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.

Non-native fish (NNF) can threaten megadiverse aquatic ecosystems throughout the planet, but limited information is available for the Amazon Region. In this study we review NNF data in the Amazonian macroregion using spatiotemporal records on the occurrence and the richness of NNF from a collaborative network of 35 regional experts, establishing the Amazon NNF database (ANNF). The NNF species richness was analyzed by river basin and by country, as well as the policies for each geopolitical division for the Amazon. The analysis included six countries (Brazil, Peru, Bolivia, Ecuador, Venezuela, and Colombia), together comprising more than 80% of the Amazon Region. A total of 1314 NNF occurrence records were gathered. The first record of NNF in this region was in 1939 and there has been a marked increase in the last 20 years (2000–2020), during which 75% of the records were observed. The highest number of localities with NNF occurrence records was observed for Colombia, followed by Brazil and Bolivia. The NNF records include 9 orders, 17 families and 41 species. Most of the NNF species are also used in aquaculture (12 species) and in the aquarium trade (12 species). The most frequent NNF detected were Arapaima gigas, Poecilia reticulata and Oreochromis niloticus. The current data highlight that there are few documented cases on NNF in the Amazon, their negative impacts and management strategies adopted. The occurrence of NNF in the Amazon Region represents a threat to native biodiversity that has been increasing “silently” due to the difficulties of large-scale sampling and low number of NNF species reported when compared to other South American regions. The adoption of effective management measures by decision-makers is urgently needed and their enforcement needed to change this alarming trend and help protect the Amazon’s native fish diversity.

-The trichomycterid catfishes known as candirus are renowned for their blood feeding, but information on their habits under natural conditions is very fragmentary and generally restricted to hosts or habitats. We recorded an undescribed species of the vandelliine genus Paracanthopoma riding the giant jau catfish, Zungaro zungaro (Pimelodidae), in the upper Amazon. The candirus were found on the host's caudal and pectoral fins, as well as the base of the dorsal fin, with their snouts buried up to the eyes in the tough skin of the catfish host. All of them had small amounts of partly digested blood in the distal part of the gut. Along the host's dorsal fin base we found a few additional tiny holes, most of them healed. We suggest that Paracanthopoma feeds on the gill chamber of its hosts, and that the individuals we found were taking a ride partly buried into the host's skin. Our assumption seems supported by the widespread behaviour of vandelliine candirus taking blood from the gill region of their hosts, and by a report of Paracanthopoma parva found on the gills of another species of giant catfish, Brachyplatystoma vaillanti. Additionally, the Paracanthopoma sp. individuals we examined were not gorged with blood as usual for several vandelliines. Species within the genus Paracanthopoma have the longest and most robust snout, and the longest and strongest dentary teeth among blood-feeding candirus, which fit their drilling needs. Taking a ride on a giant host would be advantageous for Paracanthopoma candirus for several reasons: 1) dispersal; 2) no need to search for hosts to feed; and 3) protection from predators. The alternative explanation that Paracanthopoma takes blood from the tiny holes it drills in the skin seems unlikely, due to the recent finding that species of the genus Vandellia are unable to take blood from their hosts actively and cut open a major branchial artery to gorge themselves with blood due to the host's arterial pressure instead. The body parts of the host the Paracanthopoma sp. individuals were attached on have no large vessels that would supply them with plenty of blood. Thus, drilling a hole on a giant host skin seems to serve mostly to anchor the Paracanthopoma candirus to their long-distance cruising catfish host. If our assumption holds true, then species of this genus exemplify an instance of phoresis (hitch-hiking) among the bloodfeeding candirus. Key words: Trichomycteridae, Paracanthopoma sp., candiru, blood-feeding, phoresis, dispersal, Pimelodidade, Zungaro zungaro, Amazon.Resumo -Os bagres tricomicterídeos conhecidos como candirus são famosos por se alimentarem de sangue, mas as informações sobre seus hábitos, em condições naturais, são fragmentárias e restritas aos seus hospedeiros ou ambientes. Registramos uma espécie não descrita de candiru do gênero Paracanthopoma (Vandelliinae) sobre um jaú, Zungaro zungaro (Pimelodidae), no alto Rio Amazonas. Os candirus estavam sobre as nadadeiras caudal e peitoral e junto à base da dorsal, com seus focinhos enterrados até a al...

The ichthyofauna of the headwaters of the main tributaries of the mighty Solimões/Amazonas River  has been little studied. Considering the importance of those environments for the overall fish  diversity in that river system, we surveyed the composition of the fish fauna of the upper portion  of Purus River and two of its tributaries (Caeté and Macapá rivers), state of Acre, Brazil. The collections were done in November 2004, using a seine net and a set of gillnets of different mesh  sizes. A total of 735 specimens belonging to 86 species and 28 families were collected. Eight  species, Creagrutus occidaneus, Phenacogaster pectinatus, Prionobrama filigera, Moenkhausia cf.  lepidura, Leptagoniates pi (Characidade), Henonemus punctatus (Trichomycteridae), Toracocharax  stellatus (Gateropelecidae), and Eigenmannia macrops (Sternopygidae) composed nearly half of the  specimens collected. This survey adds 48 new records to the ichthyofauna of Purus River and  elevates to 243 the number of known fish species in that river, but a greater sampling effort is necessary to produce a reasonably complete picture of the fish diversity in the basin.

The Tocantins-Araguaia Basin is one of the largest river systems in South America, located entirely within Brazilian territory. In the last decades, capital-concentrating activities such as agribusiness, mining, and hydropower promoted extensive changes in land cover, hydrology, and environmental conditions. These changes are jeopardizing the basin's biodiversity and ecosystem services. Threats are escalating as poor environmental policies continue to be formulated, such as environmentally unsustainable hydropower plants, large-scale agriculture for commodity production, and aquaculture with non-native fish. If the current model persists, it will deepen the environmental crisis in the basin, compromising broad conservation goals and social development in the long term. Better policies will require thought and planning to minimize growing threats and ensure the basin's sustainability for future generations.

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 approaches. In the tropics, where much of the diversity remains undescribed, vast reaches remain unexplored, and anthropogenic activities are constant threats; there have been few eDNA attempts for ichthyological inventories. We tested the discriminatory power of eDNA using the 12S rRNA MiFish primers with existing public reference libraries and compared this with capture-based methods in two distinct ecosystems in the megadiverse Amazon basin. eDNA provided an accurate snapshot of the fishes at higher taxonomic levels and corroborated the effectiveness of eDNA to detect specialized fish assemblages. Some flaws in fish metabarcoding studies are routine issues addressed in natural history museums. Thus, by expanding their archives to include eDNA 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.

Arapaima (Arapaima sp.) are highly overexploited fish endemic to the Amazon basin. Because the fish are obligate air‐breathers, it is possible to use surface‐breathing events to count individuals visually for population censuses important for conservation, yet uncertainties remain about body size and environmental influences on air‐breathing intervals, and thus count accuracy. This study examined relationships between breathing intervals and environmental parameters (e.g. water temperature and transparency) and body size for radio‐tagged arapaima (n = 12) in an upland river‐floodplain (Lake Ayapuá, Amazonas, Brazil). Generalized additive mixed models were used to evaluate environmental, size, and behavioural correlates of breathing intervals. Temperature was the most influential predictor of air‐breathing intervals, followed by body size. The shortest breathing intervals were associated with consecutive ‘aggressive’ breaths while the longest breathing intervals had consecutive ‘calm’ breaths. Type of breath, size, and temperature predictors revealed that breathing intervals ranged from 4 to 46 min and were not significantly different among life stages ( x¯ = 15.9 min for sub‐adults and adults (>1 m); x¯ = 14.8 min for juveniles (<1 m)). Whereas the current population census method uses fish counts in 20‐min intervals, this study found that 15% of observed breaths, and two thirds of fish, took longer than 20 min to breathe. These findings were obtained in relatively cool‐water environments, so it is recommended that future population census methods consider water temperature (e.g. extend intervals used for counts in cooler waters), which may improve the accuracy of census counts and thus further enhance arapaima conservation efforts. This study demonstrated an effective method in which fundamental biological information is used to inform and improve population census methods for an imperilled fish in a region where traditional stock assessment is ineffective. Similar approaches for adaptive stock assessments could be applied to improve conservation of other air‐breathing fishes (e.g. lungfishes) globally.

No abstract