Scale-based landmark for internal organs assessments of common carp (Cyprinus carpio) during digital radiography and ultrasonography imaging.

Medical imaging techniques such as digital radiography and ultrasonography are non-invasive and provide precise results for examining internal organs and structures within fish. Their effectiveness can be further enhanced by using body parts like scales as markers for the organs beneath them. This study utilized the number of scales as landmarks in digital radiography and ultrasonography to non-invasively evaluate the muscles, bones, and images of internal and reproductive organs of common carp (Cyprinus carpio). Digital radiography was performed in the dorsoventral and lateral views of the fish, whereas ultrasonography was conducted in longitudinal and transverse views on sequence scale numbers with brightness and colour Doppler-modes. Digital radiography of the common carp revealed the whole-body morphology, including the bony parts from the head, pectoral fins, dorsal fins, pelvic fins, anal fins, and vertebrae to the tail that appeared radiopaque. Internal organs were also observed, with the swim bladder and heart appeared radiolucent, while the intestines, liver, testes, and ovaries appeared radiopaque. Ultrasonography in brightness mode displayed the digestive organs, reproductive organs, and muscle thickness. Additionally, colour Doppler mode demonstrated blood flow within the heart's ventricle.

Finotypic plasticity: Predator-induced plasticity in fin size, darkness and display behaviour in a teleost fish.

Fish fins are remarkable devices of propulsion. Fin morphology is intimately linked to locomotor performance, and hence to behaviours that influence fitness, such as foraging and predator avoidance. This foreshadows a connection between fin morphology and variation in predation risk. Yet, whether prey can adjust fin morphology according to changes in perceived risk within their lifetime (a.k.a. predator-induced plasticity) remains elusive. Here, we quantify the structural size of five focal fins in crucian carp (Carassius carassius) following controlled manipulations to perceived predation risk (presence/absence of pike Esox lucius). We also assess if crucian carp respond to increased predation risk by shifts in dorsal fin colouration, and test for differences in how fish actively use their dorsal fins by quantifying the area of the fin displayed in behavioural trials. We find that crucian carp show phenotypic plasticity with regards to fin size as predator-exposed fish consistently have larger fins. Individuals exposed to perceived predation risk also increased dorsal fin darkness and actively displayed a larger area of the fin to potential predators. Our results thus provide compelling evidence for predator-induced fin enlargement, which should result in enhanced escape swimming performance. Moreover, fin-size plasticity may evolve synergistically with fin colouration and display behaviour, and we suggest that the adaptive value of this synergy is to enhance the silhouette of deep-bodied and hard-to-capture prey to deter gape-limited predators prior to attack. Together, our results provide new perspectives on the role of predation risk in development and evolution of fins.

Integrated morphometric and molecular approaches to screen hybrid from wild Labeo rohita and Labeo catla parent populations.

BACKGROUND: Interspecific hybrids of rohu (Labeo rohita) and catla (Labeo catla) are common, especially in India due to constrained breeding. These hybrids must segregate from their wild parents as part of conservational strategies. This study intended to screen the hybrids from wild rohu and catla parents using both morphometric and molecular approaches. METHODS & RESULTS: The carp samples were collected from Jharkhand and West Bengal, India. The correlation and regression analysis of morphometric features are considered superficial but could be protracted statistically by clustering analysis and further consolidated by nucleotide variations of one mitochondrial and one nuclear gene to differentiate hybrids from their parents. Out of 21 morphometric features, 6 were used for clustering analysis that exhibited discrete separation among rohu, catla, and their hybrids when the data points were plotted in a low-dimensional 2-D plane using the first 2 principal components. Out of 40 selected single nucleotide polymorphism (SNP) positions of the COX1 gene, hybrid showed 100% similarity with catla. Concerning SNP similarity of the 18S rRNA nuclear gene, the hybrid showed 100% similarity with rohu but not with catla; exhibiting its probable parental inheritance. CONCLUSIONS: Along with morphometric analysis, the SNP comparison study together points towards strong evidence of interspecific hybridization between rohu and catla, as these hybrids share both morphological and molecular differences with either parent. However, this study will help screen the hybrids from their wild parents, as a strategy for conservational management.

Comparative study of the ciliary body and iris morphology in the anterior eye chamber of five different vertebrate classes.

One crucial component of the optical system is the ciliary body (CB). This body secretes the aqueous humour, which is essential to maintain the internal eye pressure as well as the clearness of the lens and cornea. The histological study was designed to provide the morphological differences of CB and iris in the anterior eye chambers of the following vertebrate classes: fish (grass carp), amphibians (Arabian toad), reptiles (semiaquatic turtle, fan-footed gecko, ocellated skink, Egyptian spiny-tailed lizard, Arabian horned viper), birds (common pigeon, common quail, common kestrel), and mammals (BALB/c mouse, rabbit, golden hamster, desert hedgehog, lesser Egyptian jerboa, Egyptian fruit bat). The results showed distinct morphological appearances of the CB and iris in each species, ranging from fish to mammals. The present comparative study concluded that the morphological structure of the CB and iris is the adaptation of species to either their lifestyle or survival in specific habitats.

Morphological examination of abdominal vertebral bodies from grass carp using high-resolution micro-CT scans.

The vertebral column, a defining trait of all vertebrates, is organized as a concatenated chain of vertebrae, and therefore its support to the body depends on individual vertebral morphology. Consequently, studying the morphology of the vertebral centrum is of anatomical and clinical importance. Grass carp (GC) is a member of the infraclass Teleostei (teleost fish), which accounts for the majority of all vertebrate species; thus, its vertebral anatomical structure can help us understand vertebrate development and vertebral morphology. In this study, we have investigated the morphology and symmetry of the grass carp vertebral centrum using high-resolution micro-CT scans. To this end, three abdominal vertebrae (V9, V10, & V11) from eight grass carp were micro-CT scanned and then segmented using Dragonfly (ORS Inc.). Grass carp vertebral centrum conformed to the basic teleost pattern and demonstrated an amphicoelous shape (biconcave hourglass). The centrum's cranial endplate was smaller, less circular, and shallower compared to the caudal endplate. While the vertebral centrum demonstrated bilateral symmetry along the sagittal plane (left/right), the centrum focus was shifted dorsally and cranially, breaking dorsoventral and craniocaudal symmetry. The sum of these findings implies that the caudal aspect of grass carp vertebral centrum is bigger and more robust. Currently, we have no information whether this is due to nature, for example, differences in gene expression, or nurture, for example, environmental effect. As the vertebral parapophyses and spinous processes are slanted caudally, the direction of muscle action during swimming may create a gradient of stresses from cranial to caudal, resulting in a more robust caudal aspect of the vertebral centrum. Expanding our study to include additional quadrupedal and bipedal (i.e., human) vertebrae, as well as testing if these morphological aspects of the vertebrae are indeed plastic and can be affected by environmental factors (i.e., temperature or other stressors) may help answer this question.

Herbivorous Juvenile Grass Carp (Ctenopharyngodon idella) Fed with Genetically Modified MON 810 and DAS-59122 Maize Varieties Containing Cry Toxins: Intestinal Histological, Developmental, and Immunological Investigations.

Feeding experiments with juvenile grass carp (Ctenopharyngodon idella) fed with genetically modified maize MON 810 or DAS-59122 dried leaf biomass were carried out with 1-, 3- and 6-month exposures. Dosages of 3-7 µg/fish/day Cry1Ab or 18-55 µg/fish/day Cry34Ab1 toxin did not cause mortality. No difference occurred in body or abdominal sac weights. No differences appeared in levels of inorganic phosphate, calcium, fructosamine, bile acids, triglycerides, cholesterol, and alanine and aspartame aminotransferases. DAS-59122 did not alter blood parameters tested after 3 months of feeding. MON 810 slightly decreased serum albumin levels compared to the control, only in one group. Tapeworm (Bothriocephalus acheilognathi) infection changed the levels of inorganic phosphate and calcium. Cry34Ab1 toxin appeared in blood (12.6 ± 1.9 ng/mL), but not in the muscle. It was detected in B. acheilognathi. Cry1Ab was hardly detectable in certain samples near the limit of detection. Degradation of Cry toxins was extremely quick in the fish gastrointestinal tract. After 6 months of feeding, only mild indications in certain serum parameters were observed: MON 810 slightly increased the level of apoptotic cells in the blood and reduced the number of thrombocytes in one group; DAS-59122 mildly increased the number of granulocytes compared to the near-isogenic line.

Histological effects of sublethal concentrations of insecticide Lindane on intestinal tissue of grass carp (Ctenopharyngodon idella).

This study investigates acute toxicity and histological effects of Lindane insecticide on intestinal tissues of immature grass carp (Ctenopharyngodon idella). For these purposes, 105 fish were exposed to different concentrations of Lindane for 96 h in 5 groups with 3 replications. Samples of intestinal tissues were prepared in both control and exposure groups during and after the toxicity test. Vaculation, necrosis, bleeding and epithelial degeneration were apparent in the intestine tissue of treated individuals. The LC50 96 h of Lindane was 0.788 ppm in the present study, also the results showed besides pesticide-induced lesions, symptoms of abnormal swimming, anxiety, tendency to swim near the surface, and death due to terminal toxicity with mouth widely open. The exposed fish were pale in color, showed oxygen deficit and severe respiratory problems. Overall, our results confirm the toxicity of different concentrations of Lindane insecticide affecting behavior, intestinal function and inducing tissue lesions of immature grass carp.

Two New Types of Homodiploid Fish and Polyploid Hybrids Derived from the Distant Hybridization of Female Koi Carp and Male Bighead Carp.

Bighead carps  (Hypophthalmichthys nobilis) and silver carps (Hypophthalmichthys molitrix) represent an important component of freshwater ichthiofauna in its native range, though they might become mass propagation in other systems (North America) and the reason of concern for fisheries management. Therefore, understanding their reproductive traits and particularly in the context of hybridization with other cyprinids was of value to explain their rapid propagation as well as potential benefits for aquaculture due to their unique diet, behavior, growth potential, and tolerance to deteriorating environmental conditions in freshwater ecosystems. Distant hybridization is an effective tool to create different ploidy offspring with changed phenotypes and genotypes. In this study, we reported distant hybridization of female koi carp (Cyprinus carpio haematopterus, KOC, 2n = 100) × male bighead carp (Hypophthalmichthys nobilis, BIC, 2n = 48) and the spontaneous occurrence of two new "crucian" carp-like homodiploid fish (2nGCC-L; 2nCCC-L; 2n = 100), a new type of triploid hybrid (3nKB, 3n = 124), and a new type of tetraploid hybrid (4nKB, 4n = 148). The body color of 2nGCC-L and 2nCCC-L were gray and multicolor, respectively. Both phenotypes were similar to the crucian carp (Carassius auratus). The difference was that their heads were rounder than those of the crucian carp and they had higher backs. Compared with the KOC with two pairs of barbels and BIC without barbel, 2nGCC-L, 2nCCC-L, and 4nKB had no barbel, but 3nKB had one pair of barbels. Microsatellite patterns and 5S rDNA sequences confirmed that 2nGCC-L, 2nCCC-L, and 3nKB were of hybrid origin. In regard to feeding, KOC was omnivorous and BIC was a typical filter-feeder. However, the 2nGCC-L, 2nCCC-L, and 3nKB were omnivorous. The formation of four kinds of new offspring is a groundbreaking finding in fish genetic breeding and evolutionary biology.

One- and double-layered furcellaran/carp skin gelatin hydrolysate film system with antioxidant peptide as an innovative packaging for perishable foods products.

In this study, two active packaging types were produced: single-layer biopolymer films with a polysaccharide - furcellaran and carp skin gelatin hydrolysate; two-layer films with identical composition, but synthetic peptide Alanina-Tyrosine addition. The procedure objective was multiplying antioxidant effects of the hydrolysate complexed with furcellaran. Films were used on Atlantic mackerel (storage 4 °C, 15 days); samples were analysed for changes in microbiological quality, TVB-N, biogenic amine content, fatty acid composition, TBARS. Consumer analysis was performed characterising mackerel carcass perception depending on implemented active coatings. The developed innovative single- and double-layer coatings effectively slow down lipid oxidation processes, especially at the initial period of Atlantic mackerel storage in refrigerated conditions. The coatings effectively inhibited microorganism growth, extending shelf-life by 2 days, single-layer coatings showing greater efficiency. According to consumers, coating application did not adversely affect product attractiveness parameters. The developed innovative coatings show great applicative potential as a new active packaging for perishable foods.

Effect of polysaccharides on the gel characteristics of "Yu Dong" formed with fish (Cyprinus carpio L.) scale aqueous extract.

A novel protein-based gel named "Yu dong" prepared with fish (Cyprinus carpio L.) scale aqueous extract and enhanced by polysaccharides is described in this study. The effects of pectin, alginate, and sodium carboxyl methyl cellulose (CMC-Na) on FS gel formation, stability, textural characteristics, microstructure, and water distribution were evaluated. The results indicated the viscosity of the FS gels decreased and changed slowly as the addition of pectin. While, the addition of alginate enhanced the formation of FS gels. As pectin addition in FS gels, the transition temperature decreased. When alginate and CMC-Na was added to the FS gels, the transition temperature increased. The addition of pectin, alginate, and CMC-Na to the FS gels significantly increased Gr from 44.5% to 71.99%, 61.86%, and 71.35%, respectively. Gel strength increased significantly as the addition of pectin, alginate, and CMC-Na. LF-NMR results showed that a moderate amount (0.2%) of polysaccharides bonded the protein and water more tightly, which was consistent with the SEM results showing gel structure with more uniform pores. This study provides a direct application of FS protein in preparing of gel food, which showing a better way to utilize the abandoned fish resource.

Developmental ecomorphology of the epibranchial organ of the silver carp, Hypophthalmichthys molitrix.

Silver carp regularly consume and digest particles of food as small as 5 µm. This ability drives their efficient consumption of phytoplankton and because they feed low on the food chain they have an important place in aquaculture worldwide. In North America, where they are considered invasive, silver carp deplete food resources for native species and in so doing occupy increased niche space. Here, we determine the ontogenetic stage and size at which silver carp are morphologically capable of primarily feeding on particles <10 µm. Ecological studies on this species have shown that there is an ontogenetic shift in diet as predominantly zooplanktivorous juveniles later switch to eating much smaller phytoplankton. The occupation of this new trophic niche presents both a metabolic and a mechanical challenge to these fish, since it is unclear how they can efficiently feed on such small particles. We hypothesize that the epibranchial organ (EBO) in silver carp is essential in aggregating these small particles of food, allowing the species to consume mass quantities of tiny particles, thus mitigating metabolic constraints. In this study, we investigate early ontogeny of the EBO in silver carp to determine when this structure achieves the requisite morphology to become functional. We find that at around 80 mm standard length (SL) the EBOs are consistently filled with food, demonstrating that this accumulating organ has become functional. This size corresponds with previous ecological data documenting important shifts in the type of food consumed. While the basic bauplan of the EBO is established very early in ontogeny (by 15 mm SL), multiple waves of histological maturation of muscle, cartilage, gill rakers and epithelium ultimately form the functional structure.

Three-dimensional characterization of osteocyte volumes at multiple scales, and its relationship with bone biology and genome evolution in ray-finned fishes.

Osteocytes, cells embedded within the bone mineral matrix, inform on key aspects of vertebrate biology. In particular, a relationship between volumes of the osteocytes and bone growth and/or genome size has been proposed for several tetrapod lineages. However, the variation in osteocyte volume across different scales is poorly characterized and mostly relies on incomplete, two-dimensional information. In this study, we characterize the variation of osteocyte volumes in ray-finned fishes (Actinopterygii), a clade including more than half of modern vertebrate species in which osteocyte biology is poorly known. We use X-ray synchrotron micro-computed tomography (SRµCT) to achieve a three-dimensional visualization of osteocyte lacunae and direct measurement of their size (volumes). Our specimen sample is designed to characterize variation in osteocyte lacuna morphology at three scales: within a bone, among the bones of one individual and among species. At the intra-bone scale, we find that osteocyte lacunae vary noticeably in size between zones of organized and woven bone (being up to six times larger in woven bone), and across cyclical bone deposition. This is probably explained by differences in bone deposition rate, with larger osteocyte lacunae contained in bone that deposits faster. Osteocyte lacuna volumes vary 3.5-fold among the bones of an individual, and this cannot readily be explained by variation in bone growth rate or other currently observable factors. Finally, we find that genome size provides the best explanation of variation in osteocyte lacuna volume among species: actinopterygian taxa with larger genomes (polyploid taxa in particular) have larger osteocyte lacunae (with a ninefold variation in median osteocyte volume being measured). Our findings corroborate previous two-dimensional studies in tetrapods that also observed similar patterns of intra-individual variation and found a correlation with genome size. This opens new perspectives for further studies on bone evolution, physiology and palaeogenomics in actinopterygians, and vertebrates as a whole.

Structure and function analysis of various brain subregions and pituitary in grass carp (Ctenopharyngodon idellus).

It has been generally acknowledged that environment could alter the morphology and functional differentiation of vertebrate brain. However, as the largest group of all vertebrates, studies about the structures and functions of various brain subregions in teleost are still scarce. In this study, using grass carp as a model, histology method and RNA-sequencing were recruited to examine the microstructure and transcript levels among different brain subregions and pituitary. Histological results showed that the grass carp brain was composed of six parts, including olfactory bulb, telencephalon, hypothalamus, optic tectum, cerebellum, and medulla oblongata. In addition, compared to elasmobranchs and non-teleost bony ray-finned fishes, grass carp lost the hypothalamo-hypophyseal portal system, instead the hypophysiotropic neurons were directly terminated in the pituitary cells. At the transcriptomic level, our results suggested that the olfactory bulb might be related to reproduction and immune function. The telencephalon was deemed to be involved in the regulation of appetite and reproduction. The optic tectum might play important roles in the vision system and feeding. The hypothalamus could regulate feeding, and reproduction process. The medulla oblongata was related with the auditory system. The pituitary seemed to play pivotal roles in energy metabolism, organ development and reproduction. Finally, the correlation analysis suggested that the hypothalamus and the telencephalon were highly related, and close anatomical connection and overlapping functions suggested that the telencephalon and hypothalamus might be the regulation center of feeding and reproduction among teleost brain. This study provided a global view of the microstructures and specific functions of various brain subregions and pituitary in teleost. These results will be very helpful for further study in the neuroendocrinology regulation of growth and reproduction in teleost brain-pituitary axis.

Experimental manipulation of perceived predation risk and cortisol generates contrasting trait trajectories in plastic crucian carp.

Most animals constitute potential prey and must respond appropriately to predator-mediated stress in order to survive. Numerous prey also adaptively tailor their response to the prevailing level of risk and stress imposed by their natural enemies, i.e. they adopt an inducible defence strategy. Predator exposure may activate the stress axis, and drive the expression of anti-predator traits that facilitate survival in a high-risk environment (the predation-stress hypothesis). Here, we quantified two key morphological anti-predator traits, body morphology and coloration, in crucian carp reared in the presence or absence of a predator (pike) in addition to experimental manipulation of physiological stress via implants containing either cortisol or a cortisol inhibitor. We found that predator-exposed fish expressed a deeper-bodied phenotype and darker body coloration as compared with non-exposed individuals. Skin analyses revealed that an increase in the amount of melanophores caused the dramatic colour change in predator-exposed fish. Increased melanization is costly, and the darker body coloration may act as an inducible defence against predation, via a conspicuous signal of the morphological defence or by crypsis towards dark environments and a nocturnal lifestyle. By contrast, the phenotype of individuals carrying cortisol implants did not mirror the phenotype of predator-exposed fish but instead exhibited opposite trajectories of trait change: a shallow-bodied morphology with a lighter body coloration as compared with sham-treated fish. The cortisol inhibitor did not influence the phenotype of fish i.e. neither body depth nor body coloration differed between this group and predator-exposed fish with a sham implant. However, our results illuminate a potential link between stress physiology and morphological defence expression.

Swim Bladder as a Novel Biomaterial for Cardiovascular Materials with Anti-Calcification Properties.

Calcification is a major cause of cardiovascular materials failure and deterioration, which leads to the restriction of their wide application. To develop new materials with anti-calcification capability is an urgent clinical requirement. Herein, a natural material derived from swim bladders as one promising candidate is introduced, which is prepared by decellularization and glutaraldehyde (GA) crosslinking. Data show that the swim bladder is mainly composed of collagen I, glycosaminoglycan (GAG), and elastin, especially rich in elastin, in accordance with higher elastic modulus in comparison to bovine pericardium. Moreover, the calcification of this material is proved dramatically lower than that of bovine pericardium by in vitro calcification assessments and in vivo assay using a rat subcutaneous implantation model. Meanwhile, good cytocompatibility, hemocompatibility, and enzymatic stability are demonstrated by in vitro assays. Further, a small diameter vascular graft using this material is successfully developed by rolling method and in situ implantation assay using a rat abdominal artery replacement model shows great performances in the aspect of higher patency and lower calcification. Taken together, these superior properties of swim bladder-derived material in anti-calcification, proper mechanical strength and stability, and excellent hemocompatibility and cytocompatibility endow it a great candidate as cardiovascular biomaterials.

Improving catalase stability by its immobilization on grass carp (Ctenopharyngodon idella) scale collagen self-assembly films.

We extracted collagen (CL) from the scales of Ctenopharyngodon idella and fabricated a CL self-assembly film. Catalase (CAT) was immobilized on the films using cross-linking, adsorption, and embedding methods. The activity and operational stability of immobilized CAT were investigated, along with the influence of the concentration of glutaraldehyde (GTA) and of the initial concentration of embedded CAT. The results showed that the CL triple helix remained intact. Differential scanning calorimetry data showed that the thermal stability of CL was significantly improved by neutral salt-induced self-aggregation and GTA cross-linking. The immobilized enzyme had high activity and good operational stability. When the enzyme concentration reached 0.5 mg/mL, immobilized enzyme activity of grass carp scales reached a maximum of 2596 U/g, and after twenty-two uses, enzyme activity remained above 50%, and it could be reused >45 times (CAT = 0.5 mg/mL, GTA = 5%, Temperature = 30 °C, pH = 7). Moreover, the optimum temperature and pH of immobilized CAT were 35 °C and 7, respectively, while the same for free CAT was 30 °C and 7, respectively. This indicated that immobilization of CAT has a protective effect.

Integrated analysis of long non-coding RNA and mRNA expression in different colored skin of koi carp.

BACKGROUND: Long non-coding RNAs (lncRNAs) perform crucial roles in biological process involving complex mechanisms. However, information regarding their abundance, characteristics and potential functions linked to fish skin color is limited. Herein, Illumina sequencing and bioinformatics were conducted on black, white, and red skin of Koi carp (Cyprinus carpio L.). RESULTS: A total of 590,415,050 clean reads, 446,614 putative transcripts, 4252 known and 72,907 novel lncRNAs were simultaneously obtained, including 92 significant differentially expressed lncRNAs and 722 mRNAs. Ccr_lnc5622441 and Ccr_lnc765201 were up-regulated in black and red skin, Ccr_lnc14074601 and Ccr_lnc2382951 were up-regulated in white skin, and premelanosome protein a (Pmela), Pmelb and tyrosinase (Tyr) were up-regulated in black skin. The expression patterns of 18 randomly selected differentially expressed genes were validated using the quantitative real-time PCR method. Moreover, 70 lncRNAs acting on 107 target mRNAs in cis and 79 lncRNAs acting on 41,625 target mRNAs in trans were investigated. The resulting co-expression networks revealed that a single lncRNA can connect with numerous mRNAs, and vice versa. To further reveal their potential functions, Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were analyzed, and membrane, pigment cell development, cAMP signaling, melanogenesis and tyrosine metabolism appear to affect skin pigmentation. Additionally, three lncRNAs (Ccr_lnc142711, Ccr_lnc17214525 and Ccr_lnc14830101) and three mRNAs (Asip, Mitf and Tyr) involved in the melanogenesis pathway were investigated in terms of potential functions in embryogenesis and different tissues. CONCLUSIONS: The findings broaden our understanding of lncRNAs and skin color genetics, and provide new insight into the mechanisms underlying lncRNA-mediated pigmentation and differentiation in Koi carp.

Manual fish length measurement accuracy for adult river fish using an acoustic camera (DIDSON).

Total lengths (LT ) of 50 free-swimming fish in a tank, silver carp Hypophthalmichthys molitrix and rainbow trout Oncorhynchus mykiss, were measured using a DIDSON (Dual-frequency IDentification SONar) camera. Using Sound Metrics software, multiple measurements of each fish (LT , side aspect angle and distance from the camera) at different times were analysed by two experienced operators while a subset of data was analysed by two inexperienced operators. The main result showed high variability in intra-fish LT measurements. The number of measurements required to minimise errors and to obtain robust fish measurements (true LT ± 3 cm) was estimated by a bootstrap method. Three to five measurements per fish were recommended for fish surveys in rivers. In this experimental study, aiming to reproduce river conditions, no evidence of fish position (side aspect angle and distance from the camera) effect was detected, but an operator effect (partially explained by training) was observed. General linear mixed models also showed that lengths of the smallest fish (LT < 57 cm) were overestimated and lengths of the largest fish (LT > 57 cm) were underestimated in comparison with their true lengths. In conclusion, we highlight that this technology, like any monitoring methods, returns imperfect observations. We advise DIDSON users to ensure that measurements are carried out correctly in order to draw accurate conclusion from this new technology.

Interfibril hydrogen bonding improves the strain-rate response of natural armour.

Fish scales are laminated composites that consist of plies of unidirectional collagen fibrils with twisted-plywood stacking arrangement. Owing to their composition, the toughness of scales is dependent on the intermolecular bonding within and between the collagen fibrils. Adjusting the extent of this bonding with an appropriate stimulus has implications for the design of next-generation bioinspired flexible armours. In this investigation, scales were exposed to environments of water or a polar solvent (i.e. ethanol) to influence the extent of intermolecular bonding, and their mechanical behaviour was evaluated in uniaxial tension and transverse puncture. Results showed that the resistance to failure of the scales increased with loading rate in both tension and puncture and that the polar solvent treatment increased both the strength and toughness through interpeptide bonding; the largest increase occurred in the puncture resistance of scales from the tail region (a factor of nearly 7×). The increase in strength and damage tolerance with stronger intermolecular bonding is uncommon for structural materials and is a unique characteristic of the low mineral content. Scales from regions of the body with higher mineral content underwent less strengthening, which is most likely the result of interference posed by the mineral crystals to intermolecular bonding. Overall, the results showed that flexible bioinspired composite materials for puncture resistance should enrol constituents and complementary processing that capitalize on interfibril bonds.

Updated functional segregation of retinal ganglion cell projections in the tectum of a cyprinid fish-further elaboration based on microelectrode recordings.

Single-unit responses of retinal ganglion cells (GCs) were recorded extracellularly from their axonal terminals in the tectum opticum (TO) of the intact fish (goldfish, carp). The depths of retinal units consecutively recorded along the track of the microelectrode were measured. At the depth of around 50 µm, the responses of six types of direction-selective (DS) GCs were regularly recorded. Responses of two types of orientation-selective (OS) GCs and detectors of white and black spots occurred approximately 50 µm deeper. Responses of GCs with dark- and light-sustained activity were recorded deeper than all others, at about 200 µm. The receptive fields of consecutively recorded units overlap, so they analyze the same fragment of the visual scene, focused by eye optic on the photoreceptor raster. The responses of pairs of DS GCs (ON and OFF units that preferred same direction of stimulus movement) and OS GCs (detectors of vertical and horizontal lines) were often simultaneously recorded at one position of the microelectrode. (The paired recordings of certain units amounted about fourth part of all recordings.) This suggests that their axonal arborizations are located close to each other in the tectal retinorecipient layer. Electrophysiological method, thus, allows to indirectly clarify and make precise the morphology of the retino-tectal connections and to establish a morpho-physiological correspondence.