Serrasalmus Spilopleura Research Articles

Fish diversity in the rivers that drain the Baixada Maranhense and the Mearim basin in northeastern Brazil.

The Baixada Maranhense Environmental Protection Area of the Brazilian state of Maranhão encompasses a biologically rich region that includes the basins of four principal rivers, the Mearim, Pericumã, Pindaré, and Turiaçu, which form a complex of wetlands. The present study provides a comprehensive inventory of the fish fauna of the rivers that drain the Baixada Maranhense based on the identification of voucher specimens that were deposited in a scientific collection. Expeditions were conducted between 2014 and 2020. The inventory identified a total of 100 fish species representing 79 genera, 34 families, and 11 orders, which are found in both freshwater and estuarine environments. Six (Potamotrygon orbignyi, Leporinus piau, Moenkhausia loweae, Serrasalmus spilopleura, Pachypops fourcroi and Peckoltia greedoi) of the 100 taxa identified here are considered to be new records for one or more of the basins surveyed during this study, based on the existing data, while four - Colossoma macropomum, Megaleporinus macrocephalus, Cichla sp. and Cichla kelberi - are not native. The most speciose orders were the Siluriformes and Characiformes, while the most diverse families were the Loricariidae, Characidae, Auchenipteridae, Cichlidae, and Serrasalmidae. These data are consistent with the findings of most of the previous studies of freshwater ecosystems in the Neotropical region, in particular those of the rivers of Maranhão. The results of the present study represent an important advance in the understanding of the diversity of the fish fauna of the Mearim, Pericumã, Pindaré, and Turiaçu rivers, which are still poorly studied, and have likely had their diversity underestimated up to now.

Trophic structure of a floodplain fish assemblage in the upper Amazon basin, Bolivia.

Amazonian fish assemblages are typically high in species diversity and trophic complexity. Stable isotopes are valuable tools to describe the trophic structure of such assemblages, providing useful information for conservation and ecological management. This study aimed at estimating the relative contribution of the different basal carbon sources to the diet of primary consumer fishes (herbivores and detritivores), and determining the trophic position (TP) of the dominant fishes from each trophic guild (herbivores, detritivores, invertivores and piscivores). For this purpose we analyzed stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in potential food sources, and muscle tissue of fishes in five oxbow lakes located in the floodplain of River Ichilo, Bolivia. Terrestrial plants and C3 aquatic macrophytes were the major carbon source contributing to the diet of herbivorous fishes, whereas particulate organic matter (POM) contributed more to the diet of detritivore fishes. In general, C4 aquatic macrophytes contributed little to the diet of herbivores and detritivores. However, we found a relatively high contribution of C4 macrophytes (28 %) to the diet of the herbivores Mylossoma duriventre and Schizodon fasciatus. We found a good agreement between our estimated TP values and the trophic group assigned based on diet composition from literature. The herbivore M. duriventre was at the bottom of the food web, being the baseline organism (TP = 2). The remaining primary consumers (herbivores and algivore/detritivores) exhibited relatively high TP values (2.3 - 2.9), probably due to their opportunistic feeding behavior. Omnivore/invertivore species studied displayed TP values near the 3.0 value expected for secondary consumers. Piscivore fishes were at the top TP, with TP values varying from 3.3 (Serrasalmus spilopleura and Serrasalmus rhombeus) to 3.8 (Pseudoplatystoma fasciatum). The fact that detritivore fishes, the most abundant food source for piscivores, occupy relatively high TPs determines that food chains in these particular Amazonian floodplains are longer than previously thought.

Condition factor variations over time and trophic position among four species of Characidae from Amazonian floodplain lakes: effects of an anomalous drought.

The effects of extreme droughts on freshwater fish remain unknown worldwide. In this paper, we estimated the condition factor, a measure of relative fitness based on the relationship of body weight to length, in four fish species representing two trophic levels (omnivores and piscivores) from Amazonian floodplain lakes for three consecutive years: 2004, 2005 (an anomalous drought year), and 2006. The two omnivores, Colossoma macropomum and Mylossoma duriventre, exhibited trends consistent with their life cycles in 2004 and 2006: high values during the hydrologic seasons of high water, receding water, and low water, with a drop following reproduction following the onset of rising water. However during the drought year of 2005 the condition factor was much lower than normal during receding and low water seasons, probably as a result of an abnormal reduction in resource availability in a reduced habitat. The two piscivorous piranhas, Serrasalmus spilopleura and S. elongatus, maintained relatively stable values of condition factor over the hydrologic cycles of all three years, with no apparent effect of the drought, probably because the reduction in habitat is counterbalanced by the resulting increase in relative prey density. We suggest that if predictions of increasing drought in the Amazon are correct, predatory species may benefit, at least in the short run, while omnivores may be negatively affected.

<b>Population dynamics of the yellow piranha <i>Serrasalmus spilopleura</i> Kner, 1858 (Characidae, Serrasalminae) in Amazonian floodplain lakes</b> - doi: 10.4025/actascibiolsci.v35i3.15749

Fish is the main source of protein in the Amazon and fishing is one of the most important sources of income for the Amazonian population. Serrasalmus spilopleura is a species that have been increasingly consumed by riverside communities, although it is only occasionally commercialized at regional markets. Therefore, this work sought to generate information about the population biology of S. spilopleura captured in floodplain lakes, Jaiteua and Sao Lourenco, in Manacapuru, Amazonas State. The population parameters were estimated by analyzing the distribution of the length frequency with the help of the ELEFAN I routine of the FISAT II program. The weight/length relationship was estimated by linear regression, longevity by Taylor’s method, rate of natural mortality by Taylor’s and Pauly’s methods, and growth type by a t-test (α = 0.05). 669 specimens of S. spilopleura were captured measuring between 7 and 22 centimeters. The estimated population parameters were: k = 0.34 year -1 , L ∞ = 23.10 cm, t 0 = 0, and A 0.95 = 9 years. 7 cohorts were identified, Taylor M = 0.33 year -1 and Pauly M = 0.98 year -1 . The weight/length relationship equation was W t = 0.051320.L t 2.8727 , and negatively allometric growth. The information on the population parameters of S. spilopleura could be used to provide evaluation models for this fishery resource.

Reprodução da piranha-amarela Serrasalmus spilopleura Kner, 1858, em lagos de várzea, Amazonas, Brasil

Serrasalmus spilopleura (piranha-amarela) é fonte de proteína animal para as populações ribeirinhas, sendo ocasionalmente comercializada nos mercados e feiras da região. Considerando a escassez de informações sobre a reprodução de peixes em lagos de várzea, o trabalho propõe investigar o comprimento médio de primeira maturação sexual e a época de desova de S. spilopleura nos lagos Jaitêua-São Lourenço, Manacapuru, AM. Também são relacionados os fatores abióticos (nível de água e profundidade) e bióticos (fator de condição) com a época de desova. Foram capturadas 232 fêmeas no período de agosto de 2006 a junho 2007, utilizando rede-de-emalhar e, em laboratório, foram realizadas as biometrias e identificação dos estádios de maturação gonadal. A época de desova das fêmeas foi estabelecida através da distribuição temporal da freqüência relativa nos diferentes estádios de maturação gonadal e do fator de condição relativo, Kn = Pt/aCp b, onde: Kn = fator de condição relativo; Pt = peso total; Cp = comprimento padrão e, a e b = constantes obtidas da regressão entre peso e comprimento. E, para verificar se há correlação entre o fator de condição e época de desova com a profundidade dos lagos, utilizou-se o coeficiente de correlação de Spearman ao nível de significância 5%. A amplitude do comprimento padrão dos exemplares variou de 7 a 22 cm. A análise de correlação entre o Kn e a época de desova foi positiva (r s = 0,58, p < 0,05), ou seja, a época de desova correspondeu ao período de maior Kn, sugerindo ser um indicador para época de desova de S. spilopleura. Houve correlação negativa entre a profundidade e o Kn (r s = -0,66, p < 0,05) e entre a profundidade e a época de desova (r s = -0,25, p < 0,05). O L50 estimado correspondeu a 13,0 cm ± 0,09 e o L100 a 17,0 cm ± 0,02. S. spilopleura desenvolve o seu ciclo reprodutivo no complexo lacustre lago Grande de Manacapuru, e com base nos indicadores reprodutivos, época de desova e fator de condição relativo, a desova começa em dezembro, logo no início da enchente, se estendendo até fevereiro, meados de enchente, coincidindo com a elevação do nível da água do rio Solimões-Amazonas e da profundidade nos lagos.

Determination of heavy metals by inductively coupled plasma-optical emission spectrometry in fish from the Piracicaba River in Southern Brazil

A total of 202 fish, representing 16 species, were collected during 2008 (March–October) in the Tanquan region of the Piracicaba River using nets. Flesh samples were collected and analyzed, using inductively coupled plasma-optical emission spectroscopy for Al, As, Cd, Co Cr, Cu, Mn, Mo, Ni, Pb, Se, Sn, Sr, and Zn. The results showed that the flesh of these fish all contained extremely high levels of Al and Sr, and moderately high levels of Cr, As, Zn, Ni, Mn and Pb. The metals were higher in these fish during rainy season, with fish collected during the months of March and October being the highest. In addition, the accumulation of metals was species-dependent. Cascudos ( Hypostomus punctatus) and piranhas ( Serrasalmus spilopleura) exhibited high levels of almost all of the metals, while curimbata ( Prochilodus lineatus) had moderate levels. A few species, including pacu ( Piaractus mesopotamicus) and dourado ( Salminus maxillosus), had very low levels of most metals. The results show that the Piracicaba River Basin is widely contaminated with high levels of many toxic heavy metals, and that human consumption of some fish species is a human health concern.

Invasão da piranha Serrasalmus marginatus Valenciennes, 1847 no alto rio Paraná, Brasil (Osteichthyes, Serrasalmidae)

The building of Itaipu Dam, 150 km downstream from Sete Quedas Falls, resulted in the natural geographical barrier drowning, with subsequent mixing of the fish faunas. Serrasalmus marginatus (Osteichthyes, Serrasalmidae), a species that had been restricted to the river segment downstream from Sete Quedas, invaded the Upper Parana River. The catching of Serrasalmus spilopleura , a resident species, decreased drastically after the invasion, contrary to S. marginatus , which increased in abundance. In the Piquiri River, where the latter species does not occur, the abundance of S. spilopleura remained high, due to the presence of Nha Barbara and Apertado Falls.

Estrutura populacional de Serrasalmus spilopleura Kner, 1860 (Pisces, Serrasalmidae) da lagoa de Extremoz, Estado do Rio Grande do Norte, Brasil

Several aspects of the population structure of Serrasalmus spilopleura Kner, 1860, from the Extremoz Lake (5 o 42’76” S and 35 o 17’ 69” W), state of Rio Grande do Norte, are approached. From July 1998 to April 1999, 337 specimens were collected in each phase of the moon, with 5 gill-nets, knots spaces varying between 2,0 to 5,0 cm in four distinct points, with collection every five hours, timetable (17h00 - 22h00). The sexual proportion was 1:1, with a slight decrease of females during the winter; length classes during the entire period under analysis ranged between 6,0 and 17,0 cm, with a predominance of 9.0- 10,0 cm in all seasons; spring was the only exception since variation ranged between 11,0 and 12,0 cm. No significant relationship between total weight and total length for the sex groups was found. The value of θ = 3,2493 shows a positive allometric growth for the species

Cytochemical characterization of the endomembranous system during oocyte secondary growth in Serrasalmus spilopleura (Teleostei, Characiformes, Characidae)

AbstractThe endomembranous system of Serrasalmus spilopleura oocyte secondary growth was analysed using structural and ultrastructural cytochemical techniques. In vitellogenic oocytes, the endoplasmic reticulum components, the nuclear envelope intermembranous space, some Golgi dictiossomes, lysosomes, yolk granules, regions of the egg envelope and sites of the follicle cells react to acid phosphatase detection (AcPase). The cortical alveoli, some heterogeneous cytoplasmic structures, regions of the egg envelope, and sites of the follicle cells are strongly contrasted by osmium tetroxide and zinc iodide impregnation (ZIO). The endoplasmic reticulum components, some vesicles, and sites of the follicle cells also react to osmium tetroxide and potassium iodide impregnation (KI). The biosynthetic pathway of lysosomal proteins, such as acid phosphatase, required for vitellogenesis, involves the endoplasmic reticulum, Golgi complex, vesicles with inactive hydrolytic enzymes, and, finally, lysosomes. In S. spilopleura oocytes at secondary growth, the endomembranous system takes part in the production of the enzymes needed for vitellogenesis, and in the metabolism of yolk exogenous components (AcPase detection). The endomembranous system compartments also show reduction capacity (KI reaction) and are involved in the metabolism of proteins rich in SH‐groups (ZIO reaction).

Morphofunctional changes in Leydig cells throughout the continuous spermatogenesis of the freshwater teleost fish, Serrasalmus spilopleura (Characiformes, Characidae): an ultrastructural and enzyme study

The freshwater fish Serrasalmus spilopleura (piranha) has a continuous type of reproduction; gametes are constantly produced and released during the reproductive cycle. The testes do not undergo seasonal morphological changes but exhibit two constant regions throughout the year: the medullar region (involved with spermatogenesis) and the cortical region (involved with spermiation and sperm storage). We have evaluated the ultrastructure of the Leydig cells and the activity of 3beta-HSD (an essential enzyme related to steroid hormone biosynthesis) and acid phosphatase (AcPase; lysosomal marker enzyme) in these two regions. The activity of 3beta-HSD is stronger in the medullar region, and the Leydig cells in this region have a variety of cytological features that reflect differences in hormone synthesis and/or that could be linked to steroidogenic cells under various degrees of hormonal activity. In the cortical region, 3beta-HSD activity is weak and the Leydig cells exhibit signs of degeneration, as confirmed by their ultrastructure and intense AcPase activity. These degenerative signs are indicative of cytoplasmic remodelling to degrade steroidogenic enzymes, such as 3beta-HSD, that could lead to senescence or even to autophagic cell degeneration. S. spilopleura thus constitutes an interesting model for increasing our understanding of steroidogenesis control in freshwater teleost fish.

Cytochemical characterization of the endomembranous system during the oocyte primary growth in Serrasalmus spilopleura (Teleostei, Characiformes, Characidae)

The morphophysiological changes that occur during oocyte primary growth in Serrasalmus spilopleura were studied using ultrastructural cytochemical techniques. In the previtellogenic oocytes endoplasmic reticulum components, Golgi complex cisternae and vesicles, lysosomes, multivesicular bodies and some electron-dense vesicles react to acid phosphatase (AcPase) detection. The endoplasmic reticulum components, Golgi complex cisternae and vesicles also react to osmium tetroxide and potassium iodide impregnation (KI). These structures, except for the Golgi complex cisternae, are strongly contrasted by osmium tetroxide and zinc iodide impregnation (ZIO). Some electron-dense vesicles are ZIO-stained, while microvesicles in the multivesicular bodies and other large isolated cytoplasmic vesicles are contrasted by KI. At primary oocyte growth, the activity of the endomembranous system and the proliferation of membranous organelles are intense. The biosynthetic pathway of the lysosomal proteins such as acid phosphatase, involves the endoplasmic reticulum, Golgi complex, vesicles with inactive hydrolytic enzymes and, finally, the lysosomes. The oocyte endomembranous system have reduction capacity and are involved in the metabolism of rich in SH groups.

Diet and feeding of fish from Grande River, located below the Volta Grande Reservoir, MG-SP

We compare the classic model of feeding of tropical fish by means of six bimonthly samplings using gillnets of varying mesh sizes that were inspected every twelve hours throughout a forty-eight hour period. The stomachs of the fish caught were classified in three categories according to quantity of food found. The amount of fat in the visceral cavity with respect to the energetic reserve deposition was also studied. The relative frequencies of the different categories of stomach repletion and fat deposition were examined for patterns of feeding seasonality. The stomachs considered full were examined to record diet composition. To assess the relative importance of the different food resources, we applied Feeding Importance Degree (FID), which is a useful index when difficulties exist in determining a common basis for volume, number, or weight of a given food item in different species, a common problem when dealing with fish species having different feeding habits. The fish species whose stomach contents were analyzed using the FID index were Serrasalmus spilopleura (Characidae), L. prolixa (Loricaridae), Schizodon nasutus (Anostomidae), and Pimelodus maculatus (Pimelodidae). Our findings indicate some contrasting elements, in dietary composition in relation to the classic model for tropical rivers. These factors include the importance of aquatic macrophytes, the lack of piscivorous species, and a lesser presence of allochthonous vegetation in the diet of the species studied.

Alimentação da pirambeba Serrasalmus spilopleura Kner, 1858 (Characidae; Serrasalminae) em um reservatório do Sudeste brasileiro

We studied the feeding aspects from 158 individuals of Serrasalmus spilopleura captured in Porto Colômbia Reservoir, situated on the Grande River, at the Paraná basin, between November 2001 and August 2002. Mesh nets were used to capture the individuals, with sizes ranging from 3 cm to 16 cm, between opposed knots set at sunset, and collected in the following morning; remaining exposed during approximately 12 hours. The analysis from the stomach content of the captured individuals showed a predominantly piscivore feeding habit, and exclusive to individuals over 22 cm. Aquatic insects were also found, complementing the diet of individuals belonging to smaller size groups, indicating a clear trophic ontogeny

Piranha Attacks on Humans in Southeast Brazil: Epidemiology, Natural History, and Clinical Treatment, With Description of a Bite Outbreak

There are many tales describing ferocious schools of piranha attacking humans, but there are few scientific data supporting such behavior. The very few documented instances of humans attacked and eaten by piranha schools include 3 that occurred after death by other causes (eg, heart failure and drowning). These predaceous fishes, however, do occasionally injure bathers and swimmers in lakes and rivers. The characteristic profile of most injuries is a single bite per victim, generally related to the fish defending its brood. This paper describes an outbreak of piranha bites in a dammed river portion in southeast Brazil. The outbreak was caused by the speckled piranha, Serrasalmus spilopleura, a widespread species which benefits from the growing tendency of damming rivers all over Brazil. This article focuses on the epidemiological and clinical aspects of the injuries, as well as on piranha biology, to gain a better understanding of the natural history of bite outbreaks.

Host–parasite interaction between branchiurans (Crustacea: Argulidae) and piranhas (Osteichthyes: Serrasalminae) in the Pantanal wetland of Brazil

Ecological studies of host–parasite interactions in the tropics are generally restricted to descriptive taxonomic aspects. The present study had as its objective identification of the metazoan ectoparasites of piranhas Pygocentrus nattereri, Serrasalmus spilopleura and S. marginatus in lentic and lotic environments in the Pantanal region, Brazil. We collected the samples in the Miranda River basin and in three ponds. We caught fishes using hook and line. We found that branchiuran crustaceans infested about 30% of the piranhas. We found four branchiuran species: Dolops carvalhoi, Argulus elongatus, Argulus aff. juparanaensis and Dipterolpetis hirundo, which represent new findings in host–parasite relationships in the Neotropics. When comparing lotic and lentic environments, we observed higher infestation rates in rivers than in ponds for all the hosts. P. nattereri had the highest prevalence and the intensity rates in both the environments. The body parts of hosts with the highest frequencies of parasitism were the ventral area in P. nattereri, the gullet area in S. spilopleura and ventral areas and external gills in S. marginatus. In relation to the prevalence of the parasites we observed significant differences between the hydrological seasons and the piranha species, nevertheless hosts were more parasitized in the dry season. The species with highest rates of infestation, P. nattereri and S. spilopleura, live in schools, which indicates that the high parasite load may be a direct consequence of the proximity between individuals. We believe that the higher rates of infestation in the dry season result from the increase in host density in drying ponds imitating the conditions found in fish farming. Seasonal changes in water level and temperature can also influence the rates of parasitism.

Henneguya curvata sp. n. (Myxosporea: Myxobolidae) parasitizing the gills of Serrasalmus spilopleura (Characidae: Serrasalminae), a South American freshwater fish.

The class Myxosporea of the phylum Myxozoa contains 52 genera (Kent M.L., Andree K.B., Bartholomew J.L., ElMatbouli M., Desser S.S., Devlin R.H., Feist S.W., Hedrick R.P., Hoffmann R.W., Khattra J., Hallett S.L., Lester R.J.G., Longshaw M., Palenzeula O., Siddall M.E., Xiao C.X. 2001: J. Eukaryot. Microbiol. 48: 395–413), most of which parasitize fishes. Henneguya Thelohan, 1892 is the second most common of these genera and contains more than 150 species, some of which are important pathological agents (Dykova I., Lom J. 1978: J. Fish Biol. 12: 197–202; Kalavati C., Narasimhamurti C.C. 1985: Arch. Protistenkd. 129: 199–202; Lom J., Dykova I. 1995: In P.T.K. Woo (Ed.), Fish Diseases and Disorders. Protozoan and Metazoan Infections. Vol. 1. CAB International, Wallingford pp. 97–147; Martins M.L., Souza V.N., Moraes J.R.E., Moraes F.R. 1999: Rev. Bras. Biol. 59: 527– 534). In South America, Henneguya is the most abundant genus, with 31 species. To date, two species of Henneguya have been reported in Serrasalmus spp.: Henneguya iheringi Pinto, 1928 parasitizing Serrasalmus spilopleura caught in the state of Sao Paulo, and H. striolata Casal, Matos et Azevedo, 1997 parasitizing S. striolatus collected in the Amazon River estuary near Belem, state of Para, Brazil. Fish of the genus Serrasalmus are voracious carnivorous fish popularly known as piranhas and are widely distributed throughout South American rivers. In this study, we describe a new species of Henneguya parasitizing S. spilopleura. Eighteen adult and juvenile specimens of S. spilopleura were collected locally from a lake on a farm in the municipality of Campinas, state of Sao Paulo, Brazil, and examined for the presence of myxosporeans. The fish were captured between January and June 2001, and transported alive to the laboratory where they were killed by transection of the spinal cord then measured and necropsied. The measurements of 30 fresh mature spores (Lom J., Arthur J.R. 1989: J. Fish Dis. 12: 151–156) were obtained using a micrometer incorporated into a microscope eyepiece. The dimensions were expressed as the mean ± standard deviation (SD). India ink staining was used to detect the mucus envelope. The spores were checked for the presence of an iodinophilous vacuole after adding a drop of Lugol solution. Smears containing free spores were stained with Giemsa’s solution and mounted in low viscosity medium as permanent mounts (Adriano E.A., Arana S., Ceccarelli P.S., Cordeiro N.S. 2002: Folia Parasitol. 49: 259–262). For histological analysis, portions of the gills containing plasmodia were fixed in 10% buffered formalin for 24 h, embedded in paraffin, cut into sections 4 μm thick and stained with sirius red (Adriano et al. 2002, op. cit.), haematoxylin and eosin and PAS.

Aquatic macrophytes as feeding site for small fishes in the Rosana Reservoir, Paranapanema River, southeastern Brazil.

In the present investigation we studied the feeding habits of the fishes associated with aquatic macrophytes in the Rosana Reservoir, southeastern Brazil. Twenty fish species were collected during four field trips, regularly distributed across the dry and wet seasons. Focal snorkeling observations of the fishes were made over a total of six hours. Nine species were present in abundances of more than 1% and, therefore, had their feeding habits analyzed. Hemigrammus marginatus, Roeboides paranensis, Hyphessobrycon eques, Astyanax altiparanae, Serrasalmus spilopleura, and Bryconamericus stramineus were predominantly invertivores, with predominance of aquatic insects (Diptera, Ephemeroptera, and Trichoptera immatures) among their food items. The predominantly algivores were Apareiodon affinis, Serrapinnus notomelas, and Satanoperca pappaterra, with high frequency of filamentous blue-green algae, diatoms, clorophyts, and periderm. The different microhabitat exploitation plus diet composition suggests partitioning of resources and absence of food competition among the most representative fish species in the studied community, indicating the importance of the naturalistic approach to fish ecology studies.

Variação da alimentação natural de Serrasalmus spilopleura Kner, 1860 (Pisces, Serrasalmidae) em função do ciclo lunar e das estações do ano na lagoa de Extremoz, Rio Grande do Norte, Brasil

The present paper aims to study feeding aspects of Serrasalmus spilopleura (Kner, 1860) from Extremoz Lake (5º 42’76”S and 35º17’69”W), Rio Grande do Norte state, Brazil, in the period from July/1998 to April/1999 connecting lunar cycle to the seasons of the year. 337 specimens were collected in each phase of the moon, being used five ambush nets which varied from 2,0 to 5,0 centimeters with knots in four different points and catchings of five hours, times (17h00 - 22h00). The species showed feeding activity during the study period, independently of the season of the year and the phase of the moon, with small variations in the alimentary items. Insects appeared as principal food characterizing the species as carnivorous with tendency to insectivorous.

Follicular epithelium, theca and egg envelope formation in Serrasalmus spilopleura (Teleostei, Characiformes, Characidae)

AbstractThe follicular epithelium and theca of oocytes in Serrasalmus spilopleura differentiates during the initial primary growth phase. The follicular cells are squamous and the thecal cells are disposed in two layers. During the secondary growth phase, follicular cells become cuboidal, acquire characteristics typical of protein‐ or glycoprotein‐producing cells, and show dilated intercellular spaces. Formation of the egg envelope in S. spilopleura begins in the previtellogenic oocytes as a layer of amorphous electron‐dense material is laid down on the oolemma. During vitellogenesis, another layer of electron‐dense material appears beneath the first layer. Also during this phase, a layer of amorphous, less electron‐dense material is formed adjacent to the follicular epithelium. The secondary egg envelope appears at the postvitellogenic phase and is composed of a filamentous and undulant material. The morphology of the egg envelopes in S. spilopleura reflects not only its oviparous nature but also the fact that its eggs are adhesive.

Seasonal isotopic shifts in fish of the Pantanal wetland, Brazil

Seasonal inundations shape the floodplain characteristics of the Pantanal, a large wetland in Central South America. In the first study combining stable carbon and nitrogen isotope analysis with classical stomach content analysis in this region, we investigated the influence of the annual inundation on diet and isotopic composition of floodplain fish. Apart from potential food items, 33 fish species from the Coqueiro Lake were analyzed, 10 of which were present during both the wet and dry season 1999. A δ13C and δ15N plot of the floodplain ecosystem allowed us to assess a foodchain of 3–4 trophic levels. However, the wide overlap of nitrogen values suggested that the organisms act on trophic continua rather than on distinct levels. The foodweb was based mainly on C3-plant carbon. However, fish species capable of feeding on terrestrial invertebrates (e.g., Brycon microlepis) had δ13C values above –25‰, indicating 13–30% intake of C4-plant based carbon during the flooding period. The novel use of vector coordinates and 2-dimensional ANOVA showed that the seasonal isotopic shifts of δ13C and δ15N were highly significant for some feeding guilds. δ15N values increased from the wet to dry season in most fish species, and these shifts were highly significant for omnivores (Astyanax bimaculatus, Triportheus nematurus, Tetragonopterus argenteus and Moenkhausia dichroura), and significant for invertivores (Gymnogeophagus balzanii and Poptella paraguayensis) and carnivores (Serrasalmus spilopleura). Average carbon isotope ratios decreased at the same time in the herbivores (Methynnis mola: 3.4‰) and detritivores (Psectrogaster curviventris: 5.3‰), but they did not change in the hypostomatic herbivore Sturisoma robustum. We explain these shifts by abundant and variable food sources during the inundation period and increasing carnivory and starvation during the dry season when the lake is confined to its central basin. Isotopic shifts between seasons were more prominent in less specialized species of omnivores, invertivores and some carnivores, whereas more specialized herbivores and detritivores appeared to be more influenced by changes in the carbon isotope ratio of the diet affected by biogeochemical processes such as respiration and methanogenesis. A general model for the interpretation of isotope data of floodplain fish considering different time-scales is given.