BMP Signaling Gradient Scaling in the Zebrafish Pectoral Fin

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A specimen of Salmo trutta (Pisces: Salmonidae) possessing an additional dorsal fin

A specimen of brown trout, Salmo trutta , with a supernumerary dorsal fin located just posterior to the nape is documented from the Yarra River, Victoria, Australia.     

Effects of VIE tagging and partial tissue sampling on the immune response of three‐spined stickleback Gasterosteus aculeatus

A 14 day experiment on effects of visible implant elastomer (VIE) tagging and spine‐clipping of three‐spined stickleback Gasterosteus aculeatus showed significant increases in immune response, particularly in the granulocyte:lymphocyte ratio, in both treatments and the sham control. A minimum two‐week recovery after handling, anaesthesia, tagging and spine‐clipping is recommended to minimize effect of manipulation on the immune system.     

Function and structure in the paired fins of scorpaeniform fishes

Synopsis The paired fins of the basic, ancestral type of free-swimming acanthopterygian teleost serve primarily in guiding the forward course of movement and in maneuvering within the water column. In various scorpaeniform fishes the paired fins have taken on a number of other functions associated with a bottom-living mode of life. Among these are: defense against predation, probing for food items, propping the forward part of the body away from the bottom, progressing over it, digging into it, and the development of a suction disc for attachment to it. The relationship between these developments and paired-fin structure is the subject of the paper.     

Linking vertebral number to performance of aquatic escape responses in the axolotl (Ambystoma mexicanum)

Environmental conditions during early development in ectothermic vertebrates can lead to variation in vertebral number among individuals of the same species. It is often seen that individuals of a species raised at cooler temperatures have more vertebrae than individuals raised at warmer temperatures, although the functional consequences of this variation in vertebral number on swimming performance are relatively unclear. To investigate this relationship, we tested how vertebral number in axolotls (Ambystoma mexicanum) affected performance of aquatic escape responses (C-starts). Axolotls were reared at four temperatures (12–24 °C) encompassing their natural thermal range and then transitioned to a mean temperature (18 °C) three months before C-starts were recorded. Our results showed variation in vertebral number, but that variation was not significantly affected by developmental temperature. C-start performance among axolotls was significantly correlated with caudal vertebral number, and individuals with more caudal vertebrae were able to achieve greater curvature more quickly during their responses than individuals with fewer vertebrae. However, our results show that these individuals did not achieve greater displacements or velocities, and that developmental temperature did not have any effect on C-start performance. We highlight that the most important aspects of escape swim performance (i.e., how far individuals get from a threat and how quickly they move the most important parts of the body away from that threat) are consistent across individuals regardless of developmental temperature and morphological variation.     

Stem sarcopterygians have primitive polybasal fin articulation

Among osteichthyans, basal actinopterygian fishes (e.g. paddlefish and bowfins) have paired fins with three endoskeletal components (pro-, meso- and metapterygia) articulating with polybasal shoulder girdles, while sarcopterygian fishes (lungfish, coelacanths and relatives) have paired fins with one endoskeletal component (metapterygium) articulating with monobasal shoulder girdles. In the fin–limb transition, the origin of the sarcopterygian paired fins triggered new possibilities of fin articulation and movement, and established the proximal segments (stylopod and zeugopod) of the presumptive tetrapod limb. Several authors have stated that the monobasal paired fins in sarcopterygians evolved from a primitive polybasal condition. However, the fossil record has been silent on whether and when the inferred transition took place. Here we describe three-dimensionally preserved shoulder girdles of two stem sarcopterygians (Psarolepis and Achoania) from the Lower Devonian of Yunnan, which demonstrate that stem sarcopterygians have polybasal pectoral fin articulation as in basal actinopterygians. This finding provides a phylogenetic and temporal constraint for studying the origin of the stylopod, which must have originated within the stem sarcopterygian lineage through the loss of the propterygium and mesopterygium.     

The fish tail as a derivation from axial musculoskeletal anatomy: an integrative analysis of functional morphology

The adult morphology of the tail varies greatly among extant fishes despite sharing both ontogenetic similarities and the functional need to propel the body through a fluid medium. Both sharks (Chondrichthyes) and ray-finned fishes (Actinopterygii) control caudal fin musculature independently of axial body myomere activity to modify the stiffness and shape of their tails. For example, sharks and bony fishes possess different structural elements and muscles and move their tails in different ways, resulting in different locomotory hydrodynamic effects and a range of performance variables including speed and maneuverability. The stiffness of the heterocercal, lobate tail of the shark can be modulated during the tail beat resulting in nearly continuous thrust production. In contrast, the highly flexible tail of ray-finned fishes can be manipulated into many different shape conformations enabling increased maneuverability for these fishes. Consequently, the developmental, morphological, and functional derivation of the tail from the axial trunk has resulted in a diversity of form, the attributes of which may be of ecological and evolutionary significance.