Amago Salmon Oncorhynchus Masou Ishikawae Research Articles

Morphological evolution reduces downstream displacement in juvenile landlocked salmon.

Severe flooding often leads to downstream displacement of aquatic animals. Despite this, many salmonid populations persist in habitats located upstream of tall barriers, such as artificial check dams and/or natural waterfalls, that completely block fishes from returning to the upstream areas after flooding. The evolution of such populations may be affected by spatial sorting due to differential rates of downstream displacement. This study examined whether a morphological trait (increased body depth) that allows individuals to better maintain their position during flooding has evolved in juvenile amago salmon Oncorhynchus masou ishikawae inhabiting above-barrier habitats in two rivers. In both rivers, juveniles collected at the stations with multiple downstream barriers had deeper bodies than those collected at other stations. Similar differences were found in juveniles reared in a common-garden experiment. Field experiments with natural flooding also indicated that deep bodies help juveniles resist downstream displacement. These results consistently suggest that juveniles in some above-barrier habitats have evolved deep bodies to resist downstream displacement due to flooding. Our study is the first to show the evolutionary outcomes of passive spatial sorting during severe climate events.

Body size is the primary regulator affecting commencement of smolting in amago salmon Oncorhynchus masou ishikawae

The present study retrospectively examined relationships between growth trajectory and smolting in order to identify the key regulators in commencement of smolting using groups of all-female homozygous clonal amago salmon. We found that (1) regardless of specific growth rate, the majority of fish above the threshold size (12–13 g) by the end of the decision window (early fall) became smolt in the future; (2) even if fish smaller than the threshold size during the decision window exceeded that size afterwards, they were not recruited to smolt; (3) smolting of fish that attained sufficient size during the decision window could not be suppressed by subsequent restriction of growth rate; (4) smaller fish that had not attained the threshold size during the decision window could not smoltify, even though they showed faster growth rates than that of future smolt during/after the decision window. Taken together, these findings indicated that fish mass by the end of the decision window was responsible for the determination of whether individual amago salmon could smoltify or not and that the faster growth rates observed in future smolt after the decision window occurred as a result of commitment of smoltification.

Investigation of Population Structure and Identification of a Native Population of Amago Salmon Oncorhynchus masou ishikawae in the Nahari River System, Kochi Prefecture, Japan

Investigation of Population Structure and Identification of a Native Population of Amago Salmon Oncorhynchus masou ishikawae in the Nahari River System, Kochi Prefecture, Japan

Selectively bred juvenile F2 amago salmon Oncorhynchus masou ishikawae fed a low fishmeal diet exhibit growth comparable to unselected juveniles fed a fishmeal-based diet

Juvenile amago salmon Oncorhynchus masou ishikawae selectively bred for two generations based on growth with a low fishmeal diet and unselected juveniles reared for two generations on a commercial fishmeal-based diet, both originating from the same broodstock pairs, were used in this study. Juvenile salmon (initial weight, 8.4 g) were fed a low fishmeal diet without amino acid supplementation (LFM), a low fishmeal diet with lysine and methionine supplementation (AA) and a fishmeal-based diet (FM) for ten weeks. Growth of the selected group fed diet AA was comparable to the unselected group fed diet FM. The feed efficiency ratio in the selected groups was significantly higher than in the unselected groups. The feed intake of fish receiving the low fishmeal diets was significantly higher in the selected group than in the unselected group. Physiological conditions such as blood hemoglobin concentration, hepatosomatic index, biliary bile acid concentration and distal intestine and liver morphologies were also improved to some extent in the selected groups relative to the unselected groups, but they were still inferior to fish fed the FM diet. These results indicate that selective breeding for growth on a low fishmeal diet is an effective method for solving the problem of limited fishmeal supply and high fishmeal cost.

Growth performance and physiological condition of F1 amago salmon Oncorhynchus masou ishikawae juveniles obtained from broodstock with selective breeding for growth on a low fish-meal diet

A 10-week feeding trial was conducted to evaluate the growth and physiological condition of F1 amago salmon Oncorhynchus masou ishikawae juveniles obtained from broodstock that had been selected for growth on a low fish-meal (LFM) diet. F1 juveniles from broodstock showing superior or inferior growth on a LFM diet (LFM-S, LFM-I), and those from broodstock showing intermediate growth on a fish meal-based (FM) diet (FM-M), were fed a LFM diet and a FM diet. In fish fed the LFM diet, growth of LFM-S was significantly better than FM-M at 3 weeks; however, this superiority in growth disappeared at the end of the 10-week trial. Growth of LFM-I was significantly lower than LFM-S throughout the feeding trial. Growth of fish fed the FM diet was not significantly different among groups, and higher than fish fed the LFM diet. Improvements in the blood hemoglobin concentration and morphological conditions of the distal intestine and liver were observed in LFM-S fed the LFM diet. Although the effect of selective breeding was limited in F1 amago salmon, the present results suggest that continuous selection for growth with a LFM diet has potential as a method to adapt to the limited supply of fish meal.

Physical Characteristics of Spawning Redds of Sea-Run Form of Amago Salmon Oncorhynchus masou ishikawae in a tributary of the Nagara River System, Central Japan

Physical Characteristics of Spawning Redds of Sea-Run Form of Amago Salmon Oncorhynchus masou ishikawae in a tributary of the Nagara River System, Central Japan

Effects of stocking hatchery fish on the phenotype of indigenous populations in the amago salmonOncorhynchus masou ishikawaein Japan

The expression of colour marks (parr marks, red and black spots) of the amago salmon Oncorhynchus masou ishikawae was compared with microsatellite information, to see the effects of stocking hatchery fish on the phenotype of indigenous populations, which face extinction through extensive stocking. A Bayesian-based assignment test suggested introgression of two exotic clusters into one indigenous cluster in the stocked area and its vicinity. The number of parr marks was significantly higher in one hatchery-origin population, which exclusively comprised one exotic cluster. An increased number of red spots in stocked hatchery fish was probably a consequence of hatchery feeding conditions. The number of black spots was correlated with body size in many populations, except for hatchery and heavily introgressed populations. Coefficients of correlation and regression of black spots with body size, which were largest in indigenous populations, decreased with an increase of introgression by hatchery fish. As indigenous populations have low genetic diversity with high relatedness, it was inferred that the height of correlation and regression coefficients in black spots is caused by high genetic homogeneity and fixation of alleles in loci related to the increase of black spots, both of which might have collapsed with introgression by hatchery fish. These results suggest the possibility that introgression by stocked fish causes a change of phenotype in indigenous populations.

Mottled coloration of haploid-diploid and diploid-triploid mosaic amago salmon Oncorhynchus masou ishikawae

Mottled amago salmon Oncorhynchus masou ishikawe with both yellow- and dark-pigmented skin occurred together with typical albino individuals in a commercial farm. Out of 12 mottled fish examined by DNA content flow-cytometry and erythrocytic nucleus size, three were diploid, eight were haploid-diploid mosaic and one was diploid-triploid mosaic. This fact indicates that the mottled coloration might link to polyploid mosaicism. Genotype of diploid and non-diploid cells at the albino locus was estimated in nine mature mottled fish by observing the frequency of wild-type and albino progeny when mating to homozygous albino (aa). One diploid and three haploid-diploid mosaic mottled fish were presumed to have mosaic genotype with both hemizygous ‘a’ and heterozygous ‘Aa’ cells (a/Aa), because the segregation ratio between two phenotypes was 1∶1. Three other haploid-diploid mosaic fish were presumed to have mosaic genotype with both hemizygous ‘a’ and homozygous ‘AA’ cells (a/AA), because of exclusive occurrence of wild-type phenotype in the progeny. The diploid-triploid mosaic mottled fish was presumed to have mosaic genotypes ‘aa/AAA’, ‘aa/AAa’ or ‘aa/Aaa’, because this fish yielded only albino progeny. One diploid mottled fish produced both two phenotypes but albino mebryos appeared with much more frequency than the expectation, when assuming the genotype ‘Aa’. Thus, this fish was considered to have mosaic genotype ‘Aa/aa’.

Genetic improvement of aquaculture finfish species by chromosome manipulation techniques in Japan

The purpose of this review is to introduce recent advances in research, development and application of chromosome manipulation techniques in Japan. Triploids have been induced and utilized to improve growth. In most cases, triploids are produced as all-female populations by using spermatozoa of artificially sex-reversed males, so as to assure their complete sterility. In contrast, triploid males show better gonadal development and sometimes generate functional spermatozoa, which give rise to inviable aneuploids in most species. Although induced tetraploids can be useful for mass production of triploids by mating with normal diploids, tetraploid lines have only been produced in rainbow trout by a few institutes belonging to prefectural governments. In most cases, the techniques to inhibit the first cleavage often result in very low survival and mosaicism. In the loach (Cobitidae), polyploid lines such as hexaploids have been developed by using natural tetraploid individuals as an intermediate step. Cloned fish can be produced by the second cycle of gynogenesis in the eggs of completely homozygous diploids, which were produced by inhibiting first cleavage after induction of gynogenetic and androgenetic development. The second cycle of androgenesis, using spermatozoa of completely homozygous males, can also generate clonal lines. The most serious technical problem of cloning is the extremely low survival of homozygous gynogenetic and androgenetic diploids, probably due to the expression of deleterious recessive genes and side effect of treatments. However, cloned populations have been realized in commercially important ayu Plecoglossus altivelis, amago salmon Oncorhynchus masou ishikawae, coho salmon O. kisutch, hirame (Japanese flounder) Paralichthys olivaceus, fancy carp Cyprinus carpio, and red sea bream Pagrus major. In hirame, a practical method for mass production of clones was proposed and better performance has been reported in a heterozygous clone, produced by hybridization between two different homozygous clonal lines. Repeated meiotic (polar body) gynogenesis may be more practical than cloning from homozygous gynogens as a method to generate isogenic lines. In meiotic gynogenesis, the proximal region of chromosomes should be homozygous, whereas the distal region should be heterozygous due to high rates of gene–centromere recombination. Consequently, similar genotypes are predicted in the second and later generations of gynogenetic progeny. Their isogenic nature has been confirmed by minisatellite, microsatellite, and other DNA analyses. Gynogenesis, androgenesis and cloning can be used for elucidation of genetic sex determination. The involvement of environmental factors has been indicated from the sex ratios of chromosomally manipulated populations of several species. Finally, the regulation of chromosomally manipulated fish by the guidelines and the integration of such techniques with molecular genetics for further gene mapping and transgenics are discussed.

Effects of Freezing Rate and Lowest Cooling Pre-storage Temperature on Post-thaw Fertility of Amago and Masu Salmon Spermatozoa

Semen of amago salmon Oncorhynchus masou ishikawae was diluted 6 times with extender solution (90% 300mM glucose+10% DMSO) and frozen on dry ice (the dry ice method) or on a stainless steel case floating on constant-temperature ethyl alcohol (the alcohol method). Pellets of various volumes (50-200 μl) that were frozen on dry ice invariably showed a high percent of fertility in spite of the difference in their freezing rates (FR; 50.3 to 29.9°C/min). The fertilityof pellets frozen by the alcohol method and exposed to -30, -50, -70, or -90°C before immersion in liquid nitrogen depended on the alcohol temperature. The highest fertility (87.5%) of 100 μl pellets wasobtained with samples exposed to-70°C (FR=92.6°C/min). Pellets frozen by the alcohol method at-30°C (FR=30.6°C/min) or-90°C (FR=125.6°C/min) showed low fertility rates (58.2% and20.4%, respectively). Two hundred μl pellets frozen by the alcohol method showed a similar percent of fertility to the 100 μl pellets of the same temperature, although their freezing rates were lower. These phemomena were also found in masu salmon O. masou masou spermatozoa. The present results indicate that for spermatozoa of both species, freezing rates in the range of 29.9 to 92.6°/min have little influence on the post-thaw fertility. The most critical factor for obtaining the highest percent of fertility in pellet methods is the temperature reached before immersion in liquid nitrogen, with approximately -70°C being the most suitable temperature for amago and masu salmon spermatozoa.