The Studies of Chinese Minnow ( Rhynchocypris oxycephalus ) and Amur Minnow ( Rhynchocypris lagowskii ): A Review

and and geographic The results obtained of 2. difference two species and be used genetic them; 3. The of genic for fold higher both species were far less than the average genic variation of ABSTRACT The Rhynchocypris minnows (Teleostei: Cyprinidae) are typically small cold water fish, mainly distributed in Asia. This paper briefly reviews the studies of Chinese minnow ( Rhynchocypris oxycephalus ) and Amur minnow ( Rhynchocypris lagowskii ) based on the studies collected so far and could form the basis for a wide category of researches including zootaxy, reproduction & development, ecology, starvation, environmental biology, and techniques in order to highlight the recent progress in different fields of study using these species, which were done over a period of 21 years from 1998 to 2019.

unclear up to date [14]. Recently a sympatric area of these species was found [14]. Yang and Min [14] clarified their specific status by analyzing specimens collected from the sympatric area of these species. Isozyme analysis and morphometric comparison were performed [14]. Among 26 loci screened, 6 loci (Aco, Est-2, E-X, Gp-3, Ipo, Me) showed fixed allelic difference between them and these loci could be used as genetic markers to distinguish them. Isozyme analysis indicates that no hybridization occurs and therefore it is assumed that isolating mechanism is completed and they are distinct species. The mean number of scales above lateral line (SAL) of M. lagowskii and M. axycephalus at sympatric area was 24.93±1.95 and 17.33±0.72 respectively, and it seems like the result of character displacement. A finer microhabitat segregation between them is noticed. Yang and Min [14] noted that M. oxycephalus is found along the effluent streams whereas M. lagowskii is distributed mostly in the mainstream at sympatric area.
To clarify the systematics of the fresh-water fishes in Korea, Jeon [15] had drawn up a list and key of the genus Tribolodon, Phoxinus, and Moroco from Korea. For purpose of clarifying their distributional characteristics and distributional districts Jeon [15] had surveyed the micro-distributions of the fishes from March of Korean fresh-water fishes by Jeon [15]. Therefore, Jeon [15] suggested that more studies and examinations of the distributional districts of Korean fresh-water fishes should be undertaken.

Surveys of electrophoretic variation in isozymes and general
proteins encoded by 26 loci were conducted by Yang and Min [16] to assess species recognition and to estimate the degree of genic variation and species divergence for seven species of the genus The purpose of the study by Min and Yong [17] was to clarify the specific status of Moroco oxycephalus and M. lagowskii by analyzing 883 specimens collected from a sympatric area of these species.

Isoryme and morphometric analyses were performed by Min and
Yang [17] to identify parental species and possible hybrids. About 12% (N=104) natural hybrids were found. The rate of F 1 hybrids was higher (9%) than that of F 2 (2.7%) and decreasing frequency of The scale number of hybrids were intermediate between parental species. Min and Yang [17] pointed out that strong character displacement, fewer hybrids than expected and high mortality rate of hybrids indicate that speciation is completed and premating and postmating isolating mechanisms are both operating.
Park et al. [18] found that Rhynchocypris oxycephalus and R. steindachneri show very similar karyotypes: 2n=50 (FN=90), consisting of 12 metacentrics, 28 submetacentrics, and 10 acrocentrics with a gradual decrease in chromosome size, but with significant differences in nuclear DNA content of 2.64 and 2.52 pg/nucleus, respectively (P<0.05). Although the erythrocyte measurement and parameters of two species were similar, R. oxycephalus erythrocyte number was lower than that of R. steindachneri [18]. Park et al. [18] suggested that mode in karyological evolution within the genus Rhynchocypris shows an increase of nuclear DNA without apparent changes in karyotype and erythrocyte size.
The morphological similarity between upstream fatminnow Rhynchocypris oxycephalus and downstream fatminnow Rhynchocypris lagowskii makes it difficult to discriminate accurately between these species in rivers where they coexist [8].
For easy and precise identification of these two species, Takai et al. [8] developed a genetic discrimination method based on PCR-RFLP analysis for specimens from the Inohzawa River watershed in the Izu Peninsula, central Honshu, Japan. This genetic method was applied to the species identification of the fatminnows from two other watersheds, the Kano and Kawazu Rivers, flowing across the peninsula from north to south. Takai et al. [8] presented the genetic evidence for the restricted distribution of R. oxycephalus and the ubiquitous distribution of R. lagowskii in the peninsula.
Understanding how populations adapt to different thermal environments is an important issue for biodiversity conservation in the context of recent global warming [19]. To test the hypothesis that populations from southern region are more sensitive to climate change than northern region in cold-water species, Yu et al. [19] determined the thermal tolerance of two geographical populations of a cold-water fish, Rhynchocypris oxycephalus: the Hangzhou population from southern region and the Gaizhou population from northern region, then compared their transcriptomic responses between a control and a high temperature treatment. The results showed that the thermal tolerance range and thermal tolerance polygon area of Hangzhou population were narrower than the Gaizhou population, indicating populations from southern region were possibly more vulnerable. Further transcriptomic analysis revealed that the Gaizhou population expressed more temperature responding genes than the Hangzhou population (583 VS. 484), corresponding with their higher thermal tolerance, while some of these genes (e.g., heat shock protein) showed higher expression in the Hangzhou population under control condition, suggesting individuals from southern region possibly have already responded to the present higher environmental temperature pressure.
Therefore, Yu et al. [19] reported that these results confirm the prediction that populations from southern region are more sensitive to global warming and will be important for their future conservation.
Rhynchocypris oxycephalus (Teleostei: Cyprinidae) is a typical small cold water fish, which is distributed widely and mainly inhabits in East Asia [20]. Here, Zhang et al. [20] [21] presented genetic diversity of R. oxycephalus originated from Korea, Japan, and China.

Rhynchocypris lagowskii:
Two species of Moroco oxycephalus and M. lagowskii were studied by Min and Yang [13] to examine pattermsof genic variation and morphological differences within and between populations of two species, and to clarify their taxonomic status and geographic distribution. The results obtained from the study of Min and Yang The taxonomic status of Moroco lagowskii and M. oxycephalus, a pair of sibling species inhabiting in Korean fresh waters, has been unclear up to date [14]. Recently a sympatric area of these species was found [14]. Yang and Min [14] clarified their specific status by analyzing specimens collected from the sympatric area of these species. Isozyme analysis and morphometric comparison were performed [14]. Among 26 loci screened, 6 loci (Aco, Est-2, E-X, Gp-3, Ipo, Me) showed fixed allelic difference between them and these loci could be used as genetic markers to distinguish them. Isozyme analysis indicates that no hybridization occurs and therefore it is assumed that isolating mechanism is completed and they are distinct Kimhwanamdae-river were sympatrical distributions [15]. The above results are not it accord with the studies of distributional districts of Korean fresh-water fishes by Jeon [15]. Therefore, Jeon [15] suggested that more studies and examinations of the distributional districts of Korean fresh-water fishes should be undertaken.

Surveys of electrophoretic variation in isozymes and general
proteins encoded by 26 loci were conducted by Yang and Min [16] to assess species recognition and to estimate the degree of genic variation and species divergence for seven species of the genus The purpose of the study by Min and yong [17] was to clarify the specific status of Moroco oxycephalus and M. lagowskii by analyzing 883 specimens collected from a sympatric area of these species.

Isoryme and morphometric analyses were performed by Min and
Yang [17] to identify parental species and possible hybrids. About 12% (N=104) natural hybrids were found. The rate of F 1 hybrids was higher (9%) than that of F 2 (2.7%) and decreasing frequency of The scale number of hybrids were intermediate between parental species. Min and Yang [17] pointed out that strong character displacement, fewer hybrids than expected and high mortality rate of hybrids indicate that speciation is completed and premating and postmating isolating mechanisms are both operating.
Park et al. [18] found that Rhynchocypris oxycephalus and R. steindachneri show very similar karyotypes: 2n=50 (FN=90), consisting of 12 metacentrics, 28 submetacentrics and 10 acrocentrics with a gradual decrease in chromosome size, but with significant differences in nuclear DNA content of 2.64 and 2.52 pg/nucleus, respectively (P<0.05). Although the erythrocyte measurement and parameters of two species were similar, R. oxycephalus erythrocyte number was lower than that of R. steindachneri [18]. Park et al. [18] suggested that mode in karyological evolution within the genus Rhynchocypris shows an increase of nuclear DNA without apparent changes in karyotype and erythrocyte size.

Rhynchocypris oxycephalus and downstream fatminnow
Rhynchocypris lagowskii makes it difficult to discriminate accurately between these species in rivers where they coexist [8].
For easy and precise identification of these two species, Takai et al. [8] developed a genetic discrimination method based on PCR-RFLP analysis for specimens from the Inohzawa River watershed in the Izu Peninsula, central Honshu, Japan. This genetic method was applied to the species identification of the fatminnows from two other watersheds, the Kano and Kawazu Rivers, flowing across the peninsula from north to south. Takai et al. [8] presented the genetic evidence for the restricted distribution of R. oxycephalus and the ubiquitous distribution of R. lagowskii in the peninsula.

Rhynchocypris oxycephalus
The early gonadal development and sexual differentiation of Rhynchocypris oxycephalus were described from the stage of hatching to 150 days after hatching by Park et al. [22]. During this period, the average length of the body grew 0.64 cm to 5.94 cm. The primordial germ cells (PCGs), which could be recognized at the time of hatching, began to protrude into peritoneal cavity at a standard total length of 1.91cm. At a standard total length of 2.29 cm, initial ovarian differentiation was identified by the transformation of PGCs to meiotic oocytes. Finally, at the standard total length of 5.96 cm, the female gonads gradually developed towards migratory nucleus oocytes, characterizing the maturation.
Oocytes proliferated rapidly after sex differentiation while the testis entered a period of quiescence, as they continued to multiply but did not undergo growth until the standard total length of 4.00 cm.
At a standard total length of 4.00 cm, spermatocytes arrested in the phase of interkinesis. Sertoli-like cells and sperm duct formation, with signs of meiotic activity, were observed. Therefore, it may be concluded that R. oxycephalus belongs to the differentiated type of gonochoristic teleosts.
Kang and Min [23] investigated the reproductive cycles of two freshwater fishes, Moroco oxycephalus and M. lagowskii, in Korea.
Seasonal changes in Gonadosomatic Index (GSI) and gonads were investigated histologically from April 1998 to April 1999 [23]. The reproductive cycles of two species were not shown any differences.
In phase Ⅰ, the gonads of two species began to lose distinctly their weights from mid-April and reached the lowest GSI in late July (phase Ⅱ). In September, the GSI values of testis and ovary increased very slowly (phase Ⅲ) and gonadal developments rested during the winter season (phase Ⅳ). In March, the GSI values of M. oxycephalus and M. lagowskii began to increase and reached the maximum in April (phase Ⅴ). Kang and Min [23] pointed out that from the cyclic changes in the GSI and histological analyes, the spawning period was between mid-April and mid-May. disturbance. However, their hybrid frequencies would be reduced by postmating isolation mechanisms. Therefore, Kang et al. [26] noted that the two species are considered to be distinct species recently diverged.
For the evaluation of hormonal control of spermiation in fish, a method to quantify the spermiation response of mature Rhynchocypris oxycephalus (Sauvage and Dabry) to hormonal therapy is described by Park et al. [27]. Spermatocrit was determined after 7 min centrifrigation at 18,000 ×g and sperm density was estimated by a standard hemocytomer method. Sperm density can be predicted from spermatocrit since their relationship  quality were evaluated by Park [28]. None of the control group and sham (saline injected) control group ovulated [28]. The majority (76~96%) of the hormone treated groups ovulated within 2 days after hormone injection. Studies of egg quality, e.g., fertilization rate, and hatching demonstrated that good quality R. oxycephalus Oocyte surface in two Korean minnows, Rhynchocypris oxycephalus and R. kumgangensis was examined by light and electron microscope [29]. In two species, the development of the oocyte was similar, but the follicular layer surrounding fullgrown oocyte showed an evident difference. In R. oxycephalus, the follicular layer at the yolk vesicle stage became bilaminar with the retention of its outer squamous cell layer and the acquisition of an inner cuboidal or round cell layer just over the zona radiate.
As the oocyte grows, the cuboidal cells of the inner follicular layer began to be replaced by columnar cells. At the yolk granule stage, the columnar cells secreted mucin to their cytoplasm (adhesive materials) and then surround the entire oocyte, as bundles of fence-shaped structures. Whereas, although the follicular layer of R.
kumgangensis had an outer squamous layer and an inner cuboidal or round cell layer at the yolk vesicles as in R. oxycephalus, no inner cells were more changed with the retention of its cuboidal or round cells. Finally, in R. kumgangenesis, the adhesive materials did not ocuur. Gwak and Park [29] suggested that in Korean two minnows, the structural difference in the oocyte surface seems to be related to their habitats and spawning characteristics as well as taxonomic characters.

Rhynchocypris lagowskill:
Chinese minnow, Rhynchocypris oxycephalus is a teleost belonging to Leuciscinae, Cyprinidae [30]. The oogenesis and ultrastructure of egg envelope in Chinese minnow were investigated by light and electron microscopes by Kim et al. [30]. The ovary was of white yellowish and ellipsoidal shape with the major axis 30 mm and the minor axis 7mm. Cytoplasm of oogonia was basophilic and many nucleoli were located at inside of nuclear membrane. In primary oocytes, yolk vesicles were distributed only in the marginal area and egg envelope was not formed on the outside of an egg. In secondary oocytes, the egg envelope was formed and yolk vesicles in the cytoplasm were increased than the earlier stage. The basophilic substance of cytoplasm was changed to acidic. In case of matured egg, thickness of egg envelope and size of egg were increased.
The yolk vesicles were changed to yolk mass in accordance with development. The outer surface of egg envelope was covered by microvilli-structures and had a micropyle on the area of animal pole. Egg envelope consisted with 2 layers, an adhesive outer layer with microvilli-structures and fibrillary inner layer. Kim et al. [30] concluded that the oogenesis of Chinese minnow was characterized by the increase in cell size, the formation and accumulation of yolk, and the decrease of basophilic substance in the cytoplasm. The oogenesis of Chinese minnow seems to share common patterns in Cyprinidae, but these ultrastructural unique characters of egg envelope can be utilized in taxonomy of teleost.
The ultrastructure of spermatogenesis and sperm in Chinese minnow, Rhynchocypris oxycephalus belonging to Leuciscinae was investigated with light and electron microscopes by Kim et al. [31].
The whitish testis was located between intestine and air bladder.
The size of testis was major axis 2.3 cm, minor axis 6 mm. The testis contained numerous testicular cysts, and spermatogenesis was non-synchronized in these testicular cysts. In the case of spermatogonium, the nucleus was comparatively large ellipsoidal, and mitochondria showed a marked development. The size of primary spermatocyte was smaller than that of spermatogonia, and secondary spermatocyte was smaller than primary spermatocyte.
The chromatin of spermatocyte was highly condensed according to their development. The nucleus with electron-dense was round shape [31]. In spermiogenesis, flagella started to be formed and chromatin was more condensed. The mitochondria were rearranged in middle piece. The sperm was formed by loss of cytoplasm. The head of mature sperm was a spherical shape and have not acrosome. The microtubules of flagella were arranged 9+2 structure. Also, the tail of sperm have not lateral fins.

Rhynchocypris oxycephalus:
A series of assessments on the biological control potential Global climate change has been suggested to cause decrease of distribution area of many species [33]. However, this has not been tested for East Asian inland coldwater fish [33]. Chinese

minnow (Rhynchocypris oxycephalus) is a small typical coldwater
fish, which is endemic to East Asia and generally inhabits stream headwaters [33]. Due to its occurrence in temperate south China, there is growing concern about its future fate in the face of global warnming [33]. In this study, Yu et al. [33] employed maximum entropy approach to analyze how distribution of this species would be impacted by future climate change. Yu et al. [33] collected data of 310 independent distribution points and 20 environmental variables and conducted modelling under three general circulation models assuming two gas emission scenarios for 2020s, 2050s, and 2080s. The result obtained from study of Yu et al. [33], showed  [33] confirm that climate change clearly poses a severe threat to the Chinese minnow, and Yu et al. [33] suggested that conservation efforts should focus on lower temperature areas within the current range, because these areas will remain relatively cool and may be still suitable for the Chinese minnow even under the most drastic climate change scenarios.
The study of Yu et al. [11] demonstrated that geological events Rhynchocypris oxcephalus is a short-lived, fast-growing, highly fecund, and early-maturing species; therefore, even a short recovery time after overexploitation or disturbance would be of great use for their restoration. Liang et al. [9] pointed out that some life history traits of R. oxycephalus demonstrate obvious differences with its closely related species, indicating that latitude and local environment conditions are important selective forces for this species.
In Japan, domestic freshwater fish are accidentally introduced into non-native freshwater habitats by human activity, such as the planting of fish [34]. Introduction of the domestic alien fish may have a detrimental effect on native fish inhabitants [34]. However, investigations on the distribution and establishment of such domestic alien fish in non-native river basins and their influence on native fish remains limited [34]. Therefore, Nishida et al. [34] investigated the distribution and establishment of the domestic alien fish Rhynchocypris oxycephalus and its influence on native fish in the Tama River Basin, Japan. Specifically, Nishida et al. [34] used mitochodrial DNA and morphological analyses to clarify the influence of the invasion of this species on the distribution of the closely related fish R. lagowskii, which is native to the river basin. Fish sampled from the upstream section of the main river were mostly R. oxycephalus. This indicates that R. oxycephalus has replaced R. lagowskii in the upstream region. Fish sampled from the downstream section of the main river were mostly R. lagowskii.
R. oxycephalus was also captured from agricultural canals linked to the Tama River, and in streams connected to the river via the canals. These observations by Nishida et al. [34] indicated that the agricultural canal water metworks facilitate the invasion of R.
oxycephalus to peripheral habits, such as canals and streams. In contrast, R. lagowskii was found in streams that flowed into the upstream section of the Tama River, with these streams having many large drop structures, indicating that drop structures prevent R. oxycephalus from invading aquatic habitats in these streams. on diet items showed no significant differences between major food items (P<0.05) or between seasons, size classes and sexes. In contrast, fullness index and dietary breadth analysis both indicated significant diet changes between seasons. Consequently, this study performed by Lei et al. [36] provides information on feeding habits of R. oxynchocypris, which may be useful in cultivation trials.

Rhynchocypris lagowskii:
In Japan, domestic freshwater fish are accidentally introduced into non-native freshwater habitats by human activity, such as the planting of fish [34]. Introduction of the domestic alien fish may have a detrimental effect on native fish inhabitants [34]. However, investigations on the distribution and establishment of such domestic alien fish in non-native river basins and their influence on native fish remains limited [34]. Therefore, Nishida et al. [34] investigated the distribution and establishment of the domestic alien fish Rhynchocypris oxycephalus and its influence on native fish in the Tama River Basin, Japan. Specifically, Nishida et al. [34] used mitochodrial DNA and morphological analyses to clarify the influence of the invasion of this species on the distribution of the closely related fish R. lagowskii, which is native to the river basin. Fish sampled from the upstream section of the main river were mostly R. oxycephalus. This indicates that R. oxycephalus has replaced R. lagowskii in the upstream region. Fish sampled from the downstream section of the main river were mostly R. lagowskii.
R. oxycephalus was also captured from agricultural canals linked to the Tama River, and in streams connected to the river via the canals. These observations by Nishida et al. [34] indicated that the agricultural canal water metworks facilitate the invasion of R. oxycephalus to peripheral habits, such as canals and streams. In contrast, R. lagowskii was found in streams that flowed into the upstream section of the Tama River, with these streams having many large drop structures, indicating that drop structures prevent R. oxycephalus from invading aquatic habitats in these streams.

Rhynchocypris oxycephalus
The influence of nutritional conditions on the histological changes of hepatocyte and intestinal epithelium as well as Hepatosmatic Index (HSI), protein, RNA, and DNA concentrations of liver of Rhynchocypris oxycephalus was tested by Lee et al. [37]. Although, the starved group showed higher concentrations of protein, DNA, and RNA than the fed group, food deprivation resulted in a decrease in the HIS, hepatocyte nucleus size and nuclear height of the intestinal epithelium. The RNA-DNA ratio appears to be a useful index of nutritional status in R. oxycephalus and may be useful for determining if R. oxycephalus is in a period of rapid or slow growth at the time of sampling. Additionally, the data have been interpreted in detail and some biologically important relationships discussed by Lee et al. [37].
The effects of starvation on the morphometrical changes in sectioned body traits, condition factor, viscera index, and dressing percentage were determined for evaluating nutritional conditions of Rhynchocypris oxycephalus (Sauvage and Dabry) by Park et al. [38]. Starvation for nine weeks resulted in a decrease in most sectioned traits as well as in condition factor and viscera index (P<0.05). These findings suggest that nutritional parameters used in this study appear to be a useful index for nutritional status in this species. The data has been interpreted in detail and some important body sectioned values of interest to commercial growers discussed by Park et al. [38].
A 75-day study was conducted to determine the effect of starvation on classical and truss parameters in Rhynchocypris oxycephalus (Sauvage and Dabry) by Park et al. [4]. Truss dimensions of almost the entire head and trunk region as well as the abdomen were increased significantly through feeding or starvation (p < 0.05). Truss dimensions of the caudal region generally decreased through feeding or starvation, particularly those dimensions at the hind part of the trunk. There were some significant decreases in classical dimension of the head region during feeding, in relation to body depth characteristics in the trunk and caudal region during starvation, whereas there was only one decreasing classical dimension in the caudal region during feeding. The results of this study indicate that application of the truss network as a character set enforces classical coverage across the body form, discrimination among experimental groups thus being enhanced. Considering that the dimension of the lower part of the head and some truss and classical dimensions were least affected by feeding and starvation, these dimensions may then be useful as a taxonomical indicator to discriminate the species of Rhynchocypris sp. Park et al. [4] suggested that the value of trunk region dimensions with a large component of body depth in R. oxycephalus is most likely to be compromised by variability related to differences in feeding regimes of fish in different habitats.
Following the previous experiments, a starvation experiment was conducted to determine the influence of feeding and starvation on the histological and biochemical changes, the morphormetric changes in the sectioned body and the morphometric changes in Rhynchocypris oxycephalus (Sauvage and Dabry) [39]. The influence of starvation on nutritional conditions of the histological changes of hepatocyte and intestinal epithelium as hepatosmatic Index (HSI), protein, RNA, and DNA concentrations of liver in R. oxycephalus was tested by Park [39]. Although the starved group showed higher concentrations of protein, DNA, and RNA than the fed group, food deprivation resulted in a decrease in the HSI, hepatocyte nucleus size, and nuclear height of the intestinal epithelium. The RNA-DNA ratio appears to be a useful index of nutritional status in R. oxycephalus and may be useful for determining if R. oxycephalus is in a period of rapid or slow growth at the time of sampling. Additionally, the data have been interpreted in detail and some biologically important relationships discussed by Park [39]. The effects of starvation on the morphometrical changes in sectioned body traits, condition factor, viscera index, and dressing percentage were determined for evaluating nutritional conditions of R. oxycephalus by Park [39]. Starvation for nine weeks resulted in a decrease in most sectioned traits as well as in condition factor and viscera index (P<0.05). These findings suggest that nutritional parameters used in this study appear to be a useful index for nutritional status in this species. The data has been interpreted in detail and some important body sectioned values of interest to commercial growers discussed. A 75-day study was conducted to determine the effect of starvation on classical and truss parameters in R. oxycephalus by Park [39]. Truss dimensions of almost the entire head and trunk region as well as the abdomen were increased significantly through feeding or starvation (P<0.05). Truss dimensions of the caudal region generally decreased through feeding or starvation, particularly those dimensions at the hind part of the trunk. There were some significant decreases in classical dimensions of the head region during feeding, in relation to body depth characteristics in the trunk and caudal region during starvation, whereas there was only one decreasing classical dimension in the caudal region during feeding. The results of this study indicate that application of the truss network as a character set enforces classical coverage across the body form, discrimination among experimental groups thus being enhanced. Considering that the dimension of the lower part of the head and some truss and classical dimensions were least affected by feeding and starvation, these dimensions may then be useful as a taxonomical indicator to discriminate the species of Rhynchocypris sp. Park [39] suggested that the value of trunk region dimensions with a large component of body depth in R.
oxycephalus is most likely to be compromised by variability related to differences in feeding regimes of fish in different habitats.

Rhynchocypris oxycephalus
Deformed vertebrae by cold shock in Rhynchocypris oxycephalus were discovered by Park [40]. Deformity was externally noticed in the caudal penducle region of R. oxycephalus. Radiographic and histologic investigation confirmed the deformity. Especially, histological investigations provided the fact that extensive fusion between neighbouring vertebrae is caused by removal of endogeneous mineralized tissue. Deformed vertebrae appeared suggesting the direct evidence of vertebral fusion had arisen internally by cold shock in this species.
Twelve-week feeding trial was performed to investigate effectiveness of dietary thyroxine and iodide on growth of Rhynchocypris oxycephalus (Sauvage and Dabry) by Park et al. [41]. One hundred and twenty-day old larvae (4.48 cm in mean total length and 0.84 g in mean wet body weight) were used as the experimental fish and acclimated into the experimental conditions. Two levels of concentrations (1 and 5 ppm) of sodium-L-thyroxine (T 4 ) and three levels of concentrations (15 and 25 ppm) sodium iodide (I) were sprayed on commercial feed for carp. Commercial feed for carp without spraying T 4 or I was used as control. Fish were fed to visual satiety for 12 weeks. Water quality was regularly monitored throughout the feeding trial. The control group showed 97.5% survival. Fish in the experimental groups at the end of the feeding trial achieved similar survival to control group and their appearance was to be normal without any deformity in all treatments. Weight gain (%) and specific growth rate of fish fed the diet with T 4 at 1 ppm, in order. Daily feed intake of fish fed on the diet with T 4 at 5 ppm and I at 1 ppm were significantly (P<0.05) higher than that of fish fed on the other diets. Daily feed intake of fish fed on the diet with I at 25 ppm was highest. Feed efficiency ratio for fish fed on the diet with I at 25 ppm was highest followed by me at 5 ppm, T 4 at 1 ppm, control, I at 1 ppm and T 4 at 5 ppm in order. This indicated that high weight gain and specific growth rate for fish fed the diet with T 4 at 5 ppm resulted from high daily feed intake, and eventually led to low feed efficiency ratio. Condition factor of fish fed the diet with I at 1 ppm was significantly (P<0.05) higher than that of fish fed the other diets. The results obtained from the study of Park et al. [41] indicated that 5 ppm T 4 and 1 ppm I treatment were effective for growth promotion in R. oxycephalus.
Vitellogenin (Vtg), a phospholipoglycoprotein precursor of egg yolk is synthesized and secreted from the liver in response to estrogens in female fish [42]. Vtg is normally undetectable in the blood of male fish but can be induced by exposure to chemicals possessing estrogenic activity [42]. Thus, the presence of Vtg in blood of male fish can serve as a useful biomarker for assessing previous exposure to estrogenic compounds [42]. In the study of shin et al. [42], Vtg was abnormally expressed in Rhynchocypris oxycephalus using estradiol benzoate (E 2 ). As the result, it was found that the level of Vtg in blood from R. oxycephalus was increased by treated quantity of E 2 with dose-effect manner. Monoclonal antibodies were generated against Vtg of R. oxycephalus. The hybridoma were screened with an enzyme immunoassay for the production of specific anti-Vtg antibodies by Shin et al. [42]. Five positive cell lines with a high specificity were selected. Monoclonal antibodies against Vtg of R. oxycephalus that was developed in the study of Shin et al. [42], may be a useful bio-indicator for the detection of estrogenic contamination in the aquatic ecosystem.
An experiment measuring the concentration ratios of 137 Cs and 85 Sr in fish as an index aquatic animal was performend by Jun et al. [43]. The species was Chinese minnow (Rhynchocypris oxycephalus), a Korean native freshwater species. Chinese minnows were reared in acryl aquarium which was 45 cm wide, 85 cm long, and 50 cm high. Water in the aquarium was successively purified using filtering devices attached on the floor and the well.
Fish powder in a particulate form was supplied twice a day for feeding. After a radioactive solution was added to make the initial water concentrations approximately 0.02 μCi/l and 0.1 μCi/l for 137 Cs and 85 Sr, respectively, the fish and water were sampled 10 times for a month. The study of Jun et al. [43] pointed out that the connectration ratios were measured to 0.348 lkg -1 ~ 13.906 lkg -1 for 137 Cs and 0.474 lkg -1 ~ 13.089 lkg -1 for 85 Sr

Rhynchocypris Oxycephalus:
The effectiveness of lidocaine HCI (lidocaine HCl/sodium bicarbonate mixture) was tested as an anaesthetic for Rhynchocypris oxycephalus and R. steindachneri at three different temperatures of 10℃, 15℃, and 20℃ by Park et al. [44]. Based on the exposure and recovery time, effective doses of lidocaine HCI were proven to be 300 ppm (20℃), 400 ppm (15℃), and 600 ppm (10℃) for R. oxycephalus, and 400 ppm (20℃), 500 ppm (15℃), and 600 ppm (10℃) for R. steindachneri, respectively. Anaesthetic dose and temperature-dependent relationship in exposure and recovery time were observed for these two Rhynchocypris spps. There were size-related increases of exposure time on R. steindachneri in each dose of lidocaine HCI [44]. However, dose-dependent increase of recovery time was found in only the large size group of Rhynchocypris spp.
Rhynchocypris oxycephalus was incised through the midlateral line between the dorsal and pectoral fins and the wounds were closed with absorbable synthetic suture, and here Park et al. [45] describe histological details on the nature of second-intention wound healing, rate of healing, and the nature of granulation tissue contraction. Postoperative survivals were 95% and 99%, compared to 100% for counterpart control fish, among fish at just and 7 days after surgery, respectively. By 14~42 days after surgery, fish had no mortality. The granulation tissue was epithelialized from day 7 through day 22 postsurgery. By 28 days postsurgery, the granulation tissue had contracted the wound margins into apposition. By 35~42 days postsurgery, the granulation tissue contained collagen fiber and the epidermis contained well-differentiated alarm substance cells; thus, the epidermis over the wound site was histologically normal in most fish, showed that wound healing was essentially complete within 35 days of surgery.
The experimental transportation of Rhynchocypris steindachneri was carried out to study the effects of lidocaine-hydrochloride on water parameters by Park et al. [46]. The dissolved oxygen, ventilation rate, ammonia nitrogen, and pH of control group, sham control group, and lidocaine-hydrochloride treated groups of min, 120 min, 240 min, and 360 min after elapsed from treatment were tested. During the experiment time it was found that lidocaine-hydrochloride treated groups were most effective, followed by sham control and control, in decreasing the oxygen consumption and the excretion of ammonia by the fish. There were lidocaine-hydrochloride dose-related decrease in oxygen consumption and the excretion of ammonia. Decreasing in pH value of lidocaine-hydrochloride groups and sham control group was much higher than that of control group. The results obtained from the study of Park et al. [46] revealed lidocaine-hydrochloride is effective as sedative for transportation mixture in R. steindachneri.

Rhynchocypris lagowskii:
The effectiveness of lidocaine HCl (lidocaine HCl/sodium bicarbonate mixture) was tested as an anaesthedtic for Rhynchocypris oxcephalus and R. steindachneri at three different temperatures of 10℃, 15℃, and 20℃ by Park et al. [44]. Based on the exposure and recovery time, effective doses of lidocaine HCl were proven to be 300 ppm (20℃), 400 ppm (15℃), and 600 ppm (10℃) for R. oxcephalus, and 400 ppm (20℃), 500 ppm (15℃), and 600 ppm (10℃) for R. steindachneri, respectively. Anaesthetic dose and temperature-dependent relationship in exposure and recovery time were observed for these two Rhynchocypris spp. There were size-related increases of exposure time on R. steindachneri in cach dose of lidocaine HCl. However, dose-dependent increase of recovery time was found in only the large size group of Rhynchocypris spp.
The experimental transportation of Rhynchocypris steindachneri was carried out to study the effects of lidocaine-hydrochloride on water parameters by Park et al. [46]. The dissolved oxygen, ventilation rate, ammonia nitrogen, and pH of control group, sham control group, and lidocaine-hydrochloride treated groups of 2.5 ppm, 5 ppm, 10 ppm, and 20 ppm at time of 30 min, 60 min, 90 min, 120 min, 240 min, and 360 min after elapsed from treatment were tested. During the experiment time it was found that lidocainehydrochloride treated groups were most effective, followed by sham control and control, in decreasing the oxygen consumption and the excretion of ammonia by the fish. There were lidocainehydrochloride dose-related decrease in oxygen consumption and the excretion of ammonia. Decreasing in pH value of lidocainehydrochloride groups and sham control group was much higher than that of control group. The results obtained from the study of Park et al. [46] revealed lidocaine-hydrochloride is effective as sedative for transportation mixture in R. steindachneri.

Conclusion
Two species of Rhynchocypris oxycephalus and R. lagowskii which are an Asian species of small freshwater cyprinid fish. In this paper, I provides information on a review of studies concerning a wide category of zootaxy, reproduction & development, ecology, starvation, environmental biology, and techniques for Rhynchocypris oxycephalus and R. lagowskii, which were done over a perid of 21 years from 1998 to 2019 in order to highlight the recent progress in different fields of study using these species.