Distal Radials Research Articles

OBSERVATION ON SKELETAL DEFORMITY IN HATCHERY-REARED RED SPOTTED GROUPER, Epinephelus akaara (Temmick et Schlegel) FROM LARVAL TO JUVENILE STAGE

Skeletal deformity is a significant problem in fish culture. The skeletal deformities in red spotted grouper from yolk-sac to juvenile stages were examined through clearing and staining of the cartilage and bone using Alcian Blue and Alizarin Red S. The overall results showed that the pattern of incidence of deformities showed an increase from preflexion to juvenile stages. The rate of deformities based on ten elements of bone from preflexion to juvenile stages were as follows: vertebral (42.6%—9.0%), dorsal proximal radials (4.8%—25.2%), neural spine (0%—8.4%), haemal spine (0%—6.8%), hypural (1.3%—5.4%), anal proximal radials (0%—5.4%), epural (1.3%—4.9%), arypural (2.0%—4.5%), lower jaw (1.3%—2.5%), and upper jaw (0%). Vertebral and dorsal proximal radials were recognized as the most susceptible parts to deformation. The main types of bone deformity were lordosis, scoliosis, fusion, shortening, branching, supernumerary elements, and saddleback syndrome. Development of saddleback syndrome was detected initially in preflexion stage, which was accompanied by deformity of the neural spines, dorsal proximal radials, and disposition of the distal radials and dorsal spines in later life stages. The skeletal deformity encountered during the larval rearing period could be caused by water surface tension.

Leis' conundrum: Homology of the clavus of the ocean sunfishes. 1. Ontogeny of the median fins and axial skeleton of Monotrete leiurus (Teleostei, Tetraodontiformes, Tetraodontidae)

We describe the ontogeny of the axial skeleton and median fins of the Southeast Asian freshwater puffer Monotrete leiurus, based on a reared developmental series. Most elements of the axial skeleton in M. leiurus arise in membrane bone. Only the base of the anterior three neural arches, the base of the hemal arches of the third preural centrum, the neural and hemal arches and spines of the second preural centrum, the parhypural, the two hypural plates, and the single epural are preformed in cartilage. In contrast to most teleosts, the proximal-middle radials of the dorsal and anal fins are upright and symmetrical and their distal tips coalesce during development to form a deep band of cartilage, from which the spherical distal radials are spatially separated.

Leis' conundrum: Homology of the clavus of the ocean sunfishes. 2. Ontogeny of the median fins and axial skeleton of Ranzania laevis (Teleostei, Tetraodontiformes, Molidae)

One of the most conspicuous characters of the ocean sunfishes, family Molidae, is the punctuation of the body by a deep, abbreviated, caudal fin-like structure extending vertically between the posterior ends of the dorsal and anal fins, termed the clavus by Fraser Brunner. Homology of the clavus has been a matter of debate since the first studies on molid anatomy in the early 1800s. Two hypotheses have been proposed: 1) It is a highly modified caudal fin; 2) It is formed by highly modified elements of the dorsal and anal fins. To resolve this homology issue, we studied the ontogeny of the molid vertebral column and median fins and compared it to that of a less morphologically derived gymnodont (see Part 1 of this study), a member of the family Tetraodontidae. We show that in molids the chorda never flexes during development, that the claval rays form from the posterior ends of the dorsal and anal fins toward the middle, thus closing the gap inward, and that elements of the molid clavus have an identical development and composition as the proximal-middle and distal radials of the regular dorsal and anal fins. We thus conclude that the molid clavus is unequivocally formed by modified elements of the dorsal and anal fin and that the caudal fin is lost in molids.

Differentiation of chondrocytes and scleroblasts during dorsal fin skeletogenesis in flounder larvae.

In teleosts, the embryonic fin fold consists of a peridermis, an underlying epidermis and a small number of mesenchymal cells. Beginning from such a simple structure, the fin skeletons, including the proximal and distal radials and lepidotrichia (finrays), develop in the dorsal fin fold at the larval stage. Their process of skeletogenesis and embryonic origin are unclear. Using flounder larvae, we report the differentiation process for chondrocytes and scleroblasts prior to fin skeletogenesis and the effects of retinoic acid (RA) on it. In early larvae, the mesenchymal cells grow between the epidermis and spinal cord to form a line of periodical condensations, which are proximal radial primordia, to produce chondrocytes. The prescleroblasts, which ossify the proximal radial cartilages, differentiate in the mesenchymal cells remaining between the cartilages. Then, mesenchymal condensations occur between the distal ends of the proximal radials, forming distal radial primordia, to produce chondrocytes. Simultaneously, condensations occur between the distal radial primordia and peridermis, which are lepidotrichia primordia, to produce prescleroblasts. Exogenous RA specifically inhibits the mesenchymal condensation prior to the proximal radial formation together with the down-regulation of sonic hedgehog (shh) and patched (pta) expression, resulting in the loss of proximal radials. Thus, it was indicated that differentiation of the precursor cells of radials and lepidotrichia begins in the proximal part of the fin fold and that the initial mesenchymal condensation prior to the proximal radial formation is highly susceptible to the effects of RA. Lepidotrichia formation does not occur where proximal radials are absent, indicating that lepidotrichia differentiation requires interaction with the radial cartilages. To examine the suggestion that neural crest cells contribute to the medial fin skeletons, we localized the HNK-1 positive cells in flounder embryos and slug and msxb-positive cells in pufferfish, Fugu rubripes, embryos. That the positive cells commonly arrive at the proximal part of the fin fold does not contradict the suggestion, but their final destiny as radial chondrocytes or lepidotrichia scleroblasts, should be further investigated.

Descriptive Osteology of the Family Chaudhuriidae (Teleostei, Synbranchiformes, Mastacembeloidei), with a Discussion of Its Relationships

The little known earthworm eel family Chaudhuriidae consists of nine small to minute species of Asian freshwater fishes. In this paper, the osteology of seven representatives of the family is described in detail for the first time. We propose a list of 21 synapomorphies to support chaudhuriid monophyly. Reductive characters are: loss of basisphenoid, pterosphenoid, endopterygoid, dermopalatine, pars autopalatina, posttemporal, gill rakers, toothplate on pharyngobranchial two, distal pectoral radials, lateral line canals, dorsal- and anal-fin spines and their supporting pterygiophores, epurals, uroneurals, parhypural, and reduction in numbers of epicentrals and hypurals. Progressive characters are: presence of a long membrane bone process on autosphenotic, a boomerang-shaped ectopterygoid with a long preorbital extension, an anterior process of membrane bone of the metapterygoid, a unique arrangement of dorsal gill arch elements, separate foramina for the three trigeminal branches, and a ventromedian keel on the first vertebra. The new information is used to critically reevaluate previous hypotheses of chaudhuriid relationships. Finally, the issue of miniaturization in chaudhuriid fishes is addressed and discussed.

Walking in skates (Chondrichthyes, Rajidae): anatomy, behaviour and analogies to tetrapod locomotion

Pelvic fin walking in skates is common. However, the structure and function of pelvic fins have not been analysed. Pelvic fins of skates of the genus Psammobatis and Rioraja agassizi are externally divided into an anterior leg-like lobe and a posterior fin-like lobe. Internally, the anterior lobes are supported by a compound radial, a proximal radial and distal radials that resemble a thigh, a calf and a foot, respectively, and three associated radials arising from the pelvic girdle. A highly developed radial condyle on the pelvic girdle enables broad ‘limb’ movements. The muscular arrangement of the anterior lobes is formed by protractor, retractor, flexor and extensor muscles, clearly departing from the generalized fin muscle arrangement of elasmobranchs. Walking is composed of propulsion and recovery phases. A backward movement of the compound radial in the horizontal plane characterizes the propulsive phase. The proximal radial connects vertically the compound radial with the foot-like distal radials, which are anchored on the bottom. During the recovery phase, the foot-like structure is lifted off the bottom and the entire limb-like anterior lobe is moved forwards for starting a new cycle. Walking in skates resembles the ancestral tetrapod sprawling locomotion seen in many salamanders and lizards. Pelvic fin anatomy and walking behaviour in skates and hemiscylliid sharks are compared. Ecological and evolutionary implications of walking locomotion in skates are also discussed. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 35‐41. ADDITIONAL KEYWORDS: Elasmobranchii ‐ biomechanics ‐ vertebrate limbs ‐ morphology ‐ mosaic evolution.

The dorsal fin engine of the seahorse (Hippocampus sp.).

The muscles, fin ray joints, and supporting structures underlying the dorsal fin are described for two seahorse species: Hippocampus zosterae and Hippocampus erectus. A fan-shaped array of cartilaginous bones, the pterigiophores, form the internal supporting structure of the dorsal fin. Each pterigiophore is composed of a proximal radial that extends from a vertebra to the dorsal side of the animal, where it fuses to a middle radial. The middle radials fuse with each other to form a dorsal ridge upon which sit the spheroidal distal radials. Each distal radial articulates with a fin ray on its dorsal side and is attached to the dorsal ridge on its ventral side by a material that has been histologically identified as elastic cartilage. Together these connections form a two-axis joint that permits elevation, depression, and inclination of the ray. Each fin ray is actuated by two bilateral pairs of muscles, an anterior pair of inclinators, and a posterior pair of depressors. The anteriormost fin ray is actuated by three bilateral pair of muscles, the inclinators, the depressors, and a pair of elevator muscles that are positioned anterior to the inclinators. Preliminary examinations of the ray joints of the pectoral and anal fins of adult H. zostera and the pectoral fins of newborn H. erectus revealed structures similar to that seen in the dorsal fins. To further explore the structure and function of the dorsal fin gross dissections and simple functional tests were performed on H. erectus and H. barbouri and behavioral observations were made of all three species plus Hippocampus kuda.

Development of the pectoral, pelvic, dorsal and anal fins in cultured sea bream

The pectoral fin girdle was the first element of the fins to develop in Sparus aurata. By 3·1mm LN (notochord length) the cleithrum was ossified and the cartilaginous caracoid‐scapula was present. The fin was fully developed at 11·6 mm LS (standard length) and by 16·0 mm LS most elements of the fin were ossified. The pelvic fins were the last pair to develop and rudiments of these were first detected at 7·9 mm LS. The pelvic fin and girdle were completely formed and ossified at 16·0 mm LS. The development of dorsal and anal fins began at c. 6·5–7·0 mm LS with the formation of 10 cartilaginous dorsal proximal radials and eight cartilaginous ventral proximal radials. The three cartilaginous predorsals (supraneurals) appeared at 7·7 mm LS and the ossification of dorsal and anal proximal and distal radials began, respectively, at 10·5 mm LS and 11·3 mm LS. Ossified structures in the fins were also classified according to their origin, as being either dermal or endochondral. Finally the chronology of appearance of fin structures in S. aurata was compared with that reported for other Sparidae, Engraulidae and Haemulidae.

Development of the axial skeleton in wolffish, Anarhichas lupus (Pisces, Anarhichadidae), at different temperatures

The ontogeny of the axial skeleton, in particular the caudal skeleton, is described from embryos to adult specimens in common wolffish, Anarhichas lupus. The eggs were incubated at constant temperatures of 7.0, 11.0 and 13.0 °C. High egg mortality and structural changes in skeletal development (fusion of parts, absence of distal radials and most of dorsal and anal fin rays, abnormal neural arches and dorsal fin rays) were observed at 13 °C. The frequencies of some anomalies were lower at 11 °C than at 13 °C. The main reason of structural changes of the skeleton at high temperature is the breaking of normal correlations between developmental rates of some cartilaginous structures and other tissues and organs of the embryo. These data suggest an epigenetic mechanism of skeletal evolution.

Reevaluation of the caudal skeleton of certain actinopterygian fishes: III. Salmonidae. Homologization of caudal skeletal structures.

The ontogenetic development of caudal vertebrae and associated skeletal elements of salmonids provides information about sequence of ossification and origin of bones that can be considered as a model for other teleosts. The ossification of elements forming the caudal skeleton follows the same sequence, independent of size and age at first appearance. Dermal bones like principal caudal rays ossify earlier than chondral bones; among dermal bones, the middle principal caudal rays ossify before the ventral and dorsal ones. Among chondral bones, the ventral hypural 1 and parhypural ossify first, followed by hypural 2 and by the ventral spine of preural centrum 2. The ossification of the dorsal chondral elements starts later than that of ventral ones. Three elements participate in the formation of a caudal vertebra: paired basidorsal and basiventral arcocentra, chordacentrum, and autocentrum; appearance of cartilaginous arcocentra precedes that of the mineralized basiventral chordacentrum, and that of the perichordal ossification of the autocentrum. Each ural centrum is mainly formed by arcocentral and chordacentrum. The autocentrum is irregularly present or absent. Some ural centra are formed only by a chordacentrum. This pattern of vertebral formation characterizes basal teleosts and primitive extant teleosts such as elopomorphs, osteoglossomorphs, and salmonids. The diural caudal skeleton is redefined as having two independent ural chordacentra plus their arcocentra, or two ural chordacentra plus their autocentra and arococentra, or only two ural chordacentra. A polyural caudal skeleton is identified by more than two ural centra, variably formed as given for the diural condition. The two ural centra of primitive teleosts may result from early fusion of ural centra 1 and 2 and of ural centra 3 and 4, or 3, 4, and 5 (e.g., elopomorphs), respectively. The two centra may corespond to ural centrum 2 and 4 only (e.g., salmonids). Additionally, ural centra 1 and 3 may be lost during the evolution of teleosts. Additional ural centra form late in ontogeny in advanced salmonids, resulting in a secondary polyural caudal skeleton. The hypural, which is a haemal spine of a ural centrum, results by growth and ossification of a single basiventral ural arococentrum and its haemal spine. The proximal part of the hypural always includes part of the ventral ural arcocentrum. The uroneural is a modification of a ural neural arch, which is demonstrated by a cartilaginous precursor. The stegural of salmonids and esocids originates from only one paired cartilaginous dorsal arcocentrum that grows anteriorly by a perichondral basal ossification and an anterodorsal membranous ossification. The true epurals of teleosts are detached neural spines of preural and ural neural arches as shown by developmental series; they are homologous to the neural spines of anterior vertebrae. Free epurals without any indication of connection with the dorsal arococentra are considered herein as an advanced state of the epural. Caudal distal radials originate from the cartilaginous distal portion of neural and haemal spines of preural and ural (epurals and hypurals) vertebrae. Therefore, they result from distal growth of the cartilaginous spines and hypurals. Cartilaginous plates that support rays are the result of modifications of the plates of connective tissue at the posterior end of hypurals (e.g., between hypurals 2 and 3 in salmonids) and first preural haemal spines, or from the distal growth of cartilaginous spines (e.g., epural plates in Thymallus). Among salmonids, conditions of the caudal skeleton such as the progressive loss of cartilaginous portions of the arcocentra, the progressive fusion between the perichondral ossification of arcocentra and autocentra, the broadening of the neural spines, the enlargement and interdigitation of the stegural, and other features provide evidence that Prosopium and Thymallus are the most primitive, and that Oncorhynchus and Salmo are the most advanced salmonids respectively. This interpretation supports the current hypothesis of phylogenetic relationships of salmonids. © 1992 Wiley-Liss, Inc.

Monophyly of the catfish family Siluridae (Teleostei: Siluriformes), with a critique of previous hypotheses of the family's relationships

Monophyly of the Eurasian catfish family Siluridae is established according to five synapomorphies unique to the family: (1) palatine reduced to a small nodule; (2) lateral ethmoid and sphenotic contact by narrow extensions lateral to the frontal; (3) ossified transscapular ligament anteroposteriorly compressed; (4) distal radials of dorsal-fin pterygiophores absent; (5) articulations of anal-fin rays with pterygiophores posterodorsally shifted. Previous hypotheses of silurid non-monophyly or a close relationship of the Siluridae to the Malapteruridae, Plotosidae or Amblycipitidae are shown to be poorly supported by available evidence. Silurids share with other subgroups of the Siluroidea character states that are derived within the Siluroidea; these are described in an appendix. Additional character state evidence is needed before a hypothesis of sister-group relationship between the Siluridae and another siluroid subgroup can be proposed.