Determination of relative age using growth increments of scales as a minimally invasive method in the tropical freshwater Apteronotus leptorhynchus

This study describes a method for the determination of relative age in a tropical teleost, the brown ghost knifefish Apteronotus leptorhynchus. This method is based on identification of the maximum number of scale circuli, which is thought to be associated with the oldest scales, and thus to be the most indicative of the age of a given fish. Relative age can be inferred by relating differences in maximum circulus counts to the average rate of circulus addition, which was estimated at 34 circuli per year in adult fish through oxytetracycline marking. This method shows high inter‐investigator reliability and has a limited effect on fish because of the low number of scales required in order to determine the maximum number of circuli with a sufficiently high confidence level. Analysis of the frequency distribution of the circulus counts revealed periodic patterns that are similar among fish, presumably reflecting the environmental life history of the individuals. Regression analysis and comparison of addition rates showed that scale circulus counts and otolith ring counts are equivalent approaches for age estimation, but scale analysis is superior because of its limited invasiveness and the lower demand in terms of technical skills and expensive instrumentation.     

大鳞副泥鳅鳞片表面结构的扫描电镜观察

对大鳞副泥鳅的鳞片作了扫描电镜观察。结果表明,大鳞副泥鳅具圆鳞;基区、侧区和顶区均具有辐射沟及环沟,二者交织成网状,将鳞片分割成块状,可增加鳞片的柔软度;次级辐射沟发出部位可作为确定年轮的主要依据。     

低龄草鱼鳞片环纹的增长及幼轮和年轮特征的初步研究

幼草鱼鳞片环纹,以孵出后第二个月生长最快,往后生长减慢,冬季停止生长。幼鱼体长一般在47—70毫米形成幼轮。鳞片的“切割相”是区别年轮和幼轮的标志。幼鱼在饥饿时,环片不仅不增长,反而出现环片被吸收的现象。鳞片上各种副轮标记的形成与摄食条件的变化有关。计算了体长与鳞径、环纹数以及鳞径与环纹数的迴归方程,它们之间都呈直线正相关,相关显著性均在99%以上。       

Are scale circuli deposited daily in juvenile weakfish,Cynoscion regalis?

Synopsis Scale circuli of juvenile weakfish,Cynoscion regalis, were counted to determine if deposition was daily. Scale circuli counts were precise with little variation between counts (99% of the two counts from an individual scale were identical, N = 3580). Tetracycline marked juveniles (N = 71) had mean scale circuli deposition rates that were daily up to 24 d after marked. Data from several sources suggest that daily deposition of weakfish scale circuli occurred over a relatively narrow size range, approximately 14.3 to 111.9 mm standard length, however it is during this time that juvenile weakfish occupy estuarine nursery areas, where growth, mortality, and survival may alter subsequent year class strength. The estimated upper size limit at which scale circuli were no longer daily occurred over a wide range (82–142 mm standard length), and additional research is required to further clarify the limits of size and age of daily circuli deposition.     

Comparative morphology and scale formation in four species ofOncorhynchus during early life

Morphological divergence including scale formation in alevin and juvenile stages of masu (Oncorhynchus mason), coho (O. kisutch), chum (O. keta) and pink (O. gorbuscha) salmons reared in freshwater was investigated. Chum and coho salmons developed faster than the other species when raised at constant water tempertaure. Growth decreased suddenly at emergence from the gravel bed in all the four species. Morphology changed significantly from hatch through emergence to squamation. Two distinct morphological types were identified: the rotund type (masu and coho), and the streamlined type (chum and pink salmons). The former had well-developed parr marks, a deeper body and caudal peduncle, and higher relative growth coefficients, while the latter had parr marks which appeared only temporarily or never appeared, a slimmer body and caudal peduncle, and a more gradual and continuous change in morphology. Coho and chum developed squamation and formed circuli on scales considerably earlier than masu and pink salmons.     

The growth of Tilapia mossambica Peters (Pisces: Cichlidae) in Lake Sibaya, South Africa

The scales of Tilapia mossambica Peters * from Lake Sibaya show clear rings formed by broken, widely-spaced circuli in the anterior field. In order to determine the rate and time of scale ring formation, the number of circuli in the marginal increment was determined. Five scales from the pectoral region of 2223 fishes caught at regular intervals over two years were examined. When plotted as histograms, the number of circuli in the marginal increment showed a sharp movement to the left in September–October and again in January, indicating that the rings were formed during these months in the majority of fish examined. Pre- and postbreeding feeding migrations, and increases in condition factor, were associated with scale ring formation. Otoliths and opercula were also examined for age determination. Annual length increments were calculated for 450 T. mossambica collected throughout the year, and growth curves plotted. T. mossambica from Sibaya reach maturity after one year at a standard length of about 8 cm in females, and after two years at 10 cm in males. The breeding population had a standard length mode of 11–12 cm in females and 17 cm in males. The maximum final size was about 24 cm.     

Experimental investigation of the effects of temperature and feeding regime on scale growth in Atlantic salmon Salmo salar post-smolts

Salmo salar post-smolts were reared in seawater under controlled laboratory conditions for 12 weeks. The fish were exposed to three constant temperature treatments (15, 10.5 and 6°C) and four feeding treatments (constant feeding, food withheld for 7 days, food withheld for 14 days and food withheld intermittently for four periods of 7 days). Scale growth was proportional to fish growth across all treatments, justifying the use of scale measurements as a proxy for growth during the early marine phase. The rate of circuli deposition was dependant on temperature and feeding regime and was generally proportional to fish growth but with some decoupling of the relationship at 15°C. Deposition rates varied from 4.8 days per circulus at 15°C (constant feeding) to 15.1 days per circulus at 6°C (interrupted feeding). Cumulative degree day (^°D) was a better predictor of circuli number than age, although the rate of circuli deposition ^°D⁻¹ was significantly lower at 6°C compared with 15 and 10.5°C. Inter-circuli distances were highly variable and did not reflect growth rate; tightly packed circuli occurred during periods without food when growth was depressed, but also during periods of rapid growth at 15°C. The results further current understanding of scale growth properties and can inform investigations of declining marine growth in S. salar based on interpretations of scale growth patterns.     

Fine Structure of the Developing Scale in the Cichlid Hemichromis bimaculatus (Pisces,Teleostei, Perciformes)

The study of the formation and structure of the early teleost scale and its associated cells has been carried out on Hemichromis bimaculatus fry using in toto staining with alizarin and transmission electron microscopy techniques. Results of the study show very rapid scale formation in Hemichromis. The papilla of the scale differentiates a little in advance of the bone scale formation. No epidermal cells are involved in the constitution of the scale pocket made up of scleroblasts. In Hemichromis, as in other teleost scales, the osseous layer is the first one to be secreted by, presumably, only the scleroblasts. Then the scleroblasts specialize in their functions. Superficial ones are involved in the formation of osseous circuli; marginal scleroblasts are responsible for growth in diameter of the scale; while deep scleroblasts allow the scales to thicken owing to the progressive addition of collagen fibrils organized in a “plywood-like” structure which constitutes the fibrillary plate of the scale. Mineralization occurs very rapidly within the osseous layer in the form of hydroxyapatite-like crystal deposits. The fibrillary plate is not yet mineralized in Hemichromis at the stages studied here, but presumably is later. Results obtained in Hemichromis are discussed against similar data available in the literature on teleost scale formation.     

Studies on scale regeneration in the Common goby, Pomatoschistus microps (Pisces)

The longevity of original scales and the process and consequences of scale regeneration in the euryhaline Common goby, Pomatoschistus microps (Kroyer), has been studied by monthly sampling of two populations. Scale regeneration comprises four stages: formation of a new growth centre, a regenerated area in the form of a wide central irregular area lacking concentric circuli: formation of short and widely spaced circuli at the outermost region of the regenerated area: a check in regenerated scale growth on reaching the size of the original scales: and the commencement of normal growth similar to that of the surrounding original scales. Growth of regenerated scales within 30 days was not sufficient to attain the same size of the original ones. The average percentage of regenerated scales in successive months during the life span of P. microps is about 20% in immature fish and sharply increases up to about 60% of the total scales during the breeding season. The correlation between sharp increases in regenerated scales and the breeding season is also confirmed on examining scales from two other gobioid species, Gobius paganellus and Gobius cobitis. It is suggested that the loss of a large number of scales may result in the check in body growth during the breeding season.     

Capturing cross-scalar variation of habitat selection with grid sampling: an example with hazel grouse (Tetrastes bonasia L.)

The objective of this study was to investigate a grid-based sampling design to determine the cross-scalar selection of habitat by a territorial animal species: the hazel grouse (Tetrastes bonasia L.). In each of three sites with increasing hazel grouse nest site density, three lattice grids were used to measure both the habitat variables and the species occurrence in 100 30?×?30 m cells. We calculated the average values for habitat variables, as well as use versus non-use by the species, at three spatial scales: small (1?×?1 cell), intermediate (2?×?2 cells) and large (3?×?3 cells). Generalised linear mixed models were integrated into a method of variation and hierarchical partitioning and used to assess the relationship between the habitat variables and the species preferences at each scale. In all scales, species selection was associated with ground layer composition. Selection was also associated with the composition of the woody layer and negatively associated with dominance of tor grass (Brachypodium rupestre (Host) Roem. & Schult.) at the two larger scales. Both litter cover and thinning contributed positively to the habitat selection at the two smaller scales. The other variables were significant only at one scale or explained a relatively low proportion of the variation at multiple scales. Neither the management nor the stand structure variables played a significant independent role across scales when compared with ground layer variables. The total variation explained was highest (ca. 90 %) at the large scale. This finding indicates the possibility of obtaining cross-scalar hazel grouse preferences from grid-based sampling, provided that spatial autocorrelation in the data is handled appropriately.     

Trap cropping effect on oviposition behaviour of the leek moth Acrolepiopsis assectella and the diamondback moth Plutella xylostella

The potential of trap cropping as a pest control strategy was explored for two specialist moth species, where oviposition behaviour determines larval distribution. Oviposition behaviour was studied at three different scales: Individual plants in the laboratory, small scale field experiments with and without cages, and medium scale field trials. The study insects were the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), a specialist on Brassica species and the leek moth, Acrolepiopsis assectella (Z.) (Lepidoptera: Acrolepiidae), a specialist on Allium species. The diamondback moth preferred Indian mustard, Brassica juncea (L.) over white cabbage, B. oleracea var alba (L.). The leek moth did not show preference when offered leek, Allium porrum (L.) and chives, A. schoenoprasum (L.). However, the leek moth did prefer to oviposit on plants of a larger biomass over smaller plants. In both the small scale and the medium scale field studies the trap crops reduced the number of eggs laid on the primary crop. The total number of eggs laid in the monoculture and the trap crop treatments were the same in the small scale field cage study, but the females distributed their eggs differently. More eggs were laid on trap crops compared with primary crops and this pattern was also validated in the medium scale field trials. In this study only the direct effects of trap cropping were considered. Indirect effects of vegetation diversity such as enhancement of natural enemies could potentially increase the efficacy of trap cropping.     

Trap cropping effect on oviposition behaviour of the leek moth Acrolepiopsis assectella and the diamondback moth Plutella xylostella

The potential of trap cropping as a pest control strategy was explored for two specialist moth species, where oviposition behaviour determines larval distribution. Oviposition behaviour was studied at three different scales: Individual plants in the laboratory, small scale field experiments with and without cages, and medium scale field trials. The study insects were the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), a specialist on Brassica species and the leek moth, Acrolepiopsis assectella (Z.) (Lepidoptera: Acrolepiidae), a specialist on Allium species. The diamondback moth preferred Indian mustard, Brassica juncea (L.) over white cabbage, B. oleracea var alba (L.). The leek moth did not show preference when offered leek, Allium porrum (L.) and chives, A. schoenoprasum (L.). However, the leek moth did prefer to oviposit on plants of a larger biomass over smaller plants. In both the small scale and the medium scale field studies the trap crops reduced the number of eggs laid on the primary crop. The total number of eggs laid in the monoculture and the trap crop treatments were the same in the small scale field cage study, but the females distributed their eggs differently. More eggs were laid on trap crops compared with primary crops and this pattern was also validated in the medium scale field trials. In this study only the direct effects of trap cropping were considered. Indirect effects of vegetation diversity such as enhancement of natural enemies could potentially increase the efficacy of trap cropping.     

多齿蛇鲻鳞片表面结构的扫描电镜观察

本文对多齿蛇鲻鳞片表面结构进行扫描电镜观祭,描述了鳞纹、年轮形式、齿状粒突、辐射沟、伸缩缝、后区隆突和小棘。鳞纹嵴顶上的齿状粒突,其形态特征和排列方式可作为辅助鉴别疑难种类的依据。鳞纹和后区隆突上的伸缩缝,作者认为对鳞片的伸缩起着柔软缓冲作用。     

Macro- and microhabitat use of Telfair’s skink (Leiolopisma telfairii) on Round Island,Mauritius: implications for their translocation

The successful eradication of introduced rodents from islets off the coast of Mauritius has led to local conservation bodies investigating the possibility of translocation as a measure of safeguarding endemic reptile populations. The present study was the first to determine the habitat and microhabitat requirements of Telfair's skinks (Leiolopisma telfairii) on Round Island, Mauritius, with a view to aiding future translocation projects to islands within their historic range. Contrasting preferences found for Telfair's skink at macro- and micro- habitat levels underline the importance of sampling at multiple ecological scales in such investigations. Significantly fewer sightings of L. telfairii were recorded in bare rock habitats compared to more vegetated habitats. Conversely, at a microhabitat scale principal component analysis indicated structural characteristics were the primary determinant of microhabitat choice. The first dietary analysis of Telfair's skinks confirmed their status as omnivores. Cockroaches (Blattodea spp.) appeared to be a primary food source. Four exotic plant species were also present in faecal samples and the potential for L. telfairii to aid their dispersal is discussed. Implications for the long-term management and proposed translocation of Telfair's skinks are discussed.     

Functional response and progeny production of the Madeira mealybug parasitoid, Anagyrus sp. nov. nr. sinope: The effects of host and parasitoid densities

We tested the hypothesis that control of an herbivorous pest would be improved by providing floral resources for adult natural enemies. The herbivore was euonymus scale, Unaspis euonymi (Comstock) (Homoptera: Diaspididae), a serious pest of woody ornamental plants. The experimental landscape consisted of 3 × 3 m plots, each containing a central bed of Euonymus fortunei (Turcz.) that was infested with the scale. Floral resource plants were cultivars of four species that overlapped in bloom periods to provide a continuous supply of floral resources during summer: Trifolium repens L., Euphorbia epithymoides L., Coreopsis verticillata L. var. ‘Moonbeam,’ and Solidago canadensis L. var. ‘Golden Baby.’ Plots contained either low or high densities of all four species, or no resource plants. Densities of euonymus scale were typically lower in plots containing resource plants than in plots without them. Parasitism by Encarsia citrina (Craw.) (Hymenoptera: Aphelinidae) was rarely influenced by the experimental treatments, flower biomass, whole-plant biomass, or scale density, but in some cases was inversely correlated with density of scales within a generation and in the subsequent generation. Parasitism occasionally reduced densities of scales in plots containing resource plants, but this effect apparently was related to vegetative, not floral qualities of plants. A steady increase in parasitism rate over the three-year course of the experiment across the entire landscape was associated with decreasing density of scales, suggesting a numerical response by the parasitoid population. These findings suggest that the parasitoid is capable of effectively controlling euonymus scale in ornamental landscapes where environmental conditions are favorable.     

Scales Tell a Story on the Stress History of Fish

Fish faced with stressful stimuli launch an endocrine stress response through activation of the hypothalamic-pituitary-interrenal (HPI-) axis to release cortisol into the blood. Scientifically validated biomarkers to capture systemic cortisol exposure over longer periods of time are of utmost importance to assess chronic stress in governmental, wildlife, aquaculture and scientific settings. Here we demonstrate that cortisol in scales of common carp (Cyprinus carpio L.) is the long-sought biomarker for chronic stress. Undisturbed (CTR) and daily stressed (STRESS) carp were compared. Dexamethasone (DEX) or cortisol (CORT) fed fish served as negative and positive controls, respectively. Scale cortisol was quantified with a validated ultra-performance liquid chromatography tandem mass spectrometry method. An increase in scale cortisol content was found in STRESS and CORT but not in CTR and DEX fish. Scale cortisol content reflects its accumulation in a stressor and time dependent manner and validates the scale cortisol content as biomarker for chronic stress. Plasma analyses confirmed that (i) CTR, DEX and CORT treatments were effective, (ii) plasma cortisol of STRESS fish showed no signs of chronic HPI-axis activation, and (iii) plasma cortisol is a poor predictor for chronic stress. The expression of HPI key genes crf, pomc, and star were up-regulated in STRESS fish in the absence of a plasma cortisol response, as was the target gene of cortisol encoding subunit α1 of the Na⁺/K⁺-ATPase in gills. When lost, scales of fish regenerate fast. Regenerated scales corroborate our findings, offering (i) unsurpassed time resolution for cortisol incorporation and as such for stressful events, and (ii) the possibility to investigate stress in a well defined and controlled environment and time frame creating novel opportunities for bone physiological research. We conclude that the cortisol content in ontogenetic and regenerated scales is an innovative biomarker for chronic stress offering ample applications in science and industry.     

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.     

Invasion of the cosmopolitan species Echinochloa colona into herbaceous vegetation of a tropical wetland system

The negative effects of alien plant species on ecosystem structure and functions are increasingly recognised, and efforts to control these species are vital to restore degraded ecosystems and preserve biodiversity. However, we lack a full understanding of factors that determine alien species invasions along spatial gradients in herbaceous vegetation of tropical systems. We therefore examined the effects of community properties, environmental variables and human-related disturbance factors on the invasion of the alien grass Echinochloa colona (L.) Link at small- and large scales in the Kilombero Valley wetland, Tanzania. Generalized additive mixed models showed that E. colona abundance on a small scale was negatively related to above-ground biomass and evenness of resident species, whereas E. colona abundance was positively related to grazing intensity. On a large scale, biomass (negatively related to E. colona abundance) and distance to river (positive) were important in explaining E. colona abundance. These findings support the assertion that different factors may contribute to the invasion of alien plant species at different spatial scales, as also reported in many temperate systems. Overall, our results show that successful invasion of alien species is a function of plant community properties, human-related disturbance and favourable environmental conditions. Effective management strategies should consider mitigations that can increase the biomass and evenness of native species and a reduction of grazing pressure to restore the wetland and conserve biodiversity.     

The zebrafish scale as model to study the bone mineralization process

Danio rerio (zebrafish) shows high similarity with humans in terms of bone architecture, bone cells, matrix proteins and molecular signalling. The fish body is covered by elasmoid scales which are part of the dermal skeleton. Since few data have been published about the function of the fish scale cells, we investigated the mineralization pattern of the scale and the role of the episquamal osteoblasts in the neodeposition of the bone tissue. First, we described a specific mineralization pattern and distribution of the bone forming cells in different areas of the scale. We observed along the external circuli that, during the scale growth, the marginal cells migrate and organize in a cord-like structure just before the mineralization process takes place generating a new circulus. These cells exhibit alkaline phosphatase activity, a well known mammalian osteoblastic differentiation marker. The internal circuli are also characterized by new matrix deposition. Thus, zebrafish scale represents a useful model for analyzing the osteoblast behaviour during bone formation and mineralization and it could be useful in physiological studies and pharmacological tests.     

A multiple-scale analysis of host plant selection in Lepidoptera

Lepidoptera play an important role in terrestrial ecosystems as pollinators, as components of the food chain and as indicators for healthy ecosystems due to their sensitivity to change. Heterogeneous landscapes with variability of topographical features, vegetation structure combined with food sources for all life stages are the basis for successful lepidopteran oviposition. A multiple-scale analysis is proposed to understand the hierarchical relationships between selected site to plant characteristics and oviposition preferences for the dingy skipper (Erynnis tages). To achieve this goal, factors driving oviposition at the plant and patch scale were identified and scale dependencies at the site scale were assessed. At the plant scale, tallest host plants were used for oviposition; however relative egg height upon each plant was similar in both host plant species [bird’s-foot trefoil (Lotus corniculatus) and horseshoe vetch (Hippocrepis comosa)]. The main factors preferred by E. tages in L. corniculatus patches were sward height and percent of bare ground, and in H. comosa host plant density patches. Selected patches had slopes of greater gradients (mostly facing south) than patches with no selected host plants. At the site scale, oviposition patches were clustered at small scales and oviposition sites were dispersed at larger scales. Our study suggests that oviposition selection in E. tages is a hierarchical process varying from the site to the plant scale. Our study provides empirical evidence useful to inform landscape management strategies. These can be expanded to assess larger scale vegetation and habitat suitability beyond individual sites for systematic conservation planning.