Unpaired Fins Research Articles

Osteology of the axial and appendicular skeletons of the meagre Argyrosomus regius (Sciaenidae) and early skeletal development at two rearing facilities

Summary The meagre (Argyrosomus regius) is a new species for aquaculture diversification, presenting a high economic value and a high growth rate, reaching 1 kg year )1 . The occurrence of deformities, which generally appear in cultured larvae at early stages, is problematic for aquaculture since they reduce fish fitness and profitability. Knowledge about the stages of skeletal formation is essential to accurately assess deformities in hatchery produced fish. Here, we describe the osteology of the axial skeleton and unpaired fins of the meagre. Based on this data, the osteological development of meagre larvae reared at the IPIMAR and IRTA-SCR, under different rearing conditions, was compared. Although little literature is available on the osteology of teleosts from the same taxonomic group, the skeletal composition of the meagre is comparable to that of other Sciaenidae. All skeletal structures considered appeared at earlier stages in larvae reared at IPIMAR, which presented a more advanced skeletal development in comparison to larvae of comparable length reared at IRTA-SCR that were submitted to lower temperature and light intensity, and reduced photoperiod regimes.

Normal axial skeleton structure in common roach Rutilus rutilus (Actinopterygii: Cyprinidae) and malformations due to radiation contamination in the area of the Mayak (Chelyabinsk Province, Russia) nuclear plant

This study was designed to describe normal axial skeletal structure in common roach Rutilus rutilus from putative unaffected environmental conditions, and the occurrence of skeletal malformations in the fish from an area under radiation contamination. Specimens were collected from water bodies of the Techa Cascade Reservoirs located near the Mayak atomic industry plant in the River Ob' drainage, Chelyabinsk Province, Russia. One sample was collected from Lake Irtyash, a reservoir of drinkable water, supplying the town of Ozersk, and the other one from a technical reservoir which is a storage of liquid radioactive waste from Mayak and characterized by high radioactive contamination (mostly (90)Sr and (137)Cs). A comparison was made with historical material collected from the River Ob' before the middle of the 20th century, i.e. before the environment became affected by radioactive contamination. A high number of abnormalities of the axial skeleton were detected in both Mayak samples, in 94 and 97% of examined specimens, in contrast to about 20% in the historical specimens. The abnormalities were in both the unpaired fins and the vertebral column, including the caudal complex and included supernumerary elements, fusions, deformities and displacement of the elements. Most axial skeleton abnormalities, however, were minor, such as splitting, shortening or deformation of spines. Severe defects, such as extensive scolioses, lordoses and kyphoses, were not found. The causes of the abnormalities were not identified in this study, but the high incidence of malformations may be attributed to genetically determined imbalance during development. The almost equal distribution of abnormalities among the fish from non-contaminated and radioactive contaminated reservoirs may be explained by either recent gene flow within the population of R. rutilus in the River Techa system or the effect of unknown unfavourable environmental factors such as chemical pollution.

Chimaera opalescens n. sp., a new chimaeroid (Chondrichthyes: Holocephali) from the north-eastern Atlantic Ocean

A new species of chimaeroid, Chimaera opalescens n. sp., was described from 31 type specimens caught in the north-eastern Atlantic Ocean at 950-1400 m depth. This species differed from all its congeners by the combination of the following characters: body uniformly pale brown to bronze, iridescent on fresh specimens; unpaired fins brown to purple, uniformly coloured or with pale or whitish edges; iris black; claspers tripartite and divided for a third of their length, not extending beyond the pelvic fins in adults; dorsal spine equal to or shorter than first dorsal fin; ventral caudal lobe equal to or deeper than dorsal caudal lobe. Comparison of DNA sequences of the CO1 gene with those of related species supported C. opalescens n. sp. as a distinct species. Specimens of C. opalescens n. sp. were previously misidentified as Chimaera monstrosa, a species sharing a similar geographical distribution. Chimaera opalescens n. sp. lives in deeper water and is a larger-bodied species than C. monstrosa. The two species were newly exploited by deep-sea fisheries and confused under a single landing name.

A new species of Austrolebias Costa (Cyprinodontiformes: Rivulidae) from northeastern Uruguay, with comments on distribution patterns

A new species of Austrolebias is described based on individuals from the middle and upper río Negro (río Uruguay basin) and río Yaguarón (Patos-Merín system). The new species can be differentiated from all other species of the genus by the unique presence in males of uniform bluish gray pigmentation on flanks (without vertical bands) and unpaired fins. The new species is also distinguished by the combination of characters associated with a reduction of the squamation of the abdominal, preopercular, and opercular regions. The new species presents some morphological characteristics similar to A. gymnoventris and A. luteoflammulatus. The distribution of the new species is concordant with three other species of Austrolebias and may represent a case of drainage rearrangement of the río Negro upstream tributaries (río Uruguay basin) and tributaries of laguna Merín system.

Redescription of Astyanax erythropterus (Holmberg, 1891) (Teleostei: Characiformes: Characidae) from La Plata basin in Argentina

Astyanax erythropterus (Holmberg, 1891) originally described on the basis of one juvenile, is redescribed herein based on juveniles and adults from the type-localiy. The species differs from its congeners by the combination of 11-13 transverse rows scales above lateral line and 8-10 rows below lateral line; 49-54 perforated scales in the lateral series; iii-v,38-42 anal-fin rays, and dorsal, anal and caudal fins vermilion red in juveniles. The vermilion red coloration of unpaired fins in juveniles of Astyanax is only known in A. correntinus.

On the taxonomic identity of Fundulus beauforti Ahl, 1924 (Cyprinodontiformes, Aplocheiloidei)

The holotype of Fundulus beauforti Ahl, 1924, was studied in order to decide between two different opinions about its taxonomic identity. It was placed by several authors either as synonym to Raddaella batesii (Boulenger, 1911) or Mesoaphyosemion cameronense (Boulenger, 1903). These taxa are easily distinguished by the position of dorsal-fin origin in relation to anal-fin and slightly different numbers of dorsal- and anal-fin rays. As the unpaired fins of the type of F. beauforti are mostly missing, the number and position of the remains of fin rays and pterygophores were estimated by a µCT scan. The results clearly indicate that F. beauforti is a junior synonym of R. batesii. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Spawning Behavior and Early Life History of the Sharpnose Puffer, Canthigaster rivulata, in the Aquarium

Specimens ofCanthigaster rivulata (Temminck et Schlegel) were collected from Kominato and Hayama, central Japan, from May, 1985 to October, 1986. On the basis of the gonadosomatic index, gonadal histology and results of artificial fertilization of these specimens, the spawning season is considered to extend from late June to mid-September. The specimens exhibited the following dimorphic differences associated with sex: 1) The male is larger than the female. 2) Ventral side of the body is brownish orange in the male with vermiculated or reticulated patterns of bright violet, while it is white in the female. 3) The male has a well-developed skin fold along the mid-dorsal and mid-ventral lines, which is greatly elevated during courtship; whereas the female’s skin folds are not or slightly developed and conspicuous only during courtship. In an aquarium with the water temperatures of 22 to 26°C, a pair of fish spawned every four days late in the morning for three consecutive months. Courtship and spawning occurred in a pair. The male swam in front of the female, and elevated the skin folds both dorsally and ventrally, fully spreading the unpaired fins, with the ventral side of the body flashing bright blue and the dorsal side turning dark. Both fish swam in a circular fashion, elevating the skin folds. The male followed the female nudging her abdomen with his snout. Both fish turned upward, and released gametes. The eggs are spherical, 0.53–0.73 mm in diameter, demersal, adhesive, transparent, and pale yellowish orange in color, and contain a cross-shaped or asteroid cluster of oil globules. The egg membrane was thick and consisted of about 14 concentric layers. The incubation period ranged from 73.5 hours at 28.2–28.5°C to 145.0 hours at 22.1–22.4°C. The newly hatched larvae were 1.38–1.98 mm in total length (TL) with 84-11-13 = 19–21 myomeres. The yolk was absorbed when the larvae attained 1.49–2.22 mm TL, three days after hatching. The larvae were fed on oyster larvae, blue mussel larvae, sea-urchin larvae and rotifers, but all of them died in 16 days. During the embryonic and early larval stages, the only pigment cells that appeared on the body were the black chromatophores.

Evolution of paired fins and the lateral somitic frontier

Recent research on the evolutionary origins of the paired fins (pectoral and pelvic, evolving into the four tetrapod limbs) has focused on genetic, developmental, and fossil evidence. However, a combined synthesis of this evidence has largely been lacking. In living animals, identification of dorsal and ventrolateral zones of fin-producing competence, the distinction between primaxial and abaxial regions separated by the lateral somitic frontier, and the recognition that fin developmental mechanisms could have been co-opted from unpaired to paired fins can be used to evaluate vertebrate fin evolution, including fossil forms. These fossil taxa dominate early vertebrate history and possess an unusually wide variety of fin or fin-like structures; establishing homologies with the paired fins of jawed vertebrates has been challenging, in part owing to the absence of supporting girdles in most jawless vertebrates. An evolutionary scenario is proposed where these fin-like structures develop from somites, in the same manner as dorsal, unpaired fins. Girdles and the paired fins of osteostracans and jawed vertebrates develop from lateral plate mesoderm when the lateral somitic frontier and the abaxial region of the body evolve.

Embryonic and larval development in barfin flounder Verasper moseri (Jordan and Gilbert)

Broodstock of Verasper moseri (Jordan and Gilbert) aged 3–4 years old were selected, and reinforced cultivation was conducted to promote maturation under controlled water temperature and photoperiod conditions. Fertilized eggs were obtained by artificial fertilization, and the development of embryos, larvae and juveniles was observed continuously. The results showed that the fertilized eggs of V. moseri were spherical, with transparent yolk and homogeneous bioplasm, and had no oil globule inside. The average diameter of the eggs was 1.77±0.02 mm. The eggs of V. moseri were buoyant in water with salinity above 35. The cleavage type was typical discoidal. Young pigment cells appeared when olfactory plates began to form. Hatching occurred at 187 h after fertilization at a water temperature of 8.5°C. The newly hatched larvae, floating on the water surface, were transparent with an average total length of 4.69±0.15 mm. During the cultivation period, when the water temperature was raised from 9 to 14.5°C, 4-day old larvae showed more melanophores on the body surface, making the larvae gray in color. The pectoral fins began to develop, which enabled the larvae to swim horizontally and in a lively manner. On days 7–8, the digestive duct formed. The yolk sac was small and black. The yolk sac was absorbed on day 11. Larvae took food actively, and body length and body height clearly increased. The rudiments of dorsal and anal fin pterygiophores were discernible and caudal fin ray elements formed on day 19. On day 24, the larval notochord flexed upwards, and the rays of unpaired fins began to differentiate. Pigment cells converged on the dorsal and anal fin rays, and the mastoid teeth on the mandible appeared. On day 29, the left eyes of juveniles began to move upwards. Depigmentation began in some juveniles and they became sandy brown in color on day 37. Most juveniles began to settle on the bottom of the tank. The left eyes of juveniles migrated completely to the right side on day 50, when the average body length attained 2.5±0.18 cm, and juveniles accomplished metamorphosis to young. The embryonic and larval characters of several flounder species are compared.

A new species of tooth-carp, Aphanius mesopotamicus, from Iran and Iraq (Actinopterygii, Cyprinodontidae)

A new species of tooth-carp, Aphanius mesopotamicus (Cyprinodontidae), is described from southern Mesopotamia in Iran and Iraq. It is distinguished from related species by pigmentation (males have clear margins to the unpaired fins, no bars on the caudal fin and 10–15 clearly defined flank bars; females bear irregular blotches or spots on the flank), distribution, and a suite of morphometric and meristic characters in multivariate space (pectoral fin rays, caudal peduncle length, scales to pelvic fin and postorbital length in males and pectoral fin rays, scales to dorsal fin, predorsal length and total scales in females). The description is based on museum specimens and there have been no recent collections of the new taxon.

A review of vertebral and fin-ray counts in the genus Alburnoides (Teleostei: Cyprinidae) with a description of six new species

Variations in the different vertebral patterns and unpaired fin counts in the genus Alburnoides are discussed based on an examination of over 1100 specimens from a wide area of distribution of the genus. Though it was commonly considered that the morphological differences between subspecies and local forms of A. bipunctatus auctorum appear slight, our study shows that there are pronounced differences between many of them in vertebral and dorsal and anal fin counts. To estimate reliability of differences, statistical tests were used and a cluster analysis (UPGMA - Average Linkage clustering method) was performed based on calculated values, and tree diagrams are presented and analyzed in their taxonomic context. The differences in fin ray and vertebral counts in combination with some other morphological characters, distinguished some of the former subspecies or local forms as distinct species. Along with five nominal taxa re-established to a species level (A. rossicus, A. kubanicus, A. maculatus, A. eichwaldii, A. fasciatus), we describe six new species: A. gmelini (type locality Sunzha River, Terek River drainage, Eastern Ciscaucasia, Russia), A. varentsovi (type locality Ashkhabadka River, northern slope of the Kopetdag, Turkmenistan), A. petrubanarescui (type locality Qasemlou Chay, Orumiyeh Lake basin, Iran), A. namaki (type locality qanat at Taveh, Namak Lake basin, Iran), A. nicolausi (type locality Simareh River in Karkheh River system, Tigris River drainage, Iran), and A. idignensis (type locality Bid Sorkh River, Gav Masiab River system, Tigris River drainage, Iran).

New species of Saurichthys (Actinopterygii: Saurichthyidae) from Middle Triassic (Anisian) of Yunnan Province, China

Abstract: Saurichthys dawaziensis sp. nov., from the third member of the Gejiu Formation (Anisian of Middle Triassic) in the vicinity of Luoping, Yunnan Province, is a small to medium‐ sized saurichthyid fish. It is characterized by the efferent pseudobranchial arteries penetrating on the parasphenoid and the mandible sensory canal with a branch in the angular. The new species is more derived than the Lower Triassic species in having a relatively narrow postorbital region, short preopercular, single ossification of the sclerotic ring, small haemal arches between the pelvic fins and the anal fin without ossified spines, and in the absence of quadratojugal. It is more primitive than the Middle and Upper Triassic Saurichthys in having fringing fulcra and numerous segments in the unpaired fins, and the presence of both prae‐ and post‐zygapophyses in the neural arches. Some anatomic changes related to the vertebral column and unpaired fins of the genus are also discussed.

Threatened fishes of the world: Gambusia eurystoma Miller, 1975 (Poeciliidae)

Common names: Widemouth mosquitofish (US), Guayacon del Azufre (MX). Conservation status: Designated ‘critically endangered’ by the IUCN based on highly localized occurrence, small area inhabited, and decline of habitat quality. The species is protected by Mexican law (SEDESOL 1994). Identification: Small-bodied mosquitofish closely related to G. sexradiata. It is characterized by having a compact body with short and rounded fins; a large head with a broad mouth; 30 scales in the lateral line; small black spots irregularly distributed on the ventral part of the body and the unpaired fins; and details in the gonopodium morphology (Miller 1975). Illustration by Madlen Ziege. Distribution: Only known from the Banos del Azufre (Rio Grijalva system), west of Teapa, Tabasco and Chiapas, Mexico. Ecology: Gambusia eurystoma inhabits the outflow of hydrogen sulfide-rich springs, where it is locally abundant. Unlike Poecilia sulphuraria, with which the species co-occurs, G. eurystoma does not occur in the immediate spring areas, but prefers deeper areas with lower H2S concentrations (Tobler et al. 2008). The substrate consists mostly of a layer of anoxic mud. Threats: Gambusia eurystoma is threatened by intense habitat alterations. A hotel complex is situated in the immediate spring area and many of the springheads are used for recreational purposes. Intense cattle grazing altered the riparian vegetation of springs and outflow. Conservation recommendations: The species is protected by Mexican law, but no specific conservation actions have been taken. Steps should be taken to minimize the impact of and pollution by the recreational use of the springheads. A restoration of the riparian buffer is recommended.

Identifying patterns of diversity of the actinopterygian fulcra

AbstractFin rays, scutes or ridge scales, and fulcra have been traditionally interpreted as modified scales, but their diversity has been almost ignored. Based on results presented here, revised definitions of these elements are provided. At least two patterns of basal fulcra are found in actinopterygians: in Pattern I all or most basal fulcra are paired elements, whereas in Pattern II, a series of unpaired basal fulcra that are bifurcated proximally, and whose forking gradually becomes larger caudad, are followed by a series of paired elements. Basal fulcra are commonly present on unpaired fins of lower actinopterygians, including basal neopterygians. Among living fish they are absent in polypteriforms,Amiaand teleosts. Fringing fulcra are always paired. Three patterns of fringing fulcra series are described: the series of fringing fulcra in basal actinopterygians is formed by expanded terminal segments of marginal lepidotrichia (Pattern A). Another series is formed by a combination of slightly expanded or modified terminal segments of rays and independent spiny, small elements (Pattern B). The third series is formed of small, spiny ossified elements positioned along the leading marginal fin ray(s) (Pattern C). Other patterns of basal and fringing fulcra remain to be investigated, along with their phylogenetic implications.

A Bizarre New Species of Frogfish of the Genus Histiophryne (Lophiiformes: Antennariidae) from Ambon and Bali, Indonesia

Abstract A new species of frogfish of the teleost order Lophiiformes, family Antennariidae, is described from three specimens collected in shallow waters off Ambon and Bali, Indonesia. A member of the antennariid genus Histiophryne, the new taxon differs substantially from its congeners in having a broad flat face, surrounded by thick, fleshy, laterally expanded cheeks and chin, with eyes directed forward; skin of the body thick and loose, forming conspicuous fleshy folds that envelop the unpaired fins; a remarkable pigment pattern of white swirling stripes radiating from the eyes and continuing back to the body and tail; genetic divergence in the nuclear recombination activation gene-2 (RAG2), cytochrome oxidase-I (COI), and 16S rRNA genes; and a set of behavioral traits not previously known in fishes. The new species is described and compared with its congeners. Notes on habitat, locomotion, pigment pattern and camouflage, predation and defense, and reproduction and parental care are also provided.

Morphometric and taphonomic study of a ray-finned fish assemblage ( Lepidotes buddhabutrensis , Semionotidae) from the Late Jurassic-earliest Cretaceous of NE Thailand

Abstract Most Mesozoic vertebrate species are represented by scarce and incomplete specimens, preventing statistical studies of morphometric features. Moreover, rich vertebrate assemblages are rarely excavated in conditions that allow taphonomical studies. Lepidotes buddhabutrensis is a common species found in the Late Jurassic–Early Cretaceous locality of Phu Nam Jun, Phu Kradung Formation, in NE Thailand. Individuals, collected during systematic excavation since 2002, show great variations in preservation states and body postures. In this paper we study the mode of variation of morphometric features of the fish population, the growth mode, and the relationship between morphology and size. We assess the range of variation in preservation and taphonomy, based on arbitrarily defined scales, to test if vertical variations occur in the sample of individuals within the site. We test possible favoured orientation of specimens within the assemblage. In contrast to preliminary field observations, statistical analyses show that all individuals belong to a single Gaussian population and that gross morphological shape variations are related only to size during fish growth. L. buddhabutrensis shows a positive allometric growth for the pectoral to dorsal, and pectoral to anal fin distances, and a negative allometric growth for the unpaired fins (dorsal and anal fins lengths). We detected no relationships between the vertical location of the fishes within the fossiliferous deposit and the body shape of the specimens, nor between the state of preservation and the taphonomy, but there are significant differences in the state of preservation according to the position of the fishes in the fossiliferous deposit. The occurrence of a single Gaussian population and the absence of morphological and preservational variations through the depositional column are evidence that the fish assemblage is probably the result of a single mass mortality event. The apparent diversity in morphology is probably due to variations in the mode of preservation. The fish appear to have been oriented by a current at the time of deposition at the top of the fossiliferous deposit only.

Description of early ontogeny and osteological development of streaked mojarra Eugerres lineatus (Teleostei: Percoidei: Gerreidae)

Embryos, larvae, and juveniles of the streaked mojarra Eugerres lineatus are described and illustrated from a series of laboratory specimens. The description was based on morphometry, pigmentation pattern, squamation sequence, and osteological development. The eggs were obtained by stripping ripe adults captured in Bahía de La Paz, Baja California Sur, México. Eggs (cleavage egg and embryo phases) had a mean diameter of 0.69 mm with an oil globule of 0.19 mm mean diameter. Eleutheroembryos were 1.05 mm mean notochordal length (NL) at hatching. The yolk sac was absorbed by 2.10 mm mean NL, underwent notochord flexion at 3.16 mm NL-3.86 mm standard length (SL), and transformed to juveniles at 10.0 mm SL. Juveniles were completely scaled by 14.0 mm SL. Osteological development of the neurocranium, jaws and suspensorium, opercular series, hyoid and branchial arches, vertebral column and ribs, and the paired and unpaired fins and the supports were studied. The identification of the earliest stages of development of E. lineatus compared to the other gerreids and allied taxonomic groups present along the northwestern Mexican coast is possible only in the juvenile period (24.1 mm SL), based on anal fin ray count (II, 9-III, 8), the presence of papilliform teeth, and the number of gillrakers on the lower first pharyngeal arch (15–20).

Morphological re-examination and taxonomy of the genus Macropodus (Perciformes, Osphronemidae)

The taxonomy of the paradisefishes of the genus Macropodus (F. Osphronemidae) has been confused due to inadequate sampling and the limitations of morphometrics and meristics in distinguishing species. The validity of the five currently described species, including two species described in 2002, was investigated using morphological characters. These characters included 25 morphometric measurements, otolith morphology, colouration, and counts of scales, vertebrae and spines in unpaired fins. Samples were collected from the described distributions of M. spechti Schreitmüller, 1936 and M. erythropterus Freyhof & Herder, 2002 in central Vietnam, and of M. hongkongensis Freyhof & Herder, 2002 in Hong Kong. Populations of M. hongkongensis were newly recorded in eastern Guangdong and Fujian Provinces, P.R. China. M. opercularis (Linnaeus, 1758) was also collected close to these locations and in the major intervening drainages. Macropodus ocellatus Cantor, 1842 was collected from Chongqing Municipality, China, and samples augmented by some museum specimens. The latter species could be distinguished from other species of the genus by both meristic and morphometric characters. The species M. spechti, M. erythropterus, M. hongkongensis and M. opercularis could not be reliably distinguished from each other by meristic and morphometric characters. Otolith morphology did not distinguish any species. Colouration discriminated all species except M. spechti / M. erythropterus. As a result, M. erythropterus Freyhof & Herder, 2002 was undiagnosable on the basis of morphology. The presence of M. hongkongensis in eastern Guangdong and Fujian Provinces, in addition to Hong Kong, indicates that distribution of this recently-described species clearly requires further investigation in south-eastern China.

A new genus of ionoscopiform fish (Halecomorphi) from the Lower Cretaceous (Albian) lithographic limestones of the Tlayúa Quarry, Puebla, Mexico

Quetzalichthys perrilliataen. gen. and sp. is described based on five specimens from Lower Cretaceous (Middle-Upper Albian) limestones of the Tlayúa Quarry, near Tepexi de Rodríguez, Puebla, Mexico. This new taxon displays the diagnostic characters of Ionoscopiformes, which consequently designate it as a new member of this order of Mesozoic fishes. Additionally,Quetzalichthysn. gen. shares several derived characters withIonoscopusandOshunia, including the presence of more than 15 supraneurals, solid and well-ossified monospondylous vertebrae with two lateral longitudinal oval fossae, thin scales of the amioid type, and the ventral surface of some circumorbital bones being intensely pitted.Quetzalichthys perrilliataeis characterized by three unique characters: 26 abdominal centra, 21 principal dorsal fin rays, and two supraorbitals. Additionally, its unpaired fins and tail show conditions intermediate to those found inIonoscopusandOshunia.A cladistic analysis of Ionoscopiformes, including both taxa found in the Tlayúa Quarry (QuetzalichthysandTeoichthys), identifies two monophyletic families within the order, Ophiopsidae (includingOphiopsis, Macrepistius, Teoichthys) and Ionoscopidae (involvingIonoscopus, Oshunia, andQuetzalichthys).

Zoarces fedorovi sp. nova (Perciformes: Zoarcidae)—A new species of eelpout from the Taui Bay of the Sea of Okhotsk

The description of a new species of the genus Zoarces, Z. fedorovi, widespread in the Taui Bay of the Sea of Okhotsk in freshened sites of coastal waters and near-mouth sections of rivers is provided. The new species inhabits sympatrically with the eastern eelpout Z. elongatus; however, it differs from the latter and other Pacific species of eelpouts (Z. gillii and Z. andriashevi) by a considerably smaller number of rays in unpaired and pectoral fins, head and trunk proportions, some specific features of coloration, and the mode of life. Z. fedorovi is similar to the last two species in the presence of one (more seldom, two–three) black rounded spot at the beginning of the dorsal fin; however, like Z. elongatus, it is characterized by the absence of a direct contact between the inner edges of parietal bones separated by the upper-occipital bone. A key to identification of species of the genus Zoarces is presented.