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January 2001 - present
January 2003 - December 2012
January 1987 - December 2005
Publications
Publications (96)
Vertebrates first emerged from water to land in the Paleozoic. Our understanding about the process has been
steadily refined through paleontological studies, although the soft-body traits and behavior of these early animals
remain poorly known. Mudskippers, extant amphibious gobies, could give insight into this question. This study
reports on the o...
In Japanese flounder aquaculture, hypermelanosis occurs widely on the blind side. Rearing flounders in a net-lined tank was recently reported to prevent hypermelanosis. To effectively apply this method to larger tanks for aquaculture farming, the net setting method was examined. Juvenile flounders without darkened areas on the blind side [total len...
A correction to this paper has been published: https://doi.org/10.1007/s12562-021-01504-x
In artificially reared flatfish, especially the Japanese flounder Paralichthys olivaceus, pigmented skin (hypermelanosis) frequently appears on the fish’s blind side after normal metamorphosis. As no practical prevention method has yet been proposed, we examined the effectiveness of a loose net placed inside the rearing tank that covers the bottom...
Hypermelanosis of the blind side of Japanese flounder frequently occurs in post-metamorphic juveniles reared in hatcheries. Due to the morphological similarity between darkened blind-side skin and normal ocular-side skin, hypermelanosis is regarded as a transition from normal blind-side skin to that of the ocular side. Hypermelanosis appears only i...
Body coloration in flatfish is one of the most distinctive asymmetries in the animal kingdom, although the fundamental molecular mechanism of the pigmentation is unclear. In the dorso-ventral coloration (countershading) of other teleost fishes, ventral-specific expression of agouti signaling protein 1 (ASIP1), an endogenous antagonist of melanocort...
In the aquaculture of the Japanese flounder Paralichthys olivaceus, hypermelanosis, a malpigmentation condition in which the scales of a significant area on the blind side express the characteristics of those on the ocular side, remains a major concern. Since introducing sand into the rearing tank effectively suppresses hypermelanosis, the inhibito...
Albinos in Japanese flounder Paralichthys olivaceus are yellowish mutants which lack melanophores. To reveal the function of melanophores, U V-B tolerance was compared between wild-Type (1 00±8 mm) and albino (98 ± 6 mm) flounder juveniles. After 6 hours of U V-B exposure (1.1 W/m2), survival was examined every 1 hour for 24 hours. Control treatmen...
After metamorphosis, both eyes of the Japanese flounder Paralichthys olivaceus are located on its left side, with only the ocular side becoming pigmented. Staining, or hypermelanosis, occurs on the blind side at 2–3 months after metamorphosis, thereby lowering the market price of the fish. To understand the pigmentation expansion process, we perfor...
We previously reported that the progression of staining-type hypermelanosis spontaneously ceased at a specific time and area in Japanese flounder Paralichthys olivaceus. To examine whether time is a limiting factor in the spontaneous cessation of staining, we experimentally controlled the initiation and duration of staining by manipulating the bott...
Barfin flounder larvae exhibit unique black coloration, as well as left-right asymmetry in juvenile stage as in other flatfish. In this study, we first assessed the changes in melanophores with development and then investigated their responsiveness to melanin-concentrating hormone (MCH) during metamorphosis. Larval-type melanophores appeared on bot...
Abnormal flounder coloration frequently occurs in flounder hatcheries and diminishes the commercial value of the fish. To understand hypermelanosis, the progression of staining-type hypermelanosis in normally metamorphosed juveniles and ocular-side pigmentation in pseudoalbino juveniles were examined in the Japanese flounder Paralichthys olivaceus....
Staining-type hypermelanosis, defined as blind-side melanosis occurring after completion of metamorphosis, reduces commercial value in hatchery-produced flatfishes. Detailed characterization was performed on the stained area of juvenile Japanese flounder Paralichthys olivaceus to physiologically understand this phenomenon. From 80 to 120 days after...
Our previous studies showed that in barfin flounder, α-melanocyte-stimulating hormone (α-MSH) stimulates pigment dispersion in xanthophores, while it shows negligible effects in melanophores. The present study was undertaken to evaluate whether these results are limited to barfin flounder by using Japanese flounder. Three subtypes of proopiomelanoc...
Cortisol, the main glucocorticoid in fish, increases during flatfish metamorphosis and peaks before the surge of thyroxine. A large body of evidence indicates the essential role of thyroxine in flatfish metamorphosis, whereas information on cortisol is limited. We administered cortisol to spotted halibut Verasper variegatus larvae in order to exami...
Morphological abnormalities in eye location and/or body coloration are commonly observed in hatchery-reared juveniles of many pleuronectid species, and have become one of the most serious problems in juvenile production for stock enhancement. In this study, these morphological abnormalities of six pleuronectid species—barfin flounder Verasper moser...
We tested the hypothesis that metabolism of thyroid hormones by the brain of Atlantic salmon (Salmo salar) changes when rheotactic behavior reverses during parr-smolt transformation (PST). We measured brain and liver thyroxine (T4) and 3,5,3'-triiodo-L-thyronine (T3) outer-ring deiodination (ORD) and inner-ring deiodination (IRD) activities and pla...
The mechanism underlying malformation during flatfish metamorphosis is not clear. Here, the relationship between growth before
metamorphosis and the occurrence of malformation after metamorphosis was examined in individuals reared in a single tank.
Otoliths of starry flounder Platichthys stellatus larvae were labeled with alizarin complexone before...
This study examined the ontogenetic change in vertical distribution associated with algae and the thyroid hormone profiles
of black rockfish (Sebastes schlegelii) under rearing conditions. Experimental observations on distribution were carried on black rockfish from the newly born
larval stage to juveniles 75days after birth (DAB). Position was cat...
Flatfishes display a left–right asymmetry that is unique in the animal kingdom. In order to clarify the mechanisms of the
asymmetrical development of pigment cells, changes in pigment cell densities were examined in Japanese flounder Paralichthys olivaceus. During development from symmetrical larvae to asymmetrical juveniles, pigment cell densities...
In Japanese flounder (Paralichthys olivaceus), metamorphic period involves not only transformation from larva to juvenile but also migration from offshore areas to estuaries. In the present study, the role of endocrine systems in low-salinity adaptation was examined during early development and metamorphosis of the flounder. Survival rate 48 hr aft...
Distributional changes in branchial chloride cells were examined in Japanese sea bass (Lateolabrax japonicus) juveniles transferred from seawater (SW) to fresh water (FW) during their migration season toward low salinity habitat in nature. Chloride cells were identified by immunocytochemistry with a specific antiserum for Na+,K+-ATPase. In fish rea...
Wild-type medaka are known to have remarkable capabilities of fin, or epimorphic, regeneration. However, a hypothyroid mutant, kamaitachi (kmi), frequently suffers from injury in fins, suggesting an important role of thyroid hormone in fin regeneration. This led us to examine the relationship between thyroid hormone and fin regeneration using medak...
The aim of this work was to evaluate the effect of salinity changes on digestive enzyme activity and whole-body cortisol concentration in juveniles (46 DAH) of Japanese flounder.Two different salinity patterns were designed: a control group exposed to a constant flux of seawater (S = 32) and a treatment group exposed to changes from full seawater (...
The aim of this work was to evaluate the effect of stocking density on growth, digestive enzyme activity and cortisol level in larvae (2–35 DAH) and juveniles (46–65 DAH) of Japanese flounder. The body weight and body length were recorded, enzyme activities (trypsin and lipase) and cortisol levels were examined from frozen samples anesthetized with...
The thyroid hormone plays an essential role in the metamorphosis in flatfish, during which external asymmetry (for example, eye relocation and pigmentation) is established. However, no information is available on the expression mechanisms of metamorphic asymmetry. Since the presence of malformed juveniles (having either ocular or blind side charact...
The mRNA of the peptide hormone cholecystokinin (CCK) was isolated from juvenile Atlantic herring, Clupea harengus, by RT-PCR. The open reading frame encodes a 137 amino acid-long precursor protein. The peptide sequence of herring CCK-8, DYMGWMDF, is identical to that of higher vertebrates and elasmobranchs, and contains methionine in the sixth pos...
In order to study the physiological characteristics of neoteny in teleosts, the development of the thyroid axis and digestive tract of the ice fish, Salangichthys microdon (Salmonoidei), were examined using wild caught samples in the Yura River and its estuary. In all developmental stages examined in this study, the digestive tract was straight, an...
In large-scale rearing of juveniles of the Japanese flounder Paralichthys olivaceus, a certain morphological abnormality occurred spontaneously in 4% of the fish. These fish showed a slight but clearly different appearance from any developmental stage of this species, and did not settle when all the other juveniles in the same tank completed metamo...
The effects of larval density, rearing media, and protein additions on fish larval survival were tested by rearing larvae in small containers. Yolk-sac larvae of Japanese flounder, Paralichthys olivaceus, were transferred 1 day after hatching to plastic dishes and cell-culture microplates by Pasture pipette at densities ranging from 0.3 to 30 indiv...
The occurrence of metamorphosis-related abnormalities under different rearing water temperatures (9-21degreesC) was examined in hatchery-reared juveniles of spotted halibut Verasper variegatus. The growth and development of the larvae were accelerated at higher temperatures. After completing metamorphosis, juveniles were categorized into three morp...
The ontogenetic development of cholecystokinin-immunoreactive (CCK-IR) cells was studied in larval ayu, Plecoglossus altivelis. This species has a straight digestive tract during the larval phase. CCK-IR cells were present in all the larvae from the day of hatching (0 days after hatching, DAH). An immunoreaction to anti-trypsinogen antibody was als...
Morphological changes are described in Japanese flounder Paralichthys olivaceus larvae and juveniles with emphasis on growth during the period of metamorphosis. Ontogenetic changes in condition factor and lipid, glycogen and protein levels were also analysed to determine the utilization of stored energy. Fish grew from 6·6 to 20·3 mm LT(1·15 to 84·...
In order to clarify the mechanisms of neoteny in the ice goby (Leucopsarion petersii), we examined effects of thyroid hormone and thiourea (TU) treatments on their neotenic characteristics and the pituitary-thyroid axis. Adult ice goby were exposed to 3, 5, 3'-triiodothyronine (T3, 0.1 ppm), TU (inhibitor of thyroid hormone synthesis, 30 ppm), or t...
The internal structure of malformed Japanese flounder Paralichthys olivaceus juveniles in eye location was histologically examined and deformed bones were identified as the tissue important for eye relocation. A deformed pseudomesial bar (Pb) was the common feature for individuals with abnormal eye location (AEL individuals). Individuals with mild...
In order to study the characteristics of neoteny in teleosts, development of the thyroid system and digestive tract of a neotenic goby (ice goby, Leucopsarion petersii) and a non-neotenic goby (ukigori, Gymnogobius urotaenia) were compared. In juvenile ukigori, the intestine was found to be convoluted once in the antero-midpart, and gastric glands...
The body of a Japanese flounder (Paralichthys olivaceus) changes from a symmetrical to an asymmetrical form during metamorphosis. To obtain detailed information on the mechanisms of the migration of the right eye to the left side, soft and hard tissues in the head of larval flounders were examined using transmission electron microscopy (TEM). Retro...
In the seed production of several marine teleosts, large numbers of dead larvae are frequently observed on the water surface around the time of first feeding. We tried to prevent such “surface death” by the addition of chicken egg white (EW) into the rearing water. In the first experiment, larvae of striped bonito, Sarda orientalis, at the first fe...
The larvae of flatfish change their body structure during metamorphosis, including dramatic translocation of one of the eyes from one side of the body to the other. Such metamorphic processes are in general promoted by thyroid hormones (THs). This study focuses on the response of individual tissues to hormones, and morphological characteristics wer...
: Striped bonito Sarda orientalis larvae and juveniles were reared in a laboratory from hatching to 14 days post hatching, and the development of their digestive system was investigated histologically. On day 2 (first feeding day), the larval-type digestive system was differentiated. On day 3, a blind sac with densely distributed gastric glands dev...
The appearance and distribution of cholecystokinin (CCK)-immunoreactive (IR) cells in the digestive tract of cultured developing larvae of bluefin tuna, Thunnus thynnus, were investigated by immunohistochemistry. The CCK-IR cells had an elongated triangular shape and a thin apex pointing towards the lumen of the gut. Very few weakly stained CCK-IR...
The contribution of the thyroid hormone to the metamorphosis of the coral trout Plectropomus leopardus was examined. Juveniles, aged 35 days, were exposed to thyroxine (T4, 0.1 p.p.m) and thiourea (TU; inhibitor of thyroid hormone synthesis, 30 p.p.m) for 13 days. All the fish in the T4-treated group had completed metamorphosis (second metamorphosi...
We have isolated a clonal line reversed (rev) of homozygous Japanese flounder through gynogenesis. The homozygous offspring gynogenetically produced from rev exhibited reversal of organization of the metamorphic L/R asymmetry such as the direction of eye-migration at a high frequency (20-30%). The molecular analysis using a left-specific marker pit...
Studies were conducted on development and metamorphosis of coral trout Plectropomus leopardus. Rearing experiments were conducted at the Japan Sea Farming Association, Yaeyama Station, Okinawa in 1998 to 2000.
The findings of this study show that coral trout experience two marked developmental changes related to metamorphosis. First phase is transf...
In 1999, spotted halibut Verasper variegatus were experimentally reared at 9, 12, 15, 18, and 21°C from eggs through early juveniles at the Miyako Station of Japan Sea-Farming Association in Iwate Prefecture. Tissue concentrations of thyroxine (T4) increased to maximum levels during metamorphic climax (H-stage) at all the temperatures. The peak T4...
Japanese flounder larvae were reared for 43 days in glass aquariums with and without sand in the bottom to study the influence of the substrate on the pigmentation pattern, pituitary growth and ACTH and MSH production. Similar results were obtained in terms of survival, growth and ocular side pigmentation in both groups. However, a clear difference...
The appearance and distribution of cholecystokinin (CCK)-producing cells were investigated in the digestive tract of developing larvae of cultured Atlantic halibut, Hippoglossus hippoglossus. The CCK-producing cells were detected immunohistochemically, by use of a primary antiserum against CCK cloned for the Japanese flounder, Paralichthys olivaceu...
The patterns of entry of thyroid hormones into live tilapia oocytes were examined by incubating ovarian follicles in L-15 medium containing 125I-labeled thyroxine (T4) or 3,5,3'-triiodothyronine (T3). As judged from HPLC profiles, radioactivity in extracts of follicles immersed in T3 was identified to reside in T3, while most of the radioactivity i...
The symmetrical body of flatfish larvae dramatically changes into an asymmetrical form after metamorphosis. Eye migration results in the most significant asymmetrical development seen in any vertebrate. To understand the mechanisms involved in eye migration, bone and cartilage formation was observed during metamorphosis in laboratory-reared Japanes...
In order to examine the putative involvement of adenocorticotropin �ACTH. and melanocyte-
stimulating hormone �MSH., the two major hormones controlling melanophores, in albinism of
flounders, production of the hormones was immunocytochemically examined in fish in which
albinism had been induced by dietary arachidonic acid �ARA. supplementation. Lar...
In 1997 and 1998, spotted halibut Verasper variegatus were experimentally reared from eggs through early juveniles at the Miyako Station of Japan Sea-Farming Association in Iwate Prefecture. The primitive digestive system of V. variegatus differentiated at the C stage at which eyes pigmented and the mouth opened. The gastric gland and pyloric caeca...
The entry and metabolism of 3H-cortisol in oocytes were investigated using isolated follicles of the tilapia (Oreochromis mossambicus) in order to examine the mechanisms of incorporation of maternal hormones into oocytes. The composition of 3H-labeled steroids in the oocyte was analyzed by high-performance liquid chromatography. A significant amoun...
Three experiments were carried out to clarify the effect of thyroid hormones on the pigmentation of larval Japanese flounder Paralichthys olivaceus. The first two experiments were conducted to investigate the critical concentration of thyroxine (T4) which causes abnormal pigmentation, and the third was to determine the sensitive stage of larval dev...
The annual reproductive cycle of a small flounder (aramegarei), Tarphops oligolepis, was examined in Wakasa Bay from the appearance of recently settled juveniles in the field and the female maturity during a year. Seasonal changes in the distribution of standard length indicated the presence of two spawning periods, July and October, when small juv...
The metabolic aspects of ionic and osmotic regulation in fish are not well understood. The objective of this study was to examine changes in carbohydrate metabolism during seawater (SW) acclimation in the euryhaline tilapia (Oreochromis mossambicus). Hepatic activities of three key enzymes of the intermediary metabolism, phosphofructokinase, glycog...
To clarify the involvement of cortisol in functional differentiation of branchial chloride cells, cellular gene expression and localization of cortisol receptor were examined in chum salmon (Oncorhynchus keta) fry in freshwater (FW) and those adapted to seawater (SW) by in situ hybridization and immunocytochemical staining. Sodium-potassium adenosi...
Ontogenetic changes in whole-body immunoreactive cortisol concentrations (IRC) and aggressive behavior were examined in yellowtail Seriola quinqueradiata (Temminck & Schlegel; Carangidae). Baseline IRC significantly increased during the transition from larval to juvenile stage and was correlated with the onset of aggressive behavior. Handled fish (...
Seasonal changes in plasma levels of insulin-like growth factor I (IGF-I) in precociously maturing amago salmon (Oncorhynchus masou ishikawai), which matured as 1-year-olds, have been investigated. Profiles of plasma IGF-I levels were compared with changes in growth and maturity, and plasma growth hormone (GH) and thyroxine (T4) concentrations. The...
Cortisol is one of the central hormones in osmoregulation in fish, especially in seawater adaptation. A cDNA of 453 bp was cloned from liver mRNA of freshwater-reared tilapia (Oreochromis mossambicus), by reverse transcription polymerase chain reaction (RT-PCR) with primers designed for the hormone-binding domain of glucocorticoid receptors (GRs) i...
Survival of the seed of goldstriped amberjack Seriola lalandi was consistently enhanced by intramuscular injection of triiodothyronine (T3) to the broodstock fish at a dose of 20 mg/kg body weight. Survival rates at the time of transfer to net cages (35 d after hatching) were 2.6–5.0% for the T3 treatment while only 0.3–2.1% for the control. Surviv...
Metabolic aspects of osmoregulation were examined in two species of tilapia. Oreochromis niloticus, a moderate hypo-osmoregulator, was reared in fresh water (FW) or 50% seawater (SW) for 4 weeks with limited diet, while more euryhaline species, O. mossambicus, was keptin FW, 100% SW, or 160% SW. There was no significant difference in plasma concent...
A key to success in the culture of marine fish is the mass production of high quality fry, a process largely dependent on successful first feeding and normal development and growth of fish larvae. In this regard it is important to examine the structural and functional development of the endocrine system during early ontogeny of marine fish. To char...
To evaluate the osmoregulatory ability of eyedstage embryos of laboratory-reared chum salmon, Oncorhynchus keta, we examined changes in osmolality of the perivitelline fluid and blood following transfer to 50 and 100% seawater (SW), together with morphological changes in chloride cells present in the yolk sac membrane. Transfer to SW did not cause...
Changes in gonadal and plasma concentrations of thyroid hormones were examined at various stages of maturation in chum salmon (Oncorhynchus keta) caught in the Bering Sea and the Bay of Alaska. Plasma concentrations of thyroxine (T4) were less than 5 ng ml−1, and those of 3,5,3′-triiodo-L-thyroxine (T3) were less than 2 ng ml−1 I in both males and...
Specific radioimmunoassays (RIAs) for the pair of tilapia prolactins (tPRLs) and growth hormone (tGH) were developed using antisera raised in rabbits. Anti-tPRL177 did not cross-react with tPRL188 and tGH. Anti-tPRL188 did not cross-react with tPRL177 and showed slight cross-reaction (3.1%) with tGH. Anti-tGH showed negligible cross-reactions with...
To clarify the hormonal regulation of metamorphosis of the conger eel (Conger myriaster), changes in whole body concentrations of thyroid hormones, thyroxine (T4) and triiodothyronine (T3), and cortisol during metamorphosis were examined, as well as the changes in the histological activity of the thyroid gland. In larvae before metamorphosis, T4 an...
To examine the biological significance of thyroid hormones contained in eggs, the hormones were depleted from eggs by treating the mother fish with thiourea. Constantly spawning medaka (Oryzias latipes) were reared in fresh water containing 0.03% thiourea. The plasma thyroxine (T4) and triiodothyronine (T3) concentrations in the mother fish were ab...
The tissue concentration of L-thyroxine (T4) was measured by radioimmunoassay for whole bodies of laboratory-reared black sea bream larvae from 12 to 38 days after hatching. T4 level was less than 2ng/g body wet weight in early postlarvae. It increased markedly from 1.7ng/g on day 19 to 7.0ng/g on day 24, and then gradually decreased to 2.4ng/g by...
Thyroid hormone concentrations in unfertilized eggs of 26 species of various freshwater, marine and diadromous teleosts were examined, together with changes in their concentrations during egg development in some species. Significant quantities of both thyroxine (T4) and triiodothyronine (T3) were found in eggs of all species examined. Mean T4 and T...
The changes in tissue and blood concentrations of thyroxine (T4) and triiodothyronine (T3) were examined during development of the chum salmon (Oncorhynchus keta). Extraction methods previously established for tissue T4 were also validated for tissue T3, by parallel displacement curves to T3 standard in the radioimmunoassay and by the same elution...
Downstream migratory behavior, plasma T4 concentrations and histological changes in the thyroid gland of biwa salmon underyearlings were examined during late spring and early summer for three consecutive years. The downstream migration was observed specifically when the flux of the river increased following rainfall. A close correlation was seen be...
Seasonal changes in plasma thyroxine concentrations were examined in biwa Oncorhynchus rhodurus and amago salmon O. rhodurus reared in the pond. About 80% of biwa salmon lost parr marks and became silvery in underyearling June. Thereafter, they kept silvery body color until 2-year-old April, when the experiments were terminated. Plasma thyroxine le...
Changes in phototaxis of chum (Oncorhynchus keta) and coho (O. kisutch) salmon were examined after treatment with thyroid hormones, using troughs (0.25 × 2 m long, 20 cm deep) with open (1200–2400 lux, 1 m long) and shaded (400–680 lux, 1 m long) water. In some experiments, half of the trough was covered to provide shelter (< 10 lux). Chum fry weig...
Bovine thyroid-stimulating hormone (TSH) was microinjected (0.2 microliter/fish) into prometamorphic flounder larvae and the effects on metamorphosis as well as the tissue thyroxine (T4) and triiodothyronine (T3) levels were studied. After a single injection of TSH (5 mIU/g), the tissue T4 concentration increased markedly after 5 hr, reached a peak...
Freshwater adaptability of chum salmon was examined in juvenile fish reared in seawater for 4 months. The fish, weighing about 40g, were transferred directly to fresh water in October, when their cohorts are migrating in the North Pacific Ocean. Plasma sodium concentration decreased from 167 mM in seawater to about 130 mM during the first 24h, and...
Effects of thyroid hormones and rearing temperature on Japanese flounder metamorphosis were studied by measuring tissue concentration of thyroxine (T4) by radioimmunoassay. Larvae reared at 15 or 22°C of various developmental stages were quickly frozen and stored at about -32°C until assayed. Non-detectable values of T4 were obtained for pre-metamo...
The tissue concentration of thyroxine (T4) in larval flounder (Paralichthys olivaceus) was studied at various stages of their metamorphosis using a specific radioimmunoassay developed for samples obtained by quantitative extraction of the hormone from fish eggs and larvae. T4 concentrations were below the limit of detection in extracts of fertilize...
In order to examine the role of thyroid hormones during salmonid development, techniques were developed for quantitative extraction of thyroxine from eggs, whole embryos, and alevins of chum salmon (Oncorhynchus keta) at various stages of development. Frozen eggs, embryos, alevins, or fry were homogenized in ice-cold methanol. The homogenate was ce...
Summary Survival, growth, and number of chloride cells were measured during and after exposure to a range of osmotic conditions in anadromous Striped bass Morone saxatilis larvae (ages: 9-41 days post hatch). Larvae were held at 0.7ppt prior to salinity challenge tests at 0, 0.1, 0.7, 5, 11, and 33ppt. Higher survival rates were recorded at 11 and...
