features at maturity, and the extent of development varies among populations. In this study, we compared a suite of traits including body length, body depth, jaw length, tooth size and skin mass in male and female sockeye salmon breeding in beach and creek habitats. Both tooth size and skin mass varied positively with body length. Within each of the breeding habitats, males had longer teeth than females, and within each sex, beach spawners had longer teeth than creek spawners. Males also had heavier skin than females in each habitat but, unlike the case with tooth size, creek spawners showed a much stronger relationship between skin mass and body length than did beach spawners. Tooth length was positively related to jaw length and skin mass among individuals within a given sex and habitat. Taken together, these results suggested that variation in tooth size parallels variation in other sexually dimorphic traits. Males and beach spawners tend to exhibit large trait values relative to females and creek spawners, and ‘well‐endowed’ individuals displayed high values of all traits rather than a trade‐off as might occur if investment in one trait compromised investment in others. However, the finding that creek fish tended to have thicker skin for a given body length than did beach fish suggested that factors other than merely defense against conspecifics during battle, such as abrasion and desiccation resistance in small streams, may influence the evolution of skin mass in mature sockeye salmon.

Estimation of Stock Composition and Individual Identification of Sockeye Salmon on a Pacific Rim Basis Using Microsatellite and Major Histocompatibility Complex Variation

AbstractThe variation at 14 microsatellite loci and one major histocompatibility complex (MHC) locus was surveyed for over 48,000 sockeye salmon Oncorhynchus nerka sampled from 299 localities ranging from the Columbia River to Japan. For the microsatellite loci, the number of alleles observed at a locus was related to the power of the locus in providing accurate estimates of stock composition of single‐population mixtures. In an analysis of single‐population mixtures where the Pacific Rim baseline was used for estimation of stock identification, 80% accuracy for the average population was achieved by employing approximately 80 alleles in the analysis. Increasing the accuracy of estimated stock compositions to 90% for the average population required approximately 400 microsatellite alleles. When all loci were used to estimate stock compositions, estimates were above 80% for all sampling sites or populations, above 90% for the lake of origin, and generally above 95% for the region of origin. Analysis of known‐origin samples indicated that accurate lake or regional estimates of stock composition were obtained. The accuracy of identification of individual fish to the correct lake of origin was above 90%, regardless of whether the lakes were geographically widespread or within a single watershed. The estimated stock compositions of mixed‐fishery samples from the western Bering Sea, from the continental shelf near Kodiak Island in the Gulf of Alaska, from Southeast Alaska, and from Johnstone Strait in southern British Columbia were markedly different among samples. These stock compositions reflected geographical variation in fishery locations and variation in the migration pathways of either juvenile or maturing sockeye salmon. Variation of DNA enabled us to estimate accurately the origin of individual fish and the composition of mixed‐stock samples from any location in the Pacific Rim distribution of sockeye salmon.

Distribution, Growth, and Feeding of Sockeye Salmon in the Western Bering Sea

AbstractThe Pacific Research Institute of Fisheries and Oceanography (TINRO) in Vladivostok, Russia, conducted 12 major biological surveys in the western Bering Sea in 1986–1995. During these surveys, sockeye salmon Oncorhynchus nerka were sampled with a new pelagic trawl. We used salmon catch, age and growth, and diet data from the TINRO surveys to evaluate the role of sockeye salmon in the structure and function of pelagic communities in the western Bering Sea. Estimates of abundance (numbers and biomass) showed large annual and seasonal fluctuations in the western Bering Sea. Immature and maturing sockeye salmon migrated to the western Bering Sea in late spring from their winter (December–May) feeding grounds in the North Pacific Ocean. Maturing sockeye salmon were distributed in the western Bering Sea from June to early August before returning to their natal spawning rivers. In late August, smolts (age n.0, where the n indicates an ocean‐age cohort and zero indicates the number of ocean annuli) began to move from coastal to offshore waters, where the largest numbers occurred in September–November. We inferred from catch data that most of the other age‐groups of sockeye salmon left the western Bering Sea by the end of November and moved southward to the North Pacific Ocean. The analyses indicated that sockeye salmon fed in the seasonal thermocline layers, where they were important consumers of interzonal zooplankton and micronektonic organisms. The dietary ration of sockeye salmon was high. The high growth rates of sockeye salmon in the western Bering Sea were comparable to those in the North Pacific Ocean. The wide distribution, numerous trophic linkages, high rations, and high growth rate of sockeye salmon establish their important role in pelagic communities of the western Bering Sea.

Quantitative analysis of fushi tarazu factor 1 homolog messenger ribonucleic acids in the pituitary of salmon at different prespawning stages.

Steroidogenic factor 1 (SF-1) or Ad4BP is a member of the fushi tarazu factor 1 (FTZ-F1) family and an orphan nuclear receptor that plays an important role in the hypothalamus-pituitary-gonadal axis and the adrenal cortex. Although its critical role in the differentiation of adrenals, gonads, and pituitary gonadotropes has been well demonstrated, regulatory function of SF-1 during sexual maturation is yet to be examined. To investigate the potential role of SF-1 in sexual maturation, expression of two salmon FTZ-F1 homolog genes, sFF1-I and sFF1-II, was examined in the pituitaries of chum and sockeye salmons, using specific and sensitive RNase protection assays. Only sFF1-I mRNA was found in the pituitary and other organs, such as the ovary, spleen, liver, brain, and skeletal muscle. In chum salmon during upstream migration from the bay to the hatchery, the level of sFF1-I mRNA in the male fish was increased on the midway in the river, where the levels of gonadotropin alpha- and II beta-subunit mRNAs were increased. In maturing sockeye salmon, the expression of the sFF1-I gene was elevated in the mature male fish, but the administration of GnRH analog did not further enhance the expression. These results indicate that sFF1-I gene expression in the pituitary is upregulated in maturing salmon, and this upregulation may not depend on GnRH.

Selection on Morphology of Spawning Wild Sockeye Salmon by a Gill-Net Fishery

Abstract Human activities can cause artificial selection in wild animals. To examine the effects of gill-net selectivity on locally differentiated populations of sockeye salmon Oncorhynchus nerka in Bristol Bay, Alaska, we completed a three-part study: (1) We showed differentiation in the body form of mature sockeye salmon spawning in beach and stream habitats that were separated by less than 300 m. (2) Because gill-net selection acts directly on the girth of immature sockeye salmon, we correlated girth at capture with the morphological characters distinguishing locally differentiated populations on the spawning grounds. By tagging individual fish and measuring them both when immature and when mature, we found morphology at maturity to be highly correlated with girth during immaturity. (3) Using selection regimes from the fishery catch and escapement data for 1994, we examined the effects of gill-net selectivity on populations of mature adults. We showed that although populations of mixed ocean age-classe...

Effects of Gonadotropin-Releasing Hormone Analog on Expression of Genes Encoding the Growth Hormone/Prolactin/Somatolactin Family and a Pituitary-Specific Transcription Factor in the Pituitaries of Prespawning Sockeye Salmon

Gonadotropin-releasing hormone (GnRH) is a possible secretagogue of growth hormone (GH) and somatolactin (SL) in teleosts. Effects of GnRH on the levels of pituitary mRNAs encoding GH, prolactin (PRL), and SL were therefore examined in prespawning sockeye salmon (Oncorhynchus nerka). A capsule of GnRH analog (GnRHa) was implanted into the dorsal muscle of maturing sockeye salmon for 3 weeks. The levels of hormonal mRNAs were then determined by a quantitative dot blot analysis using single-stranded sense DNA of the same sequence of mRNA as the standard. Further, we analyzed effects of GnRHa on expression of the genes encoding pituitary-specific transcription factor (Pit-1/GHF-1). Relative levels of Pit-1/GHF-1 mRNAs were estimated by Northern blot analysis, which showed specific 2- and 3-kb bands of mRNAs. GnRHa significantly increased the level of SL mRNA in the males, but not in the females, compared to the control fish. It did not induce significant increases in the levels of GH and PRL mRNAs in both the males and the females. The levels of Pit-1/GHF-1 mRNAs in the control males tended to be higher than those in the initial controls, so that GnRHa might not be effective in enhancing expression of Pit-1/GHF-1 gene, except for the level of 3-kb Pit-1/GHF-1 mRNA in the females treated with 150 μg GnRHa. The pattern of changes in the levels of Pit-1/GHF-1 mRNAs were similar to those of GH and PRL mRNAs in both the males and the females and to that of SL mRNA in the females. These results indicate that, in prespawning sockeye salmon, GnRH can stimulate SL gene expression, but probably not through the Pit-1/GHF-1-dependent system.

Variation in smoltification age and its determinants in sockeye salmon of Lake Azabach’e

In this paper, we analyze scale samples of sexually mature sockeye salmon from Lake Azabach'e collected over many years and data on the abundance of zooplankton in this lake. For native juvenile sockeye salmon, the major limiting factor of growth and smoltification is food availability. During the observation period from 1977 to 1993, two-year-olds were the most numerous group among the downstream-migrating sockeye salmon. Short-term fluctuations in the proportion of one-year-old smolts during downstream migration are attributed to outbreaks of plankton due to the natural fertilization of the lake.

Changes in Midorbital to Hypural Length and Morphology in Maturing Sockeye Salmon

Abstract The morphology of sockeye salmon Oncorhynchus nerka changes dramatically as the fish mature. The extent of those changes and whether or not midorbital to hypural length (MOHP) also undergoes change have not been examined. We measured MOHP, body depth, girth, and snout length of migrating sockeye salmon as they entered their natal lake, tagged them, and measured them again after recapture on the spawning grounds. All measured dimensions changed; MOHP decreased 5% in males, while body depth increased 18% and snout length increased 25%. Females changed less than males. Midorbital to hypural length did not change in a way that was explained by allocation of those resources into basal metabolism, secondary sexual development, or gonadal development. In order to use MOHP of mature adults to establish harvest rates on a small population within a fishing district, the change in MOHP should be established, as well as a conversion from the length measurement used at the time of fishing.

Size-selective and sex-selective predation by brown bears on sockeye salmon.

Breeding activity increases the vulnerability of many animals to predation, and such predation can affect the subset of animals successfully reproducing. To study the ways in which predation might affect the evolution of Pacific salmon, we measured the intensity and selectivity of predation by bears (primarily brown bears, Ursus arctos) on mature sockeye salmon (Oncorhynchus nerka) breeding in a series of small, spring-fed ponds and creeks near Pedro Bay, Alaska, from 1994 to 1998. Bears killed male salmon more often than females; males constituted 60% of the kills but only 35% of the salmon that died of senescence. The bears also killed fish that were larger, on average, than those dying of senescence (males: 462 vs 452 mm; females: 453 vs 443 mm). The level of predation varied greatly, from 4% (females) and 10% (males) in 1994 to 100% of both sexes in 1996 and 1997. The rate of predation also varied among habitats, being lower in larger ponds than in smaller, shallower ponds and the very small interconnecting creeks. Despite the intense and size-selective predation, the salmon in safer habitats (large ponds) were not larger than those in riskier habitats, and salmon densities were only slightly higher in the safer areas. Compared to a nearby population that experiences no bear predation (Woody Island), the male sockeye salmon from the Pedro Pond system had shallower bodies (i.e., less exposure in shallow water) for a given length, consistent with the hypothesis that selective predation can affect the extent of sexual dimorphism among populations. However, the average length at age for both males and females was greater in the Pedro Pond fish, indicating that selective factors besides predation affect length. Overall, the results indicate that bears can be an agent of natural selection within (and perhaps between) sockeye salmon populations, and predation can greatly affect reproductive success among individuals and years for the population as a whole.

GnRH Analog Stimulates Gonadotropin II Gene Expression in Maturing Sockeye Salmon

Our previous study suggested that, in the pituitaries of pre-spawning chum salmon, salmon gonadotropin-releasing hormone (sGnRH) stimulates expression of genes for gonadotropin (GTH) IIβ but not for Iβ, since the levels of mRNAs encoding sGnRH and GTH II but not I were increased during the final stages of spawning migration. In the present study, a capsule of GnRH analog (GnRHa) was implanted into the dorsal muscle of maturing sockeye salmon to clarify function of GnRH on expression of GTH subunit genes in pre-spawning homing salmonids. The amounts of GTH subunit mRNAs in the individual pituitaries were analyzed by a quantitative dot blot analysis using single-stranded sense DNA as the standard. The levels of GTH α and IIβ mRNAs in the GnRHa-implanted fish were significantly higher than those in the control fish in both the males and females, whereas the levels of GTH Iβ mRNA did not show any significant differences in both sexes. These results indicate that GnRH elevates expression of GTH subunit genes which encode the components of GTH II, α and IIβ chains, in the pituitary of maturing sockeye salmon, and then accelerates final maturation.

Repeat swimming performance of mature sockeye salmon following a brief recovery period: a proposed measure of fish health and water quality

Measurements of swimming ability, such as critical swimming speed (Ucrit), have commonly been used as indicators of the effects of environmental challenges on the general health of fish. In this study, we introduce repeat swimming performance as a particularly sensitive means to assess fish health and the effects of environmental stressors. Adult sockeye salmon (Oncorhynchus nerka) performed two Ucrit tests separated by a 40-min recovery period. When recovery ability was expressed as a ratio of Ucrit values in the first and second swim challenges (Ucrit,2/Ucrit,1), control fish exhibited recovery ratios of unity (0.98 ± 0.01 (mean ± SEM)). In contrast, the recovery of fish pre-exposed to between 0.12 and 0.77 mg·L-1 dehydroabietic acid (DHA) for 8-14 h, and swimming in either hypoxia or normoxia, was impaired. These fish had recovery ratios significantly lower than unity (0.92 ± 0.02) despite swimming to a similar initial Ucrit as control fish. The effect of pre-exposure to DHA was also evident in measurements of oxygen consumption and plasma lactate concentration. Unhealthy fish exhibited significantly lower initial and second Ucrit values than control fish. To account for the low initial swimming performance of these fish, a normalized recovery ratio was introduced ((Ucrit,1/Ucrit,1(control) + Ucrit,2/Ucrit,1)/2). This index of recovery (0.65 ± 0.08) identified the poor physical status of these fish.

Prolonged swimming, recovery and repeat swimming performance of mature sockeye salmon Oncorhynchus nerka exposed to moderate hypoxia and pentachlorophenol.

Mature, wild sockeye salmon (Oncorhynchus nerka) demonstrated their remarkable stamina and recovery abilities by performing three consecutive critical swimming speed tests with only a 45 min interval for recovery between subsequent tests. Although the repeated swimming challenges were performed without a full recovery, normoxic fish swam just as well on the second swim, and the majority of fish swam only marginally more poorly on the third swim. In addition, metabolic loading in these fish, as measured by the rate of oxygen consumption, ventilation rate and plasma lactate levels during recovery, did not appear to be cumulative with successive swims. Fish, however, did not recover as well after a similar level of initial swimming performance under moderately hypoxic conditions (water PO2>100 mmHg; 1 mmHg=0.1333 kPa). Four out of the five fish did not swim again and their high plasma lactate levels indicated a greater anaerobic effort. In another group of fish, metabolic loading (elevated control rates of oxygen consumption) was induced with an overnight sublethal exposure to pentachlorophenol, but these fish swam as well as normoxic fish on the first swim, and five of the six fish swam for a third time at a marginally lower critical swimming speed. In contrast to expectations, pentachlorophenol pretreatment and moderate hypoxia were not additive in their effects. Instead, the effects resembled those of pentachlorophenol pretreatment alone. The results are discussed in terms of what aspects of fatigue might impair the repeat swimming performance of sockeye salmon.

Repeat swimming performance of mature sockeye salmon following a brief recovery period: a proposed measure of fish health and water quality

Measurements of swimming ability, such as critical swimming speed (Ucrit), have commonly been used as indicators of the effects of environmental challenges on the general health of fish. In this study, we introduce repeat swimming performance as a particularly sensitive means to assess fish health and the effects of environmental stressors. Adult sockeye salmon (Oncorhynchus nerka) performed two Ucrit tests separated by a 40-min recovery period. When recovery ability was expressed as a ratio of Ucrit values in the first and second swim challenges (Ucrit,2/Ucrit,1), control fish exhibited recovery ratios of unity (0.98 ± 0.01 (mean ± SEM)). In contrast, the recovery of fish pre-exposed to between 0.12 and 0.77 mg·L-1 dehydroabietic acid (DHA) for 8-14 h, and swimming in either hypoxia or normoxia, was impaired. These fish had recovery ratios significantly lower than unity (0.92 ± 0.02) despite swimming to a similar initial Ucrit as control fish. The effect of pre-exposure to DHA was also evident in measurements of oxygen consumption and plasma lactate concentration. Unhealthy fish exhibited significantly lower initial and second Ucrit values than control fish. To account for the low initial swimming performance of these fish, a normalized recovery ratio was introduced ((Ucrit,1/Ucrit,1(control) + Ucrit,2/Ucrit,1)/2). This index of recovery (0.65 ± 0.08) identified the poor physical status of these fish.

Acceleration of Gonadal Maturation in Anadromous Maturing Sockeye Salmon by Gonadotropin-Releasing Hormone Analog Implantation

Acceleration of Gonadal Maturation in Anadromous Maturing Sockeye Salmon by Gonadotropin-Releasing Hormone Analog Implantation