Divergent responses of Atlantic cod to ocean acidification and food limitation

In order to understand the effect of global change on marine fishes, it is imperative to quantify the effects on fundamental parameters such as survival and growth. Larval survival and recruitment of the Atlantic cod (Gadus morhua) were found to be heavily impaired by end-of-century levels of ocean acidification. Here, we analysed larval growth among 35–36 days old surviving larvae, along with organ development and ossification of the skeleton. We combined CO2treatments (ambient: 503 µatm, elevated: 1,179 µatm) with food availability in order to evaluate the effect of energy limitation in addition to the ocean acidification stressor. As expected, larval size (as a proxy for growth) and skeletogenesis were positively affected by high food availability. We found significant interactions between acidification and food availability. Larvae fed ad libitum showed little difference in growth and skeletogenesis due to the CO2 treatment. Larvae under energy limitation were significantly larger and had further developed skeletal structures in the elevated CO2 treatment compared to the ambient CO2 treatment. However, the elevated CO2 group revealed impairments in critically important organs, such as the liver, and had comparatively smaller functional gills indicating a mismatch between size and function. It is therefore likely that individual larvae that had survived acidification treatments will suffer from impairments later during ontogeny. Our study highlights important allocation trade-off between growth and organ development, which is critically important to interpret acidification effects on early life stages of fish

Evolution of a Functional Head Joint in Deep-Sea Fishes (Stomiidae).

The head and anterior trunk region of most actinopterygian fishes is stiffened as, uniquely within vertebrates, the pectoral girdles have a direct and often strong connection through the posttemporal to the posterior region of the skull. Members of the mesopelagic fish family Stomiidae have their pectoral girdle separated from the skull. This connection is lost in several teleost groups, but the stomiids have an additional evolutionary novelty-a flexible connection between the occiput and the first vertebra, where only the notochord persists. Several studies suggested that stomiids engulf significantly large prey items and conjectured about the functional role of the anterior part of the vertebral column; however, there has been no precise anatomical description of this complex. Here we describe a unique configuration comprising the occiput and the notochordal sheath in Aristostomias, Eustomias, Malacosteus, Pachystomias, and Photostomias that represents a true functional head joint in teleosts and discuss its potential phylogenetic implications. In these genera, the chordal sheath is folded inward ventrally beneath its connection to the basioccipital and embraces the occipital condyle when in a resting position. In the resting position (wherein the head is not manipulatively elevated), this condyle is completely embraced by the ventral fold of the notochord. A manual manipulative elevation of the head in cleared and stained specimens unfolds the ventral sheath of the notochord. As a consequence, the cranium can be pulled up and back significantly farther than in all other teleost taxa that lack such a functional head joint and thereby can reach mouth gapes up to 120°

Données histologiques sur l’os et les dents de deux poissons-dragons (Stomiidae, Stomiiformes) : Borostomias panamensis Regan & Trewavas, 1929 et Stomias boa Reinhardt, 1842

International audienceThe predatory mesopelagic fishes Borostomias panamensis and Stomias boa (Stomiidae) have typical sharp long fangs. The cross section of their teeth shows that the dentinous wall of the pulp cavity is smooth, contrary to the pleated wall found in several predatory fishes like e.g., Hoplias aimara (Erythrinidae), Anarhichas denticulatus (Anarhichadidae) or Lophius piscatorius (Lophiidae). Therewith, B. panamensis and S. boa lack the plicidentine layer in their teeth. We further confirm the acellular nature of the bone in Stomiidae, already signalled in 1859 by Kölliker for Chauliodus.Les deux espèces prédatrices, mésopélagiques, Borostomias panamensis et Stomias boa (Stomiidae), ont des dents effilées et pointues caractéristiques. Les parois de dentine de la cavité pulpaire ne sont pas plissées contrairement aux dents caniniformes de plusieurs autres téléostéens prédateurs tels que Hoplias aimara (Erythrinidae), Anarhichas denticulatus (Anarhichadidae) ou encore Lophius piscatorius (Lophiidae). Donc B. panamensis et S. boa n’ont pas de plicidentine dans leurs dents. Par ailleurs, nous confirmons l’acellularité des tissus osseux des Stomiidae, une caractéristique histologique signalée une première fois par Kölliker, en 1859, pour Chauliodu

Presence of the functional head joint mapped onto the latest molecular analysis [15] of the family Stomiidae.

<p>(A, B) Functional head joint absent in basal stomiids (blue box). The notochord does not overlap the basioccipital ventrally (small black box), e.g., in the cleared and double stained (c&s) specimen of (A) <i>Flagellostomias boureei</i>, BMNH 2002.8.5.786–788 and the histological sagittal section (hss) of (B) <i>Idiacanthus antrostomus</i>, SIO 97–85. (C–F) Intermediate stage of the functional head joint (red box), where the chordal sheath slightly overlaps the basioccipital ventrally (best seen in the histological sections (D, F). (C) <i>Grammatostomias dentatus</i>, USNM 234036 (c&s). (D) <i>Grammatostomias circularis</i>, NSMT-P 99317 (hss) and (E) <i>Bathophilus vaillanti</i>, USNM 234150 (c&s). (F) <i>Bathophilus filifer</i>, SIO 03–189 (hss). (G–P) Presence of the functional head joint (green box). The notochord overlaps the basioccipital ventrally in a resting position (G, I, K, M, O). Unfolding of the ventral sheath of the notochord during manipulative elevation of the head in c&s specimens (H, J, L, N, P). Green arrow heads indicate the two genera (<i>Aristostomias</i> and <i>Photostomias</i>) that have the occipital condyle composed of the exoccipitals and the basioccipital. (G) <i>Pachystomias microdon</i>, USNM 297922. (H) <i>Malacosteus australis</i>, USNM 296675. (I) <i>Aristostomias xenostoma</i>, USNM 296715. (J) <i>Photostomias</i> sp., USNM 296650. (K) <i>Eustomias obscurus</i>, USNM 206711. boc, basioccipital; c1, first centrum; exo, exoccipital; na1, first neural arch; nc, notochord. Scale bars, 1 mm.</p

Illustration of Fink’s [15] characters placing <i>Eustomias</i> as sister to <i>Bathophilus</i>+<i>Grammatostomias</i>.

<p>Cladogram according to Fink [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0170224#pone.0170224.ref015" target="_blank">15</a>]; left column, compound hypohyal; middle column, articulation of third epibranchial with fused third and fourth pharyngobranchials of dorsal gill arches; right column, bases of pectoral fin rays. All images show c&s specimens, except (D3) and (G3), which are modified drawings from Fink [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0170224#pone.0170224.ref014" target="_blank">14</a>]. (A) <i>Grammatostomias dentatus</i>, USNM 234036. (B1,2,4) <i>Bathophilus vaillanti</i>, USNM 234150. (B3) <i>Bathophilus filifer</i>, SIO 76–42. (C) <i>Eustomias obscurus</i>, USNM 206711. (D) <i>Pachystomias microdon</i>, USNM 297922. (E) <i>Photostomias</i> sp., USNM 296650. <i>Photostomias</i> lacks pectoral fin rays. (F) <i>Malacosteus australis</i>, USNM 296675. (G) <i>Aristostomias xenostoma</i>, USNM 296715. cl, cleithrum; co, coracoid; eb3, third epibranchial, hhd, dorsal hypohyal; hhv, ventral hypohyal; ra, radial; sc, scapula; pb3-4, fused pharyngobranchials 3+4; pfr, pectoral fin ray. Scale bars, 1 mm.</p

External and internal morphology of <i>Eustomias</i> spp.

<p>(A) <i>Eustomias fissibarbis</i>, USNM 270587. (B) X-ray of <i>Eustomias obscurus</i>, USNM 206711 showing a large, ingested myctophid.</p

Anatomy of the endocrine pancreas in actinopterygian fishes and its phylogenetic implications

Abstract The anatomy and organisation of the endocrine pancreas in ray-finned fishes vary widely. The two main morphoanatomical character states are diffuse versus compact pancreatic tissue. The latter are called Brockmann Bodies (BBs), or principal islets. The present study is the first comprehensive survey on the anatomy of the endocrine pancreas (diffuse versus compact) across 322 actinopterygian species in 39 orders and 135 families based on literature, specimen dissections, and Magnetic Resonance Imaging (MRI). The data obtained show that large endocrine pancreatic islets (BB) have appeared several times in teleost evolution: in some ostariophysian clades and within the Salmoniformes and Neoteleostei. Acanthomorpha (spiny-rayed fishes) is the largest clade of the Neoteleostei. Within this clade, an absence of BBs is only observed in flying fishes (Exocoetidae), parrotfishes (Scarinae), and some of the scarine relatives, the Labridae. The presence of BBs in examined jellynose fish species from the Ateleopodiformes indicates support for its sister-group relationship to the Ctenosquamata (Myctophiformes + Acanthomorpha). More investigations are still needed to corroborate the presence or absence of BBs as a putative synapomorphy for a clade comprising Ateleopodiformes and Ctenosquamata