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.     

Anatomy and early development of the pectoral girdle,fin, and fin spine of sturgeons (Actinopterygii: Acipenseridae)

Acipenseriformes hold an important place in the evolutionary history of bony fishes. Given their phylogenetic position as extant basal Actinopterygii, it is generally held that a thorough understanding of their morphology will greatly contribute to the knowledge of the evolutionary history and the origin of diversity for the major osteichthyan clades. To this end, we examined comparative developmental series from the pectoral girdle in Acipenser fulvescens, A. medirostris, A. transmontanus, and Scaphirhynchus albus to document, describe, and compare ontogenetic and allometric differences in the pectoral girdle. We find, not surprisingly, broad congruence between taxa in the basic pattern of development of the dermal and chondral elements of the pectoral girdle. However, we also find clear differences in the details of structure and development among the species examined in the dermal elements, including the clavicle, cleithrum, supracleithrum, posttemporal, and pectoral‐fin spine. We also find differences in the internal fin elements such as the distal radials as well as in the number of fin rays and their association with the propterygium. Further, there are clear ontogenetic differences during development of the dermal and chondral elements in these species and allometric variation in the pectoral‐fin spine. The characters highlighted provide a suite of elements for further examination in studies of the phylogeny of sturgeons. Determining the distribution of these characters in other sturgeons may aid in further resolution of phylogenetic relationships, and these data highlight the role that ontogenetic and comparative developmental studies provide in systematics. J. Morphol. 276:241–260, 2015. © 2014 Wiley Periodicals, Inc.     

Ovarian nests in cultured Russian sturgeon Acipenser gueldenstaedtii and North American paddlefish Polyodon spathula comprised of previtellogenic oocytes

Ovarian nests in the ovaries of sexually maturing Russian sturgeon Acipenser gueldenstaedtii and North American paddlefish Polyodon spathula were investigated. They comprised early previtellogenic, diplotene stage oocytes and somatic cells. In the nucleoplasm, these oocytes contained chromatin in the form of grains, threads and lampbrush chromosomes, primary nucleoli and multiple nucleoli. Two stages of oocytes in nests were distinguished by differences in the distribution of mitochondria with distorted cristae and lipid droplets in the ooplasm. These stages were as follows: pre‐early stage 1 (PE 1) and early stage 1 (EP 1) previtellogenic oocytes. In PE 1 oocytes few mitochondria with distorted cristae and lipid droplets were distributed randomly. The ooplasm of PE 1 oocytes was not differentiated into homogeneous and granular compartments. In EP 1 oocytes, mitochondria with distorted cristae were more numerous and grouped in the vicinity of the nucleus, lipid droplets accumulated near these mitochondria. In the nucleoplasm of EP 1 oocytes several low electron‐dense spherical bodies, possibly Cajal bodies, were present.     

Effects of hypercapnia on blood-gas and acid-base status in the white sturgeon, Acipenser transmontanus

The effect of environmental hypercapnia on respiratory and acid-base variables was studied in white sturgeon, Acipenser transmontanus. Blood PCO₂, PO₂, pH, hemoglobin concentration, and plasma lactate, glucose, catecholamines and cortisol were measured first under normocapnia (water PCO₂ < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25–35 Torr) and a final return to normocapnia at 19 ± 0.5 °C. Acute (≤ 2h) hypercapnia significantly increased arterial PCO₂ (8-fold increase), ventilation frequency (2-fold increase), plasma HCO₃ ⁻ (2.3-fold) and decreased arterial pH (to 7.15 ± 0.02). After 24 h, norepinephrine, epinephrine and cortisol, were significantly increased, and arterial pH reached its nadir (7.10 ± 0.03). During the 72- and 96-h-periods, arterial PCO₂ (24 ± 4.4 Torr) and ventilatory frequency (105 ± 5 breaths min⁻¹) stabilized, HCO₃ ⁻ reached its apparent maximum (23.6 ± 0.0 mmol⁻¹), glucose decreased by 32%, and pH increased significantly to 7.31 + 0.03. The return to normocapnia completely restored arterial PCO₂ (2.5 ± 0.14 Torr), HCO₃ ⁻ (7.4 ± 0.59 mmol · l⁻¹), ventilation frequency (71 ± 7 breaths · min⁻¹), and pH (7.75 ± 0.04). Overall, hypercapnia produced a respiratory acidosis, hyperventilation, a transient norepinephrine “spike”, and increased plasma catecholamines, cortisol, and arterial PO₂. The respiratory acidosis was only partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted in a significantly decreased blood-O₂ affinity (Bohr effect), as determined by construction of in vitro blood O₂ equilibrium curves at 15 °C and 20 °C. Prolonged exposure to hypercapnia may lead to acid-base disturbances and negatively affect growth of white sturgeon. Accepted: 17 August 1997     

From head to tail: the myoseptal system in basal actinopterygians

Experimental studies indicated that myomeres play several functional roles during swimming. Some of the functions in question are thought to change rostrocaudally, e.g., anterior myomeres are thought to generate forces, whereas posterior myomeres are thought to transmit forces. In order to determine whether these putative functions are reflected in myoseptal morphology we carried out an analysis of the myoseptal system that includes epaxial and hypaxial myosepta of all body regions for the first time. We combined clearing and staining, microdissections, polarized light microscopy, SEM technique, and length measurements of myoseptal parts to reveal the spatial arrangement, collagen fiber architecture, and rostrocaudal gradients of myosepta. We included representatives of the four basal actinopterygian clades to evaluate our findings in an evolutionary and in a functional context. Our comparison revealed a set of actinopterygian groundplan features. This includes a set of specifically arranged myoseptal tendons (epineural, epipleural, lateral, and myorhabdoid tendons) in all epaxial and postanal hypaxial myosepta. Only preanal hypaxial myosepta lack tendons and exclusively consist of mediolateral fibers. Laterally, myosepta generally align with the helically wound fibers of the dermis in order not to limit the body's maximum curvature. Medially, the relationship of myosepta to vertebrae clearly differs from a 1:1 relationship: a myoseptum attaches to the anterior margin of a vertebra, turns caudally, and traverses at least three vertebrae in an almost horizontal orientation in all body regions. By this arrangement, horizontal multiple layers of myosepta are formed along the trunk dorsal and ventral to the horizontal septum. Due to their reinforcement by epineural or epipleural tendons, these multiple layers are hypothesized to resist the radial expansion of underlying muscle fibers and thus contribute to modulation of body stiffness. Rostrocaudally, a dorsoventral symmetry of epaxial and hypaxial myosepta in terms of spatial arrangement and collagen fiber architecture is gradually developed towards the postanal region. Furthermore, the rostrocaudal extension of myosepta measured between anterior and posterior cones gradually increases. This myoseptal region is reinforced by longitudinal fibers of lateral tendons. Furthermore, the percentage of connective tissue in a cross section increases. These morphological data indicate that posterior myosepta are equipped for multisegmental force transmission towards the caudal fin. Anteriormost myosepta have reinforced and elongated dorsal posterior cones. They are adequately designed to transmit epaxial muscular forces to the neurocranium in order to cause its elevation during suction feeding.     

Microscopic identification of novel cell types in the integument of larval lake sturgeon,Acipenser fulvescens

Osmoregulation, respiration, nutrient/mineral transport, and defense mechanisms are all evident in the integument of fish. The role of the integument in these physiological processes is particularly important during early life history in larval fishes, as functional systems such as the gills and gastrointestinal tract are not fully developed. Using a variety of microscopy techniques, we describe the morphology of keratinocytes, mitochondria rich cells, ciliated cells and mucous cells of the skin, yolk sac, and gills. The cytology we observed was similar to previous studies describing the integument of larval fish, however, we have also identified two novel cell types on the integument of larval Lake Sturgeon, Acipenser fulvescens, between 9 and 34 days post fertilization. Our detailed analysis included a multifaceted microscopy approach using scanning electron, transmission electron, and light microscopy to elucidate the histology of the tissue and cellular morphology in addition to quantification and distribution of these novel cell types. The first cell type had a characteristic ampullary shape with a central cavity and a pore opening at the surface. The second, located on the free surface of the epidermis, had an uneven plasma membrane surface. Based on the abundance of secretory vesicles, organelles necessary for protein synthesis, and the lack of neural connection in both cell types, we propose these cells to be involved in the release of semiochemicals that may act as a pheromone, alarm substance, or chemical defense mechanism. J. Morphol. 277:86–95, 2016. © 2015 Wiley Periodicals, Inc.     

The effect of substrate rearing on growth,aerobic scope and physiology of larval white sturgeon Acipenser transmontanus

The effect of substratum on growth and metabolic rate was assessed in larval white sturgeon Acipenser transmontanus. Yolk‐sac larvae (YSL) were reared in bare tanks or tanks with gravel as substratum from hatch until approximately 16 days post hatch (dph). The effect of an artificial substratum was also evaluated on growth alone. Substratum had a significant effect on mass, with larvae reared in gravel and artificial substrata being larger than those reared without substratum. Routine metabolic rates were significantly lower and relative aerobic scope (the difference between maximum and routine metabolic rate) was significantly higher for YSL and feeding larvae (FL) reared in gravel relative to those reared in bare tanks, particularly before fish started feeding exogenously. Furthermore, gravel‐reared larvae had higher whole‐body glycogen concentrations relative to bare‐tank‐reared larvae. Routine factorial scope (maximum metabolic rate divided by routine metabolic rate) was relatively low in all treatments (< 1·7) indicating a limited ability to elevate metabolic rate above routine early in development and mass exponents for metabolic rate exceeded 1. Taken together, these data indicate that YSL reared without substratum may divert more of their energy to non‐growth related processes impairing growth. This finding underscores the importance of adequate rearing substratum for growth of A. transmontanus and may provide support for habitat restoration and alternative hatchery rearing methods associated with sturgeon conservation.     

Expression of Hoxa-11 and Hoxa-13 in the pectoral fin of a basal ray-finned fish, Polyodon spathula: implications for the origin of tetrapod limbs

Summary Paleontological and anatomical evidence suggests that the autopodium (hand or foot) is a novel feature that distinguishes limbs from fins, while the upper and lower limb (stylopod and zeugopod) are homologous to parts of the sarcopterygian paired fins. In tetrapod limb development Hoxa-11 plays a key role in differentiating the lower limb and Hoxa-13 plays a key role in differentiating the autopodium. It is thus important to determine the ancestral functions of these genes in order to understand the developmental genetic changes that led to the origin of the tetrapod autopodium. In particular it is important to understand which features of gene expression are derived in tetrapods and which are ancestral in bony fishes. To address these questions we cloned and sequenced the Hoxa-11 and Hoxa-13 genes from the North American paddlefish, Polyodon spathula, a basal ray-finned fish that has a pectoral fin morphology resembling that of primitive bony fishes ancestral to the tetrapod lineage. Sequence analysis of these genes shows that they are not orthologous to the duplicated zebrafish and fugu genes. This implies that the paddlefish has not duplicated its HoxA cluster, unlike zebrafish and fugu. The expression of Hoxa-11 and Hoxa-13 in the pectoral fins shows two main phases: an early phase in which Hoxa-11 is expressed proximally and Hoxa-13 is expressed distally, and a later phase in which Hoxa-11 and Hoxa-13 broadly overlap in the distal mesenchyme of the fin bud but are absent in the proximal fin bud. Hence the distal polarity of Hoxa-13 expression seen in tetrapods is likely to be an ancestral feature of paired appendage development. The main difference in HoxA gene expression between fin and limb development is that in tetrapods (with the exception of newts) Hoxa-11 expression is suppressed by Hoxa-13 in the distal limb bud mesenchyme. There is, however, a short period of limb bud development where Hoxa-11 and Hoxa-13 overlap similarly to the late expression seen in zebrafish and paddlefish. We conclude that the early expression pattern in tetrapods is similar to that seen in late fin development and that the local exclusion by Hoxa-13 of Hoxa-11 from the distal limb bud is a derived feature of limb developmental regulation.     

Early steps of paired fin development in zebrafish compared with tetrapod limb development

The development of zebrafish paired fins and tetrapod forelimbs and hindlimbs show striking similarities at the molecular level. In recent years, the zebrafish, Danio rerio has become a valuable model for the study of the development of vertebrate paired appendages and several large-scale mutagenesis screens have identified novel fin mutants. This review summarizes recent advances in research into zebrafish paired fin development and highlights features that are shared with and distinct from limb development in other main animal models.     

Lessons from the first dorsal fin in atheriniforms—A new mode of dorsal fin development and its phylogenetic implications

The median fins in extant actinopterygians are the product of millions of years of evolution. During this time, different developmental patterns for the dorsal and anal fins emerged leading to a high variation in median fin morphology and ontogeny. In this study, the development of anal and dorsal fins in atheriniforms is described and its consequences for the current phylogenetic hypothesis are discussed. Developmental series of five atheriniform species were investigated using clearing and staining as well as antibody staining. The skeletal elements of the second dorsal fin and the anal fin emerge in a bidirectional pattern. The first dorsal fin, however, arises separately in front of the second dorsal fin after this one is almost completely formed. The pterygiophores of the first dorsal fin, including the interdorsal pterygiophores, develop from caudal to rostral, but the fin‐spines of the first dorsal fin form in the opposite direction. This new mode of fin development has been found in all examined atheriniform species with two dorsal fins. Several morphological characters of atheriniforms, including interdorsal pterygiophores, are also found in one other taxon: the Mugiliformes. Thus, several dorsal fin characteristics may provide evidence for a closer relationship of these two taxa.     

Effect of temperature on early development of white and lake sturgeon,Acipenser transmontanus and A. fulvescens

Synopsis The effect of constant incubation temperatures (between 10°C and 26°C) on the developmental rates was found to fit a similar exponential relationship in both the lake and white sturgeon embryos and larvae. Although the lake sturgeon had an overall slower rate of development than the white sturgeon, no statistically significant difference was detected in the slopes of the exponential equations describing the effect of temperature on developmental rate. The effect of these incubation temperatures on embryonic survival also did not differ between these two species. Both species exhibited optimal survival between 14–17° C and incipient mortalities occurred at 20°C. Temperatures above 20°C were lethal for white sturgeon embryos. No effect of low incubation temperature on survival was evident from this study. A comparison of these North American species with Eurasian acipenserids suggests that all the sturgeon that have been examined exhibit a similar influence of incubation temperature on developmental rate.     

Comparative stable isotope analyses of green sturgeon (Acipenser medirostris) and white sturgeon (A. transmontanus) in the San Francisco estuary

Green sturgeon (Acipenser medirostris) and white sturgeon (A. transmontanus) are closely related, sympatric species that inhabit the San Francisco estuary. Green sturgeon have a more marine life history but both species spawn in the Sacramento River and reside for some duration in San Francisco Bay. These sturgeons are of conservation concern, yet little is known about their dietary competition when they overlap in space and time. To examine evidence of dietary differentiation, we collected whole blood and blood plasma from 26 green sturgeon and 35 white sturgeon in San Francisco Bay. Using carbon and nitrogen stable isotope analyses, we compared their relative trophic levels and foraging locations along the freshwater to marine gradient. Sampling blood plasma and whole blood allowed comparison of dietary integration over shorter and longer time scales, respectively. Plasma and whole blood δ¹³C values confirmed green sturgeon had more marine dietary sources than white sturgeon. Plasma δ¹⁵N values revealed white sturgeon fed at lower trophic levels than green sturgeon recently, however, whole blood δ¹⁵N values demonstrated the two species fed at the same trophic level over longer time scales. Larger individuals of both species had higher δ¹³C values than smaller individuals, reflecting more marine food sources in adulthood. Length did not affect δ¹⁵N values of either species. Isotope analyses supported the more marine life history of green than white sturgeon and potentially highlight a temporary trophic differentiation of diet between species during and preceding the overlapping life stage in San Francisco Bay.     

The presence of a galanin-like peptide in the gut neuroendocrine system of Lampetra fluviatilis and Acipenser transmontanus: an immunohistochemical study

Galanin is a brain-gut neuropeptide present in the central and peripheral nervous systems of vertebrates. In the present survey, the galaninergic and the diffuse endocrine systems of the alimentary canal of the river lamprey, Lampetra fluviatilis, and the white sturgeon, Acipenser transmontanus, were studied by immunohistochemistry. The results show the presence of galanin-like immunoreactive endocrine cells in the gut of L. fluviatilis. In addition, a galanin-like immunoreactivity was detected in enteric intramural neurons of both species. It is conceivable that the galaninergic system plays in both species a role in the regulation of the gut muscle contractility and in the modulation of mucosal secretive/absorptive processes. In A. transmontanus, the presence of galanin-like immunoreactive nerve fibres associated with components of the gut associated-lymphoid tissue is possibly correlated with a control of the defensive events at this site. The presence of a galanin-like immunoreactivity in the neuroendocrine system of these two ancient fishes confirms the hypothesis on the early occurrence of this regulative molecule in the gastro-enteric system of vertebrates.     

长江鲟子三代繁育技术研究

经过长达20余年的人工保种,长江鲟Acipenser dabryanus子三代苗种在2018年首次成功获得。运用B超鉴定性腺发育期技术,从6～8龄子二代长江鲟亲鱼群体中挑选出成熟雌雄亲鱼各6尾,雄鱼平均体质量(17.02±4.97) kg,雌鱼平均体质量(20.57±3.23) kg,在水温19.0～20.0℃下,实施人工催产,成功催产雄鱼5尾,雌鱼2尾,获卵约9万粒,平均卵径(2.65±0.19) mm,受精率87.53%,孵化率76.14%,共孵出子三代长江鲟仔鱼约6万尾,获开口期仔鱼约3万尾;子三代长江鲟初孵仔鱼体长(0.91±0.06) cm,体质量(0.021±0.003) g。仔鱼体质量呈指数增长,增长方程式为W=0.108 1e^{0.333 2t}(R²=0.931 8,n=105,P<0.01);体长呈直线增长,增长方程式为L=1.087 8t-1.746 2(R²=0.986 1,n=105,P<0.05);体质量与体长之间相关关系为W=0.040 6L^2.308...     

Correlated evolution of body and fin morphology in the cichlid fishes

Body and fin shapes are chief determinants of swimming performance in fishes. Different configurations of body and fin shapes can suit different locomotor specializations. The success of any configuration is dependent upon the hydrodynamic interactions between body and fins. Despite the importance of body–fin interactions for swimming, there are few data indicating whether body and fin configurations evolve in concert, or whether these structures vary independently. The cichlid fishes are a diverse family whose well‐studied phylogenetic relationships make them ideal for the study of macroevolution of ecomorphology. This study measured body, and caudal and median fin morphology from radiographs of 131 cichlid genera, using morphometrics and phylogenetic comparative methods to determine whether these traits exhibit correlated evolution. Partial least squares canonical analysis revealed that body, caudal fin, dorsal fin, and anal fin shapes all exhibited strong correlated evolution consistent with locomotor ecomorphology. Major patterns included the evolution of deep body profiles with long fins, suggestive of maneuvering specialization; and the evolution of narrow, elongate caudal peduncles with concave tails, a combination that characterizes economical cruisers. These results demonstrate that body shape evolution does not occur independently of other traits, but among a suite of other morphological changes that augment locomotor specialization.     

Dorsal fin in the white shark, Carcharodon carcharias: a dynamic stabilizer for fast swimming

Transverse sections of the skin in the dorsal fin of the white shark, Carcharodon carcharias, tiger shark, Galeocerdo cuvier, and spotted raggedtooth shark, Carcharias taurus, show large numbers of dermal fiber bundles, which extend from the body into the fin. The bundles are tightly grouped together in staggered formation (not arranged in a straight line or in rows). This arrangement of dermal fibers gives tensile strength without impeding fiber movement. Tangential sections indicate that the fibers in all three species are strained and lie at angles in excess of 60 degrees . Of the three species investigated the dermal fibers in C. carcharias are the most densely concentrated and extend furthest distally along the dorsal fin. The overall results indicate that the dorsal fin of C. carcharias functions as a dynamic stabilizer and that the dermal fibers are crucial to this role. The fibers work like riggings that stabilize a ship's mast. During fast swimming, when the problems of yaw and roll are greatest, hydrostatic pressure within the shark increases and the fibers around the body, including in the dorsal fin, become taut, thereby stiffening the fin. During slow swimming and feeding the hydrostatic pressure is reduced, the fibers are slackened, and the muscles are able to exert greater bending forces on the fin via the radials and ceratotrichia. In C. carcharias there is a trade-off for greater stiffness of the dorsal fin against flexibility.     

Retracted: Evolution and development of the homocercal caudal fin in teleosts

The vertebrate caudal skeleton is one of the most innovative structures in vertebrate evolution and has been regarded as an excellent model for functional morphology, a discipline that relates a structure to its function. Teleosts have an internally‐asymmetrical caudal fin, called the homocercal caudal fin, formed by the upward bending of the caudal‐most portion of the body axis, the ural region. This homocercal type of the caudal fin ensures powerful and complex locomotion and is thought to be one of the most important evolutionary innovations for teleosts during adaptive radiation in an aquatic environment. In this review, we summarize the past and present research of fish caudal skeletons, especially focusing on the homocercal caudal fin seen in teleosts. A series of studies with a medaka spontaneous mutant have provided important insight into the evolution and development of the homocercal caudal skeleton. By comparing developmental processes in various vertebrates, we propose a scenario for acquisition and morphogenesis of the homocercal caudal skeleton during vertebrate evolution.     

The effect of ration level and social rank on the development of fin damage in juvenile rainbow trout

The development and severity of fin damage was examined in groups of juvenile rainbow trout Oncorhynchus mykiss of different strength of feeding hierarchies. The development of dorsal and caudal fin damage over time was compared between four groups fed different ration levels (0·25, 0·5, 1·0 and 1·5% body weight day⁻¹) and between individuals of different feeding rank within each group. Dominance hierarchies were assessed from repeated daily measurements of food consumption of individuals using radiography. The feeding and growth data indicated that the strength of the social hierarchy weakened with increasing ration. Caudal fin damage developed with time in all groups whereas dorsal fin damage developed only under limited rations. The severity of both dorsal and caudal fin damage was significantly dependent on the ration size fed to the group, with lower ration groups sustaining more fin damage. The severity of dorsal fin erosion was greater than for the caudal fin. Within the two lower ration groups, subordinate fish suffered the most dorsal fin damage. The results suggested that the severity of dorsal fin damage within groups of juvenile rainbow trout can be used as an indicator of hierarchy Strength.