Linking anatomical and histological traits of the digestive tract to resource consumption and assimilation of omnivorous tetra fishes

This study explores the interplay between digestive tract traits, food intake, and assimilation in omnivorous tetra fishes (Psalidodon bifasciatus, P. aff. gymnodontus, and Bryconamericus ikaa) from the Iguaçu River basin, an ecologically significant region known for high endemism. We hypothesize that variations in digestive tracts across species would be associated with differences in diet, isotopic composition in fish tissues, and overall diet assimilation. To test this, we employed stereoscopic and light microscopy to characterize the gross anatomy, histomorphology, and histochemistry of fish digestive tracts. Additionally, we used stomach content and stable isotope analyses to trace fish diets. While these tetra fishes shared histological structures, disparities were noted in anatomical digestive traits and diet preferences. The smallest species, B. ikaa, with a shorter intestine, had fewer pyloric caeca and primarily consumed animal-based diets. Conversely, P. bifasciatus and P. aff. gymnodontus, with longer intestines, displayed numerous pyloric caeca and consumed a balanced mix of animal and plant items. Despite anatomical and dietary differences, all three species predominantly assimilated animal-origin food. The tetra fishes had histological variations among digestive tract segments, with the esophagus having the thickest muscular layer, gradually thinning towards the posterior intestine. The final portion of the intestine exhibited a significant expansion in the lumen perimeter, while the esophagus had the smallest lumen area. Goblet cells were most concentrated in the posterior intestine for all species. The gross anatomy of these tetra fishes aligns with their omnivorous habit, while diet assimilation was dominated by animal-origin food. These findings provide crucial insights into the structural and tissue characteristics of their digestive systems, laying the groundwork for deeper exploration into the physiological aspects of their digestive tracts and enhancing our understanding of their feeding strategies.

Epidermal club cells in the cardinal tetra (Paracheirodon axelrodi): Presence, distribution, and relationship to antipredator behavior

Epidermal club cells (ECCs) are present in many species of teleost fish. In an attempt to justify their presence in the epidermis of fish, they have been associated with numerous functions. One proposed function is communication with conspecifics during a predation event, as these cells may passively release substances upon rupture, which may occur during predation. We identified the presence and distribution of ECCs in the body skin of adult cardinal tetra, Paracheirodon axelrodi (Schultz, 1956) and analyzed the animal's behavioral response to conspecific skin extract in a laboratory setting. The identification and distribution of ECCs in the epidermis of the animals were confirmed by conventional histology and immunohistochemistry. Our results demonstrated that: ECCs are present in the skin of the entire body; a high density is observed in the dorsal side from head to tail, in the insertion of the fins and in the epidermis covering them; and ventral distribution is less extensive and more dispersed than dorsal distribution. Treatment of P. axelrodi specimens with skin preparations of conspecifics resulted in behavioral changes in the animals: they showed erratic swimming movements, they showed avoidance of the area of stimulus application and they decreased the time spent moving. Overall, these results allow us to conclude that P. axelrodi possesses ECCs throughout the body, with a greater presence in areas of high exposure to predation events (dorsal area and fins). Animals exposed to conspecific skin extract showed a significant increase in behaviors described as anti-predatory in other species. This supports the hypothesis that ECCs may be the origin of chemical alarm cues that are passively released when skin damage occurs, alerting the rest of the group to the risk of predation.

Comparative cytogenetics of microsatellite distribution in two tetra fishes Astyanax bimaculatus (Linnaeus, 1758) and Psalidodon scabripinnis (Jenyns, 1842)

Background

The main cytogenetic studies of the Characidae family comprise the genera Astyanax and Psalidodon involving the use of repetitive DNA probes. However, for the microsatellite classes, studies are still scarce and the function of these sequences in the genome of these individuals is still not understood. Thus, we aimed to analyze and compare the distribution of microsatellite sequences in the species Astyanax bimaculatus and Psalidodon scabripinnis.

Methods

We collected biopsies from the fins of A. bimaculatus and P. scabripinnis to perform cell culture, followed by chromosome extraction, and mapped the distribution of 14 microsatellites by FISH in both species.

Results and Discussion

The diploid number observed for both species was 2n = 50, with an acrocentric B microchromosome in A. bimaculatus and a metacentric B chromosome in P. scabripinnis. Regarding FISH, 11 probes hybridized in the karyotype of A. bimaculatus mainly in centromeric regions, and 13 probes hybridized in P. scabripinnis, mainly in telomeric regions, in addition to a large accumulation of microsatellite hybridization on its B chromosome.

Conclusion

Comparative FISH mapping of 14 microsatellite motifs revealed different patterns of distribution both in autosomes and supernumerary chromosomes of A. bimaculatus and P. scabripinnis, suggesting independent evolutionary processes in each of these species, representing excellent data on chromosome rearrangements and cytotaxonomy.

Oogenesis and in vitro reproduction of the twospot astyanax Astyanax bimaculatus (Linnaeus, 1758) exposed to conspecific alarm substance

Stress situations can be essential to trigger reproduction in fish; however, it may also inhibit it. One of those situations involves the release of the conspecific alarm substance (CAS), a natural stressor, into the water by specific fish epidermal cells after a predator attack. Little is known about the effects of that substance on fish reproduction. This study aimed to evaluate the effects of CAS exposure on the oogenesis and reproduction of the twospot astyanax Astyanax bimaculatus before the hormonal induction for artificial reproduction. No macroscopic or cellular changes in the ovaries were observed for the females exposed to CAS, and the oocyte stages show all females in the same phase of maturation (Spawning Capable). Females exposed to CAS spawned 20 min before the females without exposure. On the other hand, they ovulated only once, whereas the females from the control group ovulated multiple times for approximately two hours after hormonal induction. Moreover, the precocious ovulation of the females submitted to CAS did not generate offspring, since all generated zygotes did not develop. In contrast, the control group females produced more than 11 thousand healthy larvae. Exposing the female fish to CAS during their reproductive management in captivity may reduce breeding success.

Mitogenome of Knodus borki (Cypriniformes: Characidae): genomic characterization and phylogenetic analysis

BACKGROUND

The taxonomic status of Knodu in the family Characidae is not yet clear. This study aimed to address this by sequencing and annotating Knodu borki Zarske, 2008.

MATERIALS AND RESULTS

K. borki Zarske, 2008 was sequenced using a Hiseq platform and the complete mitogenome was assembled in SPAdes v3.15.2 and SOAPdenovo2 v.2.01. The mitogenome of K. borki from Guangzhou, the first sequenced species of the genus Knodu, is 16,837 bp in length and contains 13 protein-coding genes (PCGs), two ribosomal (r) RNAs, 22 transfer (t) RNAs, and one D-loop. Among these 37 genes, 28 are encoded by the heavy strand, while nine are encoded by the light strand. Twenty-one of the tRNAs can form typical cloverleaf secondary structures, except tRNA-Ser1, which lacks dihydrouridine arms. All PCGs have the same start codon (ATG), with the exception of COI (GTG). Four PCGs (ND1, ATP8, ND4L, and ND5) have TAA as the stop codon, ND6 has TAG as the stop codon, COI has AGG as the stop codon, and the remaining seven genes have incomplete stop codons of TA-/T-(ND2, COII, COIII, ND3, ND4, and Cyt b as T-, ATP6 as TA-). Phylogenetic analysis showed that K. borki belongs to the family Characidae.

CONCLUSIONS

Our findings demonstrate that K. borki belongs to the family Characidae, due to consistency with the morphological identification. This study provides molecular information for further research on the phylogeny of the genus Knodus and for analyses of the taxonomic status of Characidae.

Carbofuran affects behavior and metabolism of the Atlantic Forest lambari Deuterodon iguape, a native species from Brazil

One of the major causes of aquatic biodiversity loss is the contamination of the environment by pesticides. Even though there is a considerable amount of studies on the subject, there are still few that deal with the effects of carbofuran on native species in Brazil. Although carbofuran is widely used in Brazil, its action on native organisms, such as the Atlantic Forest lambari Deuterodon iguape, has not yet been studied. This work aimed to evaluate the effects of exposure to carbofuran on the fish D. iguape, considering the behavior and specific oxygen consumption as end points. Opercular movements, dorsal fin movements, and swimming speed were analyzed as behavioral parameters. To assess specific oxygen consumption, fish were subjected to concentrations of 0.0, 0.05, 0.1, 0.25, and 0.5 mg/L, for 24 h. For behavior analysis, fish remained exposed to carbofuran at concentrations of 0.0, 0.01, 0.05, 0.1, and 0.5 mg/L, in periods of 0, 2, 24, and 48 h. The behavior was studied through filming, analyzed with the free software, Tracker 4.92 (Open Source Physics). The results demonstrate an increase in opercular movements (18% ± 2.65) and a decrease in dorsal fin movements (- 21.2% ± 2.97), as well as in swimming speed (- 58.3% ± 1.83) of the experimental groups compared to the control group. There was an increase in oxygen consumption of 58.4% in fish exposed to the highest concentration of carbofuran. Thus, it is concluded that carbofuran altered D. iguape's behavior and oxygen consumption. The species was sensitive to carbofuran concentrations and can be used as a bioindicator.

Effects of intraspecific chemical cues on the behaviour of the bloodfin tetra Aphyocharax anisitsi (Ostariophysi: Characidae)

Chemical communication can induce a multitude of behaviours when detected by fish olfactory systems, from parental care, predation and alarm signalling, to foraging, schooling, reproduction, and migration. Chemical cues provide information that visual traits cannot and fish can respond to chemical cues without any additional sensory cue. In this way, pheromones play an essential role in the fitness of fishes. Given that Aphyocharax anisitsi inhabits environments characterized by cloudy and highly vegetated waters, it is interesting to evaluate the olfactory contribution in their communication. Here, we investigated the relevance of chemical cues in the types of behaviours triggered in A anisitsi by two experimental contexts: 1) non-social and olfactory context (conspecific-chemical cues), and 2) social context (conspecific female or male presence). Non-social context experiments suggest that males of A. anisitsi respond to both male and female-chemical cues even in the absence of other sensory inputs. The high olfactory sensitivity of characids in general and of A. anisitsi, in particular, could facilitate vital functions, such as foraging and conspecific recognition in habitats that impose severe restrictions on the visual system.

Mitochondrial genomes of five Hyphessobrycon tetras and their phylogenetic implications

To date, the taxonomic status and phylogenetic affinities within Hyphessobrycon, even among other genera in Characidae, remain unclear. Here, we determined five new mitochondrial genomes (mitogenomes) of Hyphessobrycon species (H. elachys, H. flammeus, H. pulchripinnis, H. roseus, and H. sweglesi). The mitogenomes were all classical circular structures, with lengths ranging from 16,008 to 17,224 bp. The type of constitutive genes and direction of the coding strand that appeared in the mitogenomes were identical to those of other species in Characidae. The highest value of the Ka/Ks ratio within 13 protein-coding genes (PCGs) was found in ND2 with 0.83, suggesting that they were subject to purifying selection in the Hyphessobrycon genus. Comparison of the control region sequences among seven Hyphessobrycon fish revealed that repeat units differ in length and copy number across different species, which led to sharp differences in mitogenome sizes. Phylogenetic trees based on the 13 PCGs did not support taxonomic relationships, as the Hyphessobrycon fish mixed with those from other genera. These data were combined to explore higher level relationships within Characidae and could aid in the understanding of the evolution of this group.

New insights into patterns and rates of tooth replacement in serrasalmid and characid fishes, with implications for the subsistence fishery of Peru's remote ribereños villages

We explored patterns, rates and unexpected socio-ecological consequences of tooth replacement in serrasalmids and characids of the Peruvian Amazon using microcomputed tomography. Of 24 specimens collected in February 2019, representing a mix of red-bellied piranha Pygocentrus nattereri, redeye piranha Serrasalmus rhombeus, silver dollar fish Ctenobrycon hauxwellianus and mojara Astyanax abramis, six individuals possessed edentulous jaw quadrants. On average, 22.9% of fish collected per day from these species featured incomplete dentition, a value three to five times higher than anticipated based on replacement rates estimated from captive fish, differences that may be driven by ontogeny, seasonality or environmental quality.

Mitochondrial Genome Structures and Phylogenetic Analyses of Two Tropical Characidae Fishes

The Characidae family contains the largest number of tropical fish species. Morphological similarities make species identification difficult within this family. Here, the complete mitogenomes of two Characidae fish were determined and comparatively analyzed with those of nine other Characidae fish species. The two newly sequenced complete mitogenomes are circular DNA molecules with sizes of 16,701 bp (Hyphessobrycon amandae; MT484069) and 16,710 bp (Hemigrammus erythrozonus; MT484070); both have a highly conserved structure typical of Characidae, with the start codon ATN (ATG/ATT) and stop codon TAR (TAA/TAG) or an incomplete T--/TA-. Most protein-coding genes of the 11 Characidae mitogenomes showed significant codon usage bias, and the protein-coding gene cox1 was found to be a comparatively slow-evolving gene. Phylogenetic analyses via the maximum likelihood and Bayesian inference methods confirmed that H. amandae and H. erythrozonus belong to the family Characidae. In all Characidae species studied, one genus was well supported; whereas other two genera showed marked differentiation. These findings provide a phylogenetic basis for improved classification of the family Characidae. Determining the mitogenomes of H. erythrozonus and H. amandae improves our understanding of the phylogeny and evolution of fish species.

Ecological impacts of pesticides on Astyanax jacuhiensis (Characiformes: Characidae) from the Uruguay river, Brazil

Brazilian freshwater ecosystems are continuously exposed to pesticides and domestic sewage. The Uruguay River was chosen for this study because of its international importance, as it flows through Brazil, Argentina, and Uruguay. It receives contaminants such as pesticides and domestic residues. Thus, the aim of this study to assess the accumulation of pesticides in muscle of the fish Astyanax jacuhiensis, its biochemical responses, and the presence of pesticides in water. In total, seven pesticides were registered in water from both river sites. Eight pesticides were detected in fish muscle. The biochemical responses showed that brain lipid peroxidation (LPO) and protein carbonyl (PC) in A. jacuhiensis were higher in the summer. Muscle showed the highest LPO levels in the spring and the highest PC in the summer. Liver LPO and PC levels were higher in the spring and summer. In the gills, the PC was higher in the spring and the LPO in the spring and winter. In the brain and in the gills, glutathione-S-transferase activity was high in the summer and autumn. Catalase activity was lower during the winter and spring. Non-protein thiol (NPSH) levels were lower in the brain in the winter and spring. Muscle tissue showed lower NPSH in the winter (site 1). Liver NPSH showed increased levels in liver in the spring and winter (site 2). The biochemical results clearly is related to pesticides and/or to the presence of other contaminants in the water such as metals or domestic sewage. The accumulation of pesticides in fish muscle added evidence that pesticides have been used in the area surrounding the Uruguay River. In conclusion, the biomarkers assayed in the present study could be used in future investigations considering other sampling sites along Uruguay River.

Riverscape properties contribute to the origin and structure of a hybrid zone in a Neotropical freshwater fish

Understanding the structure of hybrid zones provides valuable insights about species boundaries and speciation, such as the evolution of barriers to gene flow and the strength of selection. In river networks, studying evolutionary processes in hybrid zones can be especially challenging, given the influence of past and current river properties along with biological species-specific traits. Here, we suggest that a natural hybrid zone between two divergent lineages of the sexually dimorphic Neotropical fish Nematocharax venustus was probably established by secondary contact as a result of a river capture event between the Contas and Pardo river basins. This putative river capture is supported by hydrogeological evidence of elbows of capture, wind gaps and geological faults. The morphological (colour pattern) and genetic (mtDNA and RADseq) variation reveal a clinal transition between parental lineages along the main river, with predominance of F2 hybrids at the centre of the hybrid zone, absence of early generation backcrosses and different levels of hybridization in the tributaries. We highlight that different sources of information are crucial for understanding how the riverscape spatial history influences the connectivity between and within river systems and, consequently, the dynamics of gene flow between freshwater lineages/species.

Immune responses induced by inactivated vaccine against Aeromonas hydrophila in pacu, Piaractus mesopotamicus

Aeromonas hydrophila is responsible for outbreaks of a severe infectious disease in fish farms around the world and is one of the major causes of economic losses to the neotropical fish farmers. This study assessed the induction of immune responses and protection against A. hydrophila in pacu, Piaractus mesopotamicus, vaccinated through intraperitoneal and immersion route with inactivated virulent strain. Fish were randomly distributed in three vaccinated groups: intraperitoneal (i.p.) route; immersion; and immersion + booster; and control group (unvaccinated). All vaccination protocols used the concentration of 1.7 × 10⁸ CFU mL^-1 of inactivated A. hydrophila., and an oil adjuvant was used for vaccine prepararion for i.p. route vaccination. Blood and skin mucus from 9 fishes per treatment were collected at 14, 28, 42 and 84 days post-vaccination (DPV) for determination of lysozyme concentration in skin mucus, as well as antibodies anti-A. hydrophila in blood serum and skin mucus. Fish were challenged at 84 DPV with homologous and virulent strain of A. hydrophila for evaluation of resistance against bacterial infection. The results demonstrated that vaccination with inactivated A. hydrophila suspension by i.p. or immersion resulted in significant increase of skin mucus lysozyme and specific antibody levels in serum and skin mucus, at 28 and 42 DPV, and this increase in innate and adaptive immunity remained significant in pacu vaccinated through i.p. route up to 84 DPV. Although no significant differences were observed in the survival study, pacu vaccinated through i.p. route presented 31,33% of relative percentage survival (RPS) in LD_50-96h when compared unvaccinated fish challenged at 84 DPV. The results observed in this study indicate that vaccination programs with inactivated A. hydrophila, including booster doses by i.p. or immersion routes, could result in more effective protection in pacu against this bacteriosis, by increasing innate and adaptive mucosal and systemic immune responses.

Histopathological alterations in gills of a fish (Astyanax bifasciatus) in neotropical streams: negative effects of riparian forest reduction and presence of pesticides

The reduction of riparian vegetation around aquatic environments causes several physicochemical alterations and favors the entry of pesticides via surface runoff. Such changes have negative effects on aquatic organisms. In this study, we evaluated histopathological alterations in gills of Astyanax bifasciatus to test the hypothesis that more severe histopathological alterations occur in gills of fish from streams with higher agricultural impact from the surrounding area. The specimens were collected by electrofishing in seven streams of the lower Iguaçu basin between August 2015 and February 2016. The gills were processed according to routine histological methods and examined by light microscopy. The histopathological alterations, mainly stage II (lamellar aneurysm and total fusion of lamellae), were observed in fish collected in streams with higher agricultural activity. In these streams, the histopathological index indicated slight to moderate organ lesions. In contrast, in streams with more vegetation cover, fish collected presented stage I histopathological alterations (lamellar edema and lamellar hyperplasia), and the HI indicated normal functioning of the gills. In addition, chloride and acid mucous cells were more abundant in the gills of fish collected in rural streams. Our findings demonstrate that more severe histopathological alterations were registered in fish collected from streams with intense agricultural activity in the surrounding area. Therefore, it highlights that vegetation cover around the streams is a positive force for the conservation and health of aquatic organisms.

Determination of the ideal volume of activating solution and the optimal ratio of spermatozoa per oocyte for Prochilodus brevis fertilization

Prochilodus brevis is a rheophilic species with a threatened natural population that promotes studies aimed at optimizing reproduction in captivity. The correct quantity of inseminating dose and activating solution volume significantly improves fertilization rates, thereby increasing productivity in captivity. The objective of this study was to determine the proportion of sperm per oocyte and the ideal volume of activating solution to be used in the assisted fertilization of P. brevis. Gametes were collected and fertilization performed in two steps. In step 1, the ideal proportion of spermatozoa was determined based on the fertilization rate:oocyte by testing six doses of semen: D1 = 30 × 103, D2 = 150 × 103, D3 = 300 × 103, D4 = 3 × 106, D5 = 5 × 106, and D6 = 10 × 106. In step 2, the fertilization and hatching rates were evaluated using different volumes of activating solution (V1 - 25 ml, V2 - 50 ml, V3 - 75 ml,V4 - 100 ml, V5 - 125 ml, and V6 - 150 ml). A linear regression equation was estimated from steps 1 and 2. The Student-Newman-Keuls test was used to compare the means. In step 1, the percentage of fertilization increased linearly, reaching a plateau of 51.69%. In step 2, the best fertilization rates were obtained with an estimated ideal volume of 75.64 ml per 2 ml of oocytes. Therefore, the proportion of 928,410.29 sperm:oocyte, associated with the volume of 75.64 ml of water per 2 ml of oocytes, provided the maximum reproductive performance for P. brevis.

Ultrastructure of the fertilized egg envelopes in Hemigrammus erythrozonus, Characidae, Teleostei

We examined the morphology and ultrastructures of fertilized egg envelopes of glowlight tetra (Hemigrammus erythrozonus) belong to Characidae using light and electron microscopes.

The fertilized eggs were spherical, transparent, demersal, adhesive, and have no oil droplet. The perivitelline space was well-developed and the micropyle was surrounded by 15–20 uplifted lines of egg envelope in a spoke like pattern. The outer surface of egg envelope was rough side with grooves. Also, the total thickness of the fertilized egg envelope was about 2.1–2.3 μm, and the fertilized egg envelope consisted of two layers, an outer adhesive electron-dense layer with grooves and three feather-like lamellae layers. Collectively, these morphological characteristics of fertilized egg and micropyle with spoke-like structure showed family Characidae specificity, and ultrastructures of outer surface and section of fertilized egg envelope showed species specificity.

Comparison and optimization for DNA extraction of archived fish specimens

The DNA extracted from museum alcohol-fixed specimens can be a valuable source of information for solving taxonomic, phylogenetic, ecological and conservational questions. However, this type of DNA, also called ancient DNA, is routinely obtained in small portions and highly fragmented. We have tested two different extraction kits in museum type-specimens of the fish family Characidae. Aiming to increase the DNA yield, we made modifications on a Qiagen manufacturer protocol, in the elution step. Also, to overcome the issue of DNA fragmentation, we applied our efforts in Sanger sequencing, to find a highly variable and, in result, informative COI fragment. Based on our results, there is no correlation between amount of the DNA extracted and the age of the sample. The Sanger sequencing generated sequences which are useful in solving taxonomic puzzles. Here are presented the customization and guidelines that allowed us to recover DNA from the archived fish specimens.

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DNA extraction from archived fish specimens is more effective when using silica columns.

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Change of the elution times from minutes in room temperature to 24 h in freezer greatly improved the DNA yielded.

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Short but highly variable sequences replace the need to sequence the entire gene to identify a species.

Morphological and molecular characterisation of a new species of Gyrodactylus von Nordmann, 1832 (Monogenoidea: Gyrodactylidae) of cichlid fishes (Perciformes) from Mexico

Gyrodactylus mojarrae n. sp. is described from the gills of the Neotropical cichlids Thorichthys maculipinnis, Rocio octofasciata, Vieja zonata and V. fenestrata from several localities across southern Mexico. The new species is erected on the basis of the morphology of the haptoral elements (anchors, bars and hooks), and its phylogenetic position within the Gyrodactylidae is evaluated based on the analysis of partial sequences of the ITS1, 5.8 rRNA gene and ITS2. Gyrodactylus mojarrae n. sp. differs from other congeneric species by having hooks with a straight shaft and recurved point, pointed toe and convex heel, presence of reduced superficial anchor roots, by the number and disposition of spinelets of the male copulatory organ, and the absence of shield and lateral processes of the superficial bar. Molecular circumscription of isolates of G. mojarrae n. sp. from different host and hydrological basins showed that these isolates are conspecific and represent a distinct lineage from other congeners, including newly sequenced isolates of Gyodactylus sp. A and Gyrodactylus sp. B from Astyanax mexicanus (Characidae) and Gobiomorus dormitor (Eleotridae), respectively. Genetic affinities of Gyodactylus sp. A and B indicate that they might represent undescribed species infecting freshwater fish from the Americas.

Biochemical Responses in Freshwater Fish Exposed to Insecticide Propoxur

Although designed to control pests selectively, there is some evidence that environmental contamination by pesticides increases risks for humans and wildlife. In the present study, we evaluated biomarkers of oxidative stress in Astyanax jacuhiensis exposed to (5, 15 and 30 µg L^-1) of carbamate Propoxur (PPX) for 96 h. Glutathione S-transferase (GST) in liver and gills showed reduced activity in all PPX concentrations tested. Acetylcholinesterase (AChE) activities reduced in brain and muscle at concentrations 15 and 30 µg L^-1 of PPX. Lipid peroxidation (LPO) and hydrogen peroxide (HP) had no significant differences. In the brain, protein carbonyl (PC) increased in all groups treated with PPX. Although PPX is a selective pesticide, it causes oxidative damage and enzyme alteration in fish. This study pointed out some biomarkers that could be used to assess effects of environmentally relevant concentrations of pesticides, and infer about studies using fish as bioindicator.

Development of secondary sexual characters and their relationship to ontogeny and seasonal reproductive period in Hyphessobrycon igneus (Ostariophysi: Characiformes)

Sexual dimorphism in size, anal-fin shape and coloration of Hyphessobrycon igneus, Characidae, were examined. Males were more frequent at larger body sizes, confirming body size as a sexually dimorphic trait. Anal-fin shape and the colour of all fins were the same for females and juveniles, differing only in adult males. Likewise, only adult males had bony hooks on fin rays; larger and more sexually mature males had the most numerous and developed hooks and hooks were most developed in degree and number during peak reproductive periods. Fin hooks regressed in number and developmental degree after the reproductive period, but restarted development with the beginning of the new reproductive period without completely disappearing. Results show that bony hooks have a development and regression cycle related to reproductive seasonality.

Environmental pollution affects molecular and biochemical responses during gonadal maturation of Astyanax fasciatus (Teleostei: Characiformes: Characidae)

Endocrine disrupting compounds (EDCs) have the potential to alter fish reproduction at various levels of organization. The aim of this study was to assess the impact of a natural environment with heavily anthropogenic influence on the physiological processes involved in reproduction in the freshwater fish lambari (Astyanax fasciatus) using different biomarkers. Adult males and females were collected in different seasons from two distinct sites in the same watershed: Ponte Nova Reservoir (PN) considered a pristine or small anthropogenic influence reference point; and Billings Reservoir (Bil), subjected to a large anthropogenic impact. Biological indices, such as hepatosomatic index and gonadosomatic index (GSI), gonadal histomorphology, fecundity, and biomarkers such as plasma levels of estradiol (E2) as well as hepatic gene expression of its alfa nuclear receptor (ERα), were analyzed. Hepatic vitellogenin (VTG) gene expression was evaluated in both sexes, as an indicator of xenoestrogen exposure. Females collected at PN presented a typical annual variation reflected in GSI, whereas for those sampled at Bil the index did not change through the seasons. The higher concentration of E2 in males collected at Bil during spring/2013, together with the detection of VTG gene expression, suggest the presence of EDCs in the water. These EDCs may have also influenced fecundity of females from Bil, which was higher during winter and spring/2013. Gene expression of ERα and ovarian morphology did not differ between fish from both sites. Water conditions from Bil reservoir impacted by anthropic activity clearly interfered mainly with biomarkers of biological effect such as plasma E2 levels and absolute and relative fecundity, but also altered biomarkers of exposure as VTG gene expression. These facts support the notion that waterborne EDCs are capable of causing estrogenic activity in A. fasciatus.

The complete mitochondrial genome sequence of Astyanax paranae(Teleostei: characiformes)

Complete mitochondrial genome of the characiform fish Astyanax paranae was characterized in the present study. The whole mitogenome was 16,707 bp long and consisted of 13 protein-coding genes, 22 tRNAs, 2 rRNAs genes, a control region and origin of light-strand replication. The gene order is similar to those of the congeneric blind cavefish A. mexicanus. The nucleotide content of A. paranae mitogenome was 29.5% for A, 27.6% for T, 15.8% for G, 27.1% for C. Nucleotide identity between A. paranae and A. mexicanus across all the 37 genic regions ranged from 74.9% (ND2) to 90.3% (COX3).

The basement membrane and the sex establishment in the juvenile hermaphroditism during gonadal differentiation of the Gymnocorymbus ternetzi (Teleostei: Characiformes: Characidae)

Although there are several studies on morphogenesis in Teleostei, until now there is no research describing the role of the basement membrane in the establishment of the germinal epithelium during gonadal differentiation in Characiformes. In attempt to study these events that result in the formation of ovarian and testicular structures, gonads of Gymnocorymbus ternetzi were prepared for light microscopy. During gonadal development in G. ternetzi, all individuals first developed ovarian tissue. The undifferentiated gonad was formed by somatic cells (SC) and primordial germ cells (PGCs). After successive mitosis, the PGCs became oogonia, which entered into meiosis originating oocytes. An interstitial tissue developed. In half of the individuals, presumptive female, prefollicle cells synthesized a basement membrane around oocyte forming a follicle. Along the ventral region of the ovary, the tissue invaginated to form the ovigerous lamellae, bordered by the germinal epithelium. Stroma developed and the follicle complexes were formed. The gonadal aromatase was detected in interstitial cells in the early steps of the gonadal differentiation in both sexes. In another half of the individuals, presumptive male, there was no synthesis of basement membrane. The interstitium was invaded by numerous granulocytes. Pre-Leydig cells proliferated. Apoptotic oocytes were observed and afterward degenerated. Spermatogonia appeared near the degenerating oocytes and associated to SCs, forming testicular tubules. Germinal epithelium developed and the basement membrane was synthesized. Concomitantly, there was decrease of the gonadal aromatase and increase in the 3β-HSD enzyme expression. Thus, the testis was organized on an ovary previously developed, constituting an indirect gonochoristic differentiation.

Complete mitochondrial genome of the penguin tetra, Thayeria boehlkei

The penguin tetra (Thayeria boehlkei) is one of the most popular aquarium fish and belongs to the family of Characidae. The composition, phylogeny, and classification of this family are uncertain. Here, the complete mitogenome of T. boehlkei was reported to be 16,524 bp in length. It contains 13 protein-coding genes, 22 transfer RNA genes and 2 ribosomal RNA genes. Comparing the mitochondrial genome of T. boehlkei with its congener Astyanax mexicanus revealed high-sequence similarity. The mitochondrial genome of T. boehlkei will contribute to conservation studies and evolution analysis of Characidae family.

Complete mitochondrial genome sequence of Grundulus bogotensis (Humboldt, 1821)

The Grundulus bogotensis is an Endangered fish in Colombia. In this study, we report the complete mitochondrial DNA sequences of G. bogotensis. The entire genome comprised 17.123 bases and a GC content of 39.84%. The mitogenome sequence of G. bogotensis would contribute to better understand population genetics, and evolution of this lineage. Molecule was deposited at the GenBank database under the accession number KM677190.

The complete mitochondrial genome of the Piaractus brachypomus (Characiformes: Characidae)

The complete mitochondrial genome of the Piaractus brachypomus is described in the present study. The mitochondrial genome is 16,561 bp long and consists of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and a control region. The P. brachypomus mitochondrial genome shows the similar gene order and composition with those of most other vertebrates. The nucleotide compositions of the light strand in descending order is 31.57% of A, 26.19% of C, 26.18% of T and 16.06% of G. With the exception of the NADH dehydrogenase subunit 6 (ND6) and eight tRNA genes, all other mitochondrial genes are encoded on the heavy strand.

Grazing behaviour of a non-herbivorous characin: revisiting plasticity

Feeding behaviour and diet of Bryconamericus microcephalus differed between canopy conditions. At the open canopy site, a behavioural modification, grazing on algae, was observed. This was also reflected in gut content analysis and suggests behavioural plasticity in response to resource availability.