Amazonian Fish Research Articles

Tissue distribution of appetite regulation genes and their expression in the Amazon fish Colossoma macropomum exposed to climate change scenario

Climate change leads to an increase in water acidification and temperature, two environmental factors that can change fish appetite and metabolism, affecting fish population in both wild and aquaculture facilities. Therefore, our study tested if climate change affects gene expression levels of two appetite-regulating peptides – Neuropeptide Y (NPY) and Cholecystokinin (CCK) – in the brain of tambaqui, Colossoma macropomum. Additionally, we show the distribution of these genes throughout the body. Amino acid sequences of CCK and NPY of tambaqui showed high similarity with other Characiformes, with the closely related order Cypriniformes, and even with the more distantly related order Salmoniformes. High apparent levels of both peptides were expressed in all brain areas, while expression levels varied for peripheral tissues. NPY and CCK mRNA were detected in all peripheral tissues but cephalic kidney for CCK. As for the effects of climate change, we found that fish exposed to extreme climate scenario (800 ppm CO2 and 4.5 °C above current climate scenario) had higher expression levels of NPY and lower expression levels of CCK in the telencephalon. The extreme climate scenario also increased food intake, weight gain, and body length. These results suggest that the telencephalon is probably responsible for sensing the metabolic status of the organism and controlling feeding behavior through NPY, likely an orexigenic hormone, and CCK, which may act as an anorexigenic hormone. To our knowledge, this is the first study showing the effects of climate change on the endocrine regulation of appetite in an endemic and economically important fish from the Amazon. Our results can help us predict the impact of climate change on both wild and farmed fish populations, thus contributing to the elaboration of future policies regarding their conservation and sustainable use.

Investigating the mechanisms of dissolved organic matter protection against copper toxicity in fish of Amazon's black waters

We investigated how natural dissolved organic matter (DOM) of the Rio Negro (Amazon) affects acute copper (Cu) toxicity to local fish: the cardinal tetra (Paracheirodon axelrodi) and the dwarf cichlid (Apistogramma agassizii). It is established that Cu2+ complexation with DOM decreases Cu bioavailability (and thus toxicity) to aquatic organisms, as conceptualized by the Biotic Ligand Model (BLM). However, we also know that Rio Negro's DOM can interact with fish gills and have a beneficial effect on Na+ homeostasis, the main target of acute Cu toxicity in freshwater animals. We aimed to tease apart these potential protective effects of DOM against Cu-induced Na+ imbalances in fish. In the laboratory, we acclimated fish to Rio Negro water (10 mg L−1 DOC) and to a low-DOM water (1.4 mg L−1 DOC) with similar ion composition and pH (5.9). We measured 3-h Cu uptake in gills and unidirectional and net Na+ physiological fluxes across a range of Cu concentrations in both waters. Various DOM pre-acclimation times (0, 1 and 5 days) were evaluated in experiments with P. axelrodi. Copper exposure led to similar levels of net Na+ loss in the two fish, but with distinct effects on Na+ influx and efflux rates reflecting their different ionoregulation strategies. Rio Negro DOM protected against Cu uptake and toxicity in the two fish species. Both Cu uptake in fish gills and Na+ regulation disturbances were relatively well predicted by the modelled aqueous free Cu2+ ion concentration. These findings suggest that protection by DOM occurs mainly from Cu complexation under the tested conditions. The prevalence of this geochemical-type protection over a physiological-type protection agrees with the BLM conceptual framework, supporting the use of the BLM to assess the risk of Cu in these Amazonian waters.

Effects of three feeding strategies (self‐feeders, automatic feeding and apparent satiety) on growth performance, haematological parameters, waste excretion and feed cost in Amazonian fish ( Colossoma macropomum )

A 127-day experiment was conducted to evaluate the effect of feeding strategies on juvenile tambaqui's (Colossoma macropomum) growth, body composition, haematological and biochemical parameters, excretion pattern and economic indices. Fifteen tanks randomly stocked 150 juvenile tambaqui (82.0 ± 0.8 g, mean ± SEM) subjected to three feeding strategies (n = 5): self-feeder system (T1); automatic-feeding with three set meals/day (T2) and apparent satiety with three meals/day (T3). The results revealed that fish T1 and T3 showed the best feed intake, feed conversion ratio, protein efficiency ratio and protein retention rate (p < 0.05). However, no significant differences were observed in growth, survival, haematological parameters, body composition and total ammonia nitrogen excretion among treatments (p > 0.05). Cortisol obtained a significantly higher value for fish T3 (122.92 ± 5.75 ng/ml), with a low water phosphorus value for fish T1 (0.43 ± 0.06 mg/L). Lastly, the feed cost based on the values deriving from diets revealed better indices (variable cost, unitary contribution margin and contribution margin index) for fish T1 and T3. In short, our findings suggest the benefits of using self-feeders for tambaqui aquaculture.

Daily rhythm of some blood parameters in two Amazonian fish, Astronotus ocellatus and Brycon amazonicus

We evaluated the effect of the light–dark (LD) cycle on energy expenditure indicators for two species of Amazonian fish of commercial interest, oscar (Astronotus ocellatus) and matrinxã (Brycon amazonicus). Fish were exposed to a 12:12 h LD cycle, with lights on at ‘zeitgeber time’ (ZT) = 0 h. Six animals were used for blood collection every 4 h for 24 h (six time points, three in the light period and three in the dark period). Most haematological parameters exhibited daily rhythms with the acrophase at the end of the dark phase or the beginning of the light period for both species, which may be related to the greater energy demand of these species during the day. For A. ocellatus, triglycerides and total protein showed acrophases at ZT = 13:32 ± 2:45 h and ZT = 23:42 ± 1:55 h, respectively, while the other plasma parameters showed no significant daily differences. In B. amazonicus, significant rhythms were observed for glucose levels (acrophase at ZT = 04:16 ± 2:47 h), triglycerides (ZT = 6:51 ± 4:06 h) and total cholesterol (ZT = 23:22 ± 3:45 h). However, total protein and cortisol levels did not show rhythmicity in this species. Our results highlight the importance of the evaluation of biological rhythms for plasma physiological parameters related to energy expenditure in species with commercial interest and susceptible to stressful situations in farming conditions.

Evolution of an Amazonian Fish Is Driven by Allopatric Divergence Rather Than Ecological Divergence

Lowland central Amazonia is characterized by heterogeneous riverscapes dominated by two chemically divergent water types: black (ion-poor, rich in dissolved organic carbonate and acidic) and white (rich in nutrient and turbid) waters. Recent phylogeographic and genomic studies have associated the ecotone formed by these environments to an ecologically driven genetic divergence between fish present in both water types. With the objective of better understanding the evolutionary forces behind the central Amazonian teleostean diversification, we sampled 240 Mesonauta festivus from 12 sites on a wide area of the Amazonian basin. These sites included three confluences of black and white water environments to seek for repeated evidences of ecological divergence at the junction of these ecotones. Results obtained through our genetic assessment based on 41,268 single nucleotide polymorphism (SNPs) contrast with previous findings and support a low influence of diverging water physicochemical characteristics on the genetic structuration of M. festivus populations. Conversely, we detected patterns of isolation by downstream water current and evidence of past events of vicariance potentially linked to the Amazon River formation. Using a combination of population genetics, phylogeographic analysis and environmental association models, we decomposed the spatial and environmental genetic variances to assess which evolutionary forces shaped inter-population differences in M. festivus’ genome. Our sampling design, comprising three confluences of black and white water rivers, supports the main role of evolution by allopatry. While an ecologically driven evolution admittedly played a role in Amazonian fish diversification, we argue that neutral evolutionary processes explain most of the divergence between M. festivus populations.

Mosaic Evolution of Craniofacial Morphologies in Ghost Electric Fishes (Gymnotiformes: Apteronotidae)

Ghost electric knifefishes (Gymnotiformes: Apteronotidae) are a dominant component of the species diversity and biomass of large lowland rivers in Greater Amazonia, including 77 species that exhibit diverse craniofacial morphologies associated with trophic and secondary sexual traits. Here we use open-source computed micro-tomography (µCT) scans to generate 3D reconstructions for a majority of apteronotid species and almost all valid genera, and geometric morphometric and phylogenetic analyses to explore patterns of skull evolution. As with most vertebrates, principal component 1 (PC1) summarizes variance from brachycephalic to dolichocephalic morphologies, previously described as heterocephaly, and PC2 summarizes variance from recurved (upturned) to decurved (downturned) snout morphologies, described here as heterorhynchy. Phylomorphospace and traitogram analyses found instances of both convergent and divergent evolution along both of the first two PC axes, as well as a preponderance of clades characterized by morphological stasis or phylogenetic conservatism. Certain phenotypic combinations predominate among species and clades, including elongated-downturned snouts and foreshortened-upturned snouts, while other phenotypic combinations are not observed, including elongated-upturned snouts and foreshortened-downturned snouts. These results highlight the power of 3D geometric morphometrics in the study of craniofacial evolution and indicate developmental or functional constraints in the evolution of craniofacial phenotypes in an ecologically dominant clade of riverine Amazonian fishes.

Avaliação da qualidade de pescados amazônicos provenientes de piscicultura armazenados em gelo

The cultivation of natives Amazonian fish such as tambaqui (Colossoma macropomum), pirapitinga (Piaractus brachypomus), tambatinga (female, Colossoma macropomum X Piaractus brachypomus, male) and Pintando da Amazônia (female, Pseudoplatystoma sp. X Leiarius marmoratus, male) temmoratus, increased in recent years, making studies related to the validity of these foods after processing necessary. Therefore, the aimed of the study was to evaluate the sensory, microbiological (Staphylococcus coagulase positive count and presence of Salmonella spp.) and chemical (pH and Total Volatile Bases (TVB) quality of fresh gutted fish stored on ice. Nine specimens of each species were used, all cultivated in an excavated tanks. The fasting time ranged from 16 to 48 hours, depending on the species, the fish was slaughtered by means of cold shock. The fish was gutted and stored in the fish fridge. Sensory analysis was performed by a trained team available. For other analyses, it was sent to a laboratory specializing in food analysis. The sensory analysis of fresh eviscerated tambaqui was characteristic of the species until the 15th day of storage. Fresh eviscerated pirapitinga presented until the 16th day. The fresh eviscerated tambatinga hybrid was kept until the 14th day of storage. And for the Pintado da Amazônia, the organoleptic characteristics were presentable until the 12th day of storage. The microbiological and physical-chemical analyzes were in accordance with Brazilian legislation in all specimens of the analyzed species. It was observed that the longer the fasting period, there was a numerical increase in the pH of the fish meat.

Global change and physiological challenges for fish of the Amazon today and in the near future.

Amazonia is home to 15% (>2700, in 18 orders) of all the freshwater fish species of the world, many endemic to the region, has 65 million years of evolutionary history and accounts for 20% of all freshwater discharge to the oceans. These characteristics make Amazonia a unique region in the world. We review the geological history of the environment, its current biogeochemistry and the evolutionary forces that led to the present endemic fish species that are distributed amongst three very different water types: black waters [acidic, ion-poor, rich in dissolved organic carbon (DOC)], white waters (circumneutral, particle-rich) and clear waters (circumneutral, ion-poor, DOC-poor). The annual flood pulse is the major ecological driver for fish, providing feeding, breeding and migration opportunities, and profoundly affecting O2, CO2 and DOC regimes. Owing to climate change and other anthropogenic pressures such as deforestation, pollution and governmental mismanagement, Amazonia is now in crisis. The environment is becoming hotter and drier, and more intense and frequent flood pulses are now occurring, with greater variation between high and low water levels. Current projections are that Amazon waters of the near future will be even hotter, more acidic, darker (i.e. more DOC, more suspended particles), higher in ions, higher in CO2 and lower in O2, with many synergistic effects. We review current physiological information on Amazon fish, focusing on temperature tolerance and ionoregulatory strategies for dealing with acidic and ion-poor environments. We also discuss the influences of DOC and particles on gill function, the effects of high dissolved CO2 and low dissolved O2, with emphasis on water- versus air-breathing mechanisms, and strategies for pH compensation. We conclude that future elevations in water temperature will be the most critical factor, eliminating many species. Climate change will likely favour predominantly water-breathing species with low routine metabolic rates, low temperature sensitivity of routine metabolic rates, high anaerobic capacity, high hypoxia tolerance and high thermal tolerance.

Riverscape Genomics Clarifies Neutral and Adaptive Evolution in an Amazonian Characin Fish (Triportheus albus)

Understanding the role of natural selection in the evolution of wild populations is challenging due to the spatial complexity of natural systems. The richest diversity of freshwater fishes in the world is found in the Amazon Basin, a system where marked hydrochemical differences exist at the interface of major rivers with distinct “water colors” (i.e., black, white, and clear water). We hypothesize that divergent natural selection associated with these “aquatic ecotones” influences population-level adaptive divergence in the non-migratory Amazonian fish fauna. This hypothesis was tested using a landscape genomics framework to compare the relative contribution of environmental and spatial factors to the evolutionary divergence of the Amazonian characin fishTriportheus albus. The framework was based on spatial data,in situhydrochemical measurements, and 15,251 filtered SNPs (single nucleotide polymorphisms) forT. albussampled from three major Amazonian rivers. Gradient Forest, redundancy analysis (RDA) and BayPass analyses were used to test for signals of natural selection, and model-based and model-free approaches were used to evaluate neutral population differentiation. After controlling for a signal of neutral hierarchical structure which was consistent with the expectations for a dendritic system, variation in turbidity and pH were key factors contributing to adaptive divergence. Variation in genes involved in acid-sensitive ion transport pathways and light-sensitive photoreceptor pathways was strongly associated with pH and turbidity variability. This study improves our understanding of how natural selection and neutral evolution impact on the distribution of aquatic biodiversity from the understudied and ecologically complex Amazonia.

Utrastructure and molecular phylogeny of the myxozoan Kudoa ocellatus n. sp. (Myxozoa: Kudoidae), a parasite of the Oscar, Astronotus ocellatus (Agassiz, 1831; Teleostei: Cichlidae), a fish from northern Brazil.

Kudoa ocellatus n. sp. was found in the musculature of Astronotus ocelattus (Agassiz, 1831) from the Arari River on Marajó Island in Pará, Brazil. The new species forms pseudocysts in the epaxial and hypaxial musculature composed of various spores that are pseudoquadrate in the apical view. In the lateral view, the spores were triangular or pyramidal. In the lateral view, the spores were 46±0.11μm (4.5-4.8) in length and 6.6±0.3μm (6.2-7.2) in width, with four pyriform polar capsules of equal size that measured 2.0±0.16μm (1.8-2.2) in length and 1.5±0.18μm (1.3-1.8) in width. Based on the partial (1418bps) sequence of the SSU rDNA gene, Kudoa ocellatus n. sp. was distinct from all the other Kudoa species deposited in GenBank. The phylogenetic Bayesian Inference and P distance placed the new species together with the other Kudoa species that parasitize freshwater Amazonian fish. The morphological evidence, together with the SSU rDNA gene sequence, supported the description of Kudoa ocellatus n. sp., a distinct new species of the genus, which parasitizes a freshwater Amazonian cichlid.

Subfamily hypostominae: similarities and differences in testicular structure of amazonian fish

BackgroundHypostominae is a subfamily of the family Loricariidae that has a great diversity of species. Accordingly, testicular studies in fish can contribute to the phylogeny and taxonomy of species and to the comparison of reproductive aspects between species. Thus, this work aimed to characterize the testicular morphology and spermatogenesis of the Hypostominae species Baryancistrus xanthellus, Peckoltia oligospila and Hypancistrus zebra.ResultsB. xanthellus, P. oligospila and H. zebra had an anastomosed tubular type of testis. The germinal epithelium was continuous with unrestricted spermatogonia, and the proliferative, meiotic and spermiogenic phases were defined in all species. In the spermiogenic phase, spermatids were classified as initial, intermediate and final. Only in B. xanthellus in the final phase was there nuclear rotation. The sperm for the three species had a head with an oval shape and a single flagellum composed of the short midpiece, principal piece and end piece. B. xanthellus and P. oligospila showed a cylindrical flagellum and H. zebra showed projections that produced a flattened appearance.ConclusionsOn the basis testicular structure and ultrastructural characteristics of the germ cells, there was a greater relationship between B. xanthelus and P. oligospila, while H. zebra had particular characteristics. These aspects show that despite belonging to the same subfamily, the species have distinct biological characteristics.

Mitochondrial genotyping of cultured Piaractus brachypomus revealed low diversity and mutations in regions involved in metabolisms and proliferation

In Amazonia, small-oriented family businesses or communities cultivate freshwater organisms as a source of income. Although effective management is fundamental for optimizing cultivated stocks, Amazonian aquaculture belittles the importance of genetic diversity, relying primarily on phenotypical characteristics during breeders’ selection. To provide a “proof of concept” built on the premise that implementing modern technologies is crucial to optimizing fish stocks in rural Amazonian fish farms, we conducted a pilot study assessing genetic diversity on cultivated Piaractus brachypomus from Caquetá, Colombia. We used mitochondrial control region (CR) sequences to evaluate heterogeneity. Our data revealed low genetic diversity and suggested that most sampled individuals probably originated from a single maternal lineage. Haplotype diversification resulted from discrete point mutations not associated with geographical location. Polymorphisms accumulate in non-conserved CR regions, yet the most divergent haplotypes display mutations in conserved CR sequences with roles in mitochondrial metabolisms and proliferation. Overall, our results indicate a need in the local industry to design breeding strategies to enhance diversity to avoid deleterious effects caused by inbreeding and domestication.

Structure of the ichthyoplankton community in a Neotropical floodplain lake affected by environmental degradation

Many Amazonian fish' reproduction is associated to seasonality and to the conditions of habitat integrity. In a Neotropical floodplain lake of the Amazon region, the temporal structure of ichthyoplankton was investigated and the hypothesis that the density of fish eggs and larvae and the diversity of species vary between two areas with different levels of environmental changes occurred was tested. The sampling occurred monthly between September 2017 and August 2018. Six sampling stations were used, distributed in locations close to and far from the altered area. 195 eggs and 1,785 larvae from nine orders and 27 species were captured. The eggs were from non-migratory fish species and occurred during two moments. The larvae presented different abundance peaks during the sample months and all the initial stages of development occurred. Clupeiformes was the most abundant and Characiformes the species richest. The density of the ichthyoplankton and the diversity of species presented temporal variation. However, only the larval density varied between the areas of the lake. The Lake Juá is a spawning area for resident fish and is a nursery and growth area for larvae of species with different ecological categories and socioeconomic importance during different periods of the year.

Seasonal influence on centesimal composition and yield of Amazonian fish

The objective of this study was to evaluate meat yield and centesimal composition of the Amazonian fish species, A. ocellatus, P. castelnaeana, and L. friderici, in the dry and flood seasonal cycles of rivers. In each seasonal cycle (flood and dry), a total of 60 fish were collected, comprising 20 specimens of each of the following species: A. ocellatus, P. castelnaeana, and L. friderici. Were evaluated the meat yield, cuts yield and centesimal composition of the fish samples. Meat yield in the clean body cuts and skinless filet varied between species and hydrological period. The results showed that seasonal variation influenced the centesimal composition and yield of the species studied, with significant differences between the cuts produced during processing. These findings highlight the need to apply a variety of technological processes to ensure efficient use of these species throughout the year. The total waste represented more than 50% of the whole fish, and the head size was directly proportional to the amount of waste generated. These results underscore the importance of waste utilization for animal and/or human nutrition.

Evaluation of cardiotoxicity in Amazonian fish Bryconops caudomaculatus by acute exposure to aluminium in an acidic environment.

Aluminium (Al) is soluble in acidic waters and may become toxic to organisms. In this study, the acute effects of two Al concentrations were evaluated in the Amazonian fish Bryconops caudomaculatus. Antioxidant responses and lipid damage were assessed in gills, liver and muscle, along with the electrocardiography (ECG) and characterization of cardiac complex and wave intervals. Fish were essayed as follows: two control groups at neutral and acidic pH and two exposure groups at acidic pH (0.3 mg/L and 3.0 mg/L Al). Water samples were collected at 0h, 24h and 48h, for chloride (Cl-), fluoride (F-) and sulphate (SO42-) ion analyses, while total Al was quantified in muscle. Concentrations of Cl- and SO42- were constant over time whereas F- was not detected. Total Al concentrations in water and muscle were concentration-dependent. Antioxidant responses, total antioxidant capacity against peroxyl radicals (ACAP) and glutathione S-transferase were not triggered in fish tissues exposed to 0.3 mg/L Al; however, fish exposed to 3.0 mg/L Al presented increased and reduced ACAP in gills and liver, respectively. No changes in lipoperoxidation levels occurred among groups. Fish exposed to 0.3 mg/L Al showed prolonged intervals in ECG as a reflection of low heart rate (HR), with sinus bradycardia. Moreover, there was a marked prolongation of the PQ interval (time between the atrial activity and the start of ventricular activity), indicating interference on the cardiac cell automaticity. Fish exposed to the highest concentration of Al showed reduced wave intervals as a consequence of increased HR, with sinus arrhythmia, while ECG tracings did not present P waves (atrial contraction), indicating an atrioventricular blockade. In conclusion, 48h exposure sufficed to cause cardiotoxicity in B. caudomaculatus at either Al concentration. However, as oxidative stress was not observed, such cardiac alterations seem to be reversible under the experimental conditions established herein.

Temporal exposure to malathion: Biochemical changes in the Amazonian fish tambaqui, Colossoma macropomum.

The main toxicity mechanism of organophosphate insecticides such as malathion is the acetylcholinesterase enzyme inhibition. However, fish responses to organophosphates may vary depending on the activation of different defense mechanisms as well as the length of exposure. As such, the evaluation of acetylcholinesterase activity, in combination with the evaluation of biotransformation and antioxidants enzymes levels, is useful for indicating damage in fish exposed to this insecticide. Moreover, evaluating mitochondrial activity might evidence how the hierarchic responses occur in relation to the length of time that the fish is exposed. Therefore, the aim of our study is to evaluate whether the length of exposure to malathion differentially affects the biochemical responses of tambaqui. Our hypothesis is that the physiological alterations due to exposure are time dependent. Fish were exposed to sublethal concentrations of the insecticide during 6, 12, 24, 36, and 48h. Contrary to expectations, there was no acetylcholinesterase activity inhibition during the experiment, which indicates an absence of neurotoxicity. Phase II biotransformation mechanism was activated early, especially in the liver. Oxidative damage was evident in the first hours of exposure and was concurrent with the activation of antioxidant enzymes. Mitochondrial bioenergetics were differentially affected by the length of exposure. The data suggest that the tambaqui regulates mitochondrial respiration differently over time, seeking to maintain homeostasis and ATP demand, and ensures the activation of response mechanisms, thus minimizing oxidative damage and avoiding the neurotoxicity of malathion.

TRAFFICKING OF ORNAMENTAL FISH IN THE BRAZILIAN AMAZON

The trafficking of ornamental fish is growing on a yearly basis in the Brazilian Amazon. This represents a serious threat to the biodiversity of the region. The objective of this research was to evaluate the trafficking of ornamental fish in the Brazilian Amazon using data from the seizures by the Federal Police and Brazilian Institute of Environment and Renewable Natural Resources - IBAMA. To assess and quantify this illegal trade, we gathered data relating to the period between January 2003 and January 2020. Information was obtained from IBAMA - Amazon - regional superintendence; National Amazon Research Institute - INPA regarding smuggled species that have been recovered and placed in its fish collection. The results show that in 98 seizures made by IBAMA, a total of 170,849 specimens of at least 73 species of 10 families, and 5 orders were recovered. Most of the illegally trafficked species are from the Loricariidae family (31 species, 8.47%). Hypancistrus zebra (Loricariidae), Potamotrygon jabuti, Potamotrygon leopoldi (Potamotrygonidae), Osteoglossum bicirrhosum and Osteoglossum ferreirai (Osteoglossidae) are the most targeted by the traffickers, due to their high value. At least 12 species are undescribed new species and were registered and placed in INPA’s fish collection. The fish followed different routes to reach the border that Brazil, Colombia, and Peru share. We conclude that in order to fight this illegal trade, tougher laws against smugglers, agreements with neighboring countries to combat trafficking, formal environmental education programs for riverine populations, and further scientific studies of smuggled species are necessary.

Can turbid water and refuges with aquatic macrophytes increase the survival and growth of Brycon amazonicus larvae?

The productivity of aquatic organisms and higher concentration of suspended solids that occur in areas flooded by Whitewater Rivers and the presence of aquatic macrophytes are conducive to the initial development of matrinxã (Brycon amazonicus). The objective of this study was to evaluate whether turbid waters and refuges with aquatic macrophytes improve the survival and growth of the larvae of Brycon amazonicus, a species of great interest in Amazonian fish farming. For this, two experiments were conducted using a completely randomized design and with four replicas per treatment up to 120 hours after hatching (HAH), In experiment I: Brycon amazonicus larvae at 24 HAH were subjected to three treatments with different types of water: clear water (CW); clayey water (AW) and green water (GW). Experiment II: larvae with 24 HAH were maintained in clear water (CW); clear water with refuge (CWR); green water (GW); green water with refuge (GWR); clayey water (AW) and clayey water with refuge (AWR). Experiment I showed that clayey water, followed by green water, increased the survival of larvae (73.92 and 54.32%). Growth was best in larvae maintained in green water. In experiment II, the use of aquatic macrophytes did not influence the survival and growth of the larvae. Thus, we suggest the use of turbid (clayey and green) waters without refuge to increase the survival and growth of Brycon amazonicus larvae.

The critical role of natural history museums in advancing eDNA for biodiversity studies: a case study with Amazonian fishes

Ichthyological surveys have traditionally been conducted using whole-specimen, capture-based sampling with varied but conventional fishing gear. Recently, environmental DNA (eDNA) metabarcoding has emerged as a complementary, and possible alternative, approach to whole-specimen methodologies. In the tropics, where much of the diversity remains undescribed, vast reaches continue unexplored, and anthropogenic activities are constant threats; there have been few eDNA attempts for ichthyological inventories. We tested the discriminatory power of eDNA using MiFish primers with existing public reference libraries and compared this with capture-based methods in two distinct ecosystems in the megadiverse Amazon basin. In our study, eDNA provided an accurate snapshot of the fishes at higher taxonomic levels and corroborated its effectiveness to detect specialized fish assemblages. Some flaws in fish metabarcoding studies are routine issues addressed in natural history museums. Thus, by expanding their archives and adopting a series of initiatives linking collection-based research, training and outreach, natural history museums can enable the effective use of eDNA to survey Earth’s hotspots of biodiversity before taxa go extinct. Our project surveying poorly explored rivers and using DNA vouchered archives to build metabarcoding libraries for Neotropical fishes can serve as a model of this protocol.

Hypoxia tolerance in two amazon cichlids: mitochondrial respiration and cellular metabolism adjustments are result of species environmental preferences and distribution.

The amazon fishes' responses to hypoxia seem to be related to the Amazon basin diversity of aquatic environments, which present drastic daily and seasonal variations in the dissolved oxygen concentration. Among these fishes' adaptation to hypoxia, behavioral, metabolic, physiological, and biochemical responses are well known for some species. In this work, we aimed to identify how two different aquatic environments, normoxic forest streams and hypoxic lakes, dictate the responses to hypoxia for two cichlid species, Mesonauta festivus and Aequidens pallidus. In our results, we found that A. pallidus is less tolerant to hypoxia, which seems to be related to this animal's natural normoxic environment. Even though this species modulated the mitochondrial respiration in order to improve the oxygen use, it also showed a lower decrease in metabolic rate when exposed to hypoxia and no activation of the anaerobic metabolism. Instead, M. festivus showed a higher decrease in metabolic rate and an activation of the anaerobic metabolism. Our data reveal that the natural dissolved oxygen influences the hypoxia tolerance and the species' tolerance is related to its ability to perform metabolic depression. The interest results are the absence of mitochondrial respiration influences in these processes. The results observed with A. pallidus bring to light also the importance of preserving the forests, in which streams hold very specialized species acclimated to normoxia and lower temperature. The importance of hypoxia tolerance is, thus, important to keep fish assemblage and is thought to be a strong driver of fish biodiversity.