Molecular phylogenetics of the Clupeiformes based on exon-capture data and a new classification of the order.

The Clupeiformes, including among others herrings, anchovies, shads and menhadens are ecologically and commercially important, yet their phylogenetic relationships are still controversial. Previous classification of Clupeiformes were based on morphological characters or lack of synapomorphic characters. More recent studies based on molecular data as well as new morphological evidence are keeping challenging their phylogenetic relations and there is still no consensus on many interrelationships within the Clupeiformes. In this study, we collected nuclear sequence data from 4,434 single-copy protein coding loci using a gene-capture method. We obtained a robust phylogeny based on 1,165 filtered loci with less than 30 % missing data. Our major findings include: 1) reconfirmation of monophyly of the Clupeiformes, that is, Denticipitidae is sister to all other clupeiforms; 2) the polyphyletic nature of dussumieriids and early branching of Spratelloididae from all other clupeoids were confirmed using datasets curated for less missing data and more balanced base composition in the respective taxa. The next branching clade is the monophyletic Engraulidae. Pristigasteridae also is monophyletic, but it was nested in the previously defined "Clupeidae". Within Pristigasteridae there is no support for monophyletic Pelloninae. Chirocentrus is close to Dussumieria and not to engraulids. The miniaturized Sundasalanx is placed close to the ehiravine Clupeonella, however, with a relatively deep split. The genus Clupea, is not part of the diverse "Clupeidae", but part of a clade containing additionally Sprattus and Etrumeus. Within the crown group clades, Alosidae and Dorosomatidae are retrieved as sister clades. Based on new fossil calibration points, we found that major lineages of the clupeiforms diverged in the late Cretaceous and early Paleogene. The extinction event at the end of the Cretaceous may have created ecological niches, which could have fueled the diversification of clupeiform fishes. Based on the strong evidence of the present study, we propose an updated classification of Clupeiformes consisting of ten families: Denticipitidae; Spratelloididae; Engraulidae (Engraulinae + Coiliinae); Clupeidae; Chirocentridae; Dussumieriidae; Pristigasteridae; Ehiravidae; Alosidae, Dorosomatidae.

First documentation of the otoliths of the species of Gouania (Teleostei: Gobiesocidae) in the Mediterranean Sea.

Otolith morphology is a widely accepted tool for species identification in teleost fish, but whether this holds true for very small species remains to be explored. Here, the saccular otoliths of the cryptobenthic Mediterranean clingfish Gouania (Gobiesocidae) are described for the first time. The new data, although preliminary, indicate that otolith morphology and morphometry support the recognition of the recently differentiated five species of Gouania in the Mediterranean Sea. Furthermore, otoliths of phylogenetically closely related Gouania species resemble each other more than do those of the more distantly related species.

New haplochromine cichlid from the upper Miocene (9-10 MYA) of Central Kenya.

BACKGROUND: The diversification process known as the Lake Tanganyika Radiation has given rise to the most speciose clade of African cichlids. Almost all cichlid species found in the lakes Tanganyika, Malawi and Victoria, comprising a total of 12-16 tribes, belong to this clade. Strikingly, all the species in the latter two lakes are members of the tribe Haplochromini, whose origin remains unclear. The 'out of Tanganyika' hypothesis argues that the Haplochromini emerged simultaneously with other cichlid tribes and lineages in Lake Tanganyika, presumably about 5-6 million years ago (MYA), and that their presence in the lakes Malawi and Victoria and elsewhere in Africa today is due to later migrations. In contrast, the 'melting pot Tanganyika hypothesis' postulates that Haplochromini emerged in Africa prior to the formation of Lake Tanganyika, and that their divergence could have begun about 17 MYA. Haplochromine fossils could potentially resolve this debate, but such fossils are extremely rare. RESULTS: Here we present a new fossil haplochromine from the upper Miocene site Waril (9-10 million years) in Central Kenya. Comparative morphology, supported by Micro-CT imaging, reveals that it bears a unique combination of characters relating to dentition, cranial bones, caudal skeleton and meristic traits. Its most prominent feature is the presence of exclusively unicuspid teeth, with canines in the outer tooth row. †Warilochromis unicuspidatus gen. et sp. nov. shares this combination of characters solely with members of the Haplochromini and its lacrimal morphology indicates a possible relation to the riverine genus Pseudocrenilabrus. Due to its fang-like dentition and non-fusiform body, †W. unicuspidatus gen. et sp. nov. might have employed either a sit-and-pursue or sit-and-wait hunting strategy, which has not been reported for any other fossil haplochromine cichlid. CONCLUSIONS: The age of the fossil (9-10 MYA) is incompatible with the 'out of Tanganyika' hypothesis, which postulates that the divergence of the Haplochromini began only 5-6 MYA. The presence of this fossil in an upper Miocene palaeolake in the Central Kenya Rift, as well as its predatory lifestyle, indicate that Haplochromini were already an important component of freshwater drainages in East Africa at that time.

Two new species of the tooth-carp Aphanius (Teleostei: Cyprinodontidae) and the evolutionary history of the Iranian inland and inland-related Aphanius species .

Two new species of Aphanius are described from the Kol drainage in southern Iran (Aphanius darabensis n. sp.) and the endorheic Kavir Basin in northern Iran (A. kavirensis n. sp.), and compared with eight closely related species. Aphanius darabensis n. sp. is sister to A. shirini, from which it is distinguished by molecular characters (cytochrome b) and the combination of three morphological characters: 9-18 flank bars in males (vs. 7-10), females with irregular vertical patches of brown color on the flank (vs. prominent dark brown blotches of round or irregular shape), and symmetrically-shaped triangular to trapezoid otoliths with a rostrum distinctly longer than the antirostrum (vs. quadrangular to trapezoid otoliths with short and equally sized rostrum and antirostrum). Aphanius kavirensis n. sp. is closely related to a group containing A. sophiae, A. mesopotamicus and A. pluristriatus, from which it is distinguished by cytochrome b characters and the combination of three morphological characters: females with irregularly arranged large blotches of dark brown color on the flank, short pectoral fin in both sexes (13.4-18.1% SL in males, 11.2-18.3% SL in females), and asymmetrically shaped triangular to trapezoid otoliths with a pronounced predorsal region. Our tree based on the cytochrome b data demonstrates that the Iranian inland and inland-related Aphanius species (IIRAS) form a monophyletic clade with three subclades (A. vladykovi -, A. shirini -, A. sophiae subclades). The A. sophiae subclade, which is the most diverse of the three subclades, can be further divided into three lineages (A. isfahanensis -, A. farsicus -, A. sophiae lineages). The temporal diversification of the IIRAS clade is discussed and two evolutionary groups of Aphanius are depicted. Aphanius vladykovi, together with A. shirini, A. darabensis n. sp. and A. isfahanensis characterize the "old" evolutionary group. Their divergences may have happened 10-5 m.y. ago (Late Miocene-Early Pliocene). Aphanius farsicus, A. arakensis, A. sophiae, A. mesopotamicus, and A. pluristriatus, together with Aphanius kavirensis n. sp., represent the "young" evolutionary group, which developed in the Late Pleistocene (100,000-11,700 y. ago) and Early to Middle Holocene (c. 11,700-4,000 y. ago).

Scale morphology variability in cyprinid fishes and its significance in taxonomy using light and scanning electron microscopy: A case study of the genus Garra Hamilton, 1822 (Teleostei: Cyprinidae).

To evaluate scale morphological variability (shape, size, topological macro- and microstructures, ornamentation patterns) of cyprinid fishes, nine species of the genus Garra were selected and their scales from five different body regions were studied by using light and scanning electron microscopy. The scales of the examined species were thin with a central or antero-centrally positioned focus, with no cteni in the posterior part. In addition to these typical characteristics, some morphological variation was observed in the overall shape (irregular round, true oval, round-triangular, irregular pentagonal, hexagonal, irregular hexagonal, pentagonal, ovoid), and the focus shape. These variations were mainly dependent on the fish lengths and the flank region. Morphological analysis clustered the examined species into two distinct groups. Group I consisted of G. amirhosseini and G. gymnothorax, while Group II has three subgroups, which include G. persica and G. mondica (subgroup I), G. meymehensis, G. rossica, G. nudiventris, G. hormuzensis (subgroup II), and G. rufa (subgroup III). The grouping of the studied Garra species based on the current scale morphological characters and the molecular data was only consistent for G. rossica and G. nudiventris. In addition, in the phylogenetic tree, G. persica, G. mondica, G. amirhosseini, and G. hormuzensis formed a distinct clade. However, these species did not represent close relationships in the dendrogram obtained from the scale morphology. A possible explanation why the grouping of the studied Garra species based on their scale morphological characters does not match their phylogenetic relationships is that most of the scale morphological traits vary depending on the fish size and the location of the scales on the flank. Therefore, except for some traits, that is, central or antero-centrally positioned focus, having no cteni, a specific sectioned form so called "tetra-sectioned" type, the other examined variables are not useful enough to be used in the taxonomic study of the examined cyprinid fishes. Therefore, scale morphological characters should be used carefully for taxonomic purposes. RESEARCH HIGHLIGHTS: Shape, size, topological macro- and microstructures, and ornamentation patterns of nine species of the genus Garra were studied by using light and scanning electron microscopy. The scales were thin with a central or antero-centrally positioned focus, with no cteni in the posterior part. Morphological variation was observed in the overall shape (irregular round, true oval, round-triangular, irregular pentagonal, hexagonal, irregular hexagonal, pentagonal, and ovoid), and the focus shape. The grouping of Garra species based on the current scale morphological characters and the molecular data was only consistent for G. rossica and G. nudiventris.

Scale surface microstructure and scale size in the tooth-carp genus Aphanius (Teleostei, Cyprinodontidae) from endorheic basins in Southwest Iran.

A substantial number of species within the tooth-carp Aphanius Nardo, 1827 (Cyprinodontidae, Teleostei) has been recorded from the endorheic drainage systems of Iran, and several isolated populations in these systems may deserve species status. Descriptions of these species and populations have been based mainly on morphological and molecular data; however, the characters related to the fish scales have not up to now been intensively studied and employed for the identification of the species belonging to this genus. The objective of this study is to test as to whether (i) scale surface morphology, (ii) scale surface microstructure, and (iii) scale size can be used to discriminate species and/or populations and, (iv) to discuss the possible causes of the observed differences. To achieve these objectives, scales of three species of the genus Aphanius from endorheic basins in SW Iran, viz. A. sophiae (nine populations from the Kor River Basin), A. farsicus (four populations from the Maharlu Lake Basin) and A. pluristriatus (a single population from the Mond River Basin) have been studied using SEM images, scale measurements, and uni- and multivariate statistics. It is opined that scale surface morphology and microstructure cannot help in distinguishing the species, but can be employed to discriminate certain populations of A. sophiae (those from Safashahr, Kharameh, Tashk, Gol). In addition, scale size and J-indices, respectively, represent a valuable tool for species separation, which corroborates earlier studies for the use of these indices in taxonomy. Major driving forces of the differentiation within A. sophiae probably include habitat fragmentation resulting from the geological history and local adaptations. Thus the differentiation results from a balance between both genetic and environmental effects.

An integrative phylogenetic approach for inferring relationships of fossil gobioids (Teleostei: Gobiiformes).

The suborder Gobioidei is among the most diverse groups of vertebrates, comprising about 2310 species. In the fossil record gobioids date back to the early Eocene (c. 50 m.y. ago), and a considerable increase in numbers of described species is evident since the middle Miocene (c. 16 m.y. ago). About 40 skeleton-based gobioid species and > 100 otolith-based species have been described until to date. However, assignment of a fossil gobioid species to specific families has often remained tentative, even if well preserved complete specimens are available. The reasons are that synapomorphies that can be recognized in a fossil skeleton are rare (or absent) and that no phylogenetic framework applicable to gobioid fossils exists. Here we aim to overcome this problem by developing a phylogenetic total evidence framework that is suitable to place a fossil skeleton-based gobioid at family level. Using both literature and newly collected data we assembled a morphological character matrix (48 characters) for 29 extant species, representing all extant gobioid families, and ten fossil gobioid species, and we compiled a multi-gene concatenated alignment (supermatrix; 6271 bp) of published molecular sequence data for the extant species. Bayesian and Maximum Parsimony analyses revealed that our selection of extant species was sufficient to achieve a molecular 'backbone' that fully conforms to previous molecular work. Our data revealed that inclusion of all fossil species simultaneously produced very poorly resolved trees, even for some extant taxa. In contrast, addition of a single fossil species to the total evidence data set of the extant species provided new insight in its possible placement at family level, especially in a Bayesian framework. Five out of the ten fossil species were recovered in the same family as had been suggested in previous works based on comparative morphology. The remaining five fossil species had hitherto been left as family incertae sedis. Now, based on our phylogenetic framework, new and mostly well supported hypotheses to which clades they could belong can be presented. We conclude that the total evidence framework presented here will be beneficial for all future work dealing with the phylogenetic placement of a fossil skeleton-based gobioid and thus will help to improve our understanding of the evolutionary history of these fascinating fishes. Moreover, our data highlight that increased sampling of fossil taxa in a total-evidence context is not universally beneficial, as might be expected, but strongly depends on the study group and peculiarities of the morphological data.

Freshwater gobies 30 million years ago: New insights into character evolution and phylogenetic relationships of †Pirskeniidae (Gobioidei, Teleostei).

The modern Gobioidei (Teleostei) comprise eight families, but the extinct †Pirskeniidae from the lower Oligocene of the Czech Republic indicate that further families may have existed in the past. However, the validity of the †Pirskeniidae has been questioned and its single genus †Pirskenius has been assigned to the extant family Eleotridae in previous works. The objective of this study is to clarify the status of the †Pirskeniidae. Whether or not the †Pirskeniidae should be synonymised with the Eleotridae is also interesting from a biogeographical point of view as Eleotridae is not present in Europe or the Mediterranean Sea today. We present new specimens and re-examine the material on which the two known species of †Pirskenius are based (†P. diatomaceus Obrhelová, 1961; †P. radoni Prikryl, 2014). To provide a context for phylogenetically informative characters related to the palatine and the branchiostegal rays, three early-branching gobioids (Rhyacichthys, Protogobius, Perccottus), an eleotrid (Eleotris) and a gobiid (Gobius) were subjected to micro-CT analysis. The new data justify revalidation of the family †Pirskeniidae, and a revised diagnosis is presented for both †Pirskenius and †Pirskeniidae. Moreover, we provide for the first time an attempt to relate a fossil gobioid to extant taxa based on phylogenetic analysis. The results indicate a sister-group relationship of †Pirskeniidae to the Thalasseleotrididae + Gobiidae + Oxudercidae clade. Considering the fossil record, the arrival of gobioids in freshwater habitats in the early Oligocene apparently had generated new lineages that finally were not successful and became extinct shortly after they had diverged. There is currently no evidence that the Eleotridae was present in the European ichthyofauna in the past.

New fossil cichlid from the middle Miocene of East Africa revealed as oldest known member of the Oreochromini.

A new genus and species of fossil cichlid fishes of middle Miocene age (12.5 Ma) is described from the Ngorora fish Lagerstätte (Tugen Hills, Kenya) in the East African Rift Valley. Parsimony analysis of morphological characters using published phylogenetic frameworks for extant cichlids combined with the application of a comprehensive best-fit approach based on morphology was employed to place the new fossil taxon in the phylogenetic context of the African cichlids. The data reveal that the fossil specimens can be assigned to the tribe Oreochromini within the haplotilapiines. †Oreochromimos kabchorensis gen. et sp. nov. shows a mosaic set of characters bearing many similarities to the almost pan-African Oreochromis and the East African lake-endemic Alcolapia. As the striking diversity of present-day African cichlids, with 1100 recognised species, has remained largely invisible in the fossil record, the material described here adds significantly to our knowledge of the Miocene diversity of the group. It effectively doubles the age of a fossil calibration point, which has hitherto been used to calibrate divergence times of the East African cichlids in molecular phylogenetic investigations. Furthermore, the comparative dataset derived from extant cichlids presented here will greatly facilitate the classification of fossil cichlids in future studies.

Combined otolith morphology and morphometry for assessing taxonomy and diversity in fossil and extant killifish (Aphanius, Prolebias).

Systematic assignment of fossil otoliths is virtually always based on studies of otolith morphology and subsequent comparisons with otoliths from collections and/or literature. Although this usually represents a practical method, comparisons and subsequent evaluation may be biased by subjective criteria used in the individual descriptions. Quantitative morphometric studies focusing on variations in the otolith morphology of extant fishes have been conducted in fisheries research, mostly based on Fourier shape analysis and related methods. However, with regard to fossil otoliths, these approaches are generally not suitable, mainly due to preservation-related problems. Here we present a new approach for quantifying otolith variation between species and populations of killifish (cyprinodontiforms) in the genera Aphanius Nardo and daggerProlebias Sauvage that can be used with both extant and fossil otoliths. Our new approach includes the definition of 10 variables from linear and angle measurements of an otolith and statistical analyses. Best results were obtained by presorting the otoliths into three groups based on sulcus shape (straight, bent, S-shaped). In this case, canonical discriminant analysis (CDA) with jackknifed cross-validation yielded an overall species classification success of 86-96%. The three groups based on sulcus shape separate according to zoogeographic patterns (i.e., Mediterranean Aphanius, Arabian Aphanius, European daggerProlebias) and probably reflect phylogenetic lineages. Application of CDA to compare otolith variation between populations resulted in an overall classification success (jackknifed) of 33-83%. High levels of variation were observed for Aphanius dispar and daggerProlebias malzi, but not for A. fasciatus and daggerP. weileri. We suggest that otolith variation between populations results predominantly from geographic separation. Combination of qualitative characters (sulcus morphology) with quantitative approaches (otolith morphometry) presents a new approach for obtaining a better understanding of the taxonomy, diversity, and zoogeography of both fossil and extant killifishes. Moreover, the method may also be suitable for assessing taxonomy and diversity in other species-rich groups like the atheriniforms and many perciforms because these groups display otolith Bauplans that are similar to those seen in killifishes.

Correction: Otoliths of five extant species of the annual killifish Nothobranchius from the East African Savannah.

[This corrects the article DOI: 10.1371/journal.pone.0112459.].

†Kenyaichthyidae fam. nov. and †Kenyaichthys gen. nov. - First Record of a Fossil Aplocheiloid Killifish (Teleostei, Cyprinodontiformes).

The extant Cyprinodontiformes (killifishes) with their two suborders Cyprinodontoidei and Aplocheiloidei represent a diverse and well-studied group of fishes. However, their fossil record is comparatively sparse and has so far yielded members of the Cyprinodontoidei only. Here we report on cyprinodontiform fossils from the upper Miocene Lukeino Formation in the Tugen Hills of the Central Rift Valley of Kenya, which represent the first fossil record of an aplocheiloid killifish. A total of 169 specimens - mostly extraordinarily well preserved - and a sample of ten extant cyprinodontiform species were studied on the basis of morphometrics, meristics and osteology. A phylogenetic analysis using PAUP was also conducted for the fossils. Both the osteological data and the phylogenetic analysis provide strong evidence for the assignment of the fossils to the Aplocheiloidei, and justify the definition of the new family †Kenyaichthyidae, the new genus †Kenyaichthys and the new species †K. kipkechi sp. nov. The phylogenetic analysis unexpectedly places †Kenyaichthys gen. nov. in a sister relationship to the Rivulidae (a purely Neotropical group), a probable explanation might be lack of available synapomorphies for the Rivulidae, Nothobranchiidae and Aplocheilidae. The specimens of †K. kipkechi sp. nov. show several polymorphic characters and large overlap in meristic traits, which justifies their interpretation as a species flock in statu nascendi. Patterns of variation in neural and haemal spine dimensions in the caudal vertebrae of †Kenyaichthys gen. nov. and the extant species studied indicate that some previously suggested synapomorphies of the Cyprinodontoidei and Aplocheiloidei need to be revised.

Otoliths of five extant species of the annual killifish Nothobranchius from the East African savannah.

This study presents, for the first time, a comprehensive dataset that documents the range of inter- and intraspecific otolith variation in aplocheiloid killifish, based on a total of 86 individuals representing five extant species of Nothobranchius PETERS, 1868, from East Africa: the sympatric pairs N. rubripinnis SEEGERS, 1986 and N. ruudwildekampi COSTA, 2009 (Eastern Tanzania), and N. orthonotus (PETERS, 1844) and N. furzeri JUBB, 1971 (Southern Mozambique), and two isolated populations of N. korthausae MEINKEN, 1973 (Eastern Tanzania). Otolith characters were analysed based on SEM images, and otolith morphometry was conducted using uni- and multivariate statistics. Two ancient clades of probably Early to Middle Miocene age in eastern Tanzania and southern Mozambique can be recognized based on otolith morphologies, which is consistent with previous work based on molecular data. The distinctive sulcus morphologies in the otoliths of sympatric species may be linked to species-specific hearing capabilities, perhaps constituting a case of character displacement in an area of secondary sympatry. The otoliths of the studied species of Nothobranchius are diagnostic at the species level, even in the case of closely related species diagnosable otherwise only by minor differences in coloration. The two populations of N. korthausae also displayed some differences in their otolith characters. The new data may facilitate future recognition of fossil species of Nothobranchius. As no fossil remains of extant aplocheiloid killifishes have yet been described, the discovery of fossil otoliths of Nothobranchius would significantly advance understanding of the evolutionary history of this interesting group of fishes.

An extraordinary gobioid fish fossil from Southern France.

BACKGROUND: The classification of gobioid fishes is still under discussion. Several lineages, including the Eleotridae and Butidae, remain difficult to characterize because synapomorphies are rare (Eleotridae) or have not yet been determined (Butidae). Moreover, the fossil record of these groups is scarce. RESULTS: Exceptionally well-preserved fish fossils with otoliths in situ from uppermost Oligocene sediments (≈23-24 Mio. y. ago) in Southern France provide the most in-depth description of a fossil gobioid to date. The species was initially described as Cottus aries Agassiz, then transferred to †Lepidocottus Sauvage, and subsequently assigned to Gobius. Based on a comparative analysis of meristic, osteological and otolith data, this species most likely is a member of the family Butidae. This discovery is important because it represents the first record of a fossil butid fish based on articulated skeletons from Europe. SIGNIFICANCE: The Butidae and Eleotridae are currently distributed in W-Africa, Madagascar, Asia and Australia, but they do not appear in Europe and also not in the Mediterranean Sea. The new results indicate that several species of the Butidae thrived in Europe during the Oligocene and Early Miocene. Similar to the recent Butidae and Eleotridae, these fishes were adapted to a wide range of salinities and thrived in freshwater, brackish and marginal marine habitats. The fossil Butidae disappeared from Europe and the Mediterranean and Paratethys areas during the Early Miocene, due probably to their lack of competitiveness compared to other Gobioidei that radiated during this period of time. In addition, this study documents the great value of otoliths for gobioid systematics.

Aphanius arakensis, a new species of tooth-carp (Actinopterygii, Cyprinodontidae) from the endorheic Namak Lake basin in Iran.

A new species of tooth-carp, Aphanius arakensissp. n., is described from the Namak Lake basin in Iran. The new species is distinguished by the congeners distributed in Iran by the following combination of characters: 10-12 anal fin rays, 28-32 lateral line scales, 10-13 caudal peduncle scales, 8-10 gill rakers, 12-19, commonly 15-16, clearly defined flank bars in males, a more prominent pigmentation along the flank added by relatively big blotches in the middle and posterior flank segments in females, a short but high antirostrum of the otolith that has a wide excisura, and a ventral rim with some small, drop-like processes, and 19 molecular apomorphies (17 transitions, two transversions) in the cytochrome b gene. It was suggested based on the phylogenetic analysis that the new species is sister to Aphanius sophiae from the Kor River and that Aphanius farsicus from the Maharlu Lake basin is sister to Aphanius arakensis plus Aphanius sophiae. A noticeable feature of the Aphanius diversity in Iran is the conservatism of the external morphology as well as morphometric and meristic characters, while distinctive differences are present in genetic characters, otolith morphology, and male color pattern. Transformation of the latter was probably driven by sexual selection.

Geographic variation in otolith morphology among freshwater populations of Aphanius dispar (Teleostei, Cyprinodontiformes) from the southeastern Arabian Peninsula.

Aphanius Nardo is a large genus of teleost fishes in the Old World, with 19 described species. Several of these species have only recently been recognized and additional species can be expected from isolated populations in remote areas. We show here that otolith morphology and statistical analyses of otolith variables can contribute to the detection of genetic differentiation in Aphanius. We studied samples of eight Aphanius dispar populations from the southeastern part of the Arabian Peninsula. Two populations originate from freshwater habitats far inland and probably have been isolated since the late Holocene some 4,000 years ago, three populations come from freshwater habitats with occasional connections to the sea, one population originates from a coastal site, and two were artificially introduced populations. The coastal population is interpreted as possessing the basic otolith type of A. dispar. The basic otolith type also occurs in fishes from the freshwater habitat which is located closest to the coast. Otoliths from the two other freshwater populations with occasional connections to the coast differ slightly from the basic type. However, the two populations from the long-term isolated freshwater habitats far inland show distinct morphological changes. Our results are consistent with the hypotheses that i) otolith morphology is primarily genetically determined and is little influenced by physical parameters of the habitat, and ii) isolated A. dispar populations may be capable of evolving into new species within short periods of time.