Fin Shape, Asymmetry, and Evolutionary Ecomorphology in Triggerfishes and Filefishes (Superfamily: Balistoidea)

Triggerfishes and filefishes exhibit a wide range of fin and body morphologies, inhabit many marine habitats, and feed on a variety of benthic and pelagic organisms. Particular morphologies are predicted to provide functional advantages for swimming behaviors that facilitate life in diverse habitats and feeding guilds. Ecomorphological relationships can, in turn, inform evolutionary patterns of morphological convergence. We quantified morphological diversity of 80 balistoid species using geometric morphometrics and assigned each species a primary habitat and feeding mode. Results revealed strong evidence for evolutionary integration among body and fin shapes as well as widespread convergence of both high and low aspect ratio (AR) dorsal and anal fins, the fins that power steady locomotion in these fishes. Dorsal and anal fins were determined to be moderately to highly asymmetrical in most species. Families exhibited considerable overlap in fin and body shapes, but triggerfishes generally exhibited higher AR and more asymmetrical fins than filefishes. Fin asymmetry was not strongly associated with ecology. Planktivorous and offshore-pelagic species exhibited high AR dorsal and anal fins suitable for high endurance swimming performance, while benthic grazing and structured reef species exhibited convergence on low AR median fins more suitable for facilitating maneuverability.

Nothobranchius nikiforovi, a new species of seasonal killifish from the lower Matandu drainage in south-eastern coastal Tanzania (Cyprinodontiformes: Nothobranchiidae)

Nothobranchius nikiforovi, a new species known from seasonal habitats in the lower Matandu drainage in south-eastern coastal Tanzania is described. It is distinguished from all other congeners, except N. eggersi, by males presenting two colour phenotypes: the blue phenotype having a bright iridescent light blue to blue-green body, with narrow red-brown scale margins creating irregular reticulated pattern, forming chevron-shaped crossbars on the posteroventral portion of body and light blue median fins with red-brown dotted pattern; the red phenotype has a dark red head, light blue dorsal and anal fins proximally and medially, dark red distally, with dark red stripes parallel to the fin rays, and a plain dark red caudal fin. Nothobranchius nikiforovi differs from N. eggersi by male colour pattern, the blue phenotypes having median fins with dark grey distal portion, some of the rays of dorsal and anal fins with white tips (vs. median fins with distinct slender white distal band), and the caudal fin lacking a spotted pattern (vs. dots arranged into irregular curved stripes); the red phenotype with golden stripe between the nape and dorsal-fin origin (vs. light-blue stripe), the dorsal and anal fins with a plain red distal portion and lacking a light distal band (vs. with distinct narrow white distal band), the pelvic fin lacking a distal band (vs. with distinct slender light blue to white distal band), and some morphometric differences. Phylogenetic analyses also support the genetic distinction of the new species from its closest known relative, N. eggersi, and confirm its position in the N. guentheri species group within the Adiniops subgenus.

The role of Gdf5 in the development of the zebrafish fin endoskeleton

BackgroundThe development of the vertebrate limb skeleton requires a complex interaction of multiple factors to facilitate correct shaping and positioning of bones and joints. Growth and differentiation factor 5 (Gdf5), a member of the transforming growth factor-beta family (TGF-β) is involved in patterning appendicular skeletal elements including joints. Expression of gdf5 in zebrafish has been detected within the first pharyngeal arch jaw joint, fin mesenchyme condensations and segmentation zones in median fins, however little is known about the functional role of Gdf5 outside of Amniota.ResultsWe generated CRISPR/Cas9 knockout of gdf5 in zebrafish and analysed the resulting phenotype at different developmental stages. Homozygous gdf5 mutant zebrafish displayed changes in segmentation of the endoskeletal disc and, in consequence, loss of posterior radials in the pectoral fins. Mutant fish also displayed affected organisation and length of skeletal elements in the median fins, however joint formation and mineralisation process seemed unaffected.ConclusionsOur study demonstrates the importance of Gdf5 for the paired and median fin endoskeleton development in zebrafish and reveals that the severity of the effect increases from anterior to posterior side of the elements. Our findings are consistent with phenotypes observed in human and mouse appendicular skeleton in response to Gdf5 knockout, suggesting a broadly conserved role for Gdf5 in Osteichthyes.

Hydrodynamic Analysis for the Morphing Median Fins of Tuna during Yaw Motions

Tuna can change the area and shape of the median fins, including the first dorsal, second dorsal, and anal fins. The morphing median fins have the ability of adjusting the hydrodynamic forces, thereby affecting the yaw mobility of tuna to a certain extent. In this paper, the hydrodynamic analysis of the median fins under different morphing states is carried out by the numerical method, so as to clarify the influence of the erected median fins on the yaw maneuvers. By comparing the two morphing states of erected and depressed, it can be concluded that the erected median fins can increase their own hydrodynamic forces during the yaw movement. However, the second dorsal and anal fins have limited influence on the yaw maneuverability, and they tend to maintain the stability of tuna. The first dorsal fin has more lift increment in the erection state, which can obviously affect the hydrodynamic performance of tuna. Moreover, as the median fins are erected, the hydrodynamic forces of the tuna’s body increase synchronously due to the interaction between the body and the median fins, which is also very beneficial to the yaw motion. This study indicates that tuna can use the morphing median fins to adjust its mobility and stability, which provides a new idea for the design of robotic fish.

Postcranial skeletal development of Mugil cephalus (Teleostei: Mugiliformes): morphological and life-history implications for Mugiliformes

Within the fish taxon Mugiliformes, the larval development of Mugil cephalus has been studied most intensively, because it has the widest range of distribution among all mugilids and is of interest to aquaculture all over the world. Although numerous studies have dealt with larval rearing, growth and development, the osteological development of M. cephalus and mugiliforms in general has largely been neglected. Herein, we describe the skeletal development of mullets for the first time. Cleared and double-stained specimens of aquaculture-reared M. cephalus and wild-caught mugilid larvae were examined to describe the early development of the pectoral and pelvic girdle, the vertebral column and the caudal and median fins. The description of four embryonic and six larval developmental steps within the embryonic and larval period enables us to compare larval sizes of reared and wild-caught larvae. Ontogenetic fusions of ural centra 1 and 2 into a compound centrum, in addition to the fusion of two pterygiophores in the anal fin, have implications for the perception of the adult morphology. Moreover, comparison of mugilid development with that of other ovalentarian taxa shows that recent phylogenetic hypotheses need further morphological investigation.

The Shh/Gli3 gene regulatory network precedes the origin of paired fins and reveals the deep homology between distal fins and digits

One of the central problems of vertebrate evolution is understanding the relationship among the distal portions of fins and limbs. Lacking comparable morphological markers of these regions in fish and tetrapods, these relationships have remained uncertain for the past century and a half. Here we show that Gli3 functions in controlling the proliferative expansion of distal progenitors are shared among median and paired fins as well as tetrapod limbs. Mutant knockout gli3 fins in medaka (Oryzias latipes) form multiple radials and rays, in a pattern reminiscent of the polydactyly observed in Gli3 null mutant mice. In limbs, Gli3 controls both anterior-posterior patterning and cell proliferation, two processes that can be genetically uncoupled. In situ hybridization, quantification of proliferation markers, and analysis of regulatory regions reveal that in paired and median fins, gli3 plays a main role in controlling proliferation but not in patterning. Moreover, gli3 downregulation in shh mutant fins rescues fin loss in a manner similar to how Gli3-deficiency restores digits in the limbs of Shh mutant mouse embryos. We hypothesize that the Gli3/Shh pathway preceded the origin of paired appendages and was originally involved in modulating cell proliferation. Accordingly, the distal regions of median fins, paired fins, and limbs retain a deep regulatory and functional homology that predates the origin of paired appendages.