Chum Salmon Fry Research Articles

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.

Comparative studies of effect of compound feeds on fish-breeding and biochemical properties of juvenile chum salmon

Effectiveness of starter fodders is examined for the low-temperature rearing pools in the salmon fish hatchery Savushkina (Severo-Kurilsk). In May 2022, the experimental compound feed developed in TINRO was compared with the control fodder Aller Aqua (made in Denmark) when feeding of chum salmon fry. Both fodders complied with the veterinary and sanitary requirements of the Euro-Asian Economic Union in terms of quality and safety. The following fish breeding indices were determined for the experimental/control fodders after 47 days of testing: feeding ratio 0.670/0.467; mean daily gain 1.255/1.547 %; mean final weight 0.630/0.735 g; absolute weight growth 0.287/0.392 g; mortality (survival) 0.50 (99.50)/0.48 (99.52) %. Increasing of the water and minerals content and noticeable decreasing of the protein and fat content were detected in tissues of the control samples of fry by comparative biochemical analysis before and after the testing, whereas the content of protein and minerals had increased in tissues of the experimental samples. Thus, suitability and effectiveness of the experimental starter fodder for rearing of juvenile chum salmon in the low-temperature environment is proven by combination of several indices. To intensify the weight gain of juveniles, the experiments will be continued to adjust the composition of mixed feed for juvenile chum salmon in the cold-water conditions, with a principal restriction of the growth intensifiers (hormones) use. The starter compound feed developed in TINRO is recommended for using in rearing of chum salmon fry.

Morphological differentiation of Amur fall Chum salmon juveniles Oncorhynchus keta (Salmonidae) of natural and hatchery origin

The results of a comparative analysis of the number of myotomes and fin rays in the dorsal and anal fins of Amur fall chum salmon fry of artificial and natural origin are presented. Juveniles of natural origin were distinguished by large values of the analyzed morphological features. The results can be used for the determination of juvenile chum salmon of natural and artificial origin at the intra-basin level for large tributaries of the Amur River.

Spatiotemporal distribution of Ceratonova shasta in the lower Columbia River Basin and effects of exposure on survival of juvenile chum salmon Oncorhynchus keta.

In the Columbia River Basin (CRB), USA, anthropogenic factors ranging from dam construction to land use changes have modified riverine flow and temperature regimes and degraded salmon habitat. These factors are directly implicated in native salmon and steelhead (Oncorhynchus species) population declines and also indirectly cause mortality by altering outcomes of ecological interactions. For example, attenuated flows and warmer water temperatures drive increased parasite densities and in turn, overwhelm salmonid resistance thresholds, resulting in high disease and mortality. Outcomes of interactions between the freshwater myxozoan parasite, Ceratonova shasta, and its salmonid hosts (e.g., coho O. kisutch and Chinook salmon O. tshawytscha) are well-described, but less is known about effects on chum salmon O. keta, which have a comparatively brief freshwater residency. The goal of this study was to describe the distribution of C. shasta relative to chum salmon habitat in the CRB and assess its potential to cause mortality in juvenile chum salmon (listed as threatened in the CRB under the U.S. Endangered Species Act). We measured C. shasta densities in water samples collected from chum salmon habitat throughout the lower CRB during the period of juvenile chum salmon outmigration, 2018–2020. In 2019, we exposed caged chum salmon fry from two hatchery stocks at three C. shasta-positive sites to assess infection prevalence and survival. Results demonstrated: (1) C. shasta was detected in spawning streams from which chum salmon have been extirpated but was not detected in contemporary spawning habitat while juvenile chum salmon were present, (2) spatiotemporal overlap occurs between C. shasta and juvenile chum salmon in the Columbia River mainstem, and (3) low densities of C. shasta caused lethal infection in chum salmon fry from both hatchery stocks. Collectively, our results suggest C. shasta may limit recovery of chum salmon now and in the future.

The Utilization of Cold-water Zooplankton as Prey for Chum Salmon Fry in Yamada Bay, Iwate, Pacific Coast of Northern Japan

The Utilization of Cold-water Zooplankton as Prey for Chum Salmon Fry in Yamada Bay, Iwate, Pacific Coast of Northern Japan

Condition factor dependency of burst swimming ability between wild and hatchery-reared chum salmon fry (Oncorhynchus keta)

Condition factor dependency of burst swimming ability between wild and hatchery-reared chum salmon fry (Oncorhynchus keta)

Occurrence of wild chum salmon fry in the surf zone, and spawning and emergence timing in the adjacent nonstocked river in Niigata Prefecture, Japan

Occurrence of wild chum salmon fry in the surf zone, and spawning and emergence timing in the adjacent nonstocked river in Niigata Prefecture, Japan

Small biased body size of salmon fry preyed upon by piscivorous fish in riverine and marine habitats

Predator–prey interactions must be considered when aiming to enhance populations by releasing artificially reared individuals into natural environments. Released individuals create an abundance of prey for predators, and a basic hypothesis of predator–prey interactions suggests that predators select large prey due to the high caloric content. An alternative hypothesis is that small individuals are vulnerable to predation due to their poor predator avoidance. This study tested these hypotheses using stocked chum (Oncorhynchus keta) and masu (Oncorhynchus masou) salmon fry and piscivorous salmonids in marine and riverine habitats in Hokkaido, Japan. Stomach contents were sampled from predators, and fork length of prey fry was measured. Then, their fork length was compared with whole stocked fry (range of mean fork length (±SD): 45.8 ± 2.55 to 49.2 ± 2.76 mm) for each habitat. As a result, prey fry were ∼3%–6% smaller than whole stocked fry, even under a prey-abundant condition (i.e., just after hatchery reared salmon fry were stocked). Piscivorous salmonids pursue schooling fry, and small fry may be easily caught due to their slow speed in avoiding predators.

Comparative transcriptome profiling of selected osmotic regulatory proteins in the gill during seawater acclimation of chum salmon (Oncorhynchus keta) fry

Salmonid fishes, chum salmon (Oncorhynchus keta) have the developed adaptive strategy to withstand wide salinity changes from the early life stage. This study investigated gene expression patterns of cell membrane proteins in the gill of chum salmon fry on the transcriptome level by tracking the salinity acclimation of the fish in changing environments ranging from freshwater (0 ppt) to brackish water (17.5 ppt) to seawater (35 ppt). Using GO analysis of DEGs, the known osmoregulatory genes and their functional groups such as ion transport, transmembrane transporter activity and metal ion binding were identified. The expression patterns of membrane protein genes, including pump-mediated protein (NKA, CFTR), carrier-mediated protein (NKCC, NHE3) and channel-mediated protein (AQP) were similar to those of other salmonid fishes in the smolt or adult stages. Based on the protein-protein interaction analysis between transmembrane proteins and other related genes, we identified osmotic-related genes expressed with salinity changes and analyzed their expression patterns. The findings of this study may facilitate the disentangling of the genetic basis of chum salmon and better able an understanding of the osmophysiology of the species.

Relationship between egg size and body weight of chum salmon fry under an artificial rearing environment

Relationship between egg size and body weight of chum salmon fry under an artificial rearing environment

The utilization of cold-water zooplankton as prey for chum salmon fry (Oncorhynchus keta) in Yamada Bay, Iwate, Pacific coast of northern Japan

The food availability of chum salmon fry is one of the principal factors affecting survival in their coastal residence period. The aim of this study was to better understand the quality and quantity of available food resources and the feeding habits of salmon fry in nearshore waters. We examined stomach contents of salmon fry and the zooplankton community structure of the water column during salmon fry’s coastal residence period (April and May) over four years in Yamada Bay, a coastal embayment of the Pacific Ocean in northern Japan. The mean water temperatures during study period were low in 2014 and 2013 (6.7 and 8.3 °C, respectively),and high in 2016 and 2015 (11.1 and 9.4 °C, respectively). Neocalanus plumchrus and Themisto japonica, typical cold-water zooplankton dominated the stomach contents of chum fry (except for 2016), however, they were not necessarily the most dominant in the water column, suggesting that chum fry selectively preyed upon these cold-water zooplankters. On the other hand, chum fry preyed primarily on decapod larvae in 2016 the warmest water year. Condition factor of chum fry were higher in cold-water years than those of warm-water years. Because these two cold-water zooplankton species are typically abundant in the Oyashio Current, the magnitude of Oyashio inflow may affect prey availability for chum salmon fry and their nutritional status. The relationship between the food environment at the coastal residence period of chum fry and the adult return rate after three years was also discussed.

Returns of Chum Salmon Released from Net‐Pens and Rivers in Eastern Hokkaido, Japan

AbstractThe effectiveness of net‐pen release of Chum Salmon Oncorhynchus keta in improving commercial coastal and river catches was examined by releasing marked fish from seawater net‐pens in Nemuro Bay or into the Nishibetsu River, eastern Hokkaido, northern Japan. Between 100,000 and 130,000 Chum Salmon fry were reared in the hatchery and marked by clipping either the left or right pelvic fin in 2006 and 2007; the fin clip was used to distinguish between net‐pen and river releases. Returning marked fish were surveyed in 17 set nets along the coast of Nemuro Bay, a small set net at the Betsukai Fishing Port, and a salmon weir in the Nishibetsu River 2–5 years after release. No differences were observed in the coastal catch period between the net‐pen‐released and river‐released fishes. Estimated coastal return rates of the net‐pen‐released fish (0.929% and 0.845%) were twice those of the river‐released fish (0.488% and 0.406%). However, six to seven times more river‐released fish (river catch rate = 9.591% and 7.513%) migrated upstream than net‐pen‐released fish (1.292% and 1.192%). Our results suggest that the use of marine net‐pens for Chum Salmon will not sustainably improve adult salmon catches in rivers, although it might increase coastal catches.

Are hatchery chum salmon fry a native invader? Direct and indirect effects of stocking salmon fry on stream organisms

Native species may show invasiveness toward a recipient ecosystem through increases in abundance as a result of artificial stocking events. Salmonid species are typical examples of native invaders whose abundance is increased after stocking with hatchery fish. This study evaluated the effects of hatchery chum salmon fry on sympatric wild masu salmon fry, benthic invertebrate prey, and algae, after a single stocking event in Mamachi stream, Hokkaido, northern Japan. The results suggested that the stocked hatchery chum salmon fry decreased the foraging efficiency and growth of the wild masu salmon fry through interspecific competition, and depressed the abundance of Ephemerellidae and total grazer invertebrates (Glossosomatidae, Heptageniidae, and Baetidae) through predation. Also, the hatchery chum salmon fry may increase algal biomass through depression of grazer abundance by predation (top-down effect). These results suggested that a single release of hatchery chum salmon fry into a stream may influence the recipient stream ecosystem.

Nearshore fish community responses to large scale dam removal: implications for watershed restoration and fish management

The nearshore is a critical zone for northeast Pacific Ocean fish communities, including ecologically and culturally important salmon species. The largest dam removal in the world was recently completed on the Elwha River, with the goal of restoring fisheries and ecosystems to the watershed. The nearshore Elwha fish community was monitored monthly from January 2008 to November 2015 before, during and after dam removal. As of September 2015, approximately 2.6 million m3 of sediment material had increased the area of the Elwha delta to over 150 ha. Newly formed nearshore habitats were quickly colonized by fish communities during the dam removal period but the communities were similar in total species richness and Shannon diversity before and after dam removal, and were similar to a nearby reference site (Salt Creek estuary). Select fish species, including ESA-listed Pacific salmon and trout Oncorhynchus spp., and eulachon Thaleichthys pacificus, and non-native, American shad (Alosa sapidissima), appeared quickly in these new habitats. Hatchery releases of Chinook, O. tshawytscha, coho, O. kisutch, and steelhead, O. mykiss (over 3 million total fish annually to the lower river), dominated the Elwha estuary catch from April through August of each year before, during, and after dam removal. Chum salmon catch rate, size, and duration of estuary occupancy declined during and after dam removal. Overall catches of chum salmon fry prior to, during, and after dam removal were significantly negatively correlated with Chinook salmon catches but significantly, and positively, correlated with coho salmon. When assessed at the Elwha estuary separately, chum abundance was significantly positively correlated with Chinook, coho, and steelhead abundance. These patterns indicate overlap, and likely interaction between these respective groups of hatchery and wild fish. Continued hatchery releases may therefore further challenge chum salmon recovery and should be considered when planning for watershed recovery.

Geographical variation in vertebral number of chum salmon fry on Hokkaido Island, Japan

Geographical variation in vertebral number of chum salmon fry on Hokkaido Island, Japan

A Water-Recycling System for Hatchery Rearing of Chum Salmon Fry

A Water-Recycling System for Hatchery Rearing of Chum Salmon Fry

A Water-Recycling System for Hatchery Rearing of Chum Salmon Fry

A Water-Recycling System for Hatchery Rearing of Chum Salmon Fry

Effects of experimentally elevated egg cortisol on offspring traits in two species of wild Pacific salmon

In fishes, elevated levels of cortisol in eggs can have carry-over effects on phenotypic and performance traits early in life. How responses to elevations in egg cortisol differ among species remains poorly understood. Using wild populations of chum salmon (Oncorhynchus keta) and sockeye salmon (O. nerka), we investigated whether experimentally-elevated concentrations of cortisol in newly fertilized eggs had effects on offspring morphology and/or burst swimming capacity. Immediately following fertilization, eggs were incubated for 2 h with water dosed with 0 ng/mL or 1000 ng/mL of cortisol. Embryos were reared to the fry life stage (complete yolk sac absorption). Morphology and burst swimming performance of fry were then assessed. Sockeye salmon fry reared from cortisol-treated eggs were smaller overall (i.e., smaller body, fins and eyes) compared to conspecifics reared from untreated eggs. In contrast, the morphology of chum salmon fry was not affected by the experimental elevation of egg cortisol. In both species, burst swimming duration was unaffected by egg cortisol treatment, while offspring reared from the cortisol-treated eggs initiated fewer bouts of burst swimming. Our results demonstrate that closely-related species can respond differently to elevations in egg cortisol, and not all offspring traits may be affected by these elevations in cortisol. Further efforts to establish links among offspring quality, maternal stress, and egg composition need to consider the potential for divergent responses among species and examine multiple measures of phenotype and performance throughout development.

サケの雄親の回帰年齢が稚魚の初期成長に影響する可能性

サケの雌 5 尾（4 年魚）と雄 9 尾（3 年魚の雄 3 尾，4 年魚の雄 3 尾及び 5 年魚の雄 3 尾）を用いて総当たり交配を行い，稚魚の成長に影響する要因を雄親のサイズと年齢の違いから検討した。また，稚魚の体重に関する遺伝率の推定を行った。雄親の体重と稚魚の体重に明瞭な関係は見られなかったが，5 年魚の雄親から作出した稚魚の体重は 3 年魚や 4 年魚の雄親から作出した稚魚に比べて小さい傾向にあった。遺伝率は稚魚の成長に伴い高くなっていた。これよりサケの雄親の年齢は稚魚の成長に影響する要因の一つであると考えられた。

温度・餌環境が異なる河川に放流されたサケ稚魚の成長比較

サケ稚魚の河川内での成長と温度・餌環境との関係を調べるために，これらの環境条件が異なる千歳川本流とその支流ママチ川に放流を行った。その結果，ママチ川に放流した稚魚の方が胃充満度は高く，高成長だった。水温はママチ川の方が高かったため，ママチ川の方が高成長だった理由として，第一に高水温による採餌活性上昇が考えられた。餌料生物密度は千歳川の方が高密度だと推測された。ただし，餌料生物をめぐる競合個体の密度を定量化できなかったため，餌料生物密度の成長への影響については言及できなかった。