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At least 19 recordsLinked to original sources

PubMed1996

The kinematics of prey capture in Xystreurys liolepis: do all flatfish feed asymmetrically?

Previous research has shown that one species of flatfish displays several functional asymmetries of the head and jaws during prey capture. However, it is not known whether the functional asymmetries observed for this species are common to all flatfishes. In order to determine whether functional asymmetry is present in other flatfish taxa, prey-capture behavior was examined in a species of flatfish with little cephalic morphological asymmetry, Xystreurys liolepis (Pleuronectiformes: Paralichthyidae). In addition, X. liolepis is one of a few species of flatfish in which both typical (sinistral) and reversed (dextral) individuals are commonly found. Five individuals (two dextral and three sinistral) of X. liolepis were video-taped feeding at 250 fields s-1 in order to quantify prey-capture kinematics. These data were used to test two hypotheses: (1) that typical and reversed-symmetry individuals have identical prey-capture kinematics, and (2) that X. liolepis exhibit no functional asymmetry during prey capture because they have little morphological asymmetry. Analysis of prey capture indicates that the kinematic variables measured for sinistral and dextral individuals are statistically indistinguishable. In addition, X. liolepis do not exhibit the same suite of functional asymmetries that has been found in a flatfish species with more extreme cephalic morphological asymmetry (Pleuronichthys verticalis). However, asymmetrical anterior movement of the ventral portion of the maxilla does occur in X. liolepis during mouth opening. Examination of osteological preparations and cleared and stained individuals indicates that the maxilla is asymmetrical in length in this species. A simple model indicates that the differential length of the maxilla is sufficient to explain the observed functional asymmetry during prey capture. These results suggest that certain morphological asymmetries of the jaws of flatfishes are modifications for specialized prey-capture behaviors.

Journal Article↗

PubMed1997

Do flatfish feed like other fishes? A comparative study of percomorph prey-capture kinematics.

The kinematics of prey capture in two bilaterally asymmetrical pleuronectiform flatfish species (Pleuronichthys verticalis and Xystreurys liolepis) and two symmetrical percomorph species (Lepomis macrochirus, a centrarchid, and Cheilinus digrammus, a labrid) were compared to test the hypothesis that flatfish have distinct prey-capture kinematics from those quantified for other percomorph fishes. Size-matched individuals of both flatfish species were video-taped feeding using a high-speed video system. Cephalic displacement and timing variables were quantified and compared with data from similarly sized L. macrochirus and C. digrammus previously collected by other researchers using similar experimental methodology. Nested multivariate analyses of variance indicated that there was no significant difference in prey-capture kinematics between flatfish and non-flatfish taxa, but that prey-capture kinematics did differ among the four taxa. Multiple nested analyses of variance revealed that the taxa differed in 7 of 11 kinematic variables. Post-hoc tests and comparisons with other fish taxa suggest that individuals of P. verticalis possess an unusual combination of prey-capture kinematics including large hyoid depression, large neurocranial rotation, large upper jaw protrusion and small gape. Previous research has suggested that this combination of traits is associated with suction-based prey capture. Correspondingly, the ramsuction index calculated for P. verticalis is more negative (indicating a greater use of suction) than that calculated for the other taxa. When homologous kinematic variables are compared across these four taxa, flatfish do not appear to have similar prey-capture kinematics. However, both flatfish species are distinct from the two symmetrical percomorph species in their asymmetrical jaw movements.

Journal Article↗

PubMed2003

Health of flatfish from localities in Placentia Bay, Newfoundland, contaminated with petroleum and PCBs.

This study compared the health of flatfish inhabiting two areas in Placentia Bay, Newfoundland, contaminated either with polycyclic aromatic hydrocarbons (PAHs) or polychlorinated biphenyls (PCBs) with samples from reference sites. Initially, four species of flatfish, including American plaice (Hippoglossoides platessoides), yellowtail flounder (Limanda ferruginea), gray sole (Glyptocephalus cynoglossus), and winter flounder (Pleuronectes americanus), were sampled only for external lesions from commercial catches at three offshore sites. Others, captured by scuba divers at inshore sites, were autopsied to compare external lesions, condition (K) factor, hepatosomatic index (HSI), hemoglobin and lymphocyte levels, histological changes in the liver and spleen, and two parasites, metacercariae of Cryptocotyle lingua in the skin and a digenetic trematode, Steringophorus furciger, in the digestive tract. A higher prevalence of lesions occurred in the four species of flatfish caught offshore by commercial fisherman near the oil terminal and the PCB-contaminated dockyard than at a reference site. Lesions were also more prevalent in three species of flatfish captured by scuba divers inshore near the oil terminal and were associated with significantly lower K factor and lymphocyte levels but elevated HSI values and histopathological changes in the liver and spleen than in reference samples. Winter flounder sampled at two locations near the PCB-contaminated dockyard and a PAH-polluted small boat wharf also exhibited more external lesions, liver discoloration, and lower K factor, hemoglobin, and lymphocyte but higher HSI values and hepatic and splenic hemosiderosis than in reference fish. Prevalence of C. lingua in the skin was significantly greater but S. furciger in the digestive tract lower in samples taken from the aforementioned contaminated sites than from the reference locations. These results, based on several bioindicators, suggest that the health of bottom-dwelling flatfish at three sites of this embayment was impaired by chronic exposure to sediment contaminated with PAHs or PCBs.

Animals↗

PubMed2004

The brain-pituitary-gonad axis in male teleosts, with special emphasis on flatfish (Pleuronectiformes).

The key component regulating vertebrate puberty and sexual maturation is the endocrine system primarily effectuated along the brain-pituitary-gonad (BPG) axis. By far most investigations on the teleost BPG axis have been performed on salmonids, carps, catfish and eels. Accordingly, earlier reviews on the BPG axis in teleosts have focused on these species, and mainly on females (e.g. 'Fish Physiology, vol. IXA. Reproduction (1983) pp. 97'; 'Proceedings of the Fourth International Symposium on the Reproductive Physiology of Fish. FishSymp91, Sheffield, UK, 1991, pp. 2'; 'Curr. Top. Dev. Biol. 30 (1995) pp. 103'; 'Rev. Fish Biol. Fish. 7 (1997) pp. 173'; 'Proceedings of the Sixth International Symposium on the Reproductive Physiology of Fish. John Grieg A/S, Bergen, Norway, 2000, pp. 211'). However, in recent years new data have emerged on the BPG axis in flatfish, especially at the level of the brain and pituitary. The evolutionarily advanced flatfishes are important model species both from an evolutionary point of view and also because many are candidates for aquaculture. The scope of this paper is to review the present status on the male teleost BPG axis, with an emphasis on flatfish. In doing so, we will first discuss the present understanding of the individual constituents of the axis in the best studied teleost models, and thereafter discuss available data on flatfish. Of the three constituents of the BPG axis, we will focus especially on the pituitary and gonadotropins. In addition to reviewing recent information on flatfish, we present some entirely new information on the phylogeny and molecular structure of teleost gonadotropins.

Animals↗

PubMed1982

The respiratory metabolism of temperature-adapted flatfish at rest and during swimming activity and the use of anaerobic metabolism at moderate swimming speeds.

(1) The standard oxygen consumption and the oxygen consumption during measured swimming activity have been determined in three flatfish species at 5, 10 and 15 degrees C. (2) The relationship between weight and standard oxygen consumption for flatfish conform to the general relationship Y = aWb. On an interspecies basis, standard oxygen consumption of flatfish is significantly lower than that of roundfish. (3) A semilogarithmic model describes the relationship between oxygen consumption and swimming speed for the three species. Values for maximum oxygen consumption, metabolic scopes and critical swimming speeds are low in comparison to salmonids. (4) The optimum swimming speeds and critical swimming speeds of flatfish are similar. It is suggested that, over long distances, flatfish adopt a strategy of swimming at supercritical speeds with periods of intermittent rest to repay the accrued oxygen debt. (5) Elevated lactic acid levels in flounder white muscle after moderate swimming indicate an additional 15% anaerobic contribution to the cost of locomotion as calculated from aerobic considerations.

Acclimatization↗

PubMed1990

Neuronal adaptation accompanying metamorphosis in the flatfish.

Flatfish provide a natural paradigm to investigate adaptive changes in the central nervous system of vertebrates. During their metamorphosis, the animals undergo a 90 degrees tilt to one side or the other to become the bottom-adapted adult flatfish. The eye on the down side is pushed over to the up side. Thus, vestibular and oculomotor coordinate systems rotate 90 degrees relative to each other. As a result, during swimming movements different types of compensatory eye movements are produced before and after metamorphosis by the same vestibular stimulation. Intracellular staining of central neurons with horseradish peroxidase revealed that in postmetamorphic flatfish second-order horizontal canal neurons contact vertical eye muscle motoneuron pools on both sides of the brain via pathways that are absent in all other vertebrates studied. These unique connections provide the necessary and sufficient connectivity to adapt the flatfish's eye movement system to the animals' postmetamorphic existence. Although the adult fish has a bilaterally asymmetric appearance, the central nervous connectivity reestablishes symmetry in the vestibulo-oculomotor system.

Adaptation, Physiological↗

PubMed2006

Evaluation of relationships between reproductive metrics, gender and vitellogenin expression in demersal flatfish collected near the municipal wastewater outfall of Orange County, California, USA.

Estrogenic activity in fish has primarily been evaluated using vitellogenin (vtg) expression in male and juvenile animals. Although the response has been widespread in field and laboratory studies, the relevance of the response to higher level adverse effects, particularly in the field, is less than clear. Previous evaluations of vtg within flatfish species collected near the Orange County Sanitation District (OCSD) outfall and stations as far as 7.7 km down current indicated bioavailable estrogens within demersal flatfish populations. In order to evaluate the persistence of estrogenic activity and relationships to reproduction and development, fish were sampled in the winter and summer of 2003 and 2004 at the outfall and a reference location. Vtg, plasma estradiol (E2) concentrations, gonadosomatic indices (GSI), sperm DNA damage, development, and gender ratios were measured in English Sole (Pleuronectes vetulus) and Hornyhead Turbot (Pleuronichthys verticalis). Variable levels of vtg were continually observed in the plasma samples of fish collected at both locations. Vtg expression and plasma E2 levels were significantly correlated in females. A positive relationship was demonstrated between plasma E2 levels and sperm DNA damage. Rather than an expected feminization of populations, a trend toward masculinization was observed particularly at the OCSD outfall, as indicated by gender ratios and significantly higher GSI in males versus females. These results are consistent with previous studies showing vtg expression in male flatfish, but no alteration in overall flatfish abundance at the sampled sites.

Animals↗

PubMed1983

Retention of generalized hair cell patterns in the inner ear of the primitive flatfish Psettodes.

Flatfish are a group of uniquely asymmetrical vertebrates, lying always on one side. This postural control depends on the vestibular receptors of the inner ear. From the most primitive living flatfish, orientations of sensory hair cells in the inner ear were mapped by scanning electron microscopy. The maps of the three otolith organs, the three semicircular cristae, and the macula neglecta (newly discovered here for flatfish) show patterns that are very similar to those in many upright teleosts, particularly perches. Thus, peripheral sensory structure does not require modification for the unusual postural control of flatfish.

Animals↗

PubMed1975

The visual connections of the adult flatfish, Achirus lineatus.

Metamorphosis in the flatfish is characterized by the migration of one eye around the dorsal surface of the head to a position adjacent to the other eye on the new top side of the animal. The visual connections of the adult flatfish, Achirus lineatus, were examined. Either the migrating or non-migrating eye was removed and the animal allowed to survive for one to three weeks. Alternate sections of the brain were stained by a modification of the Fink-Heimer technique, or with cresyl violet. The diencephalic visual connections of the flatfish were similar to those of other teleosts with contralateral projections to the nuclei corticalis, dorsomedialis thalami, pretectalis, and the corpus geniculatum laterale. The distribution of the retinal efferents to the optic tectum is unique in the flatfish. In the medial one-third of the tectum, terminal degeneration was found in three bands in the stratum opticum (SO) and the stratum griseum et fibrosum superficiale (sgfs). In the middle part of the tectum, two bands of degeneration remained over the sgfs. The lateral part of the tectum has only a very small amount of degeneration distributed radomly in scattered clusters over the deep SO and superficial sgfs. The Nissl preparations also reflected the differences between the medial and lateral parts of the tectum. Distinct layer was lacking in the medial tectum with a conspicuously absent large cell layer in the stratum griseum centrale (sgc). In contrast, the lateral tectum had a typical tectal stratification. Most notable were the large neurons of the sgc.

Animals↗

PubMed1985

The vestibuloocular reflex of the adult flatfish. I. Oculomotor organization.

The flatfish species constitute a natural paradigm for investigating adaptive changes in the vertebrate central nervous system. During metamorphosis all species of flatfish experience a 90 degree change in orientation between their vestibular and extraocular coordinate axes. As a result, the optic axes of both eyes maintain their orientation with respect to earth horizontal, but the horizontal semicircular canals become oriented vertically. Since the flatfish propels its body with the same swimming movements when referenced to the body as a normal fish, the horizontal canals are exposed to identical accelerations, but in the flatfish these accelerations occur in a vertical plane. The appropriate compensatory eye movements are simultaneous rotations of both eyes forward or backward (i.e., parallel), in contrast to the symmetric eye movements in upright fish (i.e., one eye moves forward, the other backward). Therefore, changes in the extraocular muscle arrangement and/or the neuronal connectivity are required. This study describes the peripheral and central oculomotor organization in the adult winter flounder, Pseudopleuronectes americanus. At the level of the peripheral oculomotor apparatus, the sizes of the horizontal extraocular muscles (lateral and medial rectus) were considerably smaller than those of the vertical eye muscles, as quantified by fiber counts and area measurements of cross sections of individual muscles. However, the spatial orientations and the kinematic characteristics of all six extraocular muscles were not different from those described in comparable lateral-eyed animals. There were no detectable asymmetries between the left and the right eye. Central oculomotor organization was investigated by extracellular horseradish peroxidase injections into individual eye muscles. Commonly described distributions of extraocular motor neurons in the oculomotor, trochlear, and abducens nuclei were found. These motor neuron pools consisted of two contralateral (superior rectus and superior oblique) and four ipsilateral populations (inferior oblique, inferior rectus, medial rectus, and lateral rectus). The labeled cells formed distinct motor neuron populations, which overlapped little. As expected, the numbers of labeled motoneurons differed in horizontal and vertical eye movers. The numerical difference was especially prominent in comparing the abducens nucleus with one of the vertical recti subdivisions. Nevertheless, there was bilateral symmetry between the motoneurons projecting to the left and right eyes.(ABSTRACT TRUNCATED AT 400 WORDS)

Abducens Nerve↗

PubMed2001

Vestibuloocular reflex of the adult flatfish. III. A species-specific reciprocal pattern of excitation and inhibition.

In juvenile flatfish the vestibuloocular reflex (VOR) circuitry that underlies compensatory eye movements adapts to a 90 degrees relative displacement of vestibular and oculomotor reference frames during metamorphosis. VOR pathways are rearranged to allow horizontal canal-activated second-order vestibular neurons in adult flatfish to control extraocular motoneurons innervating vertical eye muscles. This study describes the anatomy and physiology of identified flatfish-specific excitatory and inhibitory vestibular pathways. In antidromically identified oculomotor and trochlear motoneurons, excitatory postsynaptic potentials (EPSPs) were elicited after electrical stimulation of the horizontal canal nerve expected to provide excitatory input. Electrotonic depolarizations (0.8-0.9 ms) preceded small amplitude (<0.5 mV) chemical EPSPs at 1.2-1.6 ms with much larger EPSPs (>1 mV) recorded around 2.5 ms. Stimulation of the opposite horizontal canal nerve produced inhibitory postsynaptic potentials (IPSPs) at a disynaptic latency of 1.6-1.8 ms that were depolarizing at membrane resting potentials around -60 mV. Injection of chloride ions increased IPSP amplitude, and current-clamp analysis showed the IPSP equilibrium potential to be near the membrane resting potential. Repeated electrical stimulation of either the excitatory or inhibitory horizontal canal vestibular nerve greatly increased the amplitude of the respective synaptic responses. These observations suggest that the large terminal arborizations of each VOR neuron imposes an electrotonic load requiring multiple action potentials to maximize synaptic efficacy. GABA antibodies labeled axons in the medial longitudinal fasciculus (MLF) some of which were hypothesized to originate from horizontal canal-activated inhibitory vestibular neurons. GABAergic terminal arborizations were distributed largely on the somata and proximal dendrites of oculomotor and trochlear motoneurons. These findings suggest that the species-specific horizontal canal inhibitory pathway exhibits similar electrophysiological and synaptic transmitter profiles as the anterior and posterior canal inhibitory projections to oculomotor and trochlear motoneurons. Electron microscopy showed axosomatic and axodendritic synaptic endings containing spheroidal synaptic vesicles to establish chemical excitatory synaptic contacts characterized by asymmetrical pre/postsynaptic membrane specializations as well as gap junctional contacts consistent with electrotonic coupling. Another type of axosomatic synaptic ending contained pleiomorphic synaptic vesicles forming chemical, presumed inhibitory, synaptic contacts on motoneurons that never included gap junctions. Altogether these data provide electrophysiological, immunohistochemical, and ultrastructural evidence for reciprocal excitatory/inhibitory organization of the novel vestibulooculomotor projections in adult flatfish. The appearance of unique second-order vestibular neurons linking the horizontal canal to vertical oculomotor neurons suggests that reciprocal excitation and inhibition are a fundamental, developmentally linked trait of compensatory eye movement circuits in vertebrates.

Abducens Nerve↗

PubMed1997

Opercular jetting during fast-starts by flatfishes

When attacked by predators, flatfishes perform fast-starts that result in a rapid take-off from the ocean bottom on which they lie. High-speed video recordings of the blind side of flatfishes indicate that they expel a coherent jet of water from the blind-side opercular valve during take-off. Buccal pressure recordings in winter flounder (Pseudopleuronectes americanus) show that a buccal pressure pulse begins 020 ms before the beginning of the fast-start and has a range of mean magnitudes for three individuals of 1.610.7 kPa. We hypothesize that one function of the opercular jet in flatfishes may be to reduce the effects of Stefan adhesion. Stefan adhesion occurs as the fish lifts its head up rapidly from the ocean bottom, when water must flow into the space forming beneath the fish. Water viscosity opposes this rapid shear, and a suction pressure develops under the fish, making it more difficult for the fish to escape from the bottom. To estimate the magnitude of Stefan adhesion, we simulated fast-starts using a physical model in which a dead flounder was pulled upwards with an acceleration of 95 m s-2. Results from the physical model indicate that up to 35 % of the total force required to lift the head at 20 ms into the start can be attributed to Stefan adhesion. Despite this large adhesion force, previous work has shown that live flatfish do not show improved fast-start performance when Stefan adhesion has been eliminated by starting the fish from an open wire grid. Thus, live fishes are likely to be using behavioral mechanisms to reduce the adhesion force. Both the timing and location along the body of the opercular jet indicate that it is ideally suited to attenuate the effects of Stefan adhesion. Propping the body up on the median fins may also reduce adhesion by increasing the initial distance between the fish and the ocean floor.

Journal Article↗

PubMed2003

Control of flatfish sperm motility by CO2 and carbonic anhydrase.

Sperm motility in flatfishes shows unique characteristics. The flagellar movement either in vivo or in permeabilized models is arrested by the presence of 25-100 mM HCO3-, or by gentle perfusion with CO2 gas. To understand the molecular basis of this property, sperm Triton-soluble proteins and flagellar proteins from several species were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. An abundant 29-kDa protein was observed only in flatfish species. Partial amino acid sequences identified this protein as a carbonic anhydrase, an enzyme involved in the interconversion of CO2 and HCO3-. 6-ethoxyzolamide, a specific inhibitor of carbonic anhydrase inhibits sperm motility, especially at low pH. In the case of HCO3(-)-arrested sperm, the motility is restored by addition of 6-ethoxyzolamide. Taken together, these results suggest that a novel pH/HCO3(-)-dependent regulatory mechanism mediated by carbonic anhydrase is involved in the motility control in flatfish sperm.

Animals↗

PubMed2002

The physiology of flatfish chromatophores.

Most flatfish, of the order Pleuronectiformes, possess a white lower side, and a brown or grey upper side. This upper side can display integumentary patterning with dark areas and colored or white spots. Chromatophores in flatfish are dermal and epidermal melanophores, as well as dermal xanthophores, erythrophores, iridophores, and leucophores, combinations of which contribute to the color and patterning. Cellular studies demonstrate pattern-related differences in numerical distribution between the types of chromatophores, and in their size, both of which will enhance contrast between areas of the pattern. As well as these morphological characteristics, there are also clear physiological differences, with melanophores from various areas of the patterns demonstrating differential responsiveness to background and to stress/excitement stimuli. Regulation of flatfish melanophore responses is predominantly neural, through the sympathetic nervous system; the pituitary hormones in these fish function in maintaining final equilibria in physiological adaptations to backgrounds. Melanophores from main components of patterns also respond differently in vitro to electrical stimulation, to pituitary hormones, and to sympathomimetic drugs and their antagonists. Sensitivity characteristics with alpha- and beta-adrenergic pharmacological reagents in vitro indicate the existence of a pattern-related balance in alpha- and beta-adrenoceptor mediation in melanophore regulation. The patterning mechanism is complex, with both morphological and physiological differences at the chromatophore level, as well as involvement of central processing and control, which remains to be analysed.

Animals↗

PubMed2005

Thyroid and pituitary gland development from hatching through metamorphosis of a teleost flatfish, the Atlantic halibut.

Fish larval development, not least the spectacular process of flatfish metamorphosis, appears to be under complex endocrine control, many aspects of which are still not fully elucidated. In order to obtain data on the functional development of two major endocrine glands, the pituitary and the thyroid, during flatfish metamorphosis, histology, immunohistochemistry and in situ hybridization techniques were applied on larvae of the Atlantic halibut (Hippoglossus hippoglossus), a large, marine flatfish species, from hatching through metamorphosis. The material was obtained from a commercial hatchery. Larval age is defined as day-degrees (D degrees =accumulated daily temperature from hatching). Sporadic thyroid follicles are first detected in larvae at 142 D degrees (27 days post-hatch), prior to the completion of yolk sack absorption. Both the number and activity of the follicles increase markedly after yolk sack absorption and continue to do so during subsequent development. The larval triiodothyronine (T(3)) and thyroxine (T(4)) content increases, subsequent to yolk absorption, and coincides with the proliferation of thyroid follicles. A second increase of both T(3) and T(4) occurs around the start of metamorphosis and the T(3) content further increases at the metamorphic climax. Overall, the T(3) content is lower than T(4). The pituitary gland can first be distinguished as a separate organ at the yolk sack stage. During subsequent development, the gland becomes more elongated and differentiates into neurohypophysis (NH), pars distalis (PD) and pars intermedia (PI). The first sporadic endocrine pituitary cells are observed at the yolk sack stage, somatotrophs (growth hormone producing cells) and somatolactotrophs (somatolactin producing cells) are first observed at 121 D degrees (23 days post-hatch), and lactotrophs (prolactin producing cells) at 134 D degrees (25 days post-hatch). Scarce thyrotrophs are evident after detection of the first thyroid follicles (142 D degrees ), but coincident with a phase in which follicle number and activity increase (260 D degrees ). The somatotrophs are clustered in the medium ventral region of the PD, lactotrophs in the anterior part of the PD and somatolactotrophs are scattered in the mid and posterior region of the pituitary. At around 600 D degrees , coinciding with the start of metamorphosis, somatolactotrophs are restricted to the interdigitating tissue of the NH. During larval development, the pituitary endocrine cells become more numerous. The present data on thyroid development support the notion that thyroid hormones may play a significant role in Atlantic halibut metamorphosis. The time of appearance and the subsequent proliferation of pituitary somatotrophs, lactotrophs, somatolactotrophs and thyrotrophs indicate at which stages of larval development and metamorphosis these endocrine cells may start to play active regulatory roles.

Animals↗

PubMed2001

Metamorphosis and early larval development of the flatfishes (Pleuronectiformes): an osmoregulatory perspective.

Flatfish (Pleuronectiformes) distribution in the environment is influenced by salinity, and varies among species and with developmental stage. Osmoregulatory ability likely plays an important role in defining species and developmental stage-specific distribution. Although the mechanisms of osmoregulation in adult and juvenile teleosts have been widely addressed, far less is known about their larval osmoregulatory physiology. Much of our current understanding of larval fish ion-regulation stems from studies using flatfishes, and this article reviews advances in this field, primarily from the point of view of the developing flatfishes. Addressed here are the ontogeny of salinity tolerance, the development of several important osmoregulatory tissues (the skin, gut, and gill), and the influence of the endocrine system on osmoregulation during early larval development and metamorphosis.

Animals↗

PubMed2001

Identification of flatfish (Pleuronectiforme) species using DNA-based techniques.

Identification of flatfish species using a DNA-based methodology was studied. The polymerase chain reaction was employed to obtain a 464 bp amplicon from mitochondrial cytochrome b gene. The sequences from this fragment belonging to 24 species were analyzed using a genetic distance method, and polymorphic sites were determined. The fragment was found to be highly polymorphic (231 sites), and this permitted the differentiation of most of the species. Phylogenetic tree construction was employed to allow the identification of flatfish species. As a result, each species was grouped in a well-differentiated clade, except for two pairs: Limanda ferruginea and L. limanda, and Solea impar and S. lascaris, which could not be differentiated. On the basis of the sequences obtained, restriction enzymes were selected to provide specific restriction profiles, which allow the differentiation of 21 species of flatfish in a faster and less expensive manner than sequencing. This polymerase chain reaction-restriction fragment length polymorphism methodology (PCR-RFLP) was tested using commercial samples.

Animals↗

PubMed2006

Twisted story of eye migration in flatfish.

Early molecular markers for flatfish metamorphosis and eye migration must be linked to the ethmoid region, the earliest part of the flatfish cranium to change, as well as chondral and dermal ossification processes. Serial sections, morphological landmarks, and stereology were used to determine where and when the remodeling of tissues and asymmetry occurs in the head region of metamorphosing Atlantic halibut, Hippoglossus hippoglossus. Not all parts of the head remodel or migrate, and those that do may be asynchronous. Normal metamorphosis limits the torsion of the Atlantic halibut head to the anterior part of the neurocranium and excludes the tip of the snout and the general jaw area. The first cranial structure displaying eye migration-related asymmetric development is the paraethmoid part of the ethmoid cartilage. In early eye migration the medial frontal process moves apace with the eyes, whereas near completion the migrating eye moves significantly closer to the frontal process. Structures of the jaw remain mostly symmetrical, with the exception of the adductor mandibulae muscle and the bone maxillare, which are larger on the abocular than on the ocular side, the muscle occupying the space vacated by the migration of the eye. Thus, normal eye migration involves a series of temperospatially linked events. In juveniles lacking eye migration (arrested metamorphosis), the dermal bone, the prefrontal, does not develop. The two abnormal paraethmoids develop symmetrically as two plate-like structures curving anteriorly, whereas normal elongate fused paraethmoids curve at their posterior. The abocular side retrorbital vesicles are largest in volume only after the completion of normal eye migration. Factors involved in completion of normal metamorphosis and eye migration in flatfish affect chondral and dermal ossification signals in the ethmoid group, as well as remodeling of the mineralized frontal, a series of linked events not involving the entire neurocranium.

Animals↗