Juvenile Masu Salmon Oncorhynchus Masou Research Articles

Artificially increased habitat complexity reduces predation-induced mortality for juvenile salmon in simplified environments

Many river systems have been artificially modified for various reasons worldwide. Although simplified riverbeds due to artificial modifications often alter the species compositions and interactions, methods for mitigating habitat degradation in such rivers are underdeveloped. In this study, we evaluated the effects of tree branches on the survival of juvenile masu salmon Oncorhynchus masou under predation risk by piscivorous fish (White-spotted charr Salvelinus leucomaenis) in artificially simplified environments. We found that 0.4 m2 or more of tree branches per 1.0 m2 of artificial concrete pond doubled the survival of juvenile salmon for 20 days. In addition, body sizes of predator and prey did not have a significant effect on salmon survival, whereas the number of branches did in this experiment. These results indicate that adding structural complexity can mitigate predation pressure by piscivorous fish in artificially simplified environments. This study provides important guidelines for the management and restoration of suitable habitats for stream salmonids in artificially simplified environments where the main predators are piscivorous fish.

Persistent and reparative neurogenesis in the juvenile masu salmon Oncorhynchus masou telencephalon after mechanical injury

A superficially located periventricular proliferative area with PCNA-immunopositive (PCNA+) cells, which corresponds to the pallial periventricular zone (PVZ) of other fish species, including its dorsal, lateral, and medial compartments, is discovered in the telencephalon of the juvenile masu salmon Oncorhynchus masou. The PCNA+ cells are also identified in the parenchyma of the masu salmon intact brain, and their maximum concentration is observed in the medial zone. After a mechanical injury, the zones of induced neurogenesis—neurogenic niches and sites of secondary neurogenesis surrounded by radial glial fibers—appear in the masu salmon telencephalon. The PVZ of the juvenile masu salmon pallium contains clusters of undifferentiated HuCD-immunopositive (HuCD+) neurons. A change in the HuCD+ cell topography is observed in the mechanically injured masu salmon telencephalon, namely, neurogenic niches in the lateral zone and an increase in the cell distribution density and cell migration patterns in the medial zone. A high level of persistent neurogenesis is characteristic of the juvenile masu salmon brain.

Cell proliferation and differentiation in primary cultures of the juvenile brain of the masu salmon Oncorhynchus masou

The central nervous system of fish has a high ability to produce new nerve cells in the adult organism in certain neurogenic areas of the brain throughout life. Analysis of proliferative activity and the ability to neuron differentiation was performed in cultured cells of the brain and spinal cord of the juvenile masu salmon Oncorhynchus masou. Proliferating cell nuclear antigen (PCNA) was used as a proliferative marker, while a marker of neuronal differentiation, the neuron protein HuCD, detected neurons. The results showed that cell proliferation occurs mainly in the suspension cell fraction. In monolayer, only a few cells were found to express PCNA. The results of immunocytochemical analysis allow us to conclude that proliferative activity in primary cultures from the O. masou brain is mainly connected with the suspension fraction of small cells. In contrast, the presence of the cells expressing cystathionine β-synthase, a marker of H2S synthesis, and the cells expressing PCNA in the monolayer, may indicate the possible participation of H2S in proliferative activity of neurons in primary cultures. The data obtained suggest that the hydrogen sulphide can be involved in the process of neuronal differentiation; however, the nature of its participation remains largely unknown.

Monitoring of Cell Migration and Apoptosis in Cerebellum of Juvenile Masu Salmon Oncorhynchus Masou After Injury

Apoptosis in various cerebellar zones of juvenile masu salmon Oncorhynchus masou after mechanical injury was investigated by TUNEL-labeling. In the brain of 4 month-old juveniles of O. masou growth in different parts of cerebellum and proliferative activity in secondary matrix zones of cerebellum were continued. TUNEL-labeling was observed in the injured cerebellum 2 days after damage. The induction of proliferative activity in different matrix zones: granular eminences, dorsal part of molecular layer and surface layers of corpus cerebellum were noted. The proliferative activity in regional neurogenic niches is increased after injury of cerebellum. The maximal number of apoptotic elements in the cerebellum was observed in zones of the radial cell migration. We suggest that in damaged cerebellum both adult born cells and cells formed as a result of the reparative neurogenesis can be eliminated during radial migration as result of natural morphogenetic processes. Patterns of tangential and radial migration of cells were observed near the area of injury. The highest rate of apoptosis index was detected in the dorsal matrix zone corresponding to the zone of secondary neurogenesis. This testifies to the elimination of the newly formed cells at the stage of their localization in the matrix zones. The intensity of the apoptotic response varies in different areas of O. masou cerebellum.

Undifferentiated Catecholaminergic and NO-Producing Cells of Forebrain Matrix Zones and Intercellular Relationships in Periventricular Diencephalon of Juvenile Oncorhynchus masou

Localization of TH- and NO-producing systems in the diencephalon of juvenile masu salmon Oncorhynchus masou was investigated by using histofluorescence labeling of glyoxylic acid (GA), and ICH labeling of tyrosine hydroxylase (TH) and neuronal nitric oxide synthase (nNOS). High density distribution of catecholaminergic and NO-ergic cells has been found in preoptic, posterior tuberal and hypothalamic areas. Cells revealed in above mentioned diencephalic areas were assigned to three main types: pear-shaped, bipolar and rounded. Most of the TH- and NO-producing cells had the phenotype of undifferentiated elements localized on territory of diencephalic matrix zones. Paracrine and autocrine relationships between TH- and NO-producing cells in periventricular diencephalon of juvenile O. masou before formation of blood-brain barrier have been hypothesized. The lack of differentiated cells and the presence of a large variety of size groups of cells indicate a possible heterochrony in growth and differentiation of O. masou diencephalic areas. Location of catecholaminergic and NO-producing cells in the territory of diencephalic matrix zones suggests that catecholamines and nitric oxide are involved in the regulation of post-embryonic neurogenesis in diencephalon of O. masou.

Hydrogen Sulfide in Proliferating and Differentiated Cells in Primary Cultures of Juvenile Brain of Masu Salmon <i>Oncorhynchus masou</i>

Analysis of proliferative activity and the ability to neuron differentiation was performed in cultured cells of the brain and spinal cord of juvenile masu salmon Oncorhynchus masou. Proliferating cell nuclear antigen (PCNA) was used as a proliferative marker, while the markers of neuronal differentiation—a neuron protein HuCD, and a neuron-specific transcriptional factor with two DNA- binding sites Pax6—detected neurons. The results showed that cell proliferation occurred mainly in the suspension cell fraction. In monolayer, a few cells were only found to express PCNA. The results of morphological and immunohistochemical analysis allow us to conclude that proliferative activity in primary cultures from the O. masou brain is mainly connected with the suspension fraction of small cells. In contrast, a positive correlation between the cells expressing cystathionine β-synthase (CBS), a marker of H2S synthesis, and the cells expressing PCNA in the monolayer, indicates the participation of H2S in proliferative activity of neurons in primary cultures. The data obtained suggest that the hydrogen sulphide is also involved in the process of differentiation.

Ultrastructure of chloride cells in branchial epithelium of juvenile masu salmon Oncorhynchus masou (Salmonidae) at different salinities

Ultrastructure of chloride cells in branchial epithelium of juvenile masu salmon Oncorhynchus masou (Salmonidae) at different salinities

Latitudinal Variation in the Number of Pectoral Fin Rays in Juvenile Masu Salmon Oncorhynchus masou masou on the Sea of Japan Side of Hokkaido Island

Latitudinal Variation in the Number of Pectoral Fin Rays in Juvenile Masu Salmon Oncorhynchus masou masou on the Sea of Japan Side of Hokkaido Island

Implications of Recreational Fishing on Juvenile Masu Salmon Stocked in a Hokkaido River

AbstractFreshwater recreational anglers in northern Japan sometimes catch significant numbers of juvenile masu salmon Oncorhynchus masou, thereby reducing the effectiveness of enhancement activities aimed at increasing marine catches of adult masu salmon. We stocked 66,500 juvenile masu salmon in the Shirai River, a major tributary of the Yoichi River in Hokkaido, northern Japan, during October 2005. Surveys conducted during the month after stocking revealed that approximately 65 fish/angler‐day were caught, and catch varied between fishing gears (bait or fly) and locations (upper or lower reach). Estimated total number (mean ± SE) of fish harvested was 5,647 ± 2,394, equivalent to 8.5 ± 3.6% of the fish stocked. The estimated number of fish remaining in the river at the end of the angler survey was 57,246 ± 8,595, and survival rate during this month was 86.1 ± 12.9%. While releasing hatchery‐reared masu salmon in late fall can reduce fishing mortality in rivers compared with earlier releases, mortality could be further reduced by dispersing fish over large areas that contain locations with suitable overwintering habitat.

Effects of external and surgically implanted dummy radio transmitters on mortality, swimming performance and physiological status of juvenile masu salmon Oncorhynchus masou

The effects of external and surgically implanted radio transmitters on juvenile masu salmon Oncorhynchus masou were examined. External attachment of transmitters significantly decreased the survival of fish and caused a decreased critical swimming speed compared with surgical implantation. Although plasma cortisol, plasma glucose and haematocrit values did not differ significantly among groups, it appeared that the most suitable transmitter attachment method for juvenile O. masou may be surgical implantation.

Color vision, spectral sensitivity, accommodation, and visual acuity in juvenile masu salmon Oncorhynchus masou masou

Color vision, spectral sensitivity, accommodation, and visual acuity were examined in juvenile masu salmon Oncorhynchus masou masou to obtain fundamental information about the visual system. Two types of S-potentials were recorded from 415 horizontal cells in isolated retinas from 34 cultured freshwater masu salmon (114–219 mm standard length, SL). Although horizontal cells recording S-potentials were not identified, the horizontal cells were confirmed because their responses were maintained while the stimulus remained. The variety of chromaticity (C)-type S-potentials indicated well-developed color vision. The analysis of the luminosity (L)-type S-potentials response to ultraviolet light. The direction and extent of lens movement induced by electrical stimulation was measured in 12 cultured masu salmon (99.0–142.5 mm SL). The results indicated that the visual axis was upward and forward, and that the range of accommodation was from 0.79×SL in front of the eye to infinity. In histological analysis of the retinas of five wild smolts (100–118 mm SL), the maximum cone densities (276–345 cones/0.01 mm2) were detected in the ventral to temporal regions. The visual acuities assessed by histological methods were 0.069–0.075.

Effects of Water Temperature on Infection of the Microsporidian Kabatana takedai in Salmonids

Effects of water temperature on infection of the microsporidian Kabatana takedai were investigated in salmonids under field and experimental conditions. “Cysts” of K. takedai appeared in the heart and the skeletal muscle of wild juvenile masu salmon Oncorhynchus masou from the Chitose River, Hokkaido, during summer in 2003 and 2004, when the river water temperature exceeded 15°C. Following the exposure of naive juvenile sockeye salmon Oncorhynchus nerka to river water (18-19°C) for 3 days, the fish were transferred to separate tanks where the temperatures were set to 11, 13, 15 and 17°C. Prevalence of infection reached more than 70% in the 13, 15 and 17°C groups, but in the 11°C group, it remained less than 30%. However, shifting a part of the 11°C group to 18°C increased the prevalence to 71 % by 23 days after the elevation of the temperature. When juveniles were exposed to 11°C river water and subsequently kept at 9°C for 42 days, no development of K. takedai occurred even after the temperature was elevated to 15°C. These results indicate that temperature manipulation is partially effective as a preventive method of K. takedai infection.

Dominance and predator avoidance in domesticated and wild masu salmon Oncorhynchus masou

ABSTRACT: Dominance, aggression and predator avoidance were compared among farmed, sea-ranched and wild juvenile masu salmon Oncorhynchus masou in laboratory experiments. Domesticated fish (farmed and sea-ranched), which had been exposed to artificial selection, were not dominant against wild fish in pairwise contests, nor did they show greater aggressiveness. Farmed fish did show greater feeding than wild fish. Under chemically simulated predation risk, farmed fish were more willing to leave cover and feed than wild fish, indicating reduced predator avoidance in the farmed fish. Our results indicate that selection for fast growth (domestication) in masu salmon favors fish that respond to food quickly and ignore predation risk.

Satiation and gastric evacuation in juvenile masu salmon.

The satiation time, the satiation amount and the rate of gastric evacuation for juvenile masu salmon Oncorhynchus masou having various sizes were determined at two different water temper-atures (16.2-16.8°C and 8.6-9.4°C). When there was an excess of food, the satiation time was less than 60 min, with a tendency to increase with increasing fish size in both water temperatures. The satiation amount was proportional to W0.715 (W: fish body weight), independent of the water tem-perature. A square root model was more suitable for estimating the gastric evacuation rate than an exponential model. The rate of gastric evacuation for high water temperature was greater than that for low water temperature. From the results of statistical analysis of the difference in the regression parameters between the sized groups, the instantaneous rate of gastric evacuation was constant with respect to the fish size, while the evacuation time was longer in the smaller fish, which consumed a larger meal per unit body weight than in the larger fish.