Transparent Bodies Research Articles

Simple Microfluidic Devices for <em>in vivo</em> Imaging of <em>C. elegans</em>, <em>Drosophila</em> and Zebrafish

Micro fabricated fluidic devices provide an accessible micro-environment for in vivo studies on small organisms. Simple fabrication processes are available for microfluidic devices using soft lithography techniques 1-3. Microfluidic devices have been used for sub-cellular imaging 4,5, in vivo laser microsurgery 2,6 and cellular imaging 4,7. In vivo imaging requires immobilization of organisms. This has been achieved using suction 5,8, tapered channels 6,7,9, deformable membranes 2-4,10, suction with additional cooling 5, anesthetic gas 11, temperature sensitive gels 12, cyanoacrylate glue 13 and anesthetics such as levamisole 14,15. Commonly used anesthetics influence synaptic transmission 16,17 and are known to have detrimental effects on sub-cellular neuronal transport 4. In this study we demonstrate a membrane based poly-dimethyl-siloxane (PDMS) device that allows anesthetic free immobilization of intact genetic model organisms such as Caenorhabditis elegans (C. elegans), Drosophila larvae and zebrafish larvae. These model organisms are suitable for in vivo studies in microfluidic devices because of their small diameters and optically transparent or translucent bodies. Body diameters range from ~10 μm to ~800 μm for early larval stages of C. elegans and zebrafish larvae and require microfluidic devices of different sizes to achieve complete immobilization for high resolution time-lapse imaging. These organisms are immobilized using pressure applied by compressed nitrogen gas through a liquid column and imaged using an inverted microscope. Animals released from the trap return to normal locomotion within 10 min. We demonstrate four applications of time-lapse imaging in C. elegans namely, imaging mitochondrial transport in neurons, pre-synaptic vesicle transport in a transport-defective mutant, glutamate receptor transport and Q neuroblast cell division. Data obtained from such movies show that microfluidic immobilization is a useful and accurate means of acquiring in vivo data of cellular and sub-cellular events when compared to anesthetized animals (Figure 1J and 3C-F 4). Device dimensions were altered to allow time-lapse imaging of different stages of C. elegans, first instar Drosophila larvae and zebrafish larvae. Transport of vesicles marked with synaptotagmin tagged with GFP (syt.eGFP) in sensory neurons shows directed motion of synaptic vesicle markers expressed in cholinergic sensory neurons in intact first instar Drosophila larvae. A similar device has been used to carry out time-lapse imaging of heartbeat in ~30 hr post fertilization (hpf) zebrafish larvae. These data show that the simple devices we have developed can be applied to a variety of model systems to study several cell biological and developmental phenomena in vivo.

Simple Microfluidic Devices for <em>in vivo</em> Imaging of <em>C. elegans</em>, <em>Drosophila</em> and Zebrafish

Micro fabricated fluidic devices provide an accessible micro-environment for in vivo studies on small organisms. Simple fabrication processes are available for microfluidic devices using soft lithography techniques. Microfluidic devices have been used for sub-cellular imaging, in vivo laser microsurgery and cellular imaging. In vivo imaging requires immobilization of organisms. This has been achieved using suction, tapered channels, deformable membranes, suction with additional cooling anesthetic gas, temperature sensitive gels, cyanoacrylate glue and anesthetics such as levamisole. Commonly used anesthetics influence synaptic transmission and are known to have detrimental effects on sub-cellular neuronal transport. In this study we demonstrate a membrane based poly-dimethyl-siloxane (PDMS) device that allows anesthetic free immobilization of intact genetic model organisms such as Caenorhabditis elegans (C. elegans), Drosophila larvae and zebrafish larvae. These model organisms are suitable for in vivo studies in microfluidic devices because of their small diameters and optically transparent or translucent bodies. Body diameters range from -10 μm to -800 μm for early larval stages of C. elegans and zebrafish larvae and require microfluidic devices of different sizes to achieve complete immobilization for high resolution time-lapse imaging. These organisms are immobilized using pressure applied by compressed nitrogen gas through a liquid column and imaged using an inverted microscope. Animals released from the trap return to normal locomotion within 10 min. We demonstrate four applications of time-lapse imaging in C. elegans namely, imaging mitochondrial transport in neurons, pre-synaptic vesicle transport in a transport-defective mutant, glutamate receptor transport and Q neuroblast cell division. Data obtained from such movies show that microfluidic immobilization is a useful and accurate means of acquiring in vivo data of cellular and sub-cellular events when compared to anesthetized animals (Figure 1J and 3C-F). Device dimensions were altered to allow time-lapse imaging of different stages of C. elegans, first instar Drosophila larvae and zebrafish larvae. Transport of vesicles marked with synaptotagmin tagged with GFP (syt.eGFP) in sensory neurons shows directed motion of synaptic vesicle markers expressed in cholinergic sensory neurons in intact first instar Drosophila larvae. A similar device has been used to carry out time-lapse imaging of heartbeat in -30 hr post fertilization (hpf) zebrafish larvae. These data show that the simple devices we have developed can be applied to a variety of model systems to study several cell biological and developmental phenomena in vivo.

Transparent Lu3NbO7 bodies prepared by reactive spark plasma sintering and their optical and mechanical properties

Transparent lutetium niobate (Lu3NbO7) bodies were prepared by reactive spark plasma sintering using Lu2O3 and Nb2O5 powders. Fully dense Lu3NbO7 bodies with density greater than 99.5% of the theoretical were obtained at 1300–1650°C. The grains steadily grew from 0.1 to 0.6μm with increasing sintering temperature from 1200 to 1450°C and significant grain growth from 2.2 to 9.2μm occurred at 1550–1650°C. The Lu3NbO7 body sintered at 1450°C showed the highest transmittance of 63% at 550nm after heat treatment at 850°C in air for 6h. Fully dense, submicron-size transparent Lu3NbO7 exhibited Vickers hardness of ∼13.0GPa and indentation fracture toughness of 1.0MPam1/2.

New seismo-stratigraphic and marine magnetic data of the Gulf of Pozzuoli (Naples Bay, Tyrrhenian Sea, Italy): inferences for the tectonic and magmatic events of the Phlegrean Fields volcanic complex (Campania)

A detailed reconstruction of the stratigraphic and tectonic setting of the Gulf of Pozzuoli (Naples Bay) is provided on the basis of newly acquired single channel seismic profiles coupled with already recorded marine magnetics gathering the volcanic nature of some seismic units. Inferences for the tectonic and magmatic setting of the Phlegrean Fields volcanic complex, a volcanic district surrounding the western part of the Gulf of Naples, where volcanism has been active since at least 50 ka, are also discussed. The Gulf of Pozzuoli represents the submerged border of the Phlegrean caldera, resulting from the volcano-tectonic collapse induced from the pyroclastic flow deposits of the Campanian Ignimbrite (35 ka). Several morpho-depositional units have been identified, i.e., the inner continental shelf, the central basin, the submerged volcanic banks and the outer continental shelf. The stratigraphic relationships between the Quaternary volcanic units related to the offshore caldera border and the overlying deposits of the Late Quaternary depositional sequence in the Gulf of Pozzuoli have been highlighted. Fourteen main seismic units, both volcanic and sedimentary, tectonically controlled due to contemporaneous folding and normal faulting have been revealed by geological interpretation. Volcanic dykes, characterized by acoustically transparent sub-vertical bodies, locally bounded by normal faults, testify to the magma uprising in correspondence with extensional structures. A large field of tuff cones interlayered with marine deposits off the island of Nisida, on the western rim of the gulf, is related to the emplacement of the Neapolitan Yellow Tuff deposits. A thick volcanic unit, exposed over a large area off the Capo Miseno volcanic edifice is connected with the Bacoli-Isola Pennata-Capo Miseno yellow tuffs, cropping out in the northern Phlegrean Fields.

Optical and electro-optical properties of (Pb,La)TiO3 transparent ceramics

(Pb1−xLax)TiO3 (PLT) ceramics were synthesized by solid-state reaction and densified by hot uniaxial pressed and pressureless sintering in order to reach optical transparency and characterize their electro-optical properties. Dense and transparent PLT ceramic bodies were obtained. In this work, significant changes in optical properties were observed with post-annealing temperature. The optical quality attained in the samples allowed the electro-optical coefficient to be determined for this system. Its value was comparable to those observed in other solid solutions of the transparent ferroelectric ceramic family.

The Application of Transparent Glass Sponge for Improvement of Light Distribution in Photobioreactors

A new concept for improving light dilution and light distribution in photobioreactors by applying transparent, openpored sponges was realized during cultivation experiments. A manufacturing process based on the polymer replica technique was established. A polyurethane template is impregnated with a nanoscaled SiO2 powder suspension (solids loading of 60 wt% at around pH 10) and dried. The green body is prepared by burning-out the polymer at 800°C. Subsequently the sintering of the remaining SiO2 structure to transparent cellular bodies is carried out at 1330°C. Many different factors influence the process. The slurry stabilization (viscosity, zeta-potential, pH) is important to generate a stable and self-supporting SiO2 shell around the template and achieve appropriate green bodies. The sintering temperature determines the transition of amorphous (transparent) into crystalline silica. The 8 ppi sponge has a porosity of 0.9, the specific surface area of 568 m-1 means an increase of the (inner) surface to volume ratio of the reactor. Porous glass has a very high surface to volume ratio (about 0.26 m2/g of glass at 10 μm pore size). Because of multiple and complex reflection of light into the porous glass, the algae can obtain light energy at any location of the total volume. First cultivation experiments in special designed Miniplate reactors show an increase in growth rate (about +25%) at low cell densities. The photo conversion efficiency was enlarged from 4.9% for the empty reactor to 5.6% and 5.9% for the 8 and 15 ppi sponge filled reactor. The effect and the improved efficiency of biomass build-up per applied light will be more apparent at high cell densities. Therefore concentration of the standard Tris-Phosphate (TP) medium (2.5 fold) and feeding are necessary.

Fabrication of transparent SiO2 glass by pressureless sintering and spark plasma sintering

Transparent SiO2 bodies were prepared by pressureless sintering (PLS) and spark plasma sintering (SPS). The effects of sintering and annealing temperature on the transmittance of the SiO2 bodies were investigated. The SiO2 bodies sintered by SPS and PLS at 1073–1573K were amorphous. With increasing the sintering temperature to 1673K, the SiO2 bodies sintered by PLS were crystallized while those sintered by SPS were still amorphous. The relative density of the SiO2 bodies sintered by SPS was 98.5% at 1373K and 100% at 1573K, whereas that sintered by PLS was 92.6% at 1373K and 98.9% at 1573K. The transmittance was 91.0% and 81.5% at a wavelength (λ) of 2μm for the SiO2 sintered bodies by SPS and PLS, respectively. In the ultraviolet range, the transmittance of the SiO2 bodies sintered by SPS at 1573K was about 40% at λ=200nm and increased to 75% after annealing at 1073K for 1h, which was about three times of the transmittance of the SiO2 bodies sintered by PLS (24.8%).

Swima (Annelida, Acrocirridae), holopelagic worms from the deep Pacific

Two new species of Swima, a recently established genus of annelid worms, are introduced, one from deep water off the North American West Coast and the other from the Philippines. The acrocirrid genus now contains three named species, Swima bombiviridis, Swima fulgida sp. nov., and Swima tawitawiensis sp. nov.Swima are holopelagic, occurring only in the water column, and thus far have only been observed below 2700 m. The worms are relatively large, sometimes reaching over 30 mm in length and 5 mm in width. They have gelatinous bodies and fans of long swimming chaetae, which are flattened into paddles in S. tawitawiensis sp. nov. Members of Swima are distinguished from other swimming acrocirrids by their transparent bodies, single medial subulate branchiae, and simple nuchal organs that do not skirt the bases of lateral subulate branchiae. Swima fulgida sp. nov. is distinguished from other members of the genus by its darkly pigmented anterior gut, whereas S. tawitawiensis sp. nov. is distinguished by possessing three subulate head appendages instead of just one and by the shape of its noto- and neurochaetae. Swima species possess four pairs of elliptical, transformed segmental branchiae that produce green bioluminescence when autotomized. These ‘bombs’ were observed in various states of regeneration on a single individual. Swima are neutrally buoyant, often observed hanging immobile in the water column, and are active, agile swimmers. Although not previously documented in the literature, these worms are not rare in the deep water column. Since the worms were first noticed in 2001, they have been observed on more than half of the Monterey Bay Aquarium Research Institute's midwater remotely operated vehicle dives that went to sufficient depth. The discovery of Swima underscores our lack of knowledge of deep pelagic fauna. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, 663–678.

Visualization of protein digestion in the midgut of the acarid mite Lepidoglyphus destructor

The ingestion of chromogenic or fluorescent substrates for protease detection enables the visualization of digestive processes in mites in vivo due to their transparent bodies. The substrates for protease detection were offered to Lepidoglyphus destructor, and the resulting signals were observed in specimens under a compound microscope. The protease activity was successfully localized using chromogenic substrates (azoalbumin, AAPpNA, SAAPFpNA, elastin-orcein, SA(3) pNA, ZRRpNA, ArgpNA, and MAAPMpNA) and fluorescent substrates (casein-fluorescein, albumin-fluorescein, AAPAMC, BAAMC, ZRRAMC, ArgAMC, and AGPPPAMC). No activity was detected using the keratin azure and BApNA substrates. In the mesodeum, trypsin-like activity generated by hydrolysis of the BApNA substrate was not observed, but the BAAMC substrate allowed the visualization of trypsin-like activity in food boli in the posterior mesodeum. The results indicate that cathepsins B, D, and G and cathepsin H or aminopeptidase-like activities are present in the midgut of L. destructor. Among these activities, cathepsin D-like activity was identified for the first time in the gut of L. destructor. All proteases mentioned are produced in the mesodeal lumen and form the food bolus together with ingested food, afterward passing through the gut to be defecated. The method used enables the visualization of protease activities in the gut of transparent animals.

Preparation of Optically Transparent Open‐Celled Foams and its Morphological Characterization Employing Volume Image Analysis

AbstractTransparent glass sponges are a new class of materials that can potentially be used for effective light dispersion in photobioreactors. In this work, transparent glass sponges are prepared by the polymer replica technique employing polyurethane sponges with cell sizes of 20 pores per inch as templates and commercially available nanoscaled SiO2 powders. Necessary conditions for obtaining transparent open‐celled glass sponges are presented. Topics such as slurry stabilization, temperature for burning‐out the polymer and subsequent sintering of the remaining SiO2 structure to transparent cellular bodies are discussed. It was found, that concentrated suspensions at around pH 10 offer suitable properties for both, bringing enough particles onto the polymer template for the formation of a stable and self‐supporting SiO2 shell and for successful sintering of the particulate framework to transparent bodies. Therefore, an adjusted burning‐out process and an adequate sintering regime is presented. Furthermore, the resulting sponge structure is characterized employing X‐Ray diffractometry, light, and scanning electron microscopy. In addition, volume image analysis was performed using magnetic resonance imaging. This method allows the calculation of geometrical parameters like cell‐size and specific surface area of the resulting structure, required for application of the new material.

Nanocrystalline Hydrous Zirconia from Zirconium Tungstate

Crystalline hydrous zirconia (ZrO2·2H2O) with volume-weighted average domain size of 1.5 nm was obtained by soaking zirconium tungstate (α-ZrW2O8) in boiling 1M NaOH solution for 5 h. The selected area electron diffraction pattern of hydrous zirconia particles could be indexed according to a tetragonal lattice with a=1.463(4) Å and c=2.535(6) Å. Upon heating to 60°C under a vacuum of 10−5 mbar, hydrous zirconia dehydrates reversibly. Further heating to 850° and 1000°C resulted in the formation of tetragonal and monoclinic zirconia, respectively. Some of the nanocrystalline hydrous zirconia produced from zirconium tungstate coalesced into transparent, nearly pore-free aggregates. The formation of these almost fully densified aggregates of hydrous zirconia, and the observed dehydration under very mild conditions, suggests that it could be possible to obtain transparent bodies of zirconia, with unprecedented small crystallite size, with the controlled deposition of the extremely small hydrous zirconia nanoparticles from a water-based suspension.

Pleistocene sediments of the eastern barents sea (Central Deep and Murmansk Bank Areas): Communication 1. Occurrence conditions and main structural features

The areal geological-geophysical study of Quaternary sediments was carried out in two areas of the eastern Barents Sea (Central Deep and Murmansk Bank). This communication is mainly dedicated to the results of seismoacoustic investigations. It has been established that the Quaternary sequence unconformably overlying the pre-Cenozoic strata in the studied areas is as follows (from bottom to top): marine-glaciomarine Late Glacial-Holocene sediments, massive diamictons (the main part of the section), and glaciotectonites formed after the underlying Mesozoic unconsolidated sediments. The Pleistocene diamictons, origin of which is still debatable, are the main studied object. They constitute two seismostratigraphic complexes (SSC). According to the accepted stratigraphic subdivision, they are represented by the Upper Weichselian SSC III (Maximum Last Glaciation) and Lower Weichselian SSC V (Middle Weichselian SSC IV is eroded here). Complexes SSC V and SSC III composed of till overlie the older sediments with the exaration unconformity. Complex SSC V is preserved locally, while SSC III is characterized by the regional distribution. Complex SSC III is universally enveloped unconformably without erosional surface by an acoustically uniform thin-bedded member of Late Glacial-Holocene glaciomarine and marine sediments (SSC II+I). Unlike SSC V, SSC III demonstrates lateral heterogeneity in both studied areas consisting of two seismofacies, one of which forms very specific acoustically transparent bodies (ATBs). Sediments of SSC III avoided subsequent erosion. Therefore, their glacial nature is distinctly reflected in the complex distribution of thickness and peculiar morphology of corresponding bodies.

Outside

When we love someone, we are attached to his or her surface colors, forms, warmth, movements. We avoid envisioning the inner organs and contents of his or her body. The external colors and patterns of other species are snares for our eyes.We can see nothing of what is behind our skin. We move, we act by not seeing, by not watching how we move. Nothing is more alien to us than the transparent bodies of box jellyfish.Our sensibility is turned outward. Our feet are long and set parallel; they are made to move on ahead. Nature is revealed to us through movement into it and movement with it. Our minds no longer grasp, appropriate, collect, legislate; they become rushes and rhythms and flows. They join the birds in the sky.

Numerical simulation of the effect of rarefied plasma flow on the solid surface

Based on the molecular dynamics method a numerical algorithm to calculate the effect of highenergy particles from the rarefied plasma flow on the surface of crystalline and amorphous solids is developed. Sizes and properties of generated defects are determined. It is shown that they can appreciably affect the optical properties of transparent bodies such as glass.

Fabrication of Transparent Lutetium Oxide by Spark Plasma Sintering

Transparent lutetium oxide bodies were fabricated by spark plasma sintering. The effects of sintering temperature, applied pressure, and holding time on the density, microstructure, and transmittance of these bodies were investigated. Nearly fully dense specimens were fabricated at above 1573 K and 100 MPa for 2.7 ks or at 1673 K and above 40 MPa for 2.7 ks. The grain size and transmittance steadily increased with increasing sintering temperature from 1273 to 1723 K and abnormal grain growth occurred above 1723 K, resulting in a decrease of density and transparency.

Extensive diel fish migrations in a deep ultraoligotrophic lake of Patagonia Argentina

Andean Patagonian lakes are ultraoligotrophic, highly transparent water bodies with very low densities of organisms at the different levels of their trophic food webs. Little is known about spatial distribution and habitat use by fish in these lakes. Hydroacoustic and active sampling techniques were used to study the distribution, composition, and displacement of organisms in an Andean lake throughout the diel cycle on two different moon phase days. Sound scattering layers (SSLs) were found both in the near-shore and pelagic habitats at different times of the day. These SSLs, formed by galaxiid larvae and adults, underwent displacement during the time periods of dawn and dusk, giving rise to the redistribution of organisms in the different habitats. The organisms show high sensitivity to light intensity, displaying different behaviors depending on moon phases. Extensive diel vertical migrations show that the deep pelagic habitats provide diurnal refuge for native galaxiids in Andean Patagonian lakes. Due to the high densities of galaxiid larvae and adults, it is likely that diel migrations generate an active flow of energy and matter between habitats, which could have a profound influence on whole lake dynamics.

Numerical simulation of passive and active solar strategies in buildings with complex topology

In this paper a numerical software, that simulates the building thermal behaviour with complex topology in transient conditions, was developed and used in the study of kindergarten thermal response and the occupants’ thermal comfort and air quality in Mediterranean conditions. In this numerical model a new building three-dimensional grid generation philosophy, closer to the reality, that considers the building and the surrounding buildings used in the long and short-wave calculus, the external and internal shading devices, the energy and mass balance integral equations philosophy generated by the building geometry, the equation system resolution done by the Runge-Kutta-Felberg with error control and the human thermal comfort level evaluated through human thermo-physiology, are developed. In the simulation, with a real occupation cycle, the compartments, the building opaque bodies, the building transparent bodies, and the external shading devices were considered. In passive strategies the kindergarten is equipped with multiple inclined aluminium shading devices placed above the transparent windows level and in front to the transparent door facing south, removable inclined tissue shading devices placed in front to the transparent windows facing east, and horizontal fabrics shading devices placed above the transparent panel levels facing south, south-west and west. In this study, made with natural and forced ventilation, the summer and winter conditions were used. In summer conditions, the forced ventilation active strategies in all spaces with cold air from the external environment during the night, and in occupied spaces with stored cold air from the underground space were used. In winter conditions forced ventilation from an internal greenhouse, to heat the internal occupied cold spaces, was used.

Intrinsic electromagnetic radiation shielding/absorbing characteristics of polyaniline-coated transparent thin films

The present study aims to investigate the electromagnetic wave transmission, reflection, and absorption characteristics of polyaniline (PANI)-coated transparent thin films. To investigate the intrinsic electromagnetic radiation shielding/absorbing characteristics of PANI-coated transparent thin films, the optical transmittance, sheet resistance, and electromagnetic interference (EMI) shielding efficiency (SE) of the films were systematically investigated. In addition, the applicability of an SE formula is checked by comparing the present experimentally measured SE values with calculated SE values. The results show the potential use of PANI-coated transparent thin films as an EMI shielding/absorbing material that satisfies both optical transmission and EMI SE requirements for transparent bodies such as windows or doorways of buildings.

The capacity for internal colour change is related to body transparency in fishes

Dear Sir, Chromatophores are large, stellate and spectacular pigment bearing cells, typically located in the skin, that generate body colouration. In many animals, melanocytes ⁄melanophores, the melanin containing chromatophores, are also present in various tissues inside the body, for instance in the ear, brain, abdominal cavity, around internal organs and skeleton. The presence of such internal pigmentation in puzzling as it is hidden from sight. While there is an enormous amount of studies and data on skin chromatophores, from the fine details of the motile machinery to animal behaviour (Aspengren et al., 2009), internal melanocytes have historically been largely ignored, until recently (Aoki et al., 2009; Brito and Kos, 2008; Randhawa et al., 2009; Yajima and Larue, 2008). Remarkably little is still known about their possible functions, and this uncertainty is problematic for the more general question of the role(s) of melanin in itself (Aspengren et al., 2009; Boissy and Hornyak, 2006; Braasch et al., 2009; Hill, 2000; Ito, 2009). While internal melanocytes are prevalent, internal erythrophores and xanthophores appear more uncommon. In fish, however, such cells can be found interspersed with melanocytes and reflective chromatophores in the highly pigmented peritoneum (the endothelium that covers the abdominal cavity) (Nilsson Skold et al., 2008). In juveniles, as well as in adults of species with relatively transparent bodies, internal chromatophores may actually contribute to the overall body colouration, as shown in two-spotted goby females, where abdominal trunk biopsies were analysed (Nilsson Skold et al., 2008). In fishes, skin patterns can be rapidly modified by aggregation or dispersion of the pigment-containing organelles inside the chromatophores present in the skin (i.e. physiological colour change) for background adaptation or signalling displays (Aspengren et al., 2009; Fujii and Oshima, 1994). In comparison, colour change in internal chromatophores has been largely ignored as it has been generally considered that they are not responsive (Boissy and Hornyak, 2006). However, melanocytes in the peritoneum and around the skeleton of the ice goby, Leucopsarion petersii, do indeed adapt to the background by pigment translocations in vivo and in biopsies, thus providing the first evidence for internal colour change (Goda and Fujii, 1996). Recent work on biopsies from the two-spotted goby showed that also internal erythrophores and xanthophores can be responsive (Nilsson Skold et al., 2008). As these examples come from relatively transparent species, it is possible that this phenomenon is more common than earlier believed, especially in species with some degree of body transparency. In order to test if a capacity for internal colour change was related to the degree of body transparency, and to reveal a possible function of these cells, we analysed the regulatory capability of peritoneal melanocytes in eight different teleost species, representing five different orders within the large super order Acanthopterygii and in one member of the super order Clupeomorpha, all with different degrees of body transparency. We used epinephrine and melatonin as potential pigment aggregating agents (see Appendix S1 for methodology). A positive relationship between body transparency and rate of internal colour change would suggest a special adaptive role for internal melanocytes in transparent fish species, and thus constitute a novel function for internal pigments. Our results showed that peritoneal melanocytes were present in all investigated fish species. Especially high densities were found in the gobies and in pipefish, plaice and herring (Figure 1A, B). Internal erythrophores and xanthophores were also observed in the gobies, pipefish and in plaice, but not in the other species. A capacity to regulate peritoneal melanocytes by melatonin and epinephrine was detected in six out of the eight species (Figure 1A, B and Table S1). In all species tested, peritoneal melanocytes had dispersed pigment from the start of the experiment. The epidermal melanocytes of sand goby, black goby and wrasse responded within 30 min, whereas plaice and pipefish only responded appreciably after 2 h. In herring, both controls and treated peritoneum biopsies showed a response after 30 min with an only moderate further

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