The ultrastructure and calcification of the scales of Tilapia mossambica (Peters)

Summary The scales of Tilapia are surrounded by an envelope of scleroblasts responsible for the production of layers of collagen that constitute the bulk of the scale. The scleroblasts adjoining the lateral face of the oldest scale region gradually atrophy. New collagen layers are deposited against the inner face of the scale, the adjoining scleroblasts showing evidence of high metabolic activity. Calcification occurs by inotropic deposition of crystals alongside the fibres. There is no sharp demarcation between calcified and non-calcified scale regions, a calcification front gradually moving towards newly formed collagen layers. It is felt that fish scales should be considered as calcified derivatives of dermal collagen layers.     

The relative influence of local to regional drivers of variation in reef fishes

In this study, fishes and habitat attributes were quantified, four times over 1 year, on three reefs within four regions encompassing a c. 6° latitudinal gradient across south-western Australia. The variability observed was partitioned at these spatio-temporal scales in relation to reef fish variables and the influence of environmental drivers quantified at local scales, i.e. at the scale of reefs (the number of small and large topographic elements, the cover of kelp, fucalean and red algae, depth and wave exposure) and at the scale of regions (mean and maximum nutrient concentrations and mean seawater temperature) with regard to the total abundance, species density, species diversity and the multivariate structure of reef fishes. Variation in reef fish species density and diversity was significant at the regional scale, whereas variation in the total abundance and assemblage structure of fishes was also significant at local scales. Spatial variation was greater than temporal variation in all cases. A systematic and gradual species turnover in assemblage structure was observed between adjacent regions across the latitudinal gradient. The cover of red algae within larger patches of brown macroalgae (a biological attribute of the reef) and the number of large topographic elements (a structural attribute of the reef) were correlated with variation observed at local scales, while seawater temperature correlated with variation at the scale of regions. In conclusion, conservation efforts on reef fishes need to incorporate processes operating at regional scales with processes that shape local reef fish communities at local scales.     

Evidence of denticles and attachment fibres in the superficial layer of scales in two fishes: Carassius auratus and Cyprinus carpio (Cyprinidae, Teleostei)

An attempt is made to clarify the mechanisms of the scale anchorage in two Cyprinidae, the goldfish and the carp. Scanning and transmission electron microscope investigations
revealed the presence of two different structures, denticles and collagen fibre bundles involved in the anchoring processes. These strucures are located on the upper part of the
scales. Denticles form minute processes on the circuli of the anterior areas of the scales. Collagen fibre bundles arise from the superficial layer connecting the scale to the overlying dermis. These fibre bundles show structural similarities with the Sharpey's fibres and are named Sharpey-fibre-like bundles. Such fibres of attachment, not previously reported, can be considered as usual anchoring structures in fish scales.     

Structure of the dermal scales in gymnophiona (Amphibia)

Histology and cytology of dermal scales of the gymnophionans Ichthyophis kohtaoensis and Hypogeophis rostratus reveal their structure and the nature of their mineralization. Dermal scales are small flat disks set in pockets in the transverse ridges of the skin. Each pocket contains several scales of various sizes. A ring of “hypomineralization” of varying diameter may occur on scales of a particular dermal pocket but bears no relation to the diameter of these scales. Three different layers form the scales and are seen on sections perpendicular to the surface. The cells of the basal layer lie deepest. Each of the two or three more superficial fibrous layers is composed of bundles of fibres that are oriented in parallel. The orientation varies among layers. The striation of the fiber scales has a periodicity comparable to that of the surrounding dermal fibers. Squamulae form a discontinuous layer on the scale surface and are the only mineralized part of the scale. The minerals are deposited both on the collagen fibers passing from the fibrous layers into the squamulae, and in the interfibrillar spaces. Spherical concretions, either isolated or coalescent, reaching up to 1 μm, are found on the surface of the squamulae. The dermal scales of Gymnophiona present some analogies with those of evolved bony fishes. Their characteristics could make them an original model for the study of mineralization.     

鲤鱼鱼鳞在盐酸脱钙过程中的变化

鱼鳞主要由表层的钙化层和内部的胶原纤维层构成,为提取鱼鳞胶原蛋白,首先要脱除鱼鳞表面的钙化层。本文主要研究鲤鱼鱼鳞在盐酸脱钙过程中的变化。鱼鳞在盐酸脱钙过程中外部形态首先发生变化,钙化层溶解变薄,鱼鳞的柔软性增加。随着脱钙过程的进行,盐酸逐渐渗透到鱼鳞内部。经过盐酸处理后鱼鳞的力学性质发生很大的改变,断裂强度大大降低,只有原始鱼鳞的1/3~1/4。说明鱼鳞中以羟基磷灰石为主要成分的无机物层对保护鱼鳞起到了很大的作用,也为鱼鳞坚韧的质构发挥了重要的作用。     

Imaging scale surface topography of an endemic cyprinid fish,Garra sharq from the Arabian Peninsula: An integrated optical light and scanning electron microscopy approach

The optical light microscopy and scanning electron microscopy techniques have proven to play a key and noteworthy role in the advancement of morphological studies in general, and in investigating fish scale morphology in particular. These techniques have illustrated several hidden architectural structures in scales that contribute effectively to fish identification and classification. The scale morphological and topological characters such as type, size, shape, lateral surface, focus position, circuli appearance, radii type, lepidonts, and posterior and anterior margin shapes were obtained using macro- and microscopic analysis in six body regions for three size classes of Garra sharq, a cyprinid endemic fish of the Arabian Peninsula. The general scale type in the studied G. sharq species was a basal elasmoid cycloid and a sectioned type. As a protective structure, the scales display several specific characteristics including firm attachment to the fish body, overlapping, and thin structure with a high surface area and high strength. These characteristics improve scale resistance to penetration, increase protection against mechanical injury and microbial infection, enhance scale flexibility, reduce fish weight (reduce friction drag), and increase scale transparency. The scales demonstrate plasticity in focus shape, size, and position in the six fish body parts and fish size groups. The examined scales displayed narrow or wide grooves (radii) in three types including primary, secondary, and tertiary present in all four scale fields (anterior, posterior, and laterals), thus a tetra-sectioned type that is almost specific to the genus Garra. This characteristic also increases scale flexibility. The rostral margin of scales was characterized by the presence of waved and striate types. The lepidont shape and size varied being blunt, flat, pointed, tiny, sharp, short, and long. Some of these scale characters and their morphologies could be used as an alternative tool for identification, classification, and phylogenetic interpretation among the different freshwater fish species and genera.     

Reach and catchment‐scale characteristics are relatively uninfluential in explaining the occurrence of stream fish species

The objectives of this study were (1) to determine whether the presence or absence of prairie fishes can be modelled using habitat and biotic characteristics measured at the reach and catchment scales and (2) to identify which scale (i.e. reach, catchment or a combination of variables measured at both scales) best explains the presence or absence of fishes. Reach and catchment information from 120 sites sampled from 1999 to 2004 were incorporated into tree classifiers for 20 prairie fish species, and multiple criteria were used to evaluate models. Fewer than six models were considered significant when modelling individual fish occurrences at the reach, catchment or combined scale, and only one species was successfully modelled at all three scales. The scarcity of significant models is probably related to the rigorous criteria by which these models were evaluated as well as the prevalence of tolerant, generalist fishes in these stochastic and intermittent streams. No significant differences in the amount of reduced deviance, mean misclassification error rates (MER), and mean improvement in MER metrics was detected among the three scales. Results from this study underscore the importance of continued habitat assessment at smaller scales to further understand prairie‐fish occurrences as well as further evaluations of modelling methods to examine habitat relationships for tolerant, ubiquitous species. Incorporation of such suggestions in the future may help provide more accurate models that will allow for better management and conservation of prairie‐fish species.     

Scale morphogenesis and ultrastructure of dermis during embryonic development in the alligator (Alligator mississippiensis, Crocodilia, Reptilia)

Formation of scales in different body regions of embryonic alligators is described using light and electron microscopy. Transformation of the skin surface to produce scales takes place between stages 19 and 23, after which the shape of scales is complete over most of the embryonic surface. Scalation is not synchronous; different regions develop scales at different rates. Initially scales are formed on the back and dorsal side of the proximal tail and appear as undulations of the epidermis which form symmetrical (bumps) or asymmetrical (serrated) scale anlagen. No dermal condensations are apparent beneath the epidermis, although in some areas of the skin (belly, limbs) mesenchymal cells are more numerous within the bumps than in other areas. At stage 21, scalation has spread to the neck and belly but is absent or poorly developed over most areas of the flank, gular, jaw, limb and head regions. Grooves form between the outer edges of adjacent scales or interbump regions. A superficial denser dermis and a reticulated deep subdermis are visible in many scales from stage 21. The dermis forms a superficial loose and a deep dense layer from stage 22. Both loose and deep dermis, and sometimes the deep reticulate subdermis, move towards the surface to form the dermal core of scales, although the mechanism of this movement is not known. Bundles of collagen fibrils, with almost no elastic fibrils, are progressively deposited, especially in the denser dermis. At stage 22, the flank, gular and proximal areas of limbs form scales, but the head, jaw, distal limbs and digits still lack scales. The digits become scaled at stage 23 when scalation is well advanced in the other regions. By stage 24 most of the body is scaled and subsequent scale modifications occur only by growth. Five main types of scales are recognized by their shape: symmetrical scutes, asymmetrical scutes, overlapping scutes, tuberculate scales, and elevated asymmetrical scutes (tail verticils). Pigmentation, mainly due to epidermal melanocytes, is visible at embryonic stage 23 and progresses through stages 24 and 25.     

Structure and evolution of the horizontal septum in vertebrates

Although the horizontal septum (HS) has been identified as playing a role in fish biomechanics and in path finding of cells during zebrafish development, its morphology is poorly known. However, it is generally regarded as an evolutionarily conserved structure. To test this idea, we applied a novel combination of techniques to analyse the HS of 35 species from all major gnathostome clades in which is visualized its collagen fibre architecture. Results show that the HS is a conserved trait only with respect to the presence of caudolateral [= epicentral] and craniolateral [= posterior oblique] collagen fibre tracts, but differs remarkably with respect to the specifications of these tracts. Our data revealed several evolutionary changes within vertebrates. In the gnathostome ancestor, the two tracts are represented by evenly distributed epicentral fibres (ECFs) and posterior oblique fibres (POFs). ECFs are condensed to distinct epicentral tendons (ECTs) in the actinopteran ancestor. POFs independently evolved to distinct posterior oblique tendons (POTs) at least two times within teleosts. Within basal teleostomes, POFs as well as ECFs or ECTs were lost two times independently. POTs were lost at least three times independently within teleosts. This view of a homoplastic HS remains stable regardless of the competing phylogenies used for analysis. Our data make problematic any generalization of biomechanical models on fish swimming that include the HS. They indicate that the pathfinding role of the HS in zebrafish may be extended to gnathostome fishes, but not to agnathans, sarcopterygian fishes and tetrapods.     

Macro- and microscopic morphology of the flank scales of families Lutjanidae and Serranidae from the Persian Gulf Coral Reefs (Teleosts: Perciformes)

Macro- and microscopic characteristics of flank scales for 12 species were investigated from the Persian Gulf Coral Reefs. In Lutjanus argentimaculatus and L. russellii (family Lutjanidae), the scales of different flank regions were not different, while four characters showed variation in the scale of L. lutjanus i.e., scale shape (pentagonal, hexagonal and square), anterior margin (waved, scalloped and smooth), focus shape (circular and oblong) and focus position (postero-central and central), displayed variation. Scale type (ctenoid) and posterior margin (transforming ctenii) did not show variation and could be considered to be specific in this family. In Epinephelus chlorostigma (family Serranidae), the scales of flank regions did not display variation, while in E. areolatus, E. diacanthus and E. radiates, the scales showed considerable variation. The most variable characters were scale shape, posterior margin and focus shape. Therefore, in fish systematics studies on the base of scale, it is particularly important to compare scales from the same flank regions. Also, some criteria such as size-dependent alternation, ontogenetic changes and variation between flank regions, should be considered. This study supports the potential of scale morphology to help for the understanding of fish diversity in the coral reef ecosystem.     

Collagen Extract from Marine Finfish Scales as a Potential Mosquito Larvicide

Collagen is a peptide being utilized in medical, health care, nutrient and decorative industry. Marine fish scales are one of the good sources of collagen, which is extracted using the advanced enzymatic digestion method. Scales of Sardinella longiceps (Oil Sardine) have a high proportion of collagen. This product is well absorbed with broad adaptive values that encourage the inclusion of nutriments. In this paper, we have performed the isolation and characterization of collagen from S. longiceps fish scales. The unnecessary proteins on the surface of fish scales was removed by demineralization process. The fish scale collagen was extracted in two different methods: acid (acetic acid) and enzymatic (pepsin) technique. The molecular mass of the extracted collagen was determined using sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The absorption spectra of the extracted collagen was measured to estimate its amino acid (tyrosine) content. Fourier transform infrared (FTIR) spectrum showed the existence of bands corresponding to the collagen extracted from S. longiceps fish scale and the crystallinity of extracted collagen was obtained using X-ray diffraction (XRD) analysis. The morphological micrograph was also analyzed by scanning electron microscope (SEM). The anti-larval effect of the collagen extract was determined using mosquito larvae of Aedes aegypti (Ae. aegypti) and the activity was statistically significant.     

Scales and otoliths as identity cards of the Indian oil sardine Sardinella longiceps (Teleostei: Clupeiformes) populations: Ultrastructure and ornamentation characteristics using light and scanning electron microscopy

Scale and otolith morphology and morphometry of Indian oil sardine Sardinella longiceps (Clupeidae) were investigated and described using light and scanning electron microscopy from eight different body regions for scales and the right and left otoliths. Scales of the Indian oil sardine show general characteristics of the other studied clupeids sand that are easily distinguishable from other fish groups, by having striae in the posterior field. The studied cycloid scales of S. longiceps were classified into three types based on the overall shape including circular (e.g. true circular and cordate), pentagonal and quadrilateral in the different body regions. The circular shape was the most common shape (87.5%), while the quadrilateral and pentagonal forms constituted 6.25% each. The results also showed that the relative scale size (J-index) plays a desirable contribution in separating the examined populations. The results showed that the mean (or relative) scale size for all the eight regions in the Oman Sea population is larger than the Arabian Sea population. Also, another scale variable, the scale shape index (Si index), demonstrated variation (a mean of 0.86 to 1.1) in different regions of both populations from the Oman and Arabian Seas. Interestingly, here, we found that scale characters of S. longiceps not only differ from its other congeneric species, but also differ in the populations from both sides of the Oman Sea (Iran and Oman) and the Arabian Sea. It shows a positive signal for the presence of different taxonomic and management unit in the Oman and Arabian Seas. The idea should be approved by using integrated molecular and morphological traits. The otolith morphology of S. longiceps from the Oman and Arabian Seas was more conservative than the scales, which can be due to its function actin primarily as a balance organ and also enhancing hearing. The overall shape of S. longiceps otolith was lanceolate, with an elongated morphology and a well-developed rostrum, an ostial sulcus acusticus that opens to the anterior/ dorsal margin. These morphological characters are also found in the Iranian population of S. longiceps. However, otolith displayed variation in biometric parameters among two populations and left and right otoliths and the RRL parameter were important characters to discriminate the Oman and Arabian Sea populations. Thus, the structural/biometrical variability of the otoliths may be used for population distinctness, especially in water bodies with various environmental factors, and the otolith has turned out to be a useful tool to track the life history of teleostean fishes in environments with physicochemical gradients.     

Scales and Dermal Skeletal Histology of an Early Bony Fish Psarolepis romeri and Their Bearing on the Evolution of Rhombic Scales and Hard Tissues

Recent discoveries of early bony fishes from the Silurian and earliest Devonian of South China (e.g. Psarolepis, Achoania, Meemannia, Styloichthys and Guiyu) have been crucial in understanding the origin and early diversification of the osteichthyans (bony fishes and tetrapods). All these early fishes, except Guiyu, have their dermal skeletal surface punctured by relatively large pore openings. However, among these early fishes little is known about scale morphology and dermal skeletal histology. Here we report new data about the scales and dermal skeletal histology of Psarolepis romeri, a taxon with important implications for studying the phylogeny of early gnathostomes and early osteichthyans. Seven subtypes of rhombic scales with similar histological composition and surface sculpture are referred to Psarolepis romeri. They are generally thick and show a faint antero-dorsal process and a broad peg-and-socket structure. In contrast to previously reported rhombic scales of osteichthyans, these scales bear a neck between crown and base as in acanthodian scales. Histologically, the crown is composed of several generations of odontodes and an irregular canal system connecting cylindrical pore cavities. Younger odontodes are deposited on older ones both superpositionally and areally. The bony tissues forming the keel of the scale are shown to be lamellar bone with plywood-like structure, whereas the other parts of the base are composed of pseudo-lamellar bone with parallel collagen fibers. The unique tissue combination in the keel (i.e., extrinsic Sharpey''s fibers orthogonal to the intrinsic orthogonal sets of collagen fibers) has rarely been reported in the keel of other rhombic scales. The new data provide insights into the early evolution of rhombic (ganoid and cosmoid) scales in osteichthyans, and add to our knowledge of hard tissues of early vertebrates.     

Structure and composition of teleost scales from snakehead Channa argus (Cantor) (Perciformes: Channidae)

The structure of teleost scales from snakehead Channa argus was investigated using thermogravimetric analysis (TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive analysis of X-rays (EDAX), Fourier transform infra-red spectroscopy (FTIR) and X-ray diffraction (XRD). Thermal treatment of fish scales indicates that the fibrillary plate is partially calcified. SEM shows two kinds of scale denticles, arranged along the circuli in the anterior field and the lateral fields, respectively. TEM indicates the stratum laxum with abundant fibrils, chromatophores and capillary blood vessels within the scale covering, and shows the fibrillary plate as an 'orthogonal plywood structure' of stratified lamellae, consisting of 80–100 nm diameter collagen fibres co-aligned in individual lamellae and alternated by c. 90° of the fibre alignment between adjacent lamellae. EDAX, FTIR and XRD show that the mineral phase of the scales is a carbonated hydroxyapatite with a Ca:P molar ratio of 1·85.     

Scale-dependence of fish habitat associations in a North American river system

1. Determining the appropriate measurement scale to assess habitat variables is critical for ecologists assessing biological or ecological conditions. Depth, velocity, substrate, woody debris and other fish cover variables occur on both reach and microhabitat scales, and fish habitat associations with these variables may be scale-dependent. The aim of this work was to better understand the importance of scale for fish–habitat associations with these variables in a framework consistent with environmental filtering and to test the hypothesis that habitat variable importance is scale-dependent.
2. I used prepositioned areal electrofishing in wadeable streams of the Delaware River basin to evaluate the associations of fish with the same variables summarised on different reach and microhabitat scales. The importance of scale for fish–habitat associations was assessed using two approaches that approximate an environmental filtering framework: variance partitioning with (1) ordination and (2) generalised linear mixed models.
3. Variables on both the reach and microhabitat scales explained a significant fraction of the total variation in fish community composition (p < 0.05). Variation decomposition of reach- and microhabitat-scale effects revealed 20.2% and 2.0% of all variation were due uniquely to reach and microhabitat scales, respectively. Measures of coarseness, embeddedness, amount of riffle and areal coverage of five fish cover variables were significant explanatory variables of community composition at the reach scale only (p < 0.05). Velocity and mesohabitat (amount or presence of riffle) were the only two habitat features that were significant explanatory variables of fish community composition at both the reach and microhabitat scales (p < 0.05). Individual models of species occurrence revealed similar patterns as seen with analyses of community composition.
4. For many fishes, habitat features quantified at the reach scale were more explanatory than at the microhabitat scale. Longnose dace (Rhinichthys cataractae) were more dependent upon microhabitat variables than reach-scale variables, relative to other fishes. Mean velocity at the reach scale was the most important explanatory variable for explaining fish community composition and indicated support for the concept of environmental filtering at the reach and microhabitat scales.
5. Few studies of fish occurrence have incorporated a study design and analytical framework that approximates the hierarchical nature of habitat. This study identifies important scales and predictors, demonstrates the importance of a multiscale approach, and provides support for the environmental filtering concept at the reach and microhabitat scales. These findings will allow ecologists to better account for scale-dependent habitat associations and justify the use of fish habitat associations on reach and microhabitat scales for assessing biotic integrity, restoration and conservation of fishes.

     

Does compensatory growth modify fish scale shape?

Although the shape of fish scales is useful for determining stock membership, the role of extrinsic (e.g. habitat, food type) and intrinsic (e.g. growth) factors in determining variation in fish scales shape has not been determined. This study examined whether fish scale shape changes as a result of compensatory growth in juveniles of the cyprinid roach, Rutilus rutilus (L.) reared on a fish farm in the UK. This was analyzed using geometric morphometric methods. Sufficient evidence was generated to accept the assumption that food availability and type between different growing-out facilities resulted in compensatory growth and this was sufficient to cause scale shape differences. This was tested using multivariate analysis of variance (MANOVA) analysis with the principal components scores of specimens (PCs) as dependent variables, to investigate whether fish scale shape (where the configuration of landmark coordinates were scaled, translated and rotated) form (where the configuration of landmark coordinates were translated and rotated not scaled) and allometry free (allometrically adjusting scale shape according to length) are related to holding facility (as fixed factor). Cross validated discriminant analysis was used to assess and compare the efficacy of shape, form and allometry free information. Identification rates are much better than chance with allometry free and shape alone, and classification is improved when size is taken into account.     

辽宁中华弓鳍鱼(Sinamia)一新种

记述了辽宁西部九佛堂组和义县组中华弓鳍鱼一新种:辽宁中华弓鳍鱼Sinamia liaoningensis,并与该属的其他种进行了比较.新材料具有中华弓鳍鱼科的3个定义特征:单一的顶骨,三对额外肩胛骨和膜质翼耳骨短并与顶骨等长,无疑应归入该科.新种的后眶下骨较小,背鳍长大,鳞片菱形,因此,归入中华弓鳍鱼属.辽宁中华弓鳍鱼在以下几个方面不同于中华弓鳍鱼的5个已知种:体型短粗,吻骨较短,鼻骨近四方形,围眶骨较多(6),前鳃盖骨强烈弯曲,背鳍条较少(18),尾鳍条较多(16),臀鳍鳍基起点到鱼体背缘的鳞列较多(32),鳞片后缘不具锯齿,尾鳍具有纤维状的角质鳍条.     

Microstructure,mechanical, and biomimetic properties of fish scales from Pagrus major

The fish scale of Pagrus major has an orthogonal plywood structure of stratified lamellae, 1-2 microm in thickness, consisting of closely packed 70- to 80-nm-diameter collagen fibers. X-ray diffraction, energy-dispersive X-ray analysis, and infrared spectroscopy indicate that the mineral phase in the scale is calcium-deficient hydroxyapatite containing a small amount of sodium and magnesium ions, as well as carbonate anions in phosphate sites of the apatite lattice. The tensile strength of the scale is high (approximately 90 MPa) because of the hierarchically ordered structure of mineralized collagen fibers. Mechanical failure occurs by sliding of the lamellae and associated pulling out and fracture of the collagen fibers. In contrast, demineralized scales have significantly lower tensile strength (36 MPa), indicating that interactions between the apatite crystals and collagen fibers are of fundamental importance in determining the mechanical properties. Thermal treatment of fish scales to remove the organic components produces remarkable inorganic replicas of the native orthogonal plywood structure of the fibrillary plate. The biomimetic replica produced by heating to 873 K consists of stratified porous lamellae of c-axis-aligned apatite crystals that are long, narrow plates, 0.5-0.6 microm in length and 0.1-0.2 microm in width. The textured inorganic material remains intact when heated to 1473 K, although the size of the constituent crystals increases as a result of thermal sintering.