Pigment cell development in rhesus monkey eyes: an electron microscopic and histochemical study

The ontogeny of pigment cells in the eyes of rhesus monkeys was studied by electron microscopy and histochemistry.In 60- to 80-day-old fetuses, the pigment epithelium of the iris and retina has already differentiated whereas stromal melanocytes of the uveal tract differentiate much later. The morphological and histochemical difference between melanocytes of the iris stroma and the choroid suggests that during embryonic development melanocytes migrate from the iris toward the ciliary body and choroid.Similarly, melanosomes of pigmented epithelial cells may have their origin in the epithelium of the anterior layer of the iris, which is metabolically more active than both the posterior layer and the pigment epithelium of the ciliary body and retina.     

Comparative anatomy of the dorsal hump in mature Pacific salmon

Mature male Pacific salmon (Genus Oncorhynchus ) demonstrate prominent morphological changes, such as the development of a dorsal hump. The degree of dorsal hump formation depends on the species in Pacific salmon. It is generally accepted that mature males of sockeye (O. nerka ) and pink (O. gorbuscha ) salmon develop most pronounced dorsal humps. The internal structure of the dorsal hump in pink salmon has been confirmed in detail. In this study, the dorsal hump morphologies were analyzed in four Pacific salmon species inhabiting Japan, masu (O. masou ), sockeye, chum (O. keta ), and pink salmon. The internal structure of the dorsal humps also depended on the species; sockeye and pink salmon showed conspicuous development of connective tissue and growth of bone tissues in the dorsal tissues. Masu and chum salmon exhibited less‐pronounced increases in connective tissues and bone growth. Hyaluronic acid was clearly detected in dorsal hump connective tissue by histochemistry, except for in masu salmon. The lipid content in dorsal hump connective tissue was richer in masu and chum salmon than in sockeye and pink salmon. These results revealed that the patterns of dorsal hump formation differed among species, and especially sockeye and pink salmon develop pronounced dorsal humps through both increases in the amount of connective tissue and the growth of bone tissues. In contrast, masu and chum salmon develop their dorsal humps by the growth of bone tissues, rather than the development of connective tissue.     

Genetic differentiation and the problems of conservation of masu salmon (<Emphasis Type="Italic">Oncorhynchus masou</Emphasis> Brevoort, 1856 (Pisces: Salmonidae)) populations

This study focuses on the strategy for the conservation of masu salmon, Oncorhynchus masou, in the northern part of the species range (via the masu populations in Sakhalin Oblast), based on data of its population structure. It is shown that masu populations that inhabit different rivers genetically differ from each other in allele frequencies at microsatellite markers. In the Naiba River basin, at least two genetically distinct masu populations exist: in the upper reaches and in a tributary, the Bolshoy Takoy River. The masu populations on Iturup Island significantly differ from those on Sakhalin Island; within Sakhalin, the masu salmon from the Chernaya River in the southwestern part of the island is genetically distinct from the southeastern Sakhalin and Aniva Bay populations. The genetic diversity of Iturup populations is substantially lower than that on Sakhalin, probably due to their small sizes. The measures for the conservation and recovery of masu salmon populations should be based primarily on their own genetic resources, or, in the case of a lack of spawners, on the base populations of their ecological/geographical region. In the latter case, masu populations of large rivers can be considered as base ones: for southeastern Sakhalin, this is masu salmon of the Naiba River; for Aniva Bay, this is masu salmon of the Lyutoga River. Transplantation of fish, fertilized eggs, or any other genetic material from a population that is different genetically and inhabits the waters with different ecological gradients should be strongly restricted. The formosan masu salmon from Taiwan Island is studied as an example of a strict genetic isolate.     

Species-dependent migration of fish hatching gland cells that commonly express astacin-like proteases in common

Two constituent proteases of the hatching enzyme of the medaka ( Oryzias latipes ), choriolysin H (HCE) and choriolysin L (LCE), belong to the astacin protease family. Astacin family proteases have a consensus amino acid sequence of HExxHxxGFxHExxRxDR motif in their active site region. In addition, HCE and LCE have a consensus sequence, SIMHYGR, in the downstream of the active site. Oligonucleotide primers were constructed that corresponded to the above-mentioned amino acid sequences and polymerase chain reactions were performed in zebrafish ( Brachydanio rerio ) and masu salmon ( Oncorynchus masou ) embryos. Using the amplified fragments as probes, two full-length cDNA were isolated from each cDNA library of the zebrafish and the masu salmon. The predicted amino acid sequences of the cDNA were similar to that of the medaka enzymes, more similar to HCE than to LCE, and it was conjectured that hatching enzymes of zebrafish and masu salmon also belonged to the astacin protease family. The final location of hatching gland cells in the three fish species: medaka, zebrafish and masu salmon, is different. The hatching gland cells of medaka are finally located in the epithelium of the pharyngeal cavity, those of zebrafish are in the epidermis of the yolk sac, and those of masu salmon are both in the epithelium of the pharyngeal cavity and the lateral epidermis of the head. However, in the present study, it was found that the hatching gland cells of zebrafish and masu salmon originated from the anterior end of the hypoblast, the Polster, as did those of medaka by in situ hybridization. It was clarified, therefore, that such difference in the final location of hatching gland cells among these species resulted from the difference in the migratory route of the hatching gland cells after the Polster region.     

Evolutionary-physiological aspects of adaptation of the Pacific salmon fry of the Oncorhynchus genus to migration to the sea water

A complex of adaptive changes occurring in the Pacific salmon fry in the process of migration to the sea is described, including behavior, ion content in carcasses, and morphological changes in Stannius bodies, gill epithelium, and nephron tubular epithelium. Participating in experiments with transfer from fresh water into a two-layer aquarium (the lower layer - sea water, the upper layer - fresh water) were smolts of chum salmon and underyearlings of masu salmon as well as the trachurus and leiurus forms of the three-spined stickleback Casterosteus aculeatus. All fish, regardless of their salt preference, at once after placement into the two-layer aquarium, occupied the sea water zone, at the very bottom of the aquarium. After 1 h, there started brief excursions of masu salmon and chum salmon to the upper, fresh water layer; however, both forms of the three-spined stickleback did not participate in these excursions. After 12 h, the chum salmon settled down in the lower, sea water layer, while the masu salmon - in the upper, fresh water layer. Both forms of the three-spined stickleback never left the sea water layer and felt quite comfortably on the aquarium bottom. It seems that the high tolerance of the both stickleback forms to wide salinity limits allows them to choose the convenient position regardless of the water salt composition. By analyzing the material obtained for three years (2001-2003) on structure and functions of the gill epithelium chloride cells (CC), we have come to the conclusion that the fresh water fry of two salmon species, chum and masu salmons, caught at the same time and practically in the same water reservoirs can be divided into three groups. The underyearlings of the masu salmon as a rule are characterized by the thickened epithelium of secondary gill lamellae, but by a very small number of CC. In smolts of chum salmon, on the contrary, the epithelium is sufficiently thin, but enriched in the CC that demonstrate an active structure in the very beginning of migration to sea. However, with approaching the sea (and with an increase of terms of migration) the CC activity drops, but their amount does not change. And only after migration to the sea the CC activity rises again, although their amount seems to remain unchanged. The described peculiarities of behavior and of the ion composition regulation in the migrating salmon fry confirm the hypothesis that the salmons evolutionized in fresh water, that the Oncorhynchus genus appeared in large spaces of saltish waters, such as the Japan Sea at the period of the early Pleistocene, and that learning of fry of the Oncorhynchus genus (for instance, of O. gorbuscha and O. keta) is the most specialized in the salmons migrating to the sea, whereas the fresh water species of chars (Salvelinus) and of trouts (Salmo) are more primitive.     

Ultrastructure of the retinal pigment epithelium in the young masu salmon Oncorhynchus masou

The ultrastructure of retinal pigment epithelium (RPE) cells in the masu salmon Oncorhynchus masou fry was studied. The physiological state of the pigment was dependent on the level of light/dark adaptation. Similar morphological properties were observed in the response of the RPE cells to light and a magnetic field.     

Sympatric, simultaneous, and random mating between markless trout (iwame; Oncorhynchus iwame) and red-spotted masu salmon (amago; Oncorhynchus masou ishikawae)

The markless trout (iwame, Oncorhynchus iwame) has long been suspected not to be an independent species, but rather a markless mutant form of the red-spotted masu salmon (amago, O. masou ishikawae). Nevertheless, no field study has examined this issue. Here we report a field study on the reproductive ecology of iwame and amago coexisting in the upper stream of the Inabe River. We found that iwame and amago mate sympatrically, simultaneously, and randomly, and observed five cases of heterogeneous oviposition between the two. Our results suggest that no pre-mating reproductive isolation exists between iwame and amago. Because previous studies have shown the absence of post-mating isolation, we propose that iwame and amago are the same species. Iwame should be considered as a markless form of the red-spotted masu salmon, and O. iwame as a junior synonym of O. masou ishikawae.     

Influence of weak magnetic fields on fish retina photoreceptors

It has been shown for the first time that retina photoreceptors of the salmon Oncorhynchus masou (masu salmon) fry exposed to a constant magnetic field (80 Gs) in conditions of twilight illumination demonstrated not a twilight reaction, as in the control, but a darkness (scotopic) reaction. The pigment epithelium in this case reacted as to bright light. Under the influence of long wavelength red light, the retinomotor reaction corresponded to partial light adaptation. After the indemnification of the horizontal component (0.1 Gs) of the geomagnetic field, fish retina adapted to complete darkness demonstrated changes that could not be attributed to one of standard conditions of light exposure. Thus, the rods and cones demonstrated a reaction similar to that to twilight, double cones reacted as to complete darkness ("correct" reaction), and PE borrowed a position as at twilight. Apparently, the basic stimuli of the retina reactions were not light but changes of the magnetic field. Based on these results and the results available in literature, the authors offer a new variant of the hypothesis of light-dependent magnetoreception, which is based on the assumption that the liquid crystals of retina pigments are very sensitive receptors of magnetic field and do not require the presence of magnetite crystals. We assume that the layer of retina pigment epithelium participates in the complex process of transformation of a light signal, which takes into account the influence of magnetic field but not simply absorbs light superfluous for photoreceptors. The changes in magnetic field cause a distortion of the liquid crystal line structure of the pigment, which results in the transformation of the light signal acting on the photoreceptors. Monochromatic red light in the same way deforms the response to the native magnetic signal.     

Effect of the barring gene on eye pigmentation in the fowl

Pigment cells of the iris, pecten, retinal pigment epithelium, and choroid of the wild-type jungle fowl (JF) and the barred Plymouth rock (BPR) breeds of adult chickens were studied at both light and electron microscopic levels. BPR choroidal tissues had 2.8 times fewer melanophores than the JF choroid, and BPR melanophores also contained 2.4 times fewer melanosomes, which tended to clump together in variously sized clusters. The melanosomes were often irregular in shape, smaller in diameter, and less mature (stage III) than those granules in the JF. The retinal pigment epithelium of both JF and BPR breeds contained a single epithelial layer of columnar cells. Rod-shaped melanosomes were present in the more apical regions of this cell type in both breeds. Both JF and BPR irides contained a multilayered posterior pigmented epithelium of columnar shaped cells that were densely filled with large spherical granules. Intercellular spaces with interdigitating cytoplasmic projections were present between pigment cells of both breeds. The pecten melanophores of both breeds were dendritic with melanosomes that were larger and fewer in numbers than those pigment cells of the iris and choroid. Intercellular spaces were present between cells in both breeds, with numerous villous-like pigment cell extensions. Choroid melanophores contained very little, if any, acid phosphatase activity. Approximately one-half of the retinal pigment epithelial cells observed contained small amounts of diffuse acid phosphatase activity in both breeds. The iris and pecten melanophores of both breeds contained profuse acid phosphatase activity scattered throughout their cytoplasms. Sparse tyrosinase activity was seen in iris and pecten pigment cells, whereas no tyrosine activity was observed in choroid melanophores or in retinal pigment epithelial cells in the two breeds, indicating that little new melanogenesis occurs in adult pigmented eye tissues. The results show that the barring gene reduces the number and melanin content of the choroidal melanophores in homozygous male BPR chickens as compared to the wild-type JF chickens. Whether this gene prevents the initial migration of embryonic neural crest cells (future melanophores) to the choroid or whether some of the choroidal melanophores prematurely degenerate in the embryo of young birds is yet to be determined. If the latter is the case, this choroid system may serve as a model for a genetic hypomelanotic disease such as vitiligo.     

Sequence divergence of the mitochondrial DNA of Pacific Ocean salmon

Restriction assay of mtDNA has been made in 6 salmon species form the genus Oncorhynchus and one species from the related genus, i.e. Salvelinus malma. The size of the mitochondrial genome was found to be identical and equal to 16.7 kilobases. The digestion patterns of mtDNA cleaved by 5 restriction endonucleases (Eco RI, Bgl I, Bgl II, Hind III, and Pst I) were used for analysis of the levels of interspecific variation and for estimation the matrix of mtDNA sequence differentiation. It was found that the level of nucleotide sequence divergence (p) in the genus Oncorhynchus varies within 1.7-6.7%. Minimum p value was observed in a pair O. keta--O. gorbuscha, maximum one--between O. masu and other species. With respect to similarity in their mtDNA, three groups may be distinguished: 1) O. gorbuscha--O. keta; 2) O. nerka--O. kisutch, O. tschawytscha; 3) O. masu. Mean value of intergeneric level of sequence divergence between Oncorhynchus and Salvelinus was found to be equal to 8%. On the basis of mtDNA analysis, the dendrogram of similarity of the species was plotted which is consistent in principle with current viewpoints on phylogenetic relations among the Pacific salmon.     

Persistent and reparative neurogenesis in the juvenile masu salmon <Emphasis Type="Italic">Oncorhynchus masou</Emphasis> 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.     

Size-structured Interactions between Native and Introduced Species: Can Intraguild Predation Facilitate Invasion by Stream Salmonids?

Dynamics of biological invasions may be complicated in size-structured animal populations. Differences in timing of life history events such as juvenile emergence create complex interaction webs where different life stages of native and non-native species act as predators, competitors, and prey. Stream salmonids are an ideal group for studying these phenomena because they display competition and predation in size-structured populations and have been introduced worldwide. For example, introduced rainbow trout (Oncorhynchus mykiss) are invading streams of Hokkaido Island, Japan and have caused declines in native masu salmon (O. masou) populations. However, age-0 rainbow trout emerge later than age-0 masu salmon and are smaller, which raises the question of why they are able to recruit and therefore invade in the face of a larger competitor. We conducted experiments in laboratory stream channels to test effects of increasing density of age-0 and age-1 rainbow trout on age-0 masu salmon. Age-1 rainbow trout dominated age-0 masu salmon by aggressive interference, relegating them to less favorable foraging positions downstream and reducing their foraging frequency and growth. The age-1 trout also reduced masu salmon survival by predation of about 40% of the individuals overall. In contrast, age-0 rainbow trout had little effect on age-0 masu salmon. Instead, the salmon dominated the age-0 trout by interference competition and reduced their survival by predation of 60% of the individuals. In each case, biotic interactions by the larger species on the smaller were strongly negative due to a combination of interspecific competition and intraguild predation. We predict that together these produce a positive indirect effect in the interaction chain that will allow the recruitment of rainbow trout in the face of competition and predation from age-0 masu salmon, and thereby facilitate their invasion in northern Japan.     

Population structure of the masu salmon <Emphasis Type="Italic">Oncorhynchus masou</Emphasis> from the Kol River (Western Kamchatka) and geographic variation in the species area

According to materials from original investigations in Kamchatka as well as published data, the population structure and geographical variation of the masu salmon Oncorhynchus masou are considered in the species area. The intraspecies structure, dates of their run to rivers, dates of spawning, traits of spawning, size-age and sex composition, fecundity, biological traits of parr, downstream migration of smolts are investigated. The relationship is shown between the manifestations of geographical variation of masu salmon and the factor of temperature. It is assumed that the global warming of climate would contribute to the advancement of this species to northern areas and to the increase in its abundance.     

On the Melanization of the Rat's Eye

Electron-microscopic study of the size of the melanosomes, the mean percentage of melanosomal profile area (MPMA) of the cells, and the duration of melanogenesis in the pigmented layers of the rat's eye (inbred strain BDE/Han) revealed the following: 1) The melanosomes in the cells of the retina vary in size and shape in different locations of the eye. The MPMA of the cells also differs. Only in the two layers of the iris epithelium do the minor diameters of the melanosomes not differ significantly from each other, but the MPMA of the cells is different. The pigmented outer layer of the ciliary epithelium stands out on account of its especially large, round melanosomes. 2) The melanosomes of the uveal melanocytes are uniformly small but exhibit the largest MPMA. 3) Only in the pigment epithelium of the fundus does melanogenesis cease in the fifth week of life. As a result the MPMA decreases. In the other areas of the pigmented epithelium and the uvea tyrosinase activity and premelanosomes are present from the new-born to the adult animal. These signs indicate continued melanogenesis. 4) Compound melanosomes are present in all pigmented locations of the eye. Giant melanosomes occur regularly only in the outer layer of the retina.     

The differing embryonic origins of retinal and uveal (iris/ciliary body and choroid) melanosomes are mirrored by their phospholipid composition

The phospholipids present in uveal (iris/ciliary body and choroid) and retinal bovine ocular melanosomes were identified using mass spectrometry. Similar phospholipid content is found for the two types of uveal melanosome, with sphingomyelin being the major species. Significant differences are found between the uveal and retinal melanosome. Glycerophosphoethanolamine (GPEtn) is the major species in the retinal pigment epithelium (RPE); 93% of the GPEtn contain polyunsaturated fatty acids, notably docosahexanoic acid and arachidonic acid, in the sn-2 position. RPE melanosomes also contain detectable quantities of glycerophosphoserine and glycerophosphate; these species were not detected in the uveal samples. While the structural and functional roles of melanosomal lipids largely remain to be determined, these different lipid compositions reported herein offer new insights into the roles of melanosomes in the different ocular tissues.     

Wild masu salmon is outcompeted by hatchery masu salmon,a native invader,rather than brown trout,a nonnative invader

Artificially grown native species are released into natural environments to increase biological resources or to recover threatened populations. Such stocks typically have enhanced survivability and may outcompete wild conspecifics as so-called native invaders. In addition, it is likely that the competitive effects of native invaders on native species are more intense than those of nonnative invaders. To test these hypotheses, an enclosure experiment was conducted using young-of-the-year wild and hatchery (normally grown to a relatively large size to increase survival after stocking) native masu salmon, Oncorhynchus masou, and nonnative brown trout, Salmo trutta (which attain a smaller size than masu salmon). Competitive effects between these fishes were evaluated in terms of stomach fullness and specific growth rate of the wild masu salmon. The magnitude of the relationship between stomach fullness and growth between the experimental treatments revealed a similar pattern, suggesting that competition for foraging habitat most affected their growth. Wild masu salmon were negatively affected by hatchery conspecifics, and the effects were greater than those caused by brown trout. We propose that these outcomes were caused by competitive dominance as a consequence of body size differences. In conclusion, the results support the hypothesis that size-enhanced hatchery masu salmon have the potential to function as native invaders, and the negative effects of artificial stocks on wild masu salmon could be greater than those caused by a nonnative invader.     

On the structure of retina of a fresh-water mullet, Rhinomugil corsula (Mugilidae, Pisces).

1. The structure of the eye-ball of Rhimomugil corsula has been described. 2. A mid-horizontal ridge (band) along the vitreal surface of the retina in each eye of R. corsula has been observed which divides the retina into a superior and an inferior hemispheres probably adapted for aquatic (dim-light vision) and aerial (bright-light vision) vision. 3. The superior hemisphere has been provided with poorly developed choroid gland and scarce pigment in the pigment epithelial cells. 4. The visual cell layer in the retina of the superior hemisphere contains both single and twin cones. They are alternately arranged in parallel rows. 5. The external and internal limiting membranes have been observed in both the hemispheres under light microscope. 6. The outer plexiform layer of the superior hemisphere contains many horizontal cells arranged into four distinct rows. 7. The inferior hemisphere has a well developed choroid gland, and dense pigment in the pigment epithelial cells.     

Deficiency of the Gene B Impairs Differentiation of Melanophores in the Medaka Fish,Oryzias latipes: Fine Structure Studies

In an orange-colored variant of the medaka fish, Oryzias latipes, which is homozygous for b allele, the melanophores represent a tissue-specific differentiation, manifesting an amelanotic appearance in the skin, an incomplete melanogenesis in the choroid and the peritoneum, and mosaic phenotype-like melano-iridophores in the peritoneum. In a wild-type strain of this species carrying the B gene, all melanophores are terminally differentiated irrespective of the tissues in which they are located. This indicates that the deficiency of B gene impairs the differentiation of melanophores in the medaka. Electron microscopy disclosed that the deficiency of B gene causes deterioration of melanogenesis to occur inside the melanosomes and that the manner of deterioration in the melanophores in the skin, the choroid and the peritoneum is different. The ubiquitous occurrence of reflecting platelet-laden melanophores in the peritoneum of this variant and the total absence of a mosaicism in pigment cells of the wild-type strain indicate that the deficiency of B gene predestines melanoblasts distributed in this tissue to an ambiguous state with regard to their differentiation. Little difference is observed between melanosomes maturation in pigment epithelial cells of the orange-colored variant and the wild-type strain, indicating an innocent role of the B gene in their differentiation.     

Biosynthesis and function of melanins in hepatic pigmentary system

In this report we show the most important results obtained from our study of the pigment liver cells of Amphibia and Reptilia. Contrary to the cutaneous pigment cells that derive from the neural crest, the liver pigment cells, instead, derive from the Kupffer cells: this can be seen from the results obtained from labelled precursor incorporation experiments, not only in vivo but also in vitro, using surviving liver slices or isolated melanosomes. Chemical analysis of both liver and cutaneous melanosomes reveal a great difference in their chemical composition, and this is in agreement with the different origins of these cells. We therefore propose that: liver pigment cells of Amphibia and Reptilia should be classified as "Extra Cutaneous Pigment Cells from Histocytic Origin". As regards the function of melanins, we show that O2 is trapped by these substances. Moreover, in my laboratory we have shown in several animal species, that the superoxide dismutase activity is inversely proportional to the quantity of melanin present; thus, we think that melanin could mime SOD activity.     

Reproduction ecology of masu salmon <Emphasis Type="Italic">Oncorhynchus masou</Emphasis> in the Kol basin (Western Kamchatka)

In the Kol basin, one of the typical salmon rivers of Western Kamchatka, special traits of reproduction ecology of masu salmon Oncorhynchus masou are studied (characteristics and behavior of spawners during spawning, localization of spawning grounds, topography and hydrology of redds, and interaction with other species of salmonids). The masu salmon spawns in the Kol basin in tributaries of the upper reaches of the river and only in downwelling. Spawning grounds of masu samlmon are confined to stretches with overhanging banks, log jams creating shelters for spawners and favorable hydrological conditions for spawning and egg development. All over its range, masu salmon requires similar conditions for reproduction. In the north of its range, in Kamchatka, masu salmon retains the properties of the most warm-water species in the genus Oncorhynchus and selects for spawning the grounds characterized by the highest temperature in the period of spawning and development.