Cutaneous taste buds in cod

The distribution of cutaneous taste buds was determined quantitatively in larvae, juveniles and young adults of cod, using scanning electron microscopy. Changes in these distributions associated with development were followed in laboratory reared fish. Taste buds were first seen on the snout and lips of cod at a total length of 8 mm, and on the barbel at a length of 22 mm. The highest taste bud densities were seen at a length of around 90 mm, and subsequently declined on the barbel and pelvic fins with further growth. In these late 0-group fish, mean taste bud densities over much of the head, e.g. throat, dentary and sides of the snout were <100 mm⁻². On the tip of the snout and the lips, mean densities were in the region of 350–400 mm⁻², while on projecting parts of the fish, especially the barbel, anterior naris flap and extremities of the fins, spot densities occasionally exceeded 1000 mm⁻² at some sites. Mean taste bud diameter increased rapidly from 2.23μ± 0.35 μm (S.D.) at a length of 22 mm to 7.19 ± 0.23 μm at 90 mm length, with a much slower increase to about 8 μm associated with a further doubling in body length. These changes indicate a phase of rapid proliferation and growth in size of cutaneous taste buds in the period preceding the adoption of a benthic habit in their first summer. The presence of high taste bud densities on the barbel and pelvic fins in particular appears to correlate with the known feeding behaviour of cod.     

Innervation of the early pelvic fin bud of the trout embryo, Salmo gairdneri

Innervation of the early pelvic fin bud in the trout embryo involves four nerves. Electron microscopy discloses axons in the mesodermal mesenchyme and in the epidermis of the bud as early as stage I of the development of the pelvic fins. Sensory axons alone penetrate the epidermis. Unmyelinated axons invade the pelvic fin territory before the bud is obvious on the abdomen. Schwann cells occur in the vicinity of the ventral edge of the myotomes and later in the core of the bud and in subepidermal regions. Consequently, the nerve fibers are present early in the development of the pelvic fin bud of the trout embryo. Although the role of these axons is unknown, it is speculated that they play a role in development. Our results are discussed in the light of data available in the literature dealing with the development of tetrapod appendages.     

Synchronized swimming: coordination of pelvic and pectoral fins during augmented punting by the freshwater stingray Potamotrygon orbignyi

Benthic animals live at the juncture of fluid and solid environments, an interface that shapes many aspects of their behavior, including their means of locomotion. Aquatic walking and similar substrate-dependent forms of underwater propulsion have evolved multiple times in benthic invertebrate and vertebrate taxa, including batoid elasmobranchs. Skates (Rajidae) use the pelvic fins to punt across the substrate, keeping the pectoral fin disc still. Other batoids combine pelvic fin motions with pectoral fin undulation in augmented punting, but the coordination of these two modes has not been described. In this study of an augmented punter, the freshwater stingray Potamotrygon orbignyi, we demonstrate the synchrony of pelvic and pectoral fin cycles. The punt begins as the pelvic fins, held in an anterior position, are planted into the substrate and used to push the body forward. Meanwhile, a wave of pectoral fin undulation begins, increasing to maximum height just before the cycle's halfway point, when the pelvic fins reach their furthest posterior extension. The pectoral fin wave subsides as the pelvic fins return to their starting position for subsequent punts. Despite definitive links between pectoral and pelvic fin activity, we find no significant relationship between pectoral fin kinematics (frequency, wave height, and wave speed) and punt performance. However, slip calculations indicate that pectoral undulation can produce thrust and augment punting. Pelvic fin kinematics (frequency and duty factor) have significant effects, suggesting that while both sets of fins contribute to thrust generation, the pelvic fins likely determine punt performance.     

Solitary chemoreceptor cells of Ciliata mustela (Gadidae, Teleostei) are tuned to mucoid stimuli

Summed potentials were recorded from the dorsal recurrent facialnerve innervating the solitary chemoreceptor cells on the anteriordorsal fin (ADF), from the ventral recurrent facial nerve innervatingboth taste buds and solitary chemoreceptor cells on the pectoral(PEC) and pelvic (PEL) fins, and from the anterior dorsal finmuscles in the rockling, Ciliata mustela. There is little overlapbetween the sumulus spectra of solitary chemoreceptor cellsand taste buds. The ADF solitary cells are particularly sensitiveto body mucus (skin water) of non-congeners like Gadus, Solea,Cottus, Mugil, Zoarces, Gaidropsarus, and Encheliopus, but insensitiveto amino acids and a variety of body fluids of fish, invertebrates,and extracts of potential stimuli like algae and sand. Pectoraland pelvic fins are particularly sensitive to amino acids, bodyfluids of fish and invertebrates, but less sensitive to skinmucus of fish, probably due to the abundance of taste buds.Active sampling by undulation of the anterior dorsal fin isessential for proper functioning; it induces disadaptation ofthe receptor elements. Solitary chemoreceptor cells provide,apparently, cues to discriminate between conspecifics and non-conspecifics.It is unlikely that they are involved in pheromone detection.     

Comparative morphology and osteology of pelvic fin‐derived midline suckers in lumpfishes,snailfishes and gobies

Some fishes use modified body structures – including pelvic fins – to produce suction to facilitate stability in turbulent environments. This study compares the morphology and osteology of the pelvic suckers of representative lumpfishes (Cyclopteridae), snailfishes (Liparidae) and gobies (Gobiidae). In all species studied the midline sucker (pelvic suctorial organ [PSO]) is formed from the pelvic girdle and fin rays I and 5 of the pelvic fins, comprised of similar osteological elements to those found in the pelvic girdle and pelvic fin rays although the morphology of the bony elements is species‐specific. Pelvic suctorial organs in those fishes that lack pelvic girdles are therefore homologous to pelvic girdles. The phenotypic diversity seen in so few species indicates that many sucker morphologies have arisen, origination depending on the concerted development of muscular, skeletal, nervous, and skin body tissues. The structure of the soft rays of the pelvic fins in the liparids and cyclopterids is unusual and indicative of unconventional developmental patterning of fin ray halves and of evolution in the underlying mechanisms responsible for the development of midline suckers.     

Allometric growth of the trunk leads to the rostral shift of the pelvic fin in teleost fishes

The pelvic fin position among teleost fishes has shifted rostrally during evolution, resulting in diversification of both behavior and habitat. We explored the developmental basis for the rostral shift in pelvic fin position in teleost fishes using zebrafish (abdominal pelvic fins) and Nile tilapia (thoracic pelvic fins). Cell fate mapping experiments revealed that changes in the distribution of lateral plate mesodermal cells accompany the trunk-tail protrusion. Presumptive pelvic fin cells are originally located at the body wall adjacent to the anterior limit of hoxc10a expression in the spinal cord, and their position shifts rostrally as the trunk grows. We then showed that the differences in pelvic fin position between zebrafish and Nile tilapia were not due to changes in expression or function of gdf11. We also found that hox-independent motoneurons located above the pelvic fins innervate into the pelvic musculature. Our results suggest that there is a common mechanism among teleosts and tetrapods that controls paired appendage positioning via gdf11, but in teleost fishes the position of prospective pelvic fin cells on the yolk surface shifts as the trunk grows. In addition, teleost motoneurons, which lack lateral motor columns, innervate the pelvic fins in a manner independent of the rostral-caudal patterns of hox expression in the spinal cord.     

Fibin, a novel secreted lateral plate mesoderm signal, is essential for pectoral fin bud initiation in zebrafish

We identified a novel secreted protein, fibin, in zebrafish, mice and humans. We inhibited its function in zebrafish embryos by injecting antisense fibin morpholino oligonucleotides. A knockdown of fibin function in zebrafish resulted in no pectoral fin bud initiation and abolished the expression of tbx5, which is involved in the specification of pectoral fin identification. The lack of pectoral fins in fibin-knockdown embryos was partially rescued by injection of fibin RNA. fibin was expressed in the lateral plate mesoderm of the presumptive pectoral fin bud regions. Its expression region was adjacent to that of tbx5. fibin expression temporally preceded tbx5 expression in presumptive pectoral fin bud regions, and not abolished in tbx5-knockdown presumptive fin bud regions. In contrast, fibin expression was abolished in retinoic acid signaling-inhibited or wnt2b-knockdown presumptive fin bud regions. These results indicate that fibin is a secreted signal essential for pectoral fin bud initiation in that it potentially acts downstream of retinoic acid and wnt signaling and is essential for tbx5 expression. The present findings have revealed a novel secreted lateral plate mesoderm signal essential for fin initiation in the lateral plate mesoderm.     

Early osteological development of the fins in the hatchery-reared red porgy, Pagrus pagrus (L. 1758)

The present study was undertaken to establish the normal, healthy features of morphological structures at various developmental stages as achieved under well-defined environmental culture conditions (temperature between 16 and 21°C, salinity 36 ppt, pH around 7.6, and oxygen saturation over 95%) common in aquaculture of the species. The pectoral fin supports began to develop at 2.90 mm total length (TL), followed by those of dorsal fins at 5.5 mm TL, caudal fins at 5.6 mm TL, pelvic fins at 5.9 mm TL and anal fins at 6.0 mm TL. The pelvic fins appeared fully at 7.4 mm TL. Development of dorsal lepidotrichia was first observed at 6.9 mm TL, attaining their final number at 7.6 mm TL. The dorsal spines first appeared at 6.5 mm TL and were complete at 7.4 mm TL. The anal lepidotrichia appeared during the development phase from 6.8 to 8.6 mm TL. At 5.6 mm TL, the upward flexion of the urostyle was initiated. The caudal lepidotrichia formed within the primordial fin at 5.6 mm TL and reached the final count at 7.4 mm TL. The caudal dermatotrichia first appeared at 7.3 mm TL and all forms were observed by 15.5 mm TL. The development pattern of fin supports found in Pagrus pagrus is quite similar to that described for other Sparid species.     

Revealing the mechanisms of the rostral shift of pelvic fins among teleost fishes

In teleost fishes, the position of the pelvic fins shift during evolution; this positional shift seems to have diversified their locomotion and feeding behavior, thereby expanding the habitats of these fishes. Thus, such a positional shift of the pelvic fins is one of the significant features of teleost fishes from evolutionary, embryological, and taxonomic viewpoints, but no studies to date have investigated the mechanism for the rostral shift of the pelvic fins from the anal region in teleosts. Examining the fate of the prospective pelvic fin cells of the zebrafish Danio rerio and the Nile tilapia Oreochromis niloticus embryos demonstrates that the prospective pelvic fin cells are originally located near the anus, as seen in tetrapods, but their position shifts with respect to the body trunk after its protrusion from the yolk surface. In this article, we highlight such recent findings and discuss the mechanisms of pelvic fin evolution among teleost fishes.     

Internal morphology and function of paired fins in the epaulette shark,hemiscyllium ocellatum

Paired fins and associated internal structures of the epauletic sharkHemiscyllium ocellatum, were described on the basis of three specimens. A comparison with other genera showed the epaulette shark to be, characterized by two elongated basal cartilages articulating with a distally projecting articular condyle on the coracoid, a loosely separated radial series with an intermediate series, a levator pectoralis inferior muscle and an anterolaterally developed depressor pectoralis muscle in the pectoral fin, and an elongated anterior pelvic basal cartilage articulating with a distally projecting articular condyle and an anterolaterally developed depressor pelvicus muscle in the pelvic fin. In captivity, the sharks exhibited both upright and crawling behavior on the bottom by using the pectoral and pelvic fins and bending the body. The distinctive morphological characters are shared by otherHemiscyllium species and are suggested as important factors enabling their unique behavior associated with a complex coral reef habitat.     

Developmental genetic basis for the evolution of pelvic fin loss in the pufferfish Takifugu rubripes

Paired appendages were a key developmental innovation among vertebrates and they eventually evolved into limbs. Ancient developmental control systems for paired fins and limbs are broadly conserved among gnathostome vertebrates. Some lineages including whales, some salamanders, snakes, and many ray-fin fish, independently lost the pectoral, pelvic, or both appendages over evolutionary time. When different taxa independently evolve similar developmental morphologies, do they use the same molecular genetic mechanisms? To determine the developmental genetic basis for the evolution of pelvis loss in the pufferfish Takifugu rubripes (fugu), we isolated fugu orthologs of genes thought to be essential for limb development in tetrapods, including limb positioning (Hoxc6, Hoxd9), limb bud initiation (Pitx1, Tbx4, Tbx5), and limb bud outgrowth (Shh, Fgf10), and studied their expression patterns during fugu development. Results showed that bud outgrowth and initiation fail to occur in fugu, and that pelvis loss is associated with altered expression of Hoxd9a, which we show to be a marker for pelvic fin position in three-spine stickleback Gasterosteus aculeatus. These results rule out changes in appendage outgrowth and initiation genes as the earliest developmental defect in pufferfish pelvic fin loss and suggest that altered Hoxd9a expression in the lateral mesoderm may account for pelvis loss in fugu. This mechanism appears to be different from the mechanism for pelvic loss in stickleback, showing that different taxa can evolve similar phenotypes by different mechanisms.     

Two new species and a new record of the genus Sinogastromyzon (Teleostei: Balitoridae) from Yunnan, China

Two new species and a new record of Sinogastromyzon are described from Lixianjiang River of Yunnan province, China. Sinogastromyzon lixianjiangensis, new species, can be distinguished from its congeners by the following characters: pectoral fin with XIII–XIV, 15–17 rays; pelvic fin with X–XI, 10–12 rays; 60–65 lateral-line scales; no scales on the dorsum of paired fins or the region between axilla of pectoral fin and pelvic-fin origin; tip of pelvic fin close to anus; tip of anal fin close to caudal-fin base; anal-fin origin nearer to the caudal-fin base than to the posterior pelvic-fin base; anus nearer to anal-fin origin than to the posterior pelvic-fin base; dorsal side of the body with 9–11 black blotches. Sinogastromyzon macrostoma, new species can be distinguished from its congeners by the following characters: pectoral fin with XII–XIV, 12–15 rays; pelvic fin with VII–IX, 11–13 rays; 48–56 lateral-line scales; mouth extremely big, slightly arched; no scales on the dorsum of paired fins or the region between axilla of pectoral fin and pelvic-fin origin; tip of pelvic fin far beyond anus; tip of anal fin far from caudal-fin base; anal-fin origin about midway between the posterior pelvic-fin base and caudal-fin base; anus nearer to posterior pelvic-fin base than to anal-fin origin; dorsal side of the body uniformly gray, without regular blotches in formalin preserved specimen. Sinogastromyzon cf. multiocellum is firstly recorded in China.     

Solitary chemosensory cells — taste,common chemical sense or what?

Summary Secondary solitary chemosensory cells (SCCs) occur scattered within the epidermis of lampreys, teleosts and ranid tadpoles. Counts in representative telost species revealed that SCC's outnumber chemosensory cells organized in taste buds. Therefore, SCCs may be considered the structural substrate of a basic and probably important vertebrate chemosense. However, detailed information on structure, innervation and function is only available from specialized fins in a few teleost species, where SCCs are sufficiently concentrated. The foremost research model has been the anterior dorsal fin (ADF) in rocklings, which contains millions of SCCs but no other specialized chemosensory elements. It has been shown that these ADF-SCCs are innervated from the recurrent facial nerve. Electrophysiological recordings revealed that there is virtually no overlap in stimulus spectrum between the ADF-SCCs and pelvic fin taste buds; SCC responses could only be triggered by dilutions of heterospecific fish body mucus. Results of behavioural experiments indicate that fish mucus is indeed a relevant stimulus. Therefore it is hypothesized that the biological role of the ADF-SCCs is predator avoidance rather than search for food. Whether these findings are valid for rockings only, or can be generalized for the scattered SCC systems in more than 20000 species of fish and in some amphibians, remains an open question. Further investigations on the function and biological roles of the SCC chemosense will be crucially important to improve our understanding of sensory perception and its evolution in aquatic vertebrates.     

The origins of adipose fins: an analysis of homoplasy and the serial homology of vertebrate appendages

Adipose fins are appendages found on the dorsal midline between the dorsal and caudal fins in more than 6000 living species of teleost fishes. It has been consistently argued that adipose fins evolved once and have been lost repeatedly across teleosts owing to limited function. Here, we demonstrate that adipose fins originated repeatedly by using phylogenetic and anatomical evidence. This suggests that adipose fins are adaptive, although their function remains undetermined. To test for generalities in the evolution of form in de novo vertebrate fins, we studied the skeletal anatomy of adipose fins across 620 species belonging to 186 genera and 55 families. Adipose fins have repeatedly evolved endoskeletal plates, anterior dermal spines and fin rays. The repeated evolution of fin rays in adipose fins suggests that these fins can evolve new tissue types and increased structural complexity by expressing fin-associated developmental modules in these new territories. Patterns of skeletal elaboration differ between the various occurrences of adipose fins and challenge prevailing hypotheses for vertebrate fin origin. Adipose fins represent a powerful and, thus far, barely studied model for exploring the evolution of vertebrate limbs and the roles of adaptation and generative biases in morphological evolution.     

Larval development of Argentine hake Merluccius hubbsi

The ontogeny of the developmental stages of the hake Merluccius hubbsi is described. Fish larvae and post-transitional juveniles were collected in the Nor-Patagonian area from 1989 to 2004. The opening of the mouth and the pigmentation of the eyes are coincident with yolk resorption, finishing the yolk-sac stage. This species presents pigmentation on the head, trunk and tail typical of gadiform larvae. Pectoral fin development is completed during the transformation stage. The post-transitional juvenile stage begins when the fin-ray complements are complete and squamation begins. The fins become fully formed in the following sequence: pelvic fins, first dorsal fin, second dorsal and anal fins together, caudal fin and pectoral fins. The caudal complex is totally developed in larvae of 22·0–23·0 mm standard lengths ( L _S) and all vertebral elements are first observed in larvae of 8·5 mm L _S. The rate of development of M. hubbsi observed in this study could be faster than the rates reported for other species of Merluccius by different authors.     

Does body and fin form affect the maneuverability of fish traversing vertical and horizontal slits?

Synopsis The purpose of this study was to determine if body and fin form affected the maneuverability of teleostean fishes as measured by their ability to negotiate simple obstacles. Obstacles were vertical and horizontal rectangular slits of different widths, for which width was defined as the minimum dimension of a slit irrespective of slit orientation. Performance was measured as the smallest slit width traversed. Three species with different body and fin patterns were induced to swim through slits. Species tested were; goldfish Carassius auratus with a fusiform body, anterio-ventral pectoral fins and posterio-ventral pelvic fins; silver dollars Metynnis hypsauchen with the same fin configurations but a gibbose body; angelfish Pterophyllum scalare with a gibbose body and anterio-lateral pectoral fins. Minimum slit widths negotiated were normalized with the length of various body dimensions: total length, maximum width, span at the pectoral fins, and volume^1/3 (numerically equal to mass^1/3). Goldfish had the poorest performance, requiring the largest slit widths relative to these body dimensions. No consistent patterns in performance were found for silver dollars vs. angelfish. There were no differences among species in the ratio of minimum vertical slit width negotiated to that for horizontal slits, indicating fish were equally able to control posture while swimming on their sides. There were also no consistent patterns in the times taken to transit slits. Although the deep-bodied fish were able to maneuver through smaller slits, the most striking result is the similarity of minimum slit widths traversed in spite of the large variation in body form. Body form and fin plan may be more important for maneuvering and posture control during sub-maximum routine activities.     

A comparison of different structures and methods for estimating age of northern-form Dolly Varden <Emphasis Type="Italic">Salvelinus malma malma</Emphasis> from the Canadian Arctic

Assessment of anadromous northern-form Dolly Varden Salvelinus malma malma in the Western Canadian Arctic requires reliable methods for estimating ages. Additionally, conservation efforts warrant determining whether fin rays provide a non-lethal alternative to otoliths. Precision and bias of whole and sectioned otoliths, and sectioned pectoral and pelvic fin rays were examined. Two age readers with different levels of experience ageing this species read each structure three times. Coefficient of variation (CV) was calculated to measure precision, and age bias plots were created for each method of preparation/structure within and between readers. The experienced reader demonstrated the highest precision with sectioned otoliths (CV = 1.6 %) followed by whole otoliths (CV = 4.2 %) while pectoral and pelvic fins were the lowest, CV = 7.7 % and 7.5 %, respectively. The age bias plot showed little difference between whole and sectioned otoliths, although greater imprecision/bias was evident for whole otoliths at age ≥9. Compared to otoliths, fin rays produced younger age estimates starting at 5 years; however, pelvic fins were more biased towards younger estimates than pectoral fins. The less experienced reader had greater inconsistencies, tending to overage younger and underage older samples for all methods compared to the more experienced reader, underscoring the importance of experience when estimating age for this species. We conclude that both types of fin rays are a poor non-lethal alternative to otoliths for fish ≥5 years and recommend an experienced ager could use whole otoliths up to age 8 and sectioned otoliths for fish ≥9 years (>500 mm fork length).     

A new pearleye (Teleostei,Aulopiformes) species from the Oligocene of Romania

A new pearleye species of the alepisauroid family Scopelarchidae, Scopelarchoides neamticus sp. nov., is described herein based on two specimens from the Oligocene Lower Dysodilic Shales Formation, cropping out in the Pietricica Mountain, Romanian Eastern Carpathians. The new species described herein exhibits a unique combination of features (including head length about 25% of SL; coracoid remarkably expanded; both preorbital and postorbital lengths larger than orbit diameter; 50 or 51 vertebrae; dorsal fin with nine or ten rays; anal-fin with 28 rays; length of anal fin base about 30% of SL; preanal distance almost 60% of SL; pelvic fin insertion located just under the second dorsal fin ray; pectoral fins only slightly longer than pelvic fins; caudal fin with 19 principal rays plus 14 upper and 13 lower procurrent rays) that justifies its recognition as a new species of the genus Scopelarchoides. Both morphological and meristic features suggest a certain degree of similarity between S. neamticus sp. nov. and the extant species Scopelarchoides signifer. The fossils of the new Oligocene species described herein represent the oldest known skeletal record of Scopelarchidae.