Spawning and parental care in Hoplias malabaricus (Teleostei, Characiformes, Erythrinidae) in the Southern Pantanal, Brazil

Multiple karyotype differences between populations of the Hoplias malabaricus (Teleostei; Characiformes), a species complex in the gray area of the speciation process

Neotropical fishes exhibit remarkable karyotype diversity, whose evolution is poorly understood. Here, we studied genetic differences in 60 individuals, from 11 localities of one species, the wolf fish Hoplias malabaricus, from populations that include six different "karyomorphs". These differ in Y-X chromosome differentiation, and, in several cases, by fusions with autosomes that have resulted in multiple sex chromosomes. Other differences are also observed in diploid chromosome numbers and morphologies. In an attempt to start understanding how this diversity was generated, we analyzed within- and between-population differences in a genome-wide sequence data set. We detect clear genotype differences between karyomorphs. Even in sympatry, samples with different karyomorphs differ more in sequence than samples from allopatric populations of the same karyomorph, suggesting that they represent populations that are to some degree reproductively isolated. However, sequence divergence between populations with different karyomorphs is remarkably low, suggesting that chromosome rearrangements may have evolved during a brief evolutionary time. We suggest that the karyotypic differences probably evolved in allopatry, in small populations that would have allowed rapid fixation of rearrangements, and that they became sympatric after their differentiation. Further studies are needed to test whether the karyotype differences contribute to reproductive isolation detected between some H. malabaricus karyomorphs.

Cross-habitat utilization of fish in a tropical deltaic system as a function of climate variability and body size: Are mangroves fish nurseries in a tropical delta?

The temporal variability of fish habitat utilization is poorly understood in tropical deltaic systems due to high water turbidity, which limits visual censuses, and to the lack of long-term data incorporating climate variability events. We aimed to assess the influence of body size and El Niño Southern Oscillation (ENSO) variability on the cross-habitat utilization rate of 14 fish species of commercial relevance in the Ciénaga Grande de Santa Marta (CGSM). We estimated the utilization of mangroves and coastal lagoons based on relative catch frequencies from encircling gillnets used within a long-term catch monitoring program, and then tested for significant changes in each species' habitat utilization as a function of body size and climate variability. Six species showed a high dependence on mangroves and four on coastal lagoons for most body size classes (including juveniles) and ENSO conditions. One species (Elops smithi) showed a high utilization of mangroves in some ENSO phases and body size classes, while three species showed a high utilization of both mangroves and coastal lagoons. Mangrove utilization by six species (Megalops atlanticus, E. smithi, Centropomus undecimalis, Mugil incilis, Mugil liza, and Ariopsis canteri) increased in larger body sizes at low depths, which usually occurs under dry ENSO conditions, when predatory risk is higher in coastal lagoons. Another species (Caquetaia kraussi) increased its mangrove utilization from the body size at which its feeding habits change. Mangroves and coastal lagoons are important nurseries and habitats for adults of the main commercial fish species in the CGSM. Seascape habitats and fringe/riverine mangroves must be conserved in tropical deltas to promote not only nurseries but also fish lifecycles.

DNA Barcoding unveils cryptic lineages of Hoplias malabaricus from Northeastern Brazil

The trahira or wolf fish - Hoplias malabaricus- is a valid species, although recent cytogenetic and molecular studies have indicated the existence of a species complex. In this context, the present study analyzed the mitochondrial COI marker to determine the levels of genetic diversity of specimens from the Brazilian state of Maranhão, and verify the occurrence of distinct lineages within the study area. Samples were collected from the basins of the Turiaçu, Pindaré, Mearim, Itapecuru, and Parnaíba rivers. A 630-bp fragment was obtained from 211 specimens, with 484 conserved and 108 variable sites, and 60 haplotypes (Hd = 0,947; π = 0,033). The phylogenetic analyses indicated the existence of three distinct lineages of H. malabaricus from Maranhão. Genetic distances of 1.5-8.2% were found between all the populations analyzed, while the variation between haplogroups ranged from 2.1% to 7.7%. The AMOVA indicated that most of the molecular variation was found among groups, with high FST values. The high levels of genetic variability found in the present study are supported by the available cytogenetic data. These findings reinforce the need for the development of effective programs of conservation and management independently for each river basin, in order to preserve the genetic variability found in this taxon.

Hydropower affects fish trophic structure both downstream of the dam and upstream of the reservoir

ABSTRACT Dams often cause drastic changes in freshwater environments and can compromise the quality and availability of food resources in rivers. This study aims to analyze the influence of a dam on the trophic structure of fish assemblages in lotic areas located both upstream and downstream of the Irapé Hydroelectric Power Plant. Fish sampling occurred before (2003 to 2005) and after (2011 to 2017) the impoundment, which began in 2006. The trophic structure and species composition before dam construction were similar upstream of the reservoir and downstream of the dam. After the building of the dam, both aspects of the assemblages changed along the lotic stretches - the upstream incurred an increase in biomass of detritivores and a decrease of piscivores and omnivores, while downstream went exactly the opposite, causing a differentiation between the two assemblages. Because lotic areas upstream of reservoirs are also impacted by river damming, efforts for impact mitigation should also focus on these areas.

Structure and diversity of fishes in a freshwater and coastal subtropical lagoon

This study examined the fish communities of Peri Lagoon in southern Brazil to aid in the development of an effective management plan because the area is under threat from human activities. Sampling of fish fauna, ichthyoplankton and limnological data were compared between sites, differing by habitat type and characteristics such as depth, substratum composition and vegetation type. Results were significantly related to site, with the highest diversity and abundance recorded at shallow vegetated sites. A total of 14 fish species were recorded throughout the lagoon, with the most abundant being Hyphessobrycon luetkenii. Of the 14 species, half were sampled at their larval stage, suggesting a healthy and protected system. Significantly more larvae and eggs were collected during colder months (autumn to winter) and at sites closer to stream flow, possibly owing to increased food sources and habitat protection. This study highlights the importance of Peri Lagoon as a nursery ground for a wide range of fish species, providing essential information for incorporation into the future protection of fish stocks throughout Brazil.

The role of ovarian steroids in reproductive plasticity in Hoplias malabaricus (Teleostei: Characiformes: Erythrinidae) in tropical reservoirs with different degrees of pollution

Chemicals in aquatic environments may lead to impairment of fish reproduction, but some species display plasticity levels to survive and reproduce in such localities. We investigated the reproductive cycle in a teleost species, Hoplias malabaricus, which inhabits a variety of environments with different degrees of pollution. Adult females were sampled at two locations in São Paulo State (Brazil), the reference Ponte Nova (PN) reservoir and the polluted Billings (BIL) reservoir. Metabolic and endocrine processes were analyzed throughout the annual cycle with special attention to ovarian histology, gonadosomatic index (GSI), fecundity, ovarian energetic substrates and plasma steroids analyses, in addition to physical and chemical analyses of the water. Pollutants were frequent in BIL but not in PN. The GSI, including the predominance of vitellogenic oocytes, was higher in spring and summer in both locations, but the oocyte recruitment dynamics was different. During winter, females from BIL presented vitellogenic oocytes and high levels of 11-ketotestosterone, which indicated precocity in the vitellogenic phase in relation to the females from PN. In animals from PN, high deposition of lipids occurred in the ovaries. However, plasma estradiol levels did not vary throughout the annual cycle. In animals from BIL, plasma estradiol levels peaked during the summer, but the ovarian lipid content remained unchanged throughout the year. The data suggest that the presence of pollutants cause various endocrine and metabolic responses and especially affects reproductive plasticity, which could explain why H. malabaricus survives under unfavorable environments.

DNA barcoding of freshwater ichthyoplankton in the Neotropics as a tool for ecological monitoring

Quantifying and classifying ichthyoplankton is one of the most effective ways of monitoring the recruitment process in fishes. However, correctly identifying the fish based on morphological characters is extremely difficult, especially in the early stages of development. We examined ichthyoplankton from tributaries and reservoirs along the middle stretch of the Paranapanema River, one of the areas most impacted by hydroelectric projects in the Neotropics. Matching DNA sequences of the COI gene (628-648 bp) allowed us to identify 99.25% of 536 samples of eggs (293) and larvae (243) subjected to BOLD-IDS similarity analysis with a species-level threshold of 1.3%. The results revealed 37 species in 27 genera, 15 families and four orders, some 23.8% of documented fish species in the Paranapanema River. Molecular identification meant that we could include data from egg samples that accounted for about 30% of the species richness observed. The results in this study confirm the efficacy of DNA barcoding in identifying Neotropical ichthyoplankton and show how the data produced provide valuable information for preparing plans for conserving and managing inland waters.

Genetic differentiation among distinct karyomorphs of the wolf fish Hoplias malabaricus species complex (Characiformes, Erythrinidae) and report of unusual hybridization with natural triploidy

In this study, genetic differentiation between karyomorphs A (2n = 42) and D (2n = 39/40) of the wolf fish Hoplias malabaricus, which is comprised of several cryptic species that present a wide variety of diploid chromosome numbers and sex chromosome systems, resulting in the identification of seven distinct karyomorphs (A-G), was investigated using a combination of molecular and cytogenetic tools. Deep sequence divergences for both karyomorphs were observed and indicate a long period of reproductive isolation between karyomorphs A and D. Additionally, one individual with 61 chromosomes was identified, which, as far as is known, is the first case of natural triploidy resulting from the hybridization between these highly differentiated karyomorphs of H. malabaricus. Molecular and cytogenetic analyses revealed that this allotriploid specimen carries two sets of maternal chromosomes from karyomorph D (2n = 40) and one set of chromosomes from karyomorph A (n = 21). Moreover, ribosomal sites and active nucleolus organizer regions from both parental contributors were found in the triploid hybrid. Considering the significant genetic distances between karyomorphs A and D, one of the primary reasons for the lack of recurrent reports of hybridization in the H. malabaricus species complex may be due to post-zygotic barriers, such as hybrid sterility or unviability.

Spatio-temporal distribution of fish larvae in relation to ontogeny and water quality in the oligohaline zone of a North Brazilian estuary

Larval fish assemblage in Guajará Bay was studied through four quarterly field campaigns and discussed in relation to individuals' development stages and exposure to contaminants poured out by the Pará State Capital City, Belém. Larval densities were low and diversity extremely poor with a strong dominance of clupeids, engraulids and, to a lower extent, sciaenids. The main spawning season was registered at the onset of the rainy period. Pre-flexion and flexion clupeiforms remained in the farmost stations from the city while post-flexion larvae were found near urban activity centres. Unlikely, pre-flexion and flexion sciaenids were scattered along the city waterfront. Post-flexion larvae were rare; it is suggested that sciaenids use the bay as a transitory route between their spawning grounds and more distant nursery grounds. The waters around the city of Belém showed signs of contamination. However, based on the literature, Guajará Bay environmental quality at the time of the study was suitable for fish larvae life. Nitrate with pH best explained larval distribution.

Pleistocene karyotypic divergence in Hoplias malabaricus (Bloch, 1794) (Teleostei: Erythrinidae) populations in southeastern Brazil

The lacustrine system of the middle rio Doce basin is considered a paradigm of Pleistocene geomorphology. In these lakes, two Hoplias malabaricus karyomorphs (2n = 42A and 2n = 42B) live in sintopy in Carioca Lake. Cytogenetic analyses were performed on 65 specimens from 8 lakes (including Carioca Lake) to determine the distribution and relative frequency of these karyomorphs and the degree of cytogenetic divergence caused putatively by recent geographic isolation. All fish were 2n = 42B karyomorphs, except for 1 specimen from the Marola Lake, which was 2n = 42A. Among-population variation was especially high for C-banding patterns. Other characters such as X chromosome size and CMA3/DAPI also varied among populations. Our results suggested that the karyotype of H. malabaricus is able to respond rapidly to geographic isolation, and revealed that heterochromatic variation may represent the lowest hierarchical level of chromosomal evolution.

HF, Fugi R. Effects of flooding regime on the feeding activity and body condition of piscivorous fish in the Upper Paraná River floodplain

Flood pulses affect floodplain enrichment via the incorporation of nutrients and terrestrial biomass. As a result, they positively affect the body condition of aquatic organisms. This paper evaluates whether the absence of floods (resulting from dam control) affects the feeding activity and body condition of piscivorous fish. In addition, whether piscivores respond similarly to alterations in the flooding regime was assessed. Five piscivorous species were selected (Acestrorhynchus lacustris, Hoplias aff. malabaricus, Plagioscion squamosissimus, Rhaphiodon vulpinus, and Salminus brasiliensis). The fish were captured in four distinct years and in three river subsystems with differentiated water level fluctuations (Ivinheira = not regulated; Baía = regulated by the Paraná River level; Paraná = regulated by dams). Feeding activity and body condition were evaluated using the mean values of the standard residuals generated by regression models between body and stomach weights and standard length and body weight (all log-transformed). Differences among years and subsystems were evaluated via two-way analysis of variance. Pearson and Spearman correlations were performed between flooding attributes (duration, amplitude, timing, and daily variability) and feeding activity and body condition. Feeding activity differed across subsystems, whereas body condition varied across years, depending on the subsystem. Hoplias aff malabaricus (an ambusher adapted to starvation) presented feeding activity independent of the flooding regime and also presented better body condition in times of high water levels. Rhaphidon vulpinus exhibited variations in feeding activity but did not present alterations in body condition. The other species presented poorer body condition in years or subsystems with regular floods. Correlations identified that the duration and timing of floods had negative effects on body condition, whereas amplitude and mean annual water level improved feeding activity. Therefore, regular floods affect the feeding activity and body condition of piscivorous fish, and the response of each species depends on the existence or absence of pre-adaptation to long periods of starvation. Consequently, considering the role of the flood pulse in determining the availability of feeding resources for early life stages of piscivores, control of the flood pulse by dams is also disadvantageous for piscivorous fish.