Description and scaling of pectoral muscles in ictalurid catfishes

The pectoral spine of catfishes is an antipredator adaptation that can be bound, locked, and rubbed against the cleithrum to produce stridulation sounds. We describe muscle morphology of the pectoral spines and rays in six species in four genera of North American ictalurid catfishes. Since homologies of catfish pectoral muscles have not been universally accepted, we designate them functionally as the spine abductor and adductor and the arrector dorsalis and ventralis. The four muscles of the remaining pectoral rays are the superficial and deep (profundal) abductors and adductors. The large spine abductor and spine adductor are responsible for large amplitude movements, and the smaller arrector dorsalis and arrector ventralis have more specialized functions, that is, spine elevation and depression, respectively, although they also contribute to spine abduction. Three of the four spine muscles were pennate (the abductor and two arrectors), the spine adductor can be pennate or parallel, and ray muscles have parallel fibers. Insertions of pectoral muscles are similar across species, but there is a shift of origins in some muscles, particularly of the superficial abductor of the pectoral rays, which assumes a midline position in Ictalurus and increasingly more lateral placement in Ameiurus (one quarter way out from the midline), and Pylodictis and Noturus (half way out). Coincident with this lateral shift, the attachments of the hypaxial muscle to the ventral girdle become more robust. Comparison with its sister group supports the midline position as basal and lateral migration as derived. The muscles of the pectoral spine are heavier than muscles of the remaining rays in all species but the flathead, supporting the importance of specialized spine functions above typical movement. Further, spine muscles were larger than ray muscles in all species but the flathead catfish, which lives in water with the fastest currents. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Diversity of pectoral fin structure and function in fishes with labriform propulsion

Aquatic propulsion generated by the pectoral fins occurs in many groups of perciform fishes, including numerous coral reef families. This study presents a detailed survey of pectoral fin musculoskeletal structure in fishes that use labriform propulsion as the primary mode of swimming over a wide range of speeds. Pectoral fin morphological diversity was surveyed in 12 species that are primarily pectoral swimmers, including members of all labroid families (Labridae, Scaridae, Cichlidae, Pomacentridae, and Embiotocidae) and five additional coral reef fish families. The anatomy of the pectoral fin musculature is described, including muscle origins, insertions, tendons, and muscle masses. Skeletal structures are also described, including fin shape, fin ray morphology, and the structure of the radials and pectoral girdle. Three novel muscle subdivisions, including subdivisions of the abductor superficialis, abductor profundus, and adductor medialis were discovered and are described here. Specific functional roles in fin control are proposed for each of the novel muscle subdivisions. Pectoral muscle masses show broad variation among species, particularly in the adductor profundus, abductor profundus, arrector dorsalis, and abductor superficialis. A previously undescribed system of intraradial ligaments was also discovered in all taxa studied. The morphology of these ligaments and functional ramifications of variation in this connective tissue system are described. Musculoskeletal patterns are interpreted in light of recent analyses of fin behavior and motor control during labriform swimming. Labriform propulsion has apparently evolved independently multiple times in coral reef fishes, providing an excellent system in which to study the evolution of pectoral fin propulsion.     

The pectoral anatomy of selected Ostariophysi. I. The Characiniformes.

The muscles and bones of the pectoral fin of Serrasalmus nattereri, the piranha, resemble those of generalized, lower teleosts with specializations related to a body shape adapted for high-speed carnivory; the pectoral fins being highly mobile with strong ligaments to the rays. The presence of two occipital nerves appears primitive, while the emergence of the subclavian artery within the branchial cavity, as in Gasteropelecus sternicla, appears specialized. The muscles and bones of the latter fish, a fresh-water flying fish, are specialized for self-propelled, aerial flight in the fusion of the right and left girdles greatly expanded for insertions of complex appendicular (flight) muscles, and in the consolidation of the rays and radials into one functional unit moving vertically in flight through contraction of vertical, massive ventral flight muscles. The bony pectoral anatomy of Electrophorus electricus, the electric eel, is specialized in having a mobile joint between the primary girdle and the cleithrum, the former being suspended vertically from the cleithrum by ligaments. The proximal radials and rays are very numerous and vertically aligned. The cleithrum is shaped to accommodate the extensive sternohyoid and pharyngocleithral muscles. The sheet-like appendicular muscles extend beyond the special joint and control its movement. The deeper muscles do not cross this joint. The arterial system is specialized in lacking a deep brachial artery.     

Pectoral fin and girdle development in the basal actinopterygians Polyodon spathula and Acipenser transmontanus

The pectoral fins of Acipenseriformes possess endoskeletons with elements homologous to both the fin radials of teleosts and the limb bones of tetrapods. Here we present a study of pectoral fin development in the North American paddlefish, Polyodon spathula, and the white sturgeon, Acipenser transmontanus, which reveals that aspects of both teleost and tetrapod endoskeletal patterning mechanisms are present in Acipenseriformes. Those elements considered homologous to teleost radials, the propterygium and the mesopterygial radials, form via subdivision of an initially chondrogenic plate of mesenchymal cells called the endoskeletal disc. In Acipenseriformes, elements homologous to the sarcopterygian metapterygium develop separately from the endoskeletal disc as an outgrowth of the endoskeletal shoulder girdle that extends into the posterior margin of the finbud. As in tetrapods, the elongating metapterygium and the metapterygial radials form in a proximal to distal order as discrete condensations from initially nonchondrogenic mesenchyme. Patterns of variation seen in the Acipenseriform fin also correlate with putative homology: all variants from the "normal" fin bauplan involved the metapterygium and the metapterygial radials alone. The primary factor distinguishing Polyodon and Acipenser fin development from each other is the composition of the endoskeletal extracellular matrix. Proteoglycans (visualized with Alcian Blue) and Type II collagen (visualized by immunohistochemistry) are secreted in different places within the mesenchymal anlage of the fin elements and girdle and at different developmental times. Acipenseriform pectoral fins differ from the fins of teleosts in the relative contribution of the endoskeleton and dermal rays. The fins of Polyodon and Acipenser possess elaborate endoskeletons overlapped along their distal margins by dermal lepidotrichia. In contrast, teleost fins generally possess relatively small endoskeletal radials that articulate with the dermal fin skeleton terminally, with little or no proximodistal overlap.     

Botulinum toxin injections as a method for chemically denervating skeletal muscle to test functional hypotheses: a pilot study in Lepomis cyanellus

In this study, we demonstrate that botulinum toxin can be used to chemically denervate muscles to test functional hypotheses. We injected research-grade type A botulinum toxin complex into pectoral fin abductors (abductor superficialis) of green sunfish (Lepomis cyanellus) to determine whether chemical denervation would eliminate the ability of a particular muscle to contribute to overall pectoral fin movements. Reduction of target muscle activity occurred within 8 d of the injection, and paralysis was confirmed using electromyography. No paralysis was seen in the adjacent muscles (abductor profundus) or in positive controls (saline injections). Paralysis occurred more slowly and at lower doses than previously documented for mammals. However, botulinum toxin complex (500 kDa) was used here, whereas previous studies have used purified toxin (150 kDa). Therefore, differences in physiological responses between fish and mammals cannot yet be distinguished from differences caused by the toxin type. However, we note that the toxin complex is less likely to diffuse across muscle fascia (because it is large), which should minimize paralytic effects on adjacent muscles. We suggest that botulinum toxin holds great promise as a chemical denervation agent in functional studies of animal locomotion and feeding behaviors.     

Description of Careproctus guillemi n. sp. (Pisces: Scorpaeniformes) from Weddell Sea

Careproctus guillemi differs from the other Careproctus species in the following combination of characters: pectoral fin rays 22 (11 + 4+7); pectoral girdle with three round radials (1 + 0+ 1 + 1); mouth oblique and maxillary extending beyond posterior edge of eye. Relationships between C. guillemi and C. longipectoralis are provided. The endochondral pectoral girdle of C. longipectoralis is described for the first time.     

The pectoral anatomy of selected Ostariophysi. II. The Cypriniformes and siluriformes

The pectoral myology and osteology of the cyprinoids Notemigonus crysoleucas, the golden shiner, and Catostomus commersonnii, the common white sucker, resemble those of generalized, lower teleosts in structure and function, except in features related to the manipulation of the massive fifth ceratobranchial of cyprinoids by muscles attaching on the girdle. Catostomus is more specialized in having unique intercostal muscles to the girdle, complex subclavian arteries and lack of a superficial trapezius muscle. The bony pectoral anatomy of the siluriform, Ictalurus nebulosus, the brown bullhead, is highly specialized in relation to the presence and locking of the massive pectoral spine which is formed of fused dorsal and ventral propterygial rays; there is consolidation of the girdle through fusion of bones, presence of unique stabilizing bony structures, firm symphyseal union of bilateral girdles and the presence of friction-surfaces of girdle and spine for locking. The movements of the spine are specialized in the greater guidance offered by the girdle. Myological specializations are related mainly to ventral appendicular muscles which lock the spine. The nervous and arterial systems are generalized.     

The structure and function of the dermal pectoral girdle in bony fishes with particular reference to ostariophysines

The structure of the dermal pectoral girdle of teleostean fishes is analyzed in relation to its functions. In bony fishes the vertebral column, with a horizontal axis, and the pectoral girdle, with a basically vertical axis, form the only skeletal links between the head and the body. The individual bones of the dermal girdle are considered as supporting units joined by a series of articulations that permit differential movement between adjacent bones. The movements mediated by this linkage system are: lateral swinging of the head relative to the body, expansion of the distance between the central areas of the two pectoral girdles to permit passage of large food items, and fore-and-aft movements of the anteroventral ends of the cleithra relative to the skull. Among other factors affecting the structure of the dermal pectoral girdle are the provision for the support of the pectoral fin base and the requirement for the effective operation of a sleeve valve between the girdle and the opercular cover.
Modifications of the dermal pectoral girdle in ostariophysine fishes are discussed. A brief history of the bony fish girdle in terms of its functional components is postulated.     

Development of zebrafish (Danio rerio) pectoral fin musculature

During posthatching development the fins of fishes undergo striking changes in both structure and function. In this article we examine the development of the pectoral fins from larval through adult life history stages in the zebrafish (Danio rerio), describing in detail their pectoral muscle morphology. We explore the development of muscle structure as a way to interpret the fins' role in locomotion. Genetic approaches in the zebrafish model are providing new tools for examining fin development and we take advantage of transgenic lines in which fluorescent protein is expressed in specific tissues to perform detailed three-dimensional, in vivo fin imaging. The fin musculature of larval zebrafish is organized into two thin sheets of fibers, an abductor and adductor, one on each side of an endoskeletal disk. Through the juvenile stage the number of muscle fibers increases and muscle sheets cleave into distinct muscle subdivisions as fibers orient to the developing fin skeleton. By the end of the juvenile period the pectoral girdle and fin muscles have reoriented to take on the adult organization. We find that this change in morphology is associated with a switch of fin function from activity during axial locomotion in larvae to use in swim initiation and maneuvering in adults. The examination of pectoral fins of the zebrafish highlights the yet to be explored diversity of fin structure and function in subadult developmental stages. J. Morphol. (c) 2005 Wiley-Liss, Inc.     

Osteology and myology of the cephalic region and pectoral girdle of Plotosus lineatus, with comments on Plotosidae (Teleostei: Siluriformes) autapomorphies

From comparisons of the cephalic and pectoral girdle structures of Plotosus lineatus with those of other plotosid as well as non-plotosid siluriforms, plotosid catfishes can be defined by at least six autapomorphies. These are: (1) the absence of the ventral division of the muscle arrector dorsalis; (2) the double articulation between the neurocranium and the anterior part of the suspensorium; (3) the greatly enlarged utricular otolith, which profoundly inflates the ventral surfaces of both the prootic and the pterotic; (4) the attachment of the muscle extensor tentaculi on the neurocranium lies further anteriorly than its insertion on the autopalatine; (5) the coronoid process of the mandible is linked to the maxillary by means of two thick, long ligaments; (6) the enlarged base of the maxillary barbel.     

Osteology and myology of the cephalic region and pectoral girdle of the Chinese catfish Cranoglanis bouderius,with a discussion on the autapomorphies and phylogenetic relationships of the Cranoglanididae (Teleostei: Siluriformes)

The cephalic and pectoral girdle structures of the Chinese catfish Cranoglanis bouderius are described and compared with those of other catfishes as the foundation for an analysis on the Cranoglanididae autapomorphies and also for a discussion on the phylogenetic relationships between the cranoglanidids and the other catfishes. Our observations and comparisons indicate that cranoglanidids are defined, at least, by four autapomorphies, namely: 1) the cartilages associated with the mandibular barbels are broad, somewhat circular; 2) epioccipital with a well-developed posterodorsal process, which presents a large, deep, circular posterior concavity; 3) a well-defined, deep, anteroposteriorly elongated concavity formed by both the frontal and the lateral ethmoid to receive the anteromedial surface of the metapterygoid; 4) the adductor mandibulae A3" is dorsally divided into two bundles and partially inserted on the posterior portion of the primordial ligament. With respect to the phylogenetic relationships of the Cranoglanididae, this study strongly suggests that these fishes are probably closely related to the Ariidae and the Claroteidae.     

Development of the paired fins in the paddlefish, Polyodon spathula

In Polyodon spathula, the pectoral fin radials, with the exception of the metapterygium, are derived from the decomposition of a single continuous cartilage fin plate that is continuous with the scapulocoracoid. This cartilage sheet develops two interior splits to form three precursor pieces, and these decompose in a predictable way to generate the propterygium and radials. The metapterygium is an extension of the scapulocoracoid that segments off of it during early development. To our knowledge, this has not been reported for acipenserids or other basal actinopterygians. In teleosts, the proximal radials also develop from the "break up" of an initially continuous paddle-like sheet of cartilage along the posterior edge of the scapulocoracoid, and in Polypterus and sharks a similar pattern holds. Thus, the pattern observed in Polyodon may represent the basal developmental condition for the gnathostome pectoral fin. The process underlying development of the superficially similar cartilages of the pelvic and pectoral fins is different. In the pectoral fin, the metapterygium is segmented off of the scapulocoracoid and other radials form from the decomposition of the cartilage plate. In contrast, individual rod-like basipterygial elements form in a close one-to-one correspondence with the middle radials of the pelvic fin, but later fuse to form an anterior element that is branched in appearance. To evaluate further claims of similarity among the pectoral and pelvic fin elements of various fishes, the course of the development of these structures must be observed. The pectoral fin and girdle in Polyodon ossifies in a different sequence than that proposed as ancestral (and highly conserved) for actinopterygians: the supracleithrum ossifies significantly before the cleithrum. The later ossification of the cleithrum in Polyodon may be related to the primary use of the caudal fin vs. the pectoral fins in their locomotion.     

Structure and function in the catfish

The catfish (Siluroidei) appear to have evolved from an ancestor which, in most respects other than the form of its teeth, resembled primitive Characinoidei. In the first part of this paper it is shown that most of the numerous and profound anatomical changes which have occurred in the course of their evolution from this ancestor can be related to one or other of three basic changes: depression of the body in adaptation to bottom-feeding habits, sensory modification in adaptation to nocturnal habits, and the evolution of defensive fin spines. Diplomystes is more primitive than other known catfish in the form of its maxilla and pectoral girdle, and in the posterior position of its dorsal fin.
The second part of the paper is concerned with some of the more specialized families of catfish (Mochokidae, Siluridae, Schilbeidae, Malapteruridae, Clariidae, Callichthyidae and Loricariidae). The specializations in each case are described, and related to the habits of the fish.     

Beziehungen zwischen Körperbau und Lebensweise bei Blenniidae (Pisces) des Roten Meeres

The muscle and skeleton anatomy of the pectoral, pelvic, and anal fins are described in 3 Salariin Blenniidae: Salarias fasciatus (sublittoral), Istiblennius edentulus (eulittoral), Alticus kirkii (supralittoral). In A. kirkii these organs are adapted to a climbing habit on the steep rocks beyond the water. The results are compared with those found in Periophthalmus.

---

Abbildungserklärungen B Basale - Cl Cleithrum - Co Coracoid - Creld Crista cleithri dorsalis - Crele Crista cleithri externa - H Haken an den Lepidotrichen der Ventralia - Lep Lepidotrichen - Pel Postcleithrum - Prsv Processus spinae ventralis - Pt Posttemporale - Rad Radiale - Scl Supracleithrum - SCl Symphyse des Cleithrum - Scp Scapula - abpr M. abductor profundus - adpr M. adductor profundus - arre M. arrector externus - arri M. arrector internus - cord M. coraco-radialis - dep M. depressor (Analis) - dprrd M. depressor radiorum (Pectoralia) - er M. erector - extpr M. extensor proprius - fls M. flexor superficialis - inc M. inclinator - levs M. levator superficialis - mes M. mesoventralis - rtrd M. retractor dorsalis - rtris M. retractor ischii - rtrv M. retractor ventralis Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

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.     

GYRACANTHIDES HAWKINSI SP. NOV. (ACANTHODII, GYRACANTHIDAE) FROM THE LOWER CARBONIFEROUS OF QUEENSLAND, AUSTRALIA, WITH A REVIEW OF GYRACANTHID TAXA

Abstract:  A new species of Gyracanthides from the mid-Viséan Ducabrook Formation of Middle Paddock site, near Springsure in the Drummond Basin, central Queensland, is based on isolated three-dimensionally preserved elements. The specimens comprise paired and unpaired spines and pectoral girdle elements, procoracoids and scapulocoracoids, and include growth series. The morphology, especially of the shoulder girdle bones and the form and tubercular ornamentation of the paired fin spines, is used to distinguish the new taxon. These characters also help differentiate the numerous described gyracanthid species. Aspects of palaeobiology including possible sexual dimorphism are explored. A hypothetical reconstruction of the fish is based on our interpretation of the articulation of isolated elements combined with examination of wear patterns on fin spines. Gyracanthides hawkinsi sp. nov. is compared with other Australian taxa as well as with gyracanthids from North America, Europe, Russia, Iran, Africa and Antarctica, some of which are tentatively reassigned here to the Gondwanan genus Gyracanthides .     

Paired fin skeletons and relationships of the fossil group Porolepiformes (Osteichthyes: Sardcopterygii)

The endoskeletal girdles, anocleithrum and paired fin supports of the porolepiform fish Glyptolepis (Osteichthyes: Sarcopterygii: Porolepiformes) are figured and described. The pectoral fin skeleton is known from the proximal part only and the pelvic fin skeleton is fragmentary, but the scapulocoracoid, anocleithrum and pelvic girdle can be reconstructed in their entirety. The anocleithrum is entirely subdermal. The pectoral fin skeleton in shown to be biserial, with a large number of axial mesomeres, whereas the pelvic fin contains fewer mesomeres and is strongly asymmetrical with very few postaxial radials. The scapulocoracoid is essentially similar to a reconstruction figured by Jarvik (1980), but has a more elongate glenoid; this has functional implications. The pelvic girdle consists of two separate halves as in Eusthenopteron, but differs from that genus in lacking dorsolateral rami. A brief survey of the evidence of paired fin structure in other porolepiform genera is carried out to establish whether the structures seen in Glyptolepis are likely to be representative for the Porolepiformes. A study of the morphology and muscle attachments of the paired fin skeletons indicates that the pattern of fin movement was significantly different from that in Neoceratodus. The fin supports and girdles of Glyptolepis are compared with those of other sarcopterygian groups as well as with actinopterygians, placoderms and sharks, in order to establish evolutionary polarities. Glyptolepis is shown to display a number of derived characters. The information gained from the comparison is used to construct a maximum parsimony cladogram, which places coelacanths as the sister group of porolepiforms + lungfishes, with the rhizodonts + tetrapods and osteolepiforms as successive sister groups of this clade. Characters of uncertain polarity are considered in the light of this cladogram. A comparison with recently published cladograms shows that none are completely compatible with the results from this study.     

On the phylogenetic position of monotremes (Mammalia,Monotremata)

Henosferida from the Middle-Upper Jurassic of Western Gondwana is the most probable sister group for monotremes. They share the derived pretribosphenic structure of lower molars combined with the presumably absent protocone on the upper molars and the plesiomorphic retention of postdentary bones and pseudangular process of the lower jaw. In addition, the two groups share the dental formula with three molars and the position of the Meckel’s groove, which passes ventral to the mandibular foramen. In the course of subsequent evolution, monotremes acquired the mammalian middle ear with three auditory ossicles independently of therian mammals and multituberculates. Jurassic Laurasian Shuotheriidae are probably a sister group of the Gondwanian clade Henosferida + Monotremata. The Jurassic shuotheriid Pseudotribos shows a great plesiomorphic similarity to monotremes in the structure of the pectoral girdle, with a large interclavicle immovably connected to the clavicle. In the lineages leading to therian mammals and multituberculates, the pectoral girdle changed probably independently and in parallel in connection with the establishment of the parasagittal posture of the forelimbs (reduction of the interclavicle, mobile articulation of the interclavicle with clavicle, reduction of the procoracoid, and development of a supraspinous fossa of the scapula) and formation of the mammalian middle ear with three auditory ossicles.     

Fossils and Strata

Jessen, H. L.: Schultergürtel und Pectoralflosse hci Actinopterygiern. [Shoulder girdle and pectoral fin in actinopterygians.] Fossils and Strata , Number 1, pp. 1–101, Pls. 1–25. Oslo, 5th May 1972.
The anatomy of the shoulder girdle and pectoral fin is investigated in adults and larvae of Asperser, Amia, Lepisosteus, Elops, Salmo , and Polypterus . In comparison with similar structures in other gnathostomian fishes these studies yielded certain conclusions as concerns the interrelationships of the recent actinopterygian groups and the affinities of the hrachiopterygians, the latter by this evidence belonging to an evolutionary line of their own. With regard to actinopterygian phylogeny, a comparison with the shoulder girdle and pectoral fin in fossil forms, including Chondrosteus, Moythomoasia, Palaeoniscus, Pteronisculus, Pachycormus, Catarus, Hypsocormus , and Birzeria , shows that teleosteans presumably are closer to chondrosteans than holosteans, and that holosteans seem to have branched off comparatively early from the actinopterygian stem.     

Integration and modularity of teleostean pectoral fin shape and its role in the diversification of acanthomorph fishes

Phenotypic integration and modularity describe the strength and pattern of interdependencies between traits. Integration and modularity have been proposed to influence the trajectory of evolution, either acting as constraints or facilitators. Here, we examine trends in the integration and modularity of pectoral fin morphology in teleost fishes using geometric morphometrics. We compare the fin shapes of the highly diverse radiation of acanthomorph fishes to lower teleosts. Integration and modularity are measured using two‐block partial least squares analysis and the covariance ratio coefficient between the radial bones and lepidotrichia of the pectoral fins. We show that the fins of acanthomorph fishes are more tightly integrated but also more morphologically diverse and faster evolving compared to nonacanthomorph fishes. The main pattern of shape covariation in nonacanthomorphs is concordant with the main trajectory of evolution between nonacanthomorphs and acanthomorphs. Our findings support a facilitating role for integration during the acanthomorph diversification. Potential functional consequences and developmental mechanisms of fin integration are discussed.