The first cavefish in the Dinaric Karst?Cave colonization made possible by phenotypic plasticity in Telestes karsticus

Cave animals are an excellent model system for studying adaptive evolution.At present,however,little is known about the mechanisms that enable surface colonizers to survive in the challenging environment of caves.One possibility is that these species have the necessary genetic background to respond with plastic changes to the pressures of underground habitats.To gain insight into this process,we conducted a comparative study with the fish species Telestes karsticus,which occurs in a hydrological system consisting of an interconnected stream and a cave.Results showed that T.karsticus resided year-round and spawned in Sušik cave,making it the first known cavefish in the Dinaric Karst.Cave and surface populations differed in morphological and physiological characteristics,as well as in patterns of gene expression without any evidence of genetic divergence.To test whether observed trait differences were plastic or genetic,we placed adult fish from both populations under light/dark or constant dark conditions.Common laboratory conditions erased all morphometric differences between the two morphs,suggesting phenotypic plasticity is driving the divergence of shape and size in wild fish.Lighter pigmentation and increased fat deposition exhibited by cave individuals were also observed in surface fish kept in the dark in the laboratory.Our study also revealed that specialized cave traits were not solely attributed to developmental plasticity,but also arose from adult responses,including acclimatization.Thus,we conclude that T.karsticus can adapt to cave conditions,with phenotypic plasticity playing an important role in the process of cave colonization.

Genetic identification and reiterated captures suggest that the Astyanax mexicanus El Pachón cavefish population is closed and declining

The sizes of Astyanax mexicanus blind cavefish populations of North-East Mexico are demographic parameters of great importance for investigating a variety of ecological,evolutionary,and conservation issues.However,few estimates have been obtained.For these mobile animals living in an environment difficult to explore as a whole,methods based on capture-mark-recapture are appropriate,but their feasibility and interpretation of results depend on several assumptions that must be carefully examined.Here,we provide evidence that minimally invasive genetic identification from captures at different time intervals(three days and three years)can give insights into cavefish population size dynamics as well as other important demographic parameters of interest.We also provide tools to calibrate sampling and genotyping efforts necessary to reach a given level of precision.Our results suggest that the El Pachón cave population is currently very small,of an order of magnitude of a few hundreds of individuals,and is distributed in a relatively isolated area.The probable decline in population size in the El Pachón cave since the last census in 1971 raises serious conservation issues.

Loss of behavioral stress response in blind cavefish reduces energy expenditure

The stress response is essential for animal self-defense and survival. However, species may exhibit stress response variation depending on their specific environmental and selection pressures. Blind cavefish dwell in cave environments, which differ markedly in stressors and resource availability compared to surface aquatic environments. However, whether blind cavefish exhibit differences in stress response as an adaptation to their cave environments remains unclear. Here, we investigated differences in stress response in six closely related Triplophysa species, including three blind cavefish (T. longibarbata, T. jiarongensis, and T. rosa) and three normal-sighted river fish (T. nasobarbatula, T. dongsaiensis, and T. bleekeri). Results showed that blind cavefish exhibited a range of distinct behavioral responses compared to sighted river fish, including greater levels of activity, shorter duration of freezing, absence of erratic movements or thrashing behavior, and opposite behavioral trends over time. Furthermore, the cavefish species demonstrated attenuated increases in metabolic rate in response to stressors related to novel environments. Cave-dwelling T. rosa also exhibited lower basal hypothalamic-pituitary-inter-renal (HPI) axis-related gene expression levels and stress hormone concentrations compared to river-dwelling T. bleekeri. These results suggest that blind cavefish may have lost their behavioral stress response, potentially mediated by a reduction in basal activity of the HPI axis, thus enabling the conservation of energy by reducing unnecessary expenditure in energy-limited caves.

Investigation on the Lateral Line Systems of Two Cavefish： Sinocyclocheilus Macrophthalmus and S. Microphthalmus （Cypriniformes： Cyprinidae）

Cavefish, with sensitive lateral lines, can swim freely and locate preys in invisible and complex cave environments, though their eyes are greatly degenerated. Investigations on the morphology and distribution characteristics of their lateral line systems would benefit our understanding of the high-sensitivity mechanism of the fish. In this study, the arrangement and morphology of the lateral lines are described for two species ofSinocyclocheilus： S. macrophthalmus and S. microphthalmus, which live in the karst caves in Guangxi, China. The behavior experiments indicate that the lateral line system of the S. macrophthalmus is more sensitive at a low vibration frequency range from 20 Hz to 70 Hz. The cephalic and trunk lateral line systems both contribute to the efficient object-locating capability. For both of the two species of cavefish, the diameter of the lateral canal nearby the neuromasts is narrower than that nearby the canal pores. This variation can increase the normal pressure to the surface of the cupula, and increase the sensitivity of the canal lateral line system.

Brain of the blind:transcriptomics of the golden-line cavefish brain

The genus Sinocyclocheilus (golden-line barbel) includes 25species of cave-dwelling blind fish (cavefish)and more than 30 surface-dwelling species with normal vision.Cave environments are dark and generally nutrient-poor with few predators.Cavefish of several genera evolved convergent morphological adaptations in visual,pigmentation,brain,olfactory,and digestive systems. We compared brain morphology and gene expression patterns in a cavefish Sinocyclocheilus anophthalmus with those of a closely related surface-dwelling species S.angustiporus.Results showed that cavefish have a longer olfactory tract and a much smaller optic tectum than surface fish.Transcriptomics by RNA-seq revealed that many genes upregulated in cavefish are related to lysosomes and the degradation and metabolism of proteins,amino acids,and lipids.Genes down- regulated in cavefish tended to involve "activation of gene expression in cholesterol biosynthesis" and cholesterol degradation in the brain.Genes encoding Srebfs (sterol regulatory element- binding transcription factors)and Srebf targets,including enzymes in cholesterol synthesis,were downregulated in cavefish brains compared with surface fish brains.The gene encoding Cyp46a1, which eliminates cholesterol from the brain,was also downregulated in cavefish brains,while the total level of cholesterol in the brain remained unchanged.Cavefish brains misexpressed several genes encoding proteins in the hypothalamus-pituitary axis,including Trh,Sst,Crh,Pomc,and Mc4r.These results suggest that the rate of lipid biosynthesis and breakdown may both be depressed in golden-line cavefish brains but that the lysosome recycling rate may be increased in cavefish;properties that might be related to differences in nutrient availability in caves.

Differentially-expressed opsin genes identified in Sinocyclocheilus cavefish endemic to China

Eye degeneration is a common troglomorphic character of cave-dwelling organisms. Comparing the morphology and molecular biology of cave species and their close surface relatives is a powerful tool for studying regressive eye evolution and other adaptive phenotypes. We compared two co-occurring and closely-related species of the fish genus Sinocyclocheilus, which is endemic to China and includes both surface- and cave-dwelling species. Sinocyclocheilus tileihornes, a cave species, had smaller eyes than Sinocyclocheilus angustiporus, a surface species. Histological and immunohistochemical analyses revealed that the cave- fish had shorter cones and more disorderly rods than did the surface-dwelling species. Using quantitative PCR and in situ hybri- dization, we found that rhodopsin and a long-wavelength sensitive opsin had significantly lower expression levels in the cavefish. Furthermore, one of two short-wavelength-sensitive opsins was expressed at significantly higher levels in the cavefish. Changes in the expression ofopsin genes may have played a role in the degeneration of cavefish eyes [Current Zoology 59 （2）： 170-174, 2013].

Exquisite structure of the lateral line system in eyeless cavefish Sinocyclocheilus tianlinensis contrast to eyed Sinocyclocheilus macrophthalmus(Cypriniformes:Cyprinidae)

In this study,the lateral line systems in Chinese cavefish eyeless Sinocyclocheilus tianlinensis and eyed Sinocyclocheilus macrophthalmus were investigated to reveal their morphological changes to survive in harsh environments.Compared with the eyed cavefish S.macrophthalmus(atypical),the lateral line system in the eyeless cave-fish S.tianlinensis(typical)has certain features to adapt to the dark cave environments:the superficial lateral line system in the eyeless species possesses a higher number of superficial neuromasts and more hair cells within an individual neuromast,and the trunk lateral line canal system in S.tianlinensis exhibits larger canal pores,higher canal diameter and more pronounced constrictions.Fluid–structure interaction analysis suggested that the trunk lateral line canal system in the eyeless S.tianlinensis should be more sensitive than that in the eyed S.macrophthalmus.These morphological features of the lateral line system in the eyeless S.tianlinensis probably enhance the functioning of the lateral line system and compensate for the lack of eyes.The revelation of the form–function relationship in the cavefish lateral line system provides inspiration for the design of sensitive artificial flow sensors.

高原鳅属洞穴鱼类与非洞穴鱼类听觉的比较研究

测定高原鳅属3种洞穴鱼类和3种非洞穴鱼类的听觉阈值与鳔的形态指标,结果发现:听觉阈值部分种间差异有统计学意义,但在各频率(50~6 400 Hz)下,洞穴鱼类和非洞穴鱼类的听觉阈值差异无统计学意义.鳔耳距、鳔孔面积、鳔室体积和孔室比的种间差异有统计学意义,但在洞穴鱼类与非洞穴鱼类间差异无统计学意义.种间听觉阈值与鳔室体积和鳔耳距不相关,在50 Hz和800 Hz下,与鳔孔面积显著负相关;在1 600,3 200,6 400 Hz下,与孔室比显著负相关.此外,玫瑰高原鳅的鳔膨大,在体表左右两侧呈明显的隆起,但与其听觉灵敏性并无特殊性.结果表明:高原鳅属洞穴鱼类的听觉并没有发生适应性增强,提示听觉可能对洞穴鱼类适应洞穴环境不相关.种间听觉阈值在某些频率下,与骨质鳔囊的侧孔面积负相关,提示鳔对高原鳅听觉灵敏性的作用受侧孔大小的影响.

Phylogenetic analysis and expression differences of eye-related genes in cavefish genus Sinocyclocheilus

The adaptive evolution of visual systems has been observed in many cavefish.However,little is known about the molecular mechanisms underlying these adaptations,which include regressive changes such as eye degeneration.Here,we analyzed phylogenetic and expression patterns of 6 eye-related genes(crx,foxg1b,opn1sw2,otx2,rho and sox2)in 12 Sinocyclocheilus species from China,including 8 stygobionts and 4 stygophiles,and examined photoreceptor cell morphology of these species.Those eye-degenerated species of Sinocyclocheilus were polyphyletic and showed different degrees of photoreceptor defects in responses to cave environments.The eye loss and degeneration are the result of convergent evolution.Although S.anophthalmus grouped with the eye-normal species,it displayed not only a high degree of eye degeneration but also significant expression differences in eyerelated genes compared with the eye-normal species.The gene foxg1b,which was determined to be under positive selection,might play an important role in the process of eye degeneration in S.anophthalmus based on differential expression.Eye-related gene expression and selection may have contributed to the polyphyly of the cave species.We examined gene expression and duplication in 6 eye-related genes and revealed that these genes displayed considerable diversity in relative expression in Sinocyclocheilus fishes.Otx2 and sox2 were significantly up-regulated in individual cave species,while the other 4 genes(crx,foxg1b,opn1sw2 and rho)were significantly down-regulated.These findings provide a valuable resource for elucidating molecular mechanisms associated with visual system evolution in cavefish.

Differentially expressed genes identified by cross-species microarray in the blind cavefish Astyanax

Changes in gene expression were examined by microarray analysis during development of the eyed surface dwelling(surface fish)and blind cave-dwelling(cavefish)forms of the teleost Astyanax mexicanus De Filippi,1853.The cross-species microarray used surface and cavefish RNA hybridized to a DNA chip prepared from a closely related species,the zebrafish Danio rerio Hamilton,1822.We identified a total of 67 differentially ex-pressed probe sets at three days post-fertilization:six upregulated and 61 downregulated in cavefish relative to surface fish.Many of these genes function either in eye development and/or maintenance,or in programmed cell death.The upregulated probe set showing the highest mean fold change was similar to the human ubiquitin specific protease 53 gene.The downregulated probe sets showing some of the highest fold changes corresponded to genes with roles in eye development,including those encoding gamma crystallins,the guanine nucleotide binding pro-teins Gnat1 and Gant2,a BarH-like homeodomain transcription factor,and rhodopsin.Downregulation of gam-ma-crystallin and rhodopsin was confirmed by in situ hybridization and immunostaining with specific antibodies.Additional downregulated genes encode molecules that inhibit or activate programmed cell death.The results suggest that cross-species microarray can be used for identifying differentially expressed genes in cavefish,that many of these genes might be involved in eye degeneration via apoptotic processes,and that more genes are downregulated than upregulated in cavefish,consistent with the predominance of morphological losses over gains during regressive evolution.

Metagenomic analysis reveals hidden links between gut microbes and habitat adaptation among cave and surface dwelling Sinocyclocheilus species

Intestinal microbes are closely related to vital host functions such as digestion and nutrient absorption,which play important roles in enhancing host adaptability.As a natural“laboratory”,caves provide an outstanding model for understanding the significance of gut microbes and feeding habits in the habitat adaptability of hosts.However,research on the relationship between gut microbes,feeding habits,and the adaptability of troglobites remains insufficient.In this study,we compared the characteristics of the intestinal microbes of Sinocyclocheilus cavefish and surface fish and further established the relationship between intestinal and habitat microbes.Furthermore,we conducted environmental DNA(eDNA)(metabarcoding)analysis of environmental samples to clarify the composition of potential food resources in the habitats of the Sinocyclocheilus cavefish and surface fish.Results showed that the structure of the Sinocyclocheilus gut microbes was more related to ecological type(habitat type)than phylogenetic relationships.While horizontal transfer of habitat microbes was a source of gut microbes,hosts also showed strong selection for inherent microbes as dominant microorganisms.Differences in the composition and structure of gut microbes,especially dominant microbes,may enhance the adaptability of the two Sinocyclocheilus fish types from the perspectives of food intake,nutrient utilization,and harmful substance metabolism,suggesting that food resources,predation patterns,intestinal flora,digestive and absorptive capacity,and feeding habits and preferences are linked to habitat adaptability.These results should facilitate our understanding of the significance of fish gut microbes to habitat adaptation and provide a new perspective for studying the adaptive mechanisms of cavefish.

Developmental environment contributes to rapid trait shifts among newly colonized subterranean habitats

Recent colonization of extreme environments provides unique opportunities to study the early steps of adaptation and the potential for rapid convergent evolution.However,phenotypic shifts during recent colonization may also be due to plasticity in response to changes in the rearing environment.Here,we analyzed a suite of morphological and behavioral traits in paired surface,subterranean,and facultatively subterranean Mexican tetras(Astyanax mexicanus)from recent introductions in two separate watersheds outside of their native range.We found a variety of phenotypic and behavioral shifts between subterranean and surface populations that are similar to those observed in relatively ancient populations in Mexico.Despite this rapid morphological divergence,we found that most of these trait differences were due to plasticity in response to rearing environments.While most trait assays in common-garden,lab-raised fish indicated that phenotypic shifts in wild fish were the result of plasticity,we also found evidence of genetic control in several traits present in subterranean populations.Interestingly,wall-following behavior,an important subterranean foraging behavior,was greater in lab-born subterranean fish than in lab-born surface fish,suggesting rapid divergence of this trait between subterranean and surface populations.Thus,this study sheds light on the early steps of subterranean evolution,identifies potential rapid behavioral evolution,and suggests that plasticity in traits involving exploratory behavior may facilitate subterranean colonization.

Mitochondrial phylogeography and molecular evolution of the rhodopsin visual pigment in troglobitic populations of Astyanax mexicanus(De Filippi,1853)

Cave-adapted animals provide a unique opportunity to study the evolutionary mechanisms underlying phenotypic,metabolic,behavioral,and genetic evolution in response to cave environments.The Mexican tetra(Astyanax mexicanus)is considered a unique model system as it shows both surface and cave-dwelling morphs.To date,at least 33 different cave populations have been identified,with phylogenetic studies suggesting an origin from at least two independent surface lineages,thereby providing a unique opportunity to study parallel evolution.In the present study,we carried out the most exhaustive phylogeographic study of A.mexicanus to date,including cave and surface localities,using two mitochondrial markers(cytochrome b(cyt b)and cytochrome c oxidase subunit I(COI))and nuclear rhodopsin visual pigment(rho).Additionally,we inferred the molecular evolution of rho within the two contrasting environments(cave and surface)and across three geographic regions(Sierra de El Abra,Sierra de Guatemala,and Micos).In total,267 individuals were sequenced for the two mitochondrial fragments and 268 individuals were sequenced for the rho visual pigment from 22 cave and 46 surface populations.Phylogeographic results based on the mitochondrial data supported the two-lineage hypothesis,except for the Pachón and Chica caves,whose introgression has been largely documented.The Sierra de El Abra region depicted the largest genetic diversity,followed by the Sierra de Guatemala region.Regarding the phylogeographic patterns of rho,we recovered exclusive haplogroups for the Sierra de El Abra(Haplogroup I)and Sierra de Guatemala regions(Haplogroup IV).Moreover,a 544 bp deletion in the rho gene was observed in the Escondido cave population from Sierra de Guatemala,reducing the protein from seven to three intramembrane domains.This change may produce a loss-of-function(LOF)but requires further investigation.Regarding nonsynonymous(dN)and synonymous(dS)substitution rates(omega valuesω),our results revealed the prevailing influence of purifying selection upon the rho pigment for both cave and surface populations(ω<1),but relaxation at the El Abra region.Notably,in contrast to the other two regions,we observed an increase in the number of dN mutations for Sierra de El Abra.However,given that a LOF was exclusively identified in the Sierra de Guatemala region,we cannot dismiss the possibility of a pleiotropic effect on the Rho protein.

云南红河水系金线鲃属鱼类一新种——西畴金线鲃

该文记述了采集自云南省文山州西畴县兴街镇干海子(红河水系)一洞穴的鲤科鲃亚科金线鲃属鱼类一新种,命名为西畴金线鲃(Sinocyclocheilus xichouensis Pan,Li,Yang et Chen sp.nov.)。该新种眼睛正常,背鳍末根不分枝,鳍条变粗变硬,后缘3/5具锯齿,与属内分布在邻近南盘江水系的已知种大眼金线鲃(S.macrophthalmus)、圭山金线鲃(S.guishanensis)、狭孔金线鲃(S.angustiporus)、侧条金线鲃(S.lateristritus)、丘北金线鲃(S.qiubeiensis)、滇池金线鲃(S.grahami)、曲靖金线鲃(S.qujingensis)、麻花金线鲃(S.maculatus)、紫色金线鲃(S.purpureus)及疑似红河水系易门金线鲃(S.yimenensis)相似。籍第一鳃弓外侧鳃耙9以下的特征,可与大眼金线鲃相区别;眼间距为体长的8.1%～9.9%,吻须后伸超过眼后缘,口角须后伸超过前鳃盖骨后缘,可与圭山金线鲃相区别;背鳍起点与腹鳍起点相对,体侧沿侧线无黑色横带,可与侧条金线鲃相区别;侧线鳞74～88,侧线上鳞20,侧线下鳞16,可与滇池金线鲃相区别;侧线弯曲,侧线鳞74～88,围尾柄鳞48,可与曲靖金线鲃相区别;背鳍前距为体长的47.1%～53.7%,背鳍基长为体长的12.8%～15.8%,臀鳍前距为体长的66.0%～71.0%,臀鳍长为体长的13.7%～17.1%,胸鳍前距为体长的26.0%～29.5%,尾柄长为体长的19.3%～24.7%,下颌长为体长的4.7%～7.0%,明显区别于易门金线鲃;全身被鳞,具侧线鳞,可与其分布邻近的麻花金线鲃和紫色金线鲃相区别;背鳍前鳞35～39,鳃耙6,眼间距为体长的8.1%～9.9%,可与狭孔金线鲃及丘北金线鲃相区别。

洞穴鱼类:概念、多样性及研究进展

洞穴鱼类是淡水鱼类中一个特殊的生态类群,其生活史的自然完成离不开洞穴或地下水环境。洞穴鱼类可分为典型和非典型两种类型,前者具有易辨识的特殊适应性形态结构(如眼消失、身体透明等),后者此类特征不明显。目前世界典型洞穴鱼类共记录有107种,其中鲤形目和鲇形目的种类最多,分别占49.5%和24.3%;在科级水平上以鲤科和爬鳅科最为丰富。东南亚和中南美是洞穴鱼类多样性最高的地区,有着世界上75.0%的典型洞穴鱼类。中国的洞穴鱼类具有物种多样性高、但集中出现在个别类群(如金线鲃属(Sinocyclocheilus)和高原鳅属(Triplophysa))、物种分化强烈、分布范围狭窄、种群数量小等特点。洞穴鱼类学是一门交叉科学,研究涉及系统学、生态学、生理学、保护生物学等众多学科领域,但目前研究仍多围绕演化问题展开。中国洞穴鱼类研究还处于系统分类和区系研究水平,其他有关学科的研究有待开展。

穴居盲副鳅及其性状演化

１９９５年由ＧＡｌｊａｎｃｉｃ先生在贵州荔波溶洞采到３尾体呈半透明、无眼睛的全穴居鱼类标本，经鉴定为副鳅属中的１新种，依特征命名为长须盲副鳅Ｐａｒａｃｏｂｉｔｉｓｌｏｎｇｉｂａｒｂａｔｕｓｓｐｎｏｖ。形态特征的分析表明：洞穴鱼类的性状演化，反映了物种对黑暗环境的适应性变异，同时也表达了物种适应辐射的结果，体现了性状在演化中趋同和趋异的双重意义。

茂兰自然保护区尧兰地下水体与地表水体鱼类群落结构比较研究

对贵州茂兰自然保护区尧兰的不同水系进行考察,在地下暗河,喀斯特洞穴内,暗河出、入水口处以及地表河流处共采集到鱼类标本400余号,共计30种分属于3个目,7个科23个属。研究发现,多样性指数以地表水系为最高,地下河口处次之,地下河水系最低。鱼类群落相似性以地下河出、入口处与地下河水系最为接近,达到0.825 0;地下河出、入口处与地表水系次之,为0.822 7;地下水系与地表水系相似性最低,为0.482 4。地下水系的鱼类群落与地表水系鱼类群落在结构有着较大的差异,地下水系鱼类群落物种较为单一,结构简单,环境变化承受力较小。

金线属两个同域穴居物种的mtDNA序列变异

对洞穴鱼种犀角金线(Sinocyclocheilusrhinocerous)及与之同域的软鳍金线(S.malacopterus)的线粒体细胞色素b基因的部分序列进行了测定和分析。发现两种之间有45个变异位点,占测序总位点的12 89%.其中在密码子第3位置上的变异有33个,占全部变异点的73 33%.转换与颠换比值为6 5∶1.种间遗传距离为12 9%,表明这两个同域种间的血缘关系可能较远。

阿庐金线鲃(Sinocyclocheilus aluensis Liet Xiao,2005)物种有效性及其重新描述

阿庐金线鲃(Sinocyclocheilus aluensis Li et Xiao,2005)曾为狭孔金线鲃(S.angustiporus Zheng et Xie,1985)的同物异名。该文在比对采自云南泸西县城郊龙潭的金线鲃标本和狭孔金线鲃模式标本后发现,两者间存在明显且稳定的形态差异,因此,阿庐金线鲃应为有效种。阿庐金线鲃背鳍起点位于腹鳍起点垂直线之后,可与狭孔金线鲃(背鳍起点与腹鳍起点正相对或稍前)相区别,且前者眼径及眼球径较小,而眼间距较宽(阿庐金线鲃分别为头长的22.4%～29.7%、16.0%～23.6%及21.0%～32.3%,狭孔金线鲃分别为头长的26.4%～38.9%、21.3%～29.0%及19.7%～22.6%)。

Three-dimensional morphology of the Sinocyclocheilus hyalinus(Cypriniformes: Cyprinidae) horn based on synchrotron X-ray microtomography

Sinocyclocheilus is a cave-dwelling cyprinid genus endemic to southwest China. Several species possess a conspicuous horn on their head, which has been suggested as a constructive troglomorphic trait but lacks substantial evidence. We used non- invasive, high spatial resolution synchrotron X-ray microtomography to investigate the three-dimensional （3D） morphology of the horn of Sinocyclocheilus hyalinus, one of eight such troglobiotic species. 3D renderings demonstrated the osteological components, which were comprised of a rear wall comprised of the supraoccipital bone, a remaining frontal wall with numerous fenestrae, and the bottom continuous with the parietal and epiotic. A horn cavity occurred within the horn. The fenestrae in the frontal wall were continuous in the horn cavity and showed elaborate channeling, and were, connected to the cranial cavity by soft tissue. We tentatively called this configuration the ＂otocornual connection＂ due to its anatomic and putative functional similarity to the otolateralic connection in clupeids and loricariids, which provide an indirect pathway to enhance perception of underwater sound signals. This study provides a functional morphology context for further histological and physiological investigations of such horn structures in Sinocyclocheilus cavefish, and we suggest that the horn might enhance acoustic perception to compensate for visual loss in subterranean life, which warrants future physiological examination as lab-reared S. hyalinus become available.