Chum Salmon Research Articles

Comparison of Structural and Physicochemical Characteristics of Skin Collagen from Chum Salmon (Cold-Water Fish) and Nile Tilapia (Warm-Water Fish).

This study compared collagens from cold-water and warm-water fish for their structural, rheological, and functional properties, and explored their potential applications, aiming to realize the high-value utilization of marine biological resources. To this end, chum salmon skin collagen (CSSC) and Nile tilapia skin collagen (NTSC) were both successfully extracted. Collagens from the two species had different primary and secondary structures, with NTSC having a higher molecular weight, imino acid content, and α-helices and β-turns content. The denaturation temperatures were 12.01 °C for CSSC and 31.31 °C for NTSC. CSSC was dominated by viscous behavior and its structure varied with temperature, while NTSC was dominated by elastic behavior and its structure remained stable with temperature. Both collagens had good oil holding capacity, foaming capacity, and emulsifying activity, but NTSC had better water holding capacity and foaming and emulsifying stability. Their different properties make CSSC more suitable for the preservation of frozen and chilled foods and the production of sparkling beverages, and give NTSC greater potential in biofunctional materials and solid food processing.

Does the amount of pacific salmon catch affect the wholesale prices of their products?

Since 2017, volatility of weekly wholesale prices for pacific salmon increased in the Russian domestic market, particularly in the Far East of Russia, that had coincided with higher fluctuations of the weekly and annual catch. Correlation between these variables is investigated for the period from 2010 to 2022, using graphical and regression analyses and 18-factor model for prices of the pink, chum, and sockeye salmon products. The dynamics of prices for pacific salmon products cannot be fully explained only by catch dynamics, but depends on a number of supplementary factors affecting the activities of fish industry enterprises. Anyway, a degree of the catch and price in preceding weeks influence on the wholesale prices is estimated for the main species of pacific salmon. The impact of the catch factor is not significant though more considerable for pink salmon product prices than for the other pacific salmon species.

Experimental analysis of the effect of low water temperature on oogenesis of juvenile chum salmon

The state of gonads is examined for juvenile chum salmon exposed for two weeks at low water temperature, for different stages of their embryonic-larval development. The transfer of the embryos and larvae from the water with temperature of 10.0–12.0 о C to the water with temperature of 1.3–1.8 о C slowed both somatic growth of the fish and development of their germ cells in all cases. The deficit in body weight and ovarian weight of experimental fish was not compensated later. However, the gonad weight was decreased in the somatic component and did not affect the fund of germ cells, in the medium term. The state of ovaries did not differ between the control and experimental groups of fish 50 days after the end of exposure, regardless of the initial condition of gonads in the experiment.

Plankton in the Gulf of Alaska and its contribution to feeding of pacific salmons in spring of 2020

Results of the plankton survey conducted in the Gulf of Alaska, including EEZ of Canada, aboard RV Pacific Legacy No. 1 in March-April of 2020 are presented. The samples of plankton were collected in regular grid of stations and processed according to the methodologies adopted in TINRO. The mean total biomass of zooplankton was estimated as 301.9 mg/m3 , of phytoplankton — as 41.9 mg/m3 . The large-sized fraction of zooplankton dominated (on average 214.6 mg/m3 , or 71 % of the total biomass), the portions of the smalland medium-sized fractions were 16 % and 13 %, respectively. Because of spring blooming development, both phyto- and zooplankton biomasses were increased southward from 3.2 and 188.3 mg/m3 in the northern area of the gulf to 87.9–34.6 and 305.4–397.7 mg/m3 in its central and southern areas, on average. The biomass of small- and medium-sized fractions (presented by copepods Pseudocalanus, Oithona similis, eggs and nauplii of copepods, copepodites, juvenile pteropods, hyperiids and euphausiids, and larvae of siphonophore) had slightly increased in the southern area to 50–60 and 35–38 mg/m3 , respectively, whereas the biomass of largesized fraction presented mainly by copepods (49 %) and arrowworms (36 %) had increased from 118.9 mg/m3 in the north to 293.6 mg/m3 in the south. Boreal species, as Neocalanus cristatus, N. plumchrus/N. flemingeri, Eucalanus bungii, and Metridia pacifica dominated in the zooplankton biomass.The total stock of zooplankton in the Gulf of Alaska in March-April of 2020 was amounted in 39798 . 103 t that was higher than in February-March of 2019 (25517 . 103 t), obviously because of the spring bloom beginning. Correspondingly, distribution density of phyto- and zooplankton was 8.5 and 61.4 t/km2 in March-April of 2020 against 1.0 and 36.6 t/km2 in February-March of 2019. The largest increasing was noted for the small-sized fraction (in 2 times, to 9.7 t/km2 ) and medium-sized fraction (in 4 times, to 8.0 t/km2 ), whereas the increasing for large-sized animals was moderate — from 31.0 t/km2 in 2019 to 43.6 t/km2 in 2020, and the density of euphausiids did not increase (0.8 t/km2 in both years for Euphasia pacifica). The total stock of large-sized fraction had increased from 21650 . 103 t in 2019 to 28920 . 103 t in 2020.The diet of pacific salmon corresponded with the species composition and biomass of the large-sized fraction of zooplankton, with predominance of euphausiids, pteropods, jellyfish, hyperiids, and oikopleura. The main consumers were the most abundant fish groups, as chum salmon with size of 35–60 cm and coho salmon of 30–50 cm found mainly in the central and southern areas of the gulf. E. pacifica were the favorite prey for all salmon species (67–80 % of food weight), except coho salmon — this species preferred squids (77.6 %). Monthly grazing of zooplankton by salmons in the Gulf of Alaska is estimated as 30.175 . 103 tons that is an insignificant portion of its large-sized fraction stock, so the feeding conditions during the survey are considered as favorable for pacific salmons. However, the consumption is possibly underestimated because of low biomass of consumers in the winter-spring season. Spatial and temporal variations of fish aggregations driven by variability of water temperature and other abiotic factors should be accounted for adequate evaluation of the feeding conditions.

Efficacy of Topical Application of Chum Salmon (Oncorhynchus keta) Skin-derived Collagen Extracts in Improving Oral Traumatic Ulcer Healing

Background: Traumatic ulcer is a wound on the oral mucosa that often causes pain and impaired eating function. Healing of these wounds takes a long time and can interfere with an individual’s daily activities. One therapeutic approach that is being developed is the use of topical application of chum salmon skin-derived collagen extract. Collagen is the main component of the extracellular matrix and plays a major role in wound healing. The skin of chum salmon (Oncorhynchus keta) contains collagen that is effective for the treatment of wounds. Aim: The aim of this study was to evaluate the effectiveness of topical applications of chum salmon (O. keta) skin-derived collagen extracts in improving the healing of traumatic ulcers through analysis of neutrophil and macrophage numbers and collagen density. Materials and Methods: Twenty-four male Wistar rats were randomly divided into four groups consisting of six rats each. The labial mucosa of the lower lips of the rats was injured with heated amalgam stoppers to create oral traumatic ulcers. Group 1 was a control group; in Groups 2, 3, and 4, 25%, 50%, and 75% of collagen extracts from chum salmon (O. keta) skin were applied topically once a day for 7 days, respectively. The neutrophil and macrophage numbers were observed by hematoxylin and eosin staining. Masson’s Trichrome staining was used to analyze the collagen density. Data were analyzed using one-way analysis of variance and continued with post hoc least significant difference tests. Significance is considered if P < 0.05. Results: The oral traumatic ulcers gradually healed until day 7. The number of neutrophils and macrophages was significantly decreased in the treatment groups, and collagen density was increased, compared to the control group (P < 0.05). The decrease of neutrophil and macrophage numbers occurred significantly with the increased collagen extract concentrations (P < 0.05). Collagen density also increased significantly with the increased collagen extract concentrations (P < 0.05). Conclusion: Topical applications of chum salmon (O. keta) skin-derived collagen extracts accelerate the healing process of oral traumatic ulcers by decreasing neutrophil and macrophage numbers and increasing collagen density.

Opening a can of worms: Archived canned fish fillets reveal 40 years of change in parasite burden for four Alaskan salmon species.

How has parasitism changed for Alaskan salmon over the past several decades? Parasitological assessments of salmon are inconsistent across time, and though parasite data are sometimes noted when processing fillets for the market, those data are not retained for more than a few years. The landscape of parasite risk is changing for salmon, and long-term data are needed to quantify this change. Parasitic nematodes of the family Anisakidae (anisakids) use salmonid fishes as intermediate or paratenic hosts in life cycles that terminate in marine mammal definitive hosts. Alaskan marine mammals have been protected since the 1970s, and as populations recover, the density of definitive hosts in this region has increased. To assess whether the anisakid burden has changed in salmonids over time, we used a novel data source: salmon that were caught, canned, and thermally processed for human consumption in Alaska, USA. We examined canned fillets of chum (Oncorhynchus keta, n = 42), coho (Oncorhynchus kisutch, n = 22), pink (Oncorhynchus gorbuscha, n = 62), and sockeye salmon (Oncorhynchus nerka, n = 52) processed between 1979 and 2019. We dissected each fillet and quantified the number of worms per gram of salmon tissue. Anisakid burden increased over time in chum and pink salmon, but there was no change in sockeye or coho salmon. This difference may be due to differences in the prey preferences of each species, or to differences in the parasite species detected across hosts. Canned fish serve as a window into the past, providing information that would otherwise be lost, including information on changes over time in the parasite burden of commercially, culturally, and ecologically important fish species.

Classification of set-net fish catch volumes in Iwate Prefecture, Japan using machine learning with water temperature and current distribution images at migration depth

Efficient management of set-net fisheries can be achieved by predicting fish catches in advance. We aimed to estimate fish catch volumes using machine learning based on the data obtained from past set-net fisheries. We also suggested that the estimation can be conducted without the installation of special sensors, such as fish finders, sonars, and cameras, in the set nets. Therefore, a special feature of this study is the construction of a machine learning model using marine environmental images around the set net. In particular, the distribution images of water temperature and current at a certain water depth were applied to the model. In set-nets where migratory fish are caught, ocean data related to migration routes can be useful for estimation. The images used in this study included the water temperature at a depth of 100 m, absolute velocity at a depth of 50 m, and sea surface temperature for comparison. We then classified the fish catch into three classes as follows: chum salmon, yellowtail, and Japanese common squid in Iwate Prefecture, Japan. Consequently, our results achieved an accuracy of approximately 70–80% compared with the validation and test dataset with the water temperature at depths of 100 m. They showed higher accuracy than the sea surface temperature and absolute velocity at a depth of 50 m. This study indicates the usefulness of image-based classification for predicting the volumes of fish caught by set nets.

Post-Traumatic Expressions of Aromatase B, Glutamine Synthetase, and Cystathionine-Beta-Synthase in the Cerebellum of Juvenile Chum Salmon, Oncorhynchus keta.

In adult fish, neurogenesis occurs in many areas of the brain, including the cerebellum, with the ratio of newly formed cells relative to the total number of brain cells being several orders of magnitude greater than in mammals. Our study aimed to compare the expressions of aromatase B (AroB), glutamine synthetase (GS), and cystathionine-beta-synthase (CBS) in the cerebellum of intact juvenile chum salmon, Oncorhynchus keta. To identify the dynamics that determine the involvement of AroB, GS, and CBS in the cellular mechanisms of regeneration, we performed a comprehensive assessment of the expressions of these molecular markers during a long-term primary traumatic brain injury (TBI) and after a repeated acute TBI to the cerebellum of O. keta juveniles. As a result, in intact juveniles, weak or moderate expressions of AroB, GS, and CBS were detected in four cell types, including cells of the neuroepithelial type, migrating, and differentiated cells (graphic abstract, A). At 90 days post injury, local hypercellular areas were found in the molecular layer containing moderately labeled AroB+, GS+, and CBS+ cells of the neuroepithelial type and larger AroB+, GS+, and CBS+ cells (possibly analogous to the reactive glia of mammals); patterns of cells migration and neovascularization were also observed. A repeated TBI caused the number of AroB+, GS+, and CBS+ cells to further increase; an increased intensity of immunolabeling was recorded from all cell types (graphic abstract, C). Thus, the results of this study provide a better understanding of adult neurogenesis in teleost fishes, which is expected to clarify the issue of the reactivation of adult neurogenesis in mammalian species.

Genetic characterization of juvenile chum salmon with otolith marks of Japanese salmon hatcheries in the catches of trawl surveys 2016–2021

Chum salmon sample from the catches of autumn trawl surveys in the Sea of Okhotsk (2016–2021), including individuals with otolith marks of Japanese salmon hatcheries (SHs), was analyzed based on microsatellite loci polymorphism. Reference database of eight microsatellite loci frequencies, created before and included 26 samples of chum salmon from major reproductive regions in the Sea of Okhotsk basin, has been updated with data on the microsatellite allele variety of chum salmon from Hokkaido and Honshu. Result s of the research indicate of strong similarity between chum salmon of the Kuril Islands and individuals released from Japanese SHs.

ЭКСПЕРИМЕНТАЛЬНОЕ ОБОСНОВАНИЕ РАЦИОНАЛЬНОГО СПОСОБА ВЫДЕЛЕНИЯ ЖИРА ИЗ ОТХОДОВ ИКОРНОГО ПРОИЗВОДСТВА

The purpose of the study is to substantiate a rational method for isolating fat from caviar production waste to obtain a biologically active lipid composition. Objectives: to conduct an experimental substantiation of a rational method for isolating lipids from caviar production waste; to develop an experimental installation for the extraction of the lipid part from the studied secondary fish raw materials. The research material is caviar production waste generated and collected during the punching of chum salmon shells at a fish processing plant located in the Khabarovsk Region. Sampling of raw materials and their preparation for analysis were carried out according to standard methods (GOST 31339-2006, GOST 7631-2008). Protein content was carried out according to GOST 7636-85 “Fish, marine mammals, marine invertebrates and their processed products. Methods of analysis". The mass fraction of lipids was determined using the Bly and Dyer method. Fatty acids were determined on a capillary gas-liquid chromatograph Shimadzu GC-16A (Supelcowax-10). The choice of an extraction method for separating fat from biologically valuable secondary raw materials of caviar production, which is waste after punching Pacific salmon caviar, is justified. The created experimental setup, operating according to the Soxhlet method, made it possible to obtain a lipid fraction from secondary raw materials of salmon using an extraction method using two solvents (polar and non-polar). The quality of the resulting fat was assessed by fatty acid and fractional composition. Analysis of the results obtained showed some differences between the fat of the initial secondary raw materials and the fat obtained using the extraction method in an experimental installation. In the isolated fat, the content of physiologically valuable extremely unsaturated fatty acids and triglycerides is lower than in the original raw material. In general, the quality of the resulting lipid fraction did not change significantly as a result of long-term extraction processing of secondary raw materials. In the future, ways to improve the developed and presented method for separating fat from caviar production waste are proposed.

Tide impacts the dispersion of eDNA from nearshore net pens in a dynamic high‐latitude marine environment

AbstractEnvironmental DNA (eDNA) is increasingly used to detect animals in aquatic habitats, but uncertainty remains about the relationship between the present location of an animal relative to eDNA detections. In marine environments, physical characteristics—such as tides and currents—can influence the distribution of eDNA. In this study, we make use of hatchery net pens containing >46 million juvenile chum salmon (Oncorhynchus keta) in nearshore Southeast Alaska to test for dispersion of eDNA and the effects of tide. Initially, we collected and filtered surface water every 80 m along a 2 km transect to test eDNA attenuation over surface distance during incoming and outgoing tides on a single day. The following year, we sampled at three depths (0 m, 5 m, and 10 m) every 500 m along the same transect as well as along a perpendicular transect, to understand dispersion by depth and in additional directions. Chum salmon eDNA was quantified using species‐specific qPCR. We found that surface samples showed a consistent signal of decreasing chum salmon eDNA across the 2 km transect (R2 = 0.665), with the majority of eDNA detections within 1.5 km of the net pens. Tide had a significant effect, resulting in higher concentrations of chum DNA throughout the transect during incoming tide and a steeper decline in eDNA over distance during outgoing tide (R2 = 0.759). Depth affected chum salmon DNA concentration, with the majority of eDNA at the surface and a decreasing amount of DNA with increasing depth. This study addresses one of the critical knowledge gaps in applying eDNA to marine fisheries management by providing empirical evidence of eDNA dispersion and demonstrating that most eDNA detections are likely from nearby individuals that are either currently or recently present. Yet even at close proximity, eDNA signal strength fluctuates and depends on the physical environmental variables during a given sampling event.

The effect of a startle-eliciting device on the foraging success of individual harbor seals (Phoca vitulina)

Pinniped predation on commercially and ecologically important prey has been a source of conflict for centuries. In the Salish Sea, harbor seals (Phoca vitulina) are suspected of impeding the recovery of culturally and ecologically critical Pacific salmon (Oncorhynchus spp.). In Fall 2020, a novel deterrent called Targeted Acoustic Startle Technology (TAST) was deployed at Whatcom Creek to deter harbor seals from preying on fall runs of hatchery chum (O. keta) and Chinook (O. tshawytscha) salmon in Bellingham, Washington, USA. Field observations were conducted in 2020 to compare the presence and foraging success of individual harbor seals across sound exposure (TAST-on) and control (TAST-off) conditions. Observations conducted the previous (2019) and following (2021) years were used to compare the effects observed in 2020 to two control years. Using photo-identification, individual seals were associated with foraging successes across all 3 years of the study. Generalized linear mixed models showed a significant 45.6% reduction in the duration (min) individuals remained at the creek with TAST on, and a significant 43.8% reduction in the overall foraging success of individuals. However, the observed effect of TAST varied across individual seals. Seals that were observed regularly within one season were more likely to return the year after, regardless of TAST treatment. Generalized linear models showed interannual variation in the number of seals present and salmon consumed. However, the effect of TAST in 2020 was greater than the observed variation across years. Our analyses suggest TAST can be an effective tool for managing pinniped predation, although alternate strategies such as deploying TAST longer-term and using multi-unit setups to increase coverage could help strengthen its effects. Future studies should further examine the individual variability found in this study.

Complete genome sequence and potential pathogenic assessment of Flavobacterium plurextorum RSG-18 isolated from the gut of Schlegel's black rockfish, Sebastes schlegelii.

Flavobacterium plurextorum is a potential fish pathogen of interest, previously isolated from diseased rainbow trout (Oncorhynchus mykiss) and oomycete-infected chum salmon (Oncorhynchus keta) eggs. We report here the first complete genome sequence of F. plurextorum RSG-18 isolated from the gut of Schlegel's black rockfish (Sebastes schlegelii). The genome of RSG-18 consists of a circular chromosome of 5,610,911 bp with a 33.57% GC content, containing 4858 protein-coding genes, 18 rRNAs, 63 tRNAs and 1 tmRNA. A comparative analysis was conducted on 11 Flavobacterium species previously reported as pathogens or isolated from diseased fish to confirm the potential pathogenicity of RSG-18. In the SEED classification, RSG-18 was found to have 36 genes categorized in 'Virulence, Disease and Defense'. Across all Flavobacterium species, a total of 16 antibiotic resistance genes and 61 putative virulence factors were identified. All species had at least one phage region and type I, III and IX secretion systems. In pan-genomic analysis, core genes consist of genes linked to phages, integrases and matrix-tolerated elements associated with pathology. The complete genome sequence of F. plurextorum RSG-18 will serve as a foundation for future research, enhancing our understanding of Flavobacterium pathogenicity in fish and contributing to the development of effective prevention strategies.

Correction: Growth rate characteristics of juvenile chum salmon Oncorhynchus keta originating from the Pacific coast of Japan and reaching Konbumori, eastern Hokkaido

Correction: Growth rate characteristics of juvenile chum salmon Oncorhynchus keta originating from the Pacific coast of Japan and reaching Konbumori, eastern Hokkaido

Results of approbation of three pairs of primers for identification of the causative agent of salmon furunculosis <I>Aeromonas salmonicida</I> by PCR

The aim of the work was to select and test several pairs of primers to identify the causative agent of A. salmonicida salmon furunculosis by PCR.The methods: six bacterial cultures isolated from pre-spawning chum salmon with and without external signs of furunculosis, caught in rivers in the south of Sakhalin, were used as test cultures during the testing of primers. Ready-made kits D-Cells‑250 and Intifica TaqM master mix were used to isolate bacterial DNA and prepare PCR mixtures. Amplification was carried out in a thermocycler T‑100 ThermoCycler (Bio-Rad). Detection of PCR products was carried out by electrophoresis in 1.5% agarose gel in triacetate buffer (TAE). To view the results and document them, the Bio-Rad Gel DOC XR+system was used.The results: the species specificity of three pairs of primers selected for the identification of the causative agent of furunculosis by PCR was experimentally confirmed. Testing of the selected primers was carried out on bacterial cultures isolated from pre-spawning chum salmon individuals with and without manifestations of furunculosis. According to the results of testing, all bacterial isolates were assigned to the species A. salmonicida.Novelty of the work: for the first time, a comparison of primers proposed by several authors for the identification of the causative agent of furunculosis was performed on bacterial cultures isolated from salmon of the Far Eastern region.Practical significance: the obtained results were used to prepare methodological guidelines for the identification of the causative agent of salmon furunculosis A. salmonicida by PCR, which reduces the time of diagnosis of the disease.

Impacts of sediment transported downstream from the 2015 deep‐seated landslide in Mt. Hakusan, Japan

AbstractA massive landslide occurred in May 2015 in the Mt. Hakusan Sennindani area, leading to the discharge of a substantial amount of sediment into the Tedori River. We conducted a cross‐sectional analysis of secondary data to assess the potential effects of discharged sediments on the downstream environment, including long‐term turbidity in rivers, alterations in fish habitats, and groundwater depletion. To analyse the spatio‐temporal changes in the river floodplain elevation and paddy fields, aerial photographs and airborne light detection and ranging data were assessed using the ArcGIS software. After the landslide, the turbidity of the Tedori River increased and continued flowing turbid for approximately 6 months. Turbid water spread in the alluvial fan through the irrigation canal network and sediment was deposited in the paddy fields, leading to a reduction in infiltration rates. The groundwater level in the alluvial fan area decreased by more than 2.0 m following the 2015 Sennindani landslide. The sediment deposition in the river floodplain increased by 0.58 m from 2013 to 2015 (pre‐ and post‐landslide). The sediment from upstream destroyed the spawning sites of the Ayu fish along the Tedori River, leading to a decrease in the number of eggs laid in 2015 and 2016 to the lowest levels. The Tomiyo fish disappeared in 2016 and 2017, downstream of the alluvial fan, which received water recharge from the Tedori River. Moreover, Chum salmon showed an exceptionally high anadromous movement towards the Tedori River from coastal areas during 2015 and 2016. In conclusion, discharged sediment from deep upstream landslides can have various adverse impacts on downstream ecosystems, and recovery to their original state may require a considerable amount of time.

Assessment of the regional composition of juvenile chum salmon mixed aggregations in the Sea of Okhotsk based on results of genetic assay

Genetic differentiation of chum salmon in the basin of the Sea of Okhotsk is demonstrated. Eight microsatellite loci (Ssa20.19, One101, Oke3, Oki1b, Oki23, Ogo2G, Oke11, Ots102) were used as genetic markers. Four original genetic regions of chum salmon reproduction have been figured out: West Kamchatka and northern part of the continental coast of the Sea of Okhotsk, Sakhalin, Ithurup (the Kuril Islands), the Amur basin, where the part of juvenile fish was found as a result of genetic identification in the mixed aggregations in the early period of marine feeding. The resolution ability of the reference database was within the limits 74.9–94.6 %. It was demonstrated based on results of the genetic identification, that juveniles from West Kamchatka and northern part of the continental coast of the Sea of Okhotsk dominate in the northern part of the Sea of Okhotsk. Majority of individuals examined in the central zone of the survey area (54 %) was from the Kuril Islands. A number of juvenile chum salmon from the Amur River basin and Sakhalin were recorded at the stations in vicinity of Sakhalin coast.

Critical periods in the marine life history of juvenile western Alaska chum salmon in a changing climate

Recent precipitous declines in western Alaska chum salmon Oncorhynchus keta returns followed unprecedented warming in the northern Bering Sea ecosystem. To better understand the role of anomalous events on the early marine ecology of juvenile chum salmon in the northern Bering Sea, we utilized time-series observations over a 17 yr period (2003-2019) of sea surface temperature (SST) and juvenile chum salmon size (length and weight), diet, energy density, and relative abundance. Particular attention was paid to more recent (2014-2019) years in which there was unprecedented loss of sea ice in the northern Being Sea in comparison to previous warm (2003-2005) and cold (2006-2013) periods. Our findings indicate significant correlations between SST and juvenile chum salmon relative biomass (positive) and energy density (negative). We found that juvenile chum salmon were larger during warm periods than during cold periods; however, there was no significant difference in their length and weight between the warm periods. Juvenile chum salmon fed on lower quality prey during warm periods than during cold periods, with an increase in the proportion of lower quality prey during the recent warm period. Consequently, the energy density of juvenile chum salmon was also lower during warm periods than during cold periods, with the lowest values occurring during the recent warm period (2014-2019). These results identify a shift in energy allocation and/or prey quality of juvenile chum salmon with temperature and illustrate how marine ecosystems have altered the nutritional condition of juvenile chum salmon prior to winter, when energy reserves are considered critical to survival.

Massive stocking of chum salmon (Oncorhynchus keta) fry fattens non-native brown trout (Salmo trutta) in Hokkaido, Japan.

In Japan, stocked chum salmon (Oncorhynchus keta) fry may have become the perfect prey for non-native brown trout (Salmo trutta), which are popular targets of anglers. If this is the case, fry stocking which is intended to boost commercial fishing may be helping to sustain the populations of an invasive predator. We used dietary and biochemical analyses to examine whether brown trout quickly restore their nutritional status following wintertime declines by preying upon chum salmon fry that are stocked in spring. We targeted six rivers in Hokkaido, Japan, three with fry stocking and three without. Changes in brown trout condition factor, triglyceride contents in muscle and serum, serum insulin-like growth factor-1 (IGF-1; an indicator of short-term growth), and docosahexaenoic acid (DHA; an essential fatty acid abundant in fish) content in muscle were examined between before stocking and during the stocking period in the six rivers. Dietary analysis showed that brown trout preyed on fry during the stocking period in all stocked rivers. Their nutritional status tended to be higher during the stocking period than before stocking in stocked rivers, but not in unstocked rivers. These results suggest that the massive stocking of chum salmon fry provides brown trout with the perfect prey to quickly restore their nutritional status and fuel increased growth; this may therefore be a controversial issue among stakeholders.

Age Assessment Using Chum Salmon Scale by Neural Networks and Image Processing

Age Assessment Using Chum Salmon Scale by Neural Networks and Image Processing