Search

Trichomycterid catfishes have long been considered as absent in the Parnaíba River basin, Northeastern Brazil, in what constitutes their most conspicuous gap in geographic distribution. Herein we report on the first occurrence of the family in that basin. The new species is described from the riacho da Volta, right tributary to the upper rio Parnaíba, Piauí State. It is distinguished from its congeners by the combination of two or three pairs of ribs; 36–38 post Weberian vertebrae; a color pattern composed of round, similar-sized, non-coalescent spots; I,5 pectoral-fin rays; the first haemal arch on the 5th or 6th vertebrae; and the first completely fused (to the tip) haemal spine on the 15th vertebra. A putative autapomorphy is the partial (minimally 50% of their length) or total fusion between the anterior arms of the basipterygium. Preliminary evidence suggests that the new species can be related to northern South American forms, a pattern that fits the general Amazonian relationships of the fishes in the Parnaíba River drainage. Although the new species fills in an important qualitative gap in trichomycterid continental distribution, the taxon is apparently rare and extremely restricted in distribution, with the type series being its only record so far. The paucity of trichomycterids in the Parnaíba remains a puzzling biogeographical phenomenon. Resumo Os bagres tricomicterídeos têm estado surpreendentemente ausentes na bacia do rio Parnaíba, Nordeste do Brasil, no que constitui sua lacuna mais evidente na distribuição. Relatamos a primeira ocorrência da família na bacia. A espécie nova é descrita do riacho da Volta, tributário do lado direito do alto rio Parnaíba em Uruçuí, Piauí. Ela é distinguida de suas congêneres pela combinação de dois ou três pares de costelas; 36–38 vértebras pós weberianas; padrão de coloração composto de manchas arredondas, de tamanhos semelhantes e não coalescentes; I,5 raios nas nadadeiras peitorais; o primeiro arco haemal na 5° ou 6° vértebra, e o primeiro espinho haemal completamente fusionado (até a extremidade) na 15° vértebra. Uma possível autapomorfia é a fusão parcial (mínimo de 50% do seu comprimento) ou total entre os braços anteriores do basiopterígio. Evidências preliminares sugerem que a espécie nova pode estar relacionada com as formas do norte da América do Sul, padrão que se encaixa nas relações amazônicas dos peixes da drenagem do rio Parnaíba. Embora a espécie nova preencha uma importante lacuna na distribuição continental dos tricomicterídeos, o táxon é aparentemente raro e extremamente restrito em distribuição, sendo a série-tipo seu único registro até o momento.

Insufficient knowledge about ecology of weed macrophytes from a large-scale perspective narrows the necessary decision-making for biodiversity conservation. The present study aimed to assess the occurrence frequency of Egeria densa in lotic and lentic/semi-lotic environments from a Brazilian dammed river, as well as to quantify the attributed explanation (pure or combined) by limnological and spatial variables on species occurrence frequency. Between 2006 and 2010, we repeatedly visited sample points classified as lotic (45) or lentic/semi-lotic environments (23) to collect data on species occurrence and limnological variables. We also generated spatial variables derived from latitude and longitude of sample points. E. densa showed a recurrent occurrence in the sample points classified as lentic/semi-lotic. Both spatial variables (16) and limnological variables (total phosphorus, nitrate, nitrite, transparency and turbidity) significantly contributed to explaining the species occurrence frequency. Forty-nine percent of the occurrence frequency variation was accounted purely by spatial variables. However, less than five percent of occurrence frequency variation was accounted purely by limnological variables. The several dams placed along the river determined the lentic/semi-lotic environments formation and regulated the dispersion processes of individuals of E. densa, consequently causing a recurrent occurrence of this species in particular environmental classes.

This research evaluated the growth of Daphnia similis in wastewater from Nile tilapia (Oreochromis niloticus) farmed in a biofloc system (carbohydrate:nitrogen of 12:1). During 30 days, physical-chemical and growth variables were measured in the following treatments: DCWC—D. similis growth in clear water with the addition of C. vulgaris (autotrophic culture); DB—D. similis growth in biofloc wastewater from Nile tilapia farmed without the addition of C. vulgaris (mixotrophic culture); and DBC—D. similis growth in biofloc wastewater from Nile tilapia farmed with the addition of C. vulgaris (mixotrophic culture). The biofloc wastewater (DB and DBC) underwent significant changes in water quality (P 0.05) from DB in relation to MAD in the second cycle. Thus, wastewater from Nile tilapia cultivation in a biofloc system as a culture medium for raising D. similis, with the addition of C. vulgaris, proved to be a promising option for producing live food for aquaculture.

The objective of this study was to evaluate the effect of the addition of Navicula sp. on the growth and fatty acids profile of Litopenaeus vannamei postlarvae in a biofloc system (BFT). Four treatments were used: BFT; BFT 2.5N (addition of 2.5 × 10⁴ cells/ml of Navicula sp.); BFT 5N (addition of 5 × 10⁴ cells/ml of Navicula sp.) and BFT 10N (addition of 10 × 10⁴ cells/ml of Navicula sp.), all in triplicate. The shrimp (1 ± 0.01 mg) were stocked at a density of 3,000 postlarvae/m³ and fed with commercial feed. The diatom was added every 10 days, and at the end of 42 days, shrimp performance, water quality and proximal composition were evaluated. The BFT 5N and BFT 10N treatments had higher performance values, highlighting the values of productivity (2.30 and 2.42 kg/m³) and specific growth rate (15.92 and 16.08%/day), which were higher than the other treatments. In addition, the highest levels of fatty acids were observed in treatments with diatom (BFT 5N and BFT 10N), indicating the benefits of Navicula sp. on growth enhancement and fatty acid content of L. vannamei postlarvae grown in biofloc systems.

Dams have altered the physiography and ecology of large rivers, causing severe environmental changes at a global scale. Assuming that series of reservoirs induce physical, chemical, and biological longitudinal changes in rivers, we tested the hypotheses that (i) the structure of biological communities in reservoir cascades is not only affected by changes in water quality, but also by cumulative hydrological alteration and impacts on river connectivity; and (ii) fish are more affected by cumulative effects of reservoirs when compared to other aquatic assemblages. Samplings of three assemblages (phytoplankton, benthic macroinvertebrates, and fish) were conducted in the reservoir cascade of Sao Francisco River, Brazil. We estimated the relative role of environmental and spatial predictors through variation partitioning analyses. Environmental variables, cumulative reservoir volume, longitudinal position, and distances from nearest reservoirs were used as explanatory variables. Environmental variables were the most important for the phytoplankton community. No significant effects of the predictors used were found for benthic macroinvertebrates, whereas spatial variables and cumulative reservoir volume were the most important predictors for fish. Therefore, our results provide evidence of impacts along reservoir cascades, and suggest that their effects mainly influence fish assemblages.

We assessed the relationships among native and introduced fish species richness and a set of explanatory variables, including area, altitude, reservoir age, temperature, human influence index and fish abundance. We expected to find different relationships based on species origin (i.e., native or introduced). Based on compiled data from Brazilian reservoirs, we modeled the variation in the number of native and introduced fish species by generalized linear mixed models with different spatial autocorrelation structures. Reservoirs located in warmer regions and with higher fish abundance showed higher species richness of both native and introduced fish. Reservoir age tended to be negatively correlated with native species richness. Our results suggest that reservoir communities in warmer regions may be more resistant to local extinctions caused by impoundments, but they are more susceptible to species introductions. Our results also highlight that an extinction debt can be expected for native species because older reservoirs showed lower native species richness.

Dam construction alters flow regimes and can change the composition of aquatic communities. Using data from three Brazilian hydrographic basins, we tested the hypothesis that reservoir cascades act as environmental filters for fish traits. This dataset included information on different environmental variables and fish traits (diet, migration, fecundation, parental care, position in the water column, and body size), and we used multivariate analysis (partial RLQ) to quantify the relationships between environmental variables, species abundance and traits. We found that the abundance of migratory species declined towards downstream reservoirs, which tend to be smaller and less turbid with a shorter water residence time than upstream reservoirs. We also found evidence of an association between reservoir age and the domination of fish communities by small-sized species with parental care, external fecundation, and benthic habits. Our findings suggest that particular fish traits are selected for across reservoir cascades.

The aim of this study was to evaluate the effect of the addition of Chaetoceros calcitrans, Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and the growth of Litopenaeus vannamei postlarvae reared in a biofloc system. Four treatments were used: BFT (biofloc system without feed and no addition of diatoms); BFT-F (biofloc system with feed and no addition of diatoms); BFT-D (biofloc system with the addition of diatoms and no feed); and BFT-FD (biofloc system with the addition of feed and diatoms), all in triplicate. The shrimp (16 ± 0.02 mg) were stocked at 2500 postlarvae m−3 and fed a commercial feed. Diatoms were added on the 1st, 5th, 10th and 15th day at a density of 5 × 104 cells mL−1 for each species. No significant differences (P > 0.05) between treatments were observed for gross primary production, net ecosystem production and water column respiration rate. However, significant differences (P

The aim of this study was to evaluate the effect of supplementation with Chlorella vulgaris and molasses application rates on water quality, zootechnical performance, proximate composition and health status of Nile tilapia (Oreochromis niloticus) fingerlings cultivated in low-salinity (10 g L-1) biofloc systems. Four treatments were tested in a factorial design (supplemented with microalgae and molasses application rates): BFT-C30 (Biofloc supplemented with C. vulgaris and molasses application rates of 30% of the total daily feed); BFT-30 (Biofloc with molasses application rates of 30% of the total daily feed); BFT-C50 (Biofloc supplemented with C. vulgaris and molasses application rates of 50% of the total daily feed) and BFT-50 (Biofloc with molasses application rates of 50% of the total daily feed), for 70 days. Fingerlings of O. niloticus (initial mean weight of 3.15 ± 0.5 g) were stocked at a density of 680 fish m-3 in experimental units (50L), where 50% of this volume was biofloc previously matured. Throughout the experiment, they were supplemented with C. vulgaris every five days at the concentration of 5x104 cells mL-1. A significant interaction between supplementation with C. vulgaris and molasses application rates for final weight and length, survival, feed conversion ratio, specific growth rate, water consumption, protein efficiency ratio, sedimentation time, planktonic community and hematological indices were observed. The results indicated that the high molasses application rates (50%) in the biofloc system affects the zootechnical performance, water consumption, sedimentation time and the hematological indices of the Nile Tilapia fingerlings, hampering their development. Therefore, molasses application rates of 30% of the total daily feed for the tilapia fingerlings culture in low-salinity biofloc system is recommended.

The assemblage and functional structure of the fish fauna of the Maracaí­­pe River, municipality of Ipojuca - PE, was characterized by monthly beach trawls carried out from March of 2012 to February of 2013. A beach trawl net (picaré) was used at three different points of the estuary (EST 1, EST 2 and EST 3) during day and night trawls. The captured specimens were measured and weighed in the laboratory, identified and separated into use and trophic guilds using appropriate literature. Abiotic variables (temperature, salinity, dissolved oxygen, pH, turbidity and chlorophyll-a) were analyzed as for differences between day periods (night and day) and seasons (dry and rainy), and correlated to fish abundance. No difference was detected between day periods (p>0.07 for all variables), but they differed between seasons for most variables (pâ"°¤0.02), and between sampling points only for dissolved oxygen (p=0.03). In one year of collection, 11,513 specimens were captured, belonging to 92 species, 38 families and 15 orders. Gerreidae, Atherinopsidae, Clupeidae, Gobiidae and Hemiramphidae were responsible for 82.9% of the total abundance. The estuary of the Maracaí­­pe River presents a rich ichthyofauna, but with the quantitative predominance of seven species (Atherinella brasiliensis, Eucinostomus argenteus, E. melanopterus, Ulaema lefroyi, Lile piquitinga, Ctenogobius boleosoma and Hyporhamphus unifasciatus). In the estuary, six species classified as vulnerable on the IUCN Endangered Species List were reported. The estuary presents a high diversity of species, most of them marine, carnivorous, and opportunistic, showing the high resilience of this environment. The predominance of juvenile fish underscores the importance of the Maracaí­­pe River estuary for the maintenance of population stocks of coastal species, demonstrating the urgent demand of management of this environment.

O hábito alimentar do beijupirá, Rachycentron canadum, foi descrito ao longo da costa do Estado de Pernambuco, Nordeste do Brasil. Foram capturados 110 exemplares entre fevereiro/2004 e agosto/2006, com comprimento furcal ou zoológico variando entre 40,0 e 137,0 cm (média e desvio padrão: 85,8±18,0 cm) e peso total entre 0,4 e 29,8 kg (7,5±4,4 kg). Foi avaliada a importí­¢ncia de cada item alimentar na dieta utilizando o í­­ndice de importí­¢ncia relativa (IIR). Dentre os 110 estômagos analisados (52 fêmeas e 58 machos), 92 (83,6%) com algum item alimentar e 18 (16,4%) vazios. Os peixes ósseos foram os principais itens consumidos na dieta alimentar (IIR = 98,7%), entre os quais a mariquita (Holocentrus adscensionis) e o baiacu (Diodon sp.) foram as presas mais consumidas (IIR = 30,7% e 8,2%, respectivamente). A dieta foi composta, ainda, por elasmobrí­¢nquios, crustáceos e cefalópodes (IIR

The aim of this study was to evaluate the effect of the addition of Navicula spp. and Brachionus plicatilis on water quality and growth of postlarvae shrimp Litopenaeus vannamei reared in a biofloc system. Four treatments were considered: a control (biofloc system – BFT); BFT with the addition of Navicula spp. (BFT-N); BFT with the addition of Brachionus plicatilis (BFT-B) and BFT with the addition of Navicula spp. and Brachionus plicatilis (BFT-NB), each in triplicate. Shrimp (16.2 ± 0.03 mg) were stocked at a density of 2500 shrimp m−3 and plankton were added on days 1, 5, 10, 15, 20, 25 and 30 at a density of 5 × 104 cells mL−1 (Navicula spp.) and 30 organisms L−1 (Brachionus plicatilis). The shrimp were fed a formulated feed in four daily rations composed of 40% crude protein and 8% lipids. Significant differences between treatments were observed for final weight, yield, feed conversion ratio, specific growth rate, protein efficiency ratio and protein content of the shrimp. The combined plankton addition of Navicula spp. and B. plicatilis had better performance parameters, indicating their benefit as natural food sources for postlarvae L. vannamei in biofloc systems.

The use of probiotics within shrimp farms has increased as an alternative to antibiotic use because of an increasing demand for more environment-friendly aquaculture. This has improved growth performance and health of shrimp, and improved pathogen control as well as water and soil quality in culture systems. However, efficacy of probiotics in intensive systems using biofloc remains uncertain. Here, bioremediation and biocontrol of a commercial probiotic was investigated through analysis of water quality and main bacterial groups that influence a Litopenaeus vannamei culture using biofloc. Furthermore, additional knowledge was gained on phytoplankton and shrimp performance. Treatments consisted of four different probiotic concentrations ( Bacillus subtilis and B. licheniformis ): 0.5 g -3 (P0.5), 1 g m -3 (P1.0), 2 g m -3 (P2.0), 3 g m -3 (P3.0), and a control without probiotic (CTL). All variables were shown to be balanced and within the recommended limits for shrimp farming. Under the culture conditions adopted in this study, the commercial probiotic did not result in a significant effect ( P ≥ 0.05) on water quality, bacteria, phytoplankton, or shrimp performance. Bacteria naturally present in biofloc were sufficient for maintaining the balance of culture and continued to exert excellent bioremediation and biocontrol when management was conducted properly.

An indoor trial was conducted for 42 days to evaluate water quality, Vibrio density and growth of Litopenaeus vannamei in an integrated biofloc system (IBS) with Gracilaria birdiae. Four treatments were used, each in triplicate: Control (monoculture shrimp); IBS 2.5 (L. vannamei and 2.5 kg wet weight seaweed m−3); IBS 5.0 (L. vannamei and 5.0 kg wet weight seaweed m−3) and IBS 7.5 (L. vannamei and 7.5 wet weight seaweed m−3). Shrimp individuals (0.34 ± 0.01 g) were stocked at a density of 500 shrimp m−3. No water exchange was carried out during the experimental period. Molasses was added once a day as an organic carbon source to maintain the C:N ratio at 12:1. The IBS significantly decreased (P

A 28-day indoor trial was conducted to evaluate the water quality, phytoplankton composition and growth of Litopenaeus vannamei in an integrated biofloc system with Gracilaria birdiae and Gracilaria domingensis. The experimental design was completely randomized with three treatments: control (shrimp monoculture); SB (shrimp and G. birdiae) and SD (shrimp and G. domingensis), all with three replicates. Random sampling was done (6 % of total population per experimental unit) to confirm white spot syndrome Virus (WSSV) infection using nested-PCR analysis due to suspicion of presence of the virus in the experiment (treatment and control groups). Shrimp L. vannamei (2.63 ± 0.10 g) were stocked in experimental tanks at a density of 425 shrimp m−3, and the Gracilaria was stocked at a biomass of 2.0 kg m−3. Shrimp mortality began in both the experimental and control groups at 10 days of culture. The integrated biofloc system (shrimp and seaweed) increased settleable solids (by 26–52 %); final weight (by 6–21 %); weekly growth (by 17–43 %); weight gain (by 17–43 %); specific growth rate (by 16–36 %); and yield (by 5–7 %) and decreased feed conversion ratio (by 21–28 %) and Cyanobacteria density about 16 % as compared to the control (shrimp monoculture). The use of red seaweed Gracilaria in an integrated biofloc system can enhance shrimp growth and reduce Cyanobacteria density in the presence of WSSV.

A genetic analysis was conducted of the critically endangered migratory catfish Pseudoplatystoma corruscans from the Sao Francisco River basin, the basin with the second highest hydropower capacity installed in Brazil. The analysis was conducted using five microsatellite markers previously described in the literature. Genetic diversity was analyzed and compared in three wild populations and a captive broodstock for a restocking program. Catfish populations of this river showed high genetic diversity in terms of heterozygosities; however, only half of the total number of alleles found in other basins were detected. Seven private alleles occurred in this basin and most of them at low frequencies, indicating they are under threat of extinction. Overall FST and assignment test suggested low differentiation among the three wild populations; however, a marked distinction between these populations and the captive broodstock was observed. The number of alleles and low average relatedness estimates found for the c...

The genusAchirusis made up of demersal fish that have a close relationship with the substrate and exhibit peculiar aspects during their larval stage. The aim of the present study was to determine whether the abundance ofAchiruslarvae differed among a set of habitats in the estuary of the Formoso River in the State of Pernambuco (north-eastern Brazil). Sampling was performed monthly between April 2009 and March 2010, and comprised horizontal hauls with plankton net during the day and night in mangrove, beach and reef habitats. Fish larvae were sorted, identified, measured and larval stage recorded. Density and body length values were used in a non-parametric analysis of variance for the determination of variations between seasons, habitats and diel periods. A total of 204 larvae were collected, with an average density of 2.1 larvae.100 m−3. Density was greater in the nocturnal samplings, with no differences found between habitats. The larvae occurred in the yolk-sac to post-flexion stage, with pre-flexion the most abundant stage (78%). Size segregation was observed. Larger larvae were captured at night and in the mangrove. The smallest larvae were caught on the reef, with length increasing toward the mangrove. The results indicate thatAchiruslarvae come from deeper regions near reefs, where spawning probably occurs, and perform ontogenetic migration towards the shallow waters of mangrove, where they settle.

The present study describes the external morphology and morphometry of the initial development of Atherinella brasiliensis, and contributes toward broadening knowledge on its biology. A total of 88 larvae and 14 juveniles were used to characterize the morphological development and analyze body proportions. Fish with standard lengths (SL) from 1.4 to 77 mm were used in the study. Larvae hatch at an average of 1.4 mm SL. In the preflexion stage, the larval body is enveloped by a finfold, which begins behind the head. Pectoral fins are the first to be formed and preflexion larvae have four characteristic dendritic chromatophores on the head. The flexion stage begins at an average of 4.4 mm SL; dorsal and anal fins already exhibit pterygiophores and a terminal, somewhat up-turned mouth. At 6.8 mm SL, the flexion stage ends. In the postflexion stage, larvae present greater ossification of the dorsal and anal fin rays, exhibit pelvic fin buds and a darkening of lateral pigmentation. At an average of 8.8 mm SL, head pigmentation intensifies and pelvic fins exhibit conspicuous ossifying rays. Larvae at 11.8 mm SL have all fins formed; the second dorsal fin is the last to be formed at an insertion point posterior to the anal fin. The juvenile period begins at approximately 12 mm SL. At this stage, A. brasiliensis has an anal fin located at the median portion of the body and the posterior end of pectorals surpasses the origin of pelvic fins, which are located at the midpoint between the pectoral and anal fins. Scales are present on the dorsal-lateral region behind the head. The morphological features of A. brasiliensis herein described allow an adequate identification of its larvae and differentiate them from hemiramphid and other atheriniform larvae, thus broadening knowledge on the larval biology of the species. O presente trabalho descreve a morfologia externa e a morfometria do desenvolvimento inicial de Atherinella brasiliensis, contribuindo para a ampliação do conhecimento biológico da espécie. Um total de 88 larvas e 14 juvenis foram empregados para a caracterização do desenvolvimento morfológico e a análise das relações corporais. Peixes com comprimento padrão (CP) de 1,4 a 77 mm foram usados no estudo. As larvas eclodem com CP médio de 1,4 mm. No estágio de pré-flexão, as larvas apresentam o corpo envolvido por uma membrana embrionária, a qual inicia atrás da cabeça. As nadadeiras peitorais são as primeiras a se formarem e larvas em pré-flexão apresentam quatro cromatóforos dendríticos característicos na cabeça. O estágio de flexão inicia com um CP de aproximadamente 4,4 mm, as nadadeiras dorsal e anal já apresentam pterigióforos e uma boca terminal, ligeiramente inclinada para cima. Com um CP de 6,8 mm, o estágio de flexão termina. No estágio de pós-flexão, as larvas apresentam uma maior ossificação dos raios das nadadeiras dorsal e anal, juntamente com o surgimento dos botões das nadadeiras pélvicas e o escurecimento da pigmentação lateral. Com um CP médio de 8,8 mm, a pigmentação da cabeça se intensifica e as nadadeiras pélvicas apresentam raios conspícuos em ossificação. Com 11,8 mm a larva já apresenta todas as nadadeiras formadas, a segunda dorsal sendo a última a ser formada, num ponto de inserção posterior ao da anal. O estágio juvenil inicia-se com aproximadamente 12 mm CP. Neste estágio, A. brasiliensis apresenta a nadadeira anal localizada na porção mediana do corpo, e a extremidade posterior das peitorais ultrapassam a origem das pélvicas, as quais estão localizadas no ponto médio entre as peitorais e a anal. Escamas estão presentes na região dorso-lateral, atrás da cabeça. As características morfológicas das larvas de A. brasiliensis descritas permitem sua adequada identificação, bem como as diferenciam daquelas de hemiramphídeos e outros atheriniformes, assim ampliando o conhecimento sobre a biologia larval da espécie.

Rhinelepis strigosa did not surface for air breathing in normoxic or moderate hypoxic water. This species initiated air breathing when the Pio2 in the water reached 22 ± 1 mmHg. Once begun, the air-breathing frequency increased with decreasing Pio2. Aquatic oxygen consumption was 21·0 ± 1·9ml O2 kg−1h−1 in normoxic water, and was almost constant during progressive hypoxia until the Pio2 reached 23·9 mmHg, considered the critical oxygen tension (Pco2). Gill ventilation increased until close to the Pco2 (7·9-fold) as a consequence of a greater increase in ventilatory volume than in breathing frequency. Gill oxygen extraction was 42 ± 5% and decreased with hypoxia, but under severe hypoxia returned to values characteristic of normoxic. The critical threshold for air breathing was coincident with the Pco2 during aquatic respiration. This suggests that the air-breathing response is evoked by the aquatic oxygen tension at which the respiratory mechanisms fail to compensate for environmental hypoxia, and the gill O2 uptake becomes insufficient to meet O2 requirements.

Measurements of gill dimensions were carried out on two ecologically distinct active rheophilic teleost species, the curvina Plagioscion squamosissimus and the curimbataProchilodus scrofa, and were analysed in relation to body mass according to the equation Y=aWb. The gill respiratory areas of P. squamosissimus and P. scrofa were large as expected for active fish and increased with increasing body mass (b=0.70 and 0.72, respectively) showing no significant difference between them. However, the large respiratory area of both species was realized in a different way revealing an adaptation to the plasticity of head components related to feeding habits. Consequently, significant differences were found between the number and average length of gill filaments and the bilateral area of secondary lamellae. The respiratory area of P. scrofa was due mainly to larger bilateral surface area of the secondary lamellae and its growth coefficient (b=0.51) that was significantly higher (P

Gill element dimensions of pacu Piaractus mesopotamicus were estimated and correlated to body mass (W), according to the power equation Y=aWb. The filament number (b=0.154) and length (b=0.457) increased with body mass, markedly influencing the respiratory gill surface area (b=0.769). The high filament number and length, associated with a high secondary lamellae frequency (a=40.21), are typical of active fish species and may be an adaptation to its migratory movements during reproduction. The comparatively small dimensions of its secondary lamellae are found more commonly in less active species, and may be related to the environmental conditions prevailing in lentic environments, where the species is normally found most of the year. Such features, together with its ability to compensate for oxygen reduction by means of a high ventilatory volume, and the use of aquatic surface respiration (ASR), may account for its adaptative capacity to withstand hypoxic conditions, with a low respiratory energy cost.

The adductor muscles in the gills of loricariid fish of genus Hypostomus and Rhinelepis are restricted to the distal end of the interbranchial septum. These muscles in Hypostomus comprise longitudinal and oblique striated muscle fibres.

The considerable similarity in the early life stages of different fish species makes egg and larvae identification in fishery biology and ichthyoplankton surveys a difficult task. Knowledge on early larval development of morphologically similar taxa and species-rich orders, such as Clupeiformes, mainly in the Neotropical fresh waters is rather limited. The aim of the present study was to describe morphological and meristic aspects of the larvae and early juveniles of Anchoviella vaillanti, an endemic species of the São Francisco River basin in Brazil. The characterization was based on an ontogenetic series of 132 individuals (1.3-51.0 mm SL). In the larval period, body varies from elongated to very elongated and the head is small, which is typical of Clupeiformes. The finfold is present beginning in the yolk-sac stage, when larvae have a large yolk sac, until the flexion stage. Pectoral fin buds are the first to form during the preflexion stage, when dorsal- and anal-fin pterygiophores and hypural bones are first visible. The total vertebra count ranges from 36 to 39 and the myomere number ranges from 31 to 45. Complete fin formation obeys the following sequence: anal and dorsal fins during flexion stage; and pectoral, pelvic and caudal fins during postflexion stage. Despite being the only freshwater clupeiform representative in the São Francisco River, A. vaillanti may occur sympatrically with A. lepidentostole in the lower stretches of the river basin. Although early larvae characteristics of A. lepidentostole are not known, its late larvae and early juveniles may be distinguished from those of A. vaillanti, by the higher number of dorsal-fin rays (15 or 16 vs. 12 or 13 in A. vaillanti), higher total vertebra count (40 vs. 37 to 40) and shorter pre-pectoral length (14 to 16 vs. 22.8 to 28.9% SL). A grande semelhança entre larvas de diferentes espécies de peixes torna a identificação de ovos e larvas em estudos de biologia pesqueira e ecologia do ictioplâncton uma tarefa difícil. O conhecimento sobre o desenvolvimento inicial de táxons com grande similaridade morfológica no período larval e riqueza taxonômica, como Clupeiformes, em particular daqueles de água doce na região neotropical, é bastante limitado. Neste sentido, o presente trabalho contribui para a redução desta lacuna, através da descrição morfológica e merística de larvas e juvenis iniciais de Anchoviella vaillanti, espécie endêmica da bacia do rio São Francisco. A caracterização foi realizada a partir de uma série ontogênica de 132 indivíduos (1,3-51,0 mm CP). No período larval, o corpo varia de muito alongado a alongado e a cabeça é pequena, características de Clupeiformes. A nadadeira embrionária está presente desde o estágio larval vitelino, no qual as larvas apresentam um saco vitelino grande, até o estágio de flexão. Os botões das nadadeiras peitorais são os primeiros a surgir, no estágio de pré-flexão, quando surgem também os pterigióforos das nadadeiras dorsal, anal e os ossos hipurais. O número total de vértebras varia de 36 a 39 e de miômeros de 31 a 45; a completa formação das nadadeiras obedece à seguinte ordem: anal e dorsal no estágio de flexão; e peitoral, pélvica e caudal no estágio de pós-flexão. Embora seja o único engraulídeo de água doce da bacia do rio São Francisco, A. vaillanti pode ocorrer simpatricamente com A. lepidentostole no trecho inferior da bacia. Embora as características de larvas iniciais de A. lepidentostole não sejam conhecidas, seus estágios larvais finais e juvenis podem ser distinguidos daqueles de A. vaillanti pelo maior número de raios da nadadeira dorsal (15 ou 16 vs. 12 ou 13 em A. vaillanti), maior número total de vértebras (40 vs. 37 a 40) e menor comprimento pré-peitoral (14 a 16 vs. 22,8 a 28,9% CP).