Bioacoustics supports genus identification in piranhasa)

In different teleost species, sound production can utilize specific coding schemes to avoid confusion between species during communication. Piranhas are vocal Neotropical fishes, and both Pygocentrus and Serrasalmus produce similar pulsed sounds using the same sound-producing mechanism. In this study, we analysed the sounds of three Pygocentrus and nine Serrasalmus species to determine whether sounds can be used to discriminate piranha species at both the species and genus levels. Our analysis of temporal and frequency data supports the idea that the sounds of Serrasalmus and Pygocentrus species are species specific, and that different acoustic features can be used to differentiate taxa at the genus level. Specifically, the sounds of Serrasalmus species are shorter, louder, and have a shorter pulse period (as determined after correction for standard length). This suggests that sounds can be used to support taxonomy at the genus level as well as the species level.

NEOTROPICAL FRESHWATER FISHES: A dataset of occurrence and abundance of freshwater fishes in the Neotropics

The Neotropical region hosts 4225 freshwater fish species, ranking first among the world's most diverse regions for freshwater fishes. Our NEOTROPICAL FRESHWATER FISHES data set is the first to produce a large-scale Neotropical freshwater fish inventory, covering the entire Neotropical region from Mexico and the Caribbean in the north to the southern limits in Argentina, Paraguay, Chile, and Uruguay. We compiled 185,787 distribution records, with unique georeferenced coordinates, for the 4225 species, represented by occurrence and abundance data. The number of species for the most numerous orders are as follows: Characiformes (1289), Siluriformes (1384), Cichliformes (354), Cyprinodontiformes (245), and Gymnotiformes (135). The most recorded species was the characid Astyanax fasciatus (4696 records). We registered 116,802 distribution records for native species, compared to 1802 distribution records for nonnative species. The main aim of the NEOTROPICAL FRESHWATER FISHES data set was to make these occurrence and abundance data accessible for international researchers to develop ecological and macroecological studies, from local to regional scales, with focal fish species, families, or orders. We anticipate that the NEOTROPICAL FRESHWATER FISHES data set will be valuable for studies on a wide range of ecological processes, such as trophic cascades, fishery pressure, the effects of habitat loss and fragmentation, and the impacts of species invasion and climate change. There are no copyright restrictions on the data, and please cite this data paper when using the data in publications.

Use of bioacoustics in species identification: Piranhas from genus Pygocentrus (Teleostei: Serrasalmidae) as a case study

The genus Pygocentrus contains three valid piranha species (P. cariba, P. nattereri and P. piraya) that are allopatric in tropical and subtropical freshwater environments of South America. This study uses acoustic features to differentiate the three species. Sounds were recorded in P. cariba, two populations of P. nattereri (red- and yellow-bellied) and P. piraya; providing sound description for the first time in P. cariba and P. piraya. Calls of P. cariba were distinct from all the other studied populations. Red- and yellow-bellied P. nattereri calls were different from each other but yellow-bellied P. nattereri calls were similar to those of P. piraya. These observations can be explained by considering that the studied specimens of yellow-bellied P. nattereri have been wrongly identified and are actually a sub-population of P. piraya. Morphological examinations and recent fish field recordings in the Araguari River strongly support our hypothesis. This study shows for the first time that sounds can be used to discover identification errors in the teleost taxa.

Functional diversity in biters: the evolutionary morphology of the oral jaw system in pacus, piranhas and relatives (Teleostei: Serrasalmidae)

Serrasalmid fishes form a highly specialized group of biters that show a large trophic diversity, ranging from pacus able to crush seeds to piranhas capable of cutting flesh. Their oral jaw system has been hypothesized to be forceful, but variation in bite performance and morphology with respect to diet has not previously been investigated. We tested whether herbivorous species have higher bite forces, larger jaw muscles and more robust jaws than carnivorous species. We measured in vivo and theoretical bite forces in 27 serrasalmid species. We compared the size of the adductor mandibulae muscle, the jaw mechanical advantages, the type of jaw occlusion, and the size and shape of the lower jaw. We also examined the association between bite performance and functional morphological traits of the oral jaw system. Contrary to our predictions, carnivorous piranhas deliver stronger bites than their herbivorous counterparts. The size of the adductor mandibulae muscle varies with bite force and muscles are larger in carnivorous species. Our study highlights an underestimated level of functional morphological diversity in a fish group of exclusive biters. We provide evidence that the trophic specialization towards carnivory in piranhas results from changes in the configuration of the adductor mandibulae muscle and the lower jaw shape, which have major effects on bite performance and bite strategy.

Fisheries, life-history and conservation status of the catfish pirá Conorhynchos conirostris (Ostariophysi: Siluriformes) in Brazil

ABSTRACT Pirá, Conorhynchos conirostris (Valenciennes, 1840), a large migratory catfish endemic to the São Francisco River (SFR), is listed as threatened in the red lists of both Brazil and the state of Minas Gerais. Although fishing for pirá has been prohibited, it is still an important fishery resource, particularly in the middle SFR. We used historical and current occurrence and abundance data regarding pirá to determine if it meets the IUCN criteria of a threatened species. Pirá occurs in the main course of the SFR as well as in its major tributaries. Unlike the most well-known migratory fishes of the SFR, pirá does not use floodplain lakes as nurseries. In the first half of the 20th century, pirá occurred from the upper to the lower SFR. Currently, it is most abundant in the middle SFR, and is rare in the upper SFR and even rarer in the sub-middle SFR. Pirá has not been captured in the lower SFR since around the mid-1980’s. Despite the reduction in its geographic distribution, we did not find evidence to justify considering pirá as threatened. Thus, we recommend that it be removed from the red lists of Brazil and the state of Minas Gerais.

Do different sampling designs produce differences in the metrics of curimba, Prochilodus lineatus (Characiformes: Prochilodontidae)?

ABSTRACT Probabilistic sampling, a classical recommendation for unbiased data, has been often overlooked. Fish sampling in reservoirs, unlike most rivers, can be accomplished by a variety of probabilistic sampling designs due to few restrictions in the choice of sampling sites (SSs). We evaluated whether population metrics of Prochilodus lineatus differ between fixed SSs (do not change with each sampling trip) and variable SSs (change with each sampling trip) in the Volta Grande (VGR) and Jaguara (JR) reservoirs of the Grande River, Paraná River basin, Brazil. We used gillnets to sample fish at nine probabilistic fixed SSs and nine probabilistic variable SSs per sampling trip. We conducted 25 sampling trips in VGR and 22 in JR during 2011 to 2015, and performed 35 analyses of 8 metrics for each reservoir. We found sampling design influenced only 7% of the analyses involving three metrics, apparently caused by biased data of fixed SSs. We attribute the small percentage of analyses influenced by sampling design to the low spatial heterogeneity of the reservoirs. The choice of the most appropriate sampling design seems to depend on the type of variation (temporal or spatial) that one wishes to detect, and the availability of time and financial resources.

Allometric larval growth of the bottom-dwelling catfish Lophiosilurus alexandri Steindachner, 1876 (Siluriformes: Pseudopimelodidae)

ABSTRACT We investigated the early life growth pattern of pacamã, Lophiosilurus alexandri , a catfish endemic to the rio São Francisco basin, Brazil. Pacamã larvae were kept in a galvanized trough for 29 days after hatching. We collected approximately 10 larvae daily (total number = 285). We obtained from each specimen the total length (independent variable) and 11 other body measurements (dependent variables). We performed linear regressions on the log-transformed data to determine the growth pattern of the body measurements and the respective inflexion point on the growth curves. Except for trunk length, trunk width and yolk sac volume, the remaining body measurements showed a positive allometric growth coefficient up to the respective IP followed by a decrease in the rate of relative growth afterwards. Although trunk width presented a positive allometric growth, no significant inflexion point was detected. The dorsal-ventral head flattening seen in the adult pacamã was quickly expressed in the larvae as indicated by the large allometric growth of head width. Maxillary barbels showed the highest growth rate. The exceptionally high growth rates of eyes and maxillary barbels and the acquired ability to capture prey (as suggested by mouth length growth) strengthened the hypothesis of growth priorities in which the most essential organs develop first.

Evaluation of techniques used to protect tailrace fishes during turbine maneuvers at Três Marias Dam, Brazil

Turbine dewatering and stop/startup may lead to the death of tons of fish at Brazilian power dams. The Três Marias Dam (TMD) on the São Francisco River has adopted two techniques to reduce the quantity of fish, mostly mandi (Pimelodus maculatus, Pimelodidae), affected by these maneuvers. They are: (i) spill before turbine dewatering to attract fish out of the tailrace, and (ii) fish screens in the stop log slots during turbine stop/startup to prevent fish from entering the draft tube. Here, we investigated whether spill and fish screens reduced the quantity of fish affected by turbine dewatering and stop/startup at TMD. We also determined whether the biomass of mandi trapped during turbine dewatering may be predicted by turbine discharge (Q) and/or catch per unit effort (CPUE) of mandis in the tailrace. Due to insufficient statistical power, our data were inconclusive as to whether spill attracted mandi out of the tailrace. We verified that the presence of fish screens significantly reduced the biomass of dead/moribund fish during turbine stop/startup. The biomass of mandis trapped in the draft tube during turbine dewatering was mainly influenced by Q (r² = 0.67), followed by CPUE (r² = 0.49). Since the trapped fish biomass correlated negatively with Q, we recommend that Q be maximized before turbine dewatering to reduce quantity of mandi trapped in the draft tube. The information presented here may be useful for reducing the quantity of fish affected by turbine maneuvers at TMD, as well as other dams.

Radiotelemetry of a female jaú, Zungaro jahu (Ihering, 1898) (Siluriformes: Pimelodidae), passed upstream of Funil Dam, rio Grande, Brazil

Jaú, Zungaro jahu (Ihering, 1898), a large migratory catfish endemic to the rio da Prata basin, has a fragile conservation status and its ecology is poorly known. We radio-tracked a female jaú with a total length of 1.5 m that was passed upstream of Funil Dam, rio Grande, to describe its migratory movements, habitat use, linear home range, and diel activity. To track the fish, we made five tracking trips in the period from April, 2003 to January, 2004. In addition to the main body of Funil Reservoir, the fish also used a reservoir-river transition zone located in a branch of Funil Reservoir that flooded part of rio das Mortes. Most of the times, we found the fish in the former beds of streams flooded by the reservoir, at depths that ranged from 8-9 m in the reservoir-river transition zone to 18-21 m in Funil Reservoir. Linear home range of the fish was 31.4 km. The onset of activity occurred early in the evening, but we also detected daytime activity. The conclusion from our study was that the passed adult female jaú used reservoir habitats, migrated between the main body and the reservoir-river transition zone, preferred deep habitats, showed a relatively short home range, and had diurnal and nocturnal activities.