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Invasive fish species can play an important role in aquatic ecosystems and have a significant impact on ecosystem dynamics, which influences primary production, planktonic communities, and aquatic macrophytes. The presence and density of invasive fish can disrupt nutrient ratios and ecological processes, leading to potential ecological consequences for invaded habitats. This experimental investigation focused on the invasive armored catfish species P. ambrosettii (Loricariidae) and postulated that high densities of armored catfish in invaded environments may affect nutrient cycling due to high N: P excretion rates. Furthermore, we sought to identify how these changes in nutrient concentration impact phytoplankton, protozooplankton, and the biomass of two invasive macrophytes. We carried out a 30-day experimental study at the Nupélia Applied Ecology Laboratory at the State University of Maringá with 20 fiber cement mesocosms with a volume of 135 L. These mesocosms had continuous water circulation and were used to simulate the natural conditions of lakes invaded by P. ambrosettii. We simulated five treatments that represented density at different levels of invasion: control (no fish), low-density (one fish), medium–low (two fish), medium–high (three fish) and high-density (four fish). The treatments affected abiotic variables such as pH, dissolved oxygen, and electrical conductivity, and nitrogen and phosphorus concentrations increased with increasing fish density, as expected. In turn, nutrient concentrations had effects on chlorophyll-a and macrophyte biomass. The chlorophyll-a and Eichhornia crassipes biomass were positively related to the increase in phosphorus, while Hydrilla verticillata showed a positive relationship with both nutrients nitrogen and phosphorous. The zooplankton community showed different density behaviors in relation to treatments. Its composition was influenced by the different treatments, and it underwent significant variations along the nutrient gradient. As predicted, the different densities of P. ambrosettii led to changes in the structure of the ecosystem. In treatments with higher fish densities, the environment was characterized by low oxygenation, high conductivity, and high concentrations of nitrogen and phosphorus. These conditions favored the dominance of phytoplankton and aquatic macrophytes, while the density and species composition of zooplankton was low. The effects observed in this experimental study contribute to insights into the field of invasion biology and its relationships with nutrient dynamics. The effects that may arise from the invasion and high population density of the armored catfish Pterygoplichthys in invaded locations reinforce the importance of understanding these processes in the functioning of the ecosystem and how this directly or indirectly impacts the dynamics of coexisting communities in natural environments. [ABSTRACT FROM AUTHOR]

Despite significant advancements in ichthyoplankton collection and data processing, challenges persist in the taxonomic identification of these organisms, particularly their eggs. To overcome these challenges, a novel technique has been developed to facilitate the identification of live eggs collected directly in wild. This user-friendly technique includes the collection, processing of the material, and field incubation. Sampling must be conducted using a pelagic net towed at low speed, preferably during early evening. The material processing involves pre-sorting and sorting to remove eggs and larvae. The separated eggs, kept in an aerated bowl, can be identified based on their morphological and meristic characteristics. Unidentified eggs can be placed in plastic bags with oxygen and incubated directly in the aquatic environment for 48–72 h. After this incubation period, the hatched larvae at the yolk-sac or preflexion stage, are identified to the lowest possible taxonomic level. Depending on the study's purpose, hatched larvae and field-collected larvae can be transported to research centers for further development, released back into the natural environment, or fixed to complete the collection. The application of this technique supports management and monitoring programs by identifying spawning areas through egg identification, forming broodstock, and replenishing threatened species, thereby enhancing scientific collections of ichthyoplankton. Additionally, it reduces mortality in ichthyoplankton techniques, including endangered species. Therefore, we believe that this novel taxonomic technique for identifying live ichthyoplankton represents a paradigm shift in the monitoring, management, and conservation of fish, as well as in ecological stewardship and advances in this area of research. [ABSTRACT FROM AUTHOR]

We assessed the importance of different types of riverine environments (river channels, tributaries, and floodplain lagoons) for the early development of fish larvae from different reproductive guilds. With samples from 25 sites scattered along a 230 km stretch of the upper Paraná River we classified 29 fish taxa into two reproductive guilds depending on their ability to perform long migrations (> 100 km): short-distance (SM) and long-distance (LM) migratory. We used network-based metrics (connectance and nestedness) to evaluate species-environment relationships, and potential effects on species' persistence after primary losses of environments. Both reproductive guilds had low connectance and no nested structure. Regarding spatial co-occurrence patterns, SM taxa were significantly spatially segregated, whereas LM taxa showed random co-occurrence patterns. These patterns likely emerge from the dispersal of eggs and larvae throughout the main rivers and adjacent floodplain environments during floods. The average proportion of lost taxa was 25% for SM and 75% for LM when environments were randomly removed from the network, meaning that LM taxa are potentially more sensitive to habitat loss compared with SM taxa. In this study, we propose a new approach to ichthyoplankton studies using spatial networks that could contribute to support decisions about habitat prioritization. We also highlight the importance of preserving tributaries mainly used by long-distance migratory species, which spawn in these sites so the larvae can drift towards nursery areas. [ABSTRACT FROM AUTHOR]

Spatial heterogeneity is one of the major sources of compositional dissimilarity among fish in different biotopes. The availability and distribution of refuge, food, and habitats for breeding are determinants of the presence of fish species with different life histories, and understanding how this composition is organized along an environmental gradient is important for the protection of fish spawning sites and preservation of conditions that favor the dispersion and growth of their larvae. Thus, this study aimed to evaluate how the ichthyoplankton community is structured in different biotopes (river, lake, and transitional) of a fluvial system and to determine the factors involved in the structuring process. We conducted sampling in the lower Ivinhema River, upper Paraná River floodplain, Brazil, during two consecutive reproductive periods between 2010 and 2012. Larvae of long-distance migratory species were more related to the river biotope, while the non-migratory or short-distance migrators were more associated with transitional and lake biotopes. Therefore, our results indicate that the hydrodynamic conditions of the river, especially the flow velocity, as well as the parental reproductive guild, influence the distribution patterns of the ichthyoplankton community. [ABSTRACT FROM AUTHOR]

The diet and distribution of native (Hypostomus ancistroides, Hypostomus sp.) and exotic juvenile Loricariidae fish (Hypostomus cochliodon, Loricariichthys platymetopon, Pterygoplichthys ambrosettii) from a Neotropical floodplain were analyzed, aiming to understand if these factors contribute to coexistence. Sampling was conducted from 2002 to 2015 in two biotopes (river and lake) of the Ivinheima River basin, Brazil. In the river, abundance was similar between species, whereas, in the lake, P. ambrosettii differed from the other species, showing high abundance. Diet analysis revealed a predominance of detritus, plant material, and algae. Pterygoplichthys ambrosettii and L. platymetopon presented distinct diets. By contrast, the three Hypostomus consumed the same resources. We found trophic differences between the two biotopes. Niche breadth and overlap showed that similarity in the diet cannot explain species coexistence, but the high availability of the consumed items supports resource partitioning, promoting coexistence. However, the high population size of P. ambrosetti suggests a possible competitive relationship, potentially harming native species. The results suggest the importance of monitoring sympatric species in fish assemblages, especially where exotic species have been successfully established. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate fish eggs and larvae dispersal in a river stretch influenced by small hydropower plants in Southeast Brazil. The main hypothesis is that the downstream dispersal of free-flowing eggs and larvae is likely to occur given the small size of the studied reservoirs and that passage through the dam may occur, with the fish ladder contributing to it. Eggs and larvae were collected fortnightly, between November 2016 and February 2017, from locations upstream of two dams, including lotic, transition and lentic zones. Additional samples were collected inside the fish ladders at each dam. Downstream dispersal of eggs and larvae was influenced by a combination of rainfall/flow variation and stage of the reproductive cycle, with the peak of rainfall during the summer coinciding with higher abundances. Under these conditions, eggs and larvae drifted downstream through the reservoirs and reached the dams. Once in the dam, they could pass through the fish ladder. This passage was correlated with larval density in the reservoir immediately upstream, although at very low densities compared with the other sampling sites located upstream of the fish ladders. [ABSTRACT FROM AUTHOR]

Caffeine is a contaminant frequently detected in water bodies. Growth trends in both human population and caffeine consumption per capita are expected to exacerbate the occurrence of caffeine in freshwaters. Yet the effects of caffeine on native fish fauna are poorly understood. We exposed larvae of an endemic Neotropical catfish (Rhamdia quelen) to a range of caffeine concentrations for 30 days. We found that larvae exposed to the highest concentration (16 mg L−1) showed skeletal deformations and reduced growth. We further compiled measured environmental concentrations of caffeine in surface freshwater globally and performed a risk assessment. Our analysis points to a low risk to R. quelen and equally sensitive fish species in ~90% of the freshwater ecosystems considered in our analysis. The risk quotient is higher in freshwater ecosystems of South and Central America, where R. quelen is endemic. Although the ecotoxicological risk is currently low in most places, increased caffeine consumption, exacerbated by the lack of sanitation, is expected to increase caffeine concentrations in many parts of the world, posing a threat of sublethal morphological effects to local fish species. [ABSTRACT FROM AUTHOR]

The diversity of fish larvae in floodplain environments exhibits spatial and temporal variations since fish have different ontogenetic requirements, and is influenced by their reproductive period. In order to evaluate how the diversity of fish larvae is structured in different temporal and spatial scales in the sub-basin of the Ivinhema River, Upper Paraná River floodplain (MS, Brazil), we performed monthly samplings in two reproductive periods (2010/2011 and 2011/2012). Variation in alpha (α) diversity was evaluated through a nested ANOVA, while beta (β) diversity was evaluated with distance-based tests for the homogeneity of multivariate dispersions (PERMDISP). Additive partitioning of diversity was used to verify the relative contribution of each scale to gamma (γ) diversity. The first reproductive period showed higher intensity and duration of flooding, which favored a higher γ diversity. Alpha and beta diversities also varied among the different habitats, each one being occupied by species with distinct reproductive strategies. Components β (variation among months) and β (variation among habitats) significantly explained γ diversity in both reproductive periods, indicating that more intense floods favor reproduction and increase diversity of fish larvae. This study reinforces the importance of temporal and spatial scales in the maintenance of fish larvae diversity in floodplains. [ABSTRACT FROM AUTHOR]

Fish, like other animals, choose environments for reproduction that are favorable for their offspring's initial development. For example, these environments may be chosen to provide shelter and food. This study examined the fish larvae inhabiting the Ivinheima River sub-basin. The study aimed to (i) characterize the taxonomic composition of the larval fish fauna, (ii) analyze the structure of the larval assemblage, and (iii) verify the relationship between the larval assemblages and environmental variables. The sampling areas included three environments: the Ivinheima River, the Finado Raimundo Lagoon and the Patos Lagoon. Sampling was performed between October 2002 and March 2006 during four reproductive periods (RPs). The data were analyzed with correspondence analysis (CA) and canonical correlation analysis (CCA). A total of 120 619 larvae were collected. These larvae belonged to several species characterized by different reproductive strategies. Our results showed differences between the composition of the Ivinheima River's assemblages, where there were more larvae of migratory fish, and the lagoons, where larvae of sedentary species were predominant. In addition, differences were found among the RPs evaluated in the Ivinheima River: the first and second RPs were characterized by milder floods and by a greater abundance of migratory piscivore larvae, whereas the third and fourth RPs had more outflow and a greater abundance of larvae of detritivore and omnivore species. We conclude that the Ivinheima River plays a significant role in the maintenance of native migratory fish stocks in the upper Paraná River basin and that the environment shows a segregation of the spatial and temporal composition and abundance of larvae related to running and flooding/standing water. [ABSTRACT FROM AUTHOR]

Studies that assess reproduction dynamics and ichthyoplankton distributions are scarce for the upper Uruguay River, especially in environments such as tributary mouths. Therefore, this study aimed to evaluate: (i) ichthyoplankton composition; (ii) spatial and temporal variation in ichthyoplankton abundance; and (iii) relationships between environmental variables and the abundance of ichthyoplankton during one annual cycle in this region. Monthly samples were collected from September 2001 to August 2002 in 48 h cycles at 6 h intervals between each sampling. Samples of eggs and larvae were collected from three of the main tributaries of the region (Ligeiro, Palomas and Chapecó rivers) and from three stretches of the Uruguay River near the confluence of these tributaries. Surface samples were collected with a 0.5 mm mesh cylindro-conical net. In general, reproductive seasonality was well-defined between October and February. It was most intense from November to January, when the photoperiod reached its highest values, flow was decreased, and the water temperature was increased. Based on egg and larval distributions, we found that spawning occurred mainly in the Ligeiro and Chapecó tributaries and in the Uruguay/Chapecó section. In contrast, fish spawning in the sites downstream of dams was more restricted. Finally, a difference was observed between the egg and larval distributions of the main river and its tributaries: the greatest reproductive activity in the tributaries occurred during periods of high flow and increased water temperature, while in the main river, more eggs and larvae were observed when the flow decreased and the water temperature increased. [ABSTRACT FROM AUTHOR]

We sampled the Baía River (Mato Grosso do Sul State, Brazil) monthly, to survey taxonomic composition and temporal and spatial distribution of fish larvae. The ichthyoplankton was mainly composed by larvae of small and medium sized sedentary species and it was numerically dominated by six taxa:Plagioscion squamosissimus,Hypophthalmus edentatus,Hopliasaff.malabaricus,Bryconamericus stramineus,Serrasalmusspp. andCatathyridium jenynsii. These taxa present distinct temporal and spatial occurrence patterns:H. edentatus, B. stramineusandC. jenynsiiare abundant between September and March in lentic areas;H. aff.malabaricusandSerrasalmusspp. were caught between October and February in lotic areas; whereasP. squamosissimusoccurs in all sampled areas, with peak of capture in January.Hypophthalmus edentatus,H. aff.malabaricus, Serrasalmusspp. andB. stramineuswere the taxa that most contributed to structure the assemblages temporally and spatially, and their abundances were influenced by the interaction of several environmental variables. [ABSTRACT FROM AUTHOR]

We analyzed the ontogenetic shifts in digestive tract morphology and diets of the young ofIheringichthys labrosus,Hypophthalmus edentatusandPlagioscion squamosissimus, sampled in the Itaipu Reservoir, Brazil-Paraguay. We described the dental structures, the gill rakers and the digestive tract, and analyzed the diet of the young fish. We observed teeth in the jaws and pharynx in young of the three species. InH. edentatus, the gill rakers developed more rapidly, and were longer and more numerous on the first arch, related to their planktivorous feeding habit.I. labrosusandP. squamosissimushad long gill rakers only on the first arch, they were short and thick on the rest. The stomach was defined only inP. squamosissimus, with pyloric caeca. Their diets were mainly zooplankton.I. labrosusfed particularly on cladocerans and rotifers;H. edentatusconsumed essentially cladocerans; andP. squamosissimusfed basically on copepods. We observed greater similarity in diet between the young ofI. labrosusandH. edentatus, especially for the first length classes. The diet ofI. labrosusbecame more diversified at the end of the larval period, indicating a transition in the feeding habit and habitat for this species.P. squamosissimusshowed a very different diet from the others species. The differences in oral anatomy, allied to the morphology of the digestive tract, visual acuity, swimming hability, way of foraging, and especially mouth position, form and size, were determining factors in the diets of these species. [ABSTRACT FROM AUTHOR]

We studied the timing of migratory fish spawning in the last dam-free stretch of the upper Paraná River and in Itaipu Reservoir. Eggs were more common in the Amambai and Ivaï Rivers, while larvae predominated in the Paraná River and in Itaipu Reservoir. Both eggs and larvae were more abundant at night. The highest abundance of eggs was in October and that of larvae in November. Migratory species predominated in the Amambai and Paraná Rivers, and non-migratory species in the Ivaï River and Itaipu Reservoir. The predominance of eggs in the upper and middle portions, and larvae in the lower, infer that there are spawning sites in the former and nurseries in the latter. The high nocturnal abundance of eggs is associated with spawning at sunset and that of larvae with feeding, avoidance of predators and nocturnal disorientation. The presence of tributaries such as the Amambai and Ivaí Rivers in the last dam-free stretch of the Paraná River is extremely important to the maintenance of regional fish diversity and fish stocks in both the Paraná River and Itaipu Reservoir. [ABSTRACT FROM AUTHOR]