We evaluated the factors that affect the food resource use by Plagioscion ternetzi using three approaches: spatial, seasonal, and ontogenetic changes. Fish were sampled between March 2000 and February 2001 and March 2003 and February 2004 in the Sinhá Mariana and Chacororé lagoons, wetlands of the Pantanal Matogrossense. Fish was the predominant food in the diet, but shrimps and insects have been also consumed. The diet of P. ternetzi was significantly different between lagoons, but no difference was detected between dry and flood periods. In Sinhá Mariana lagoon, the diet mainly consisted of Psectrogaster curviventris, in both periods. In the flood period in Chacororé lagoon, fish was the dominant food (especially Astyanax spp., Leporinus spp. and Schizodon borellii), and in dry, shrimp and Eigenmannia spp. The Spearman coefficient indicated no correlation between the abundance of caught fish species and their abundances in the diet of P. ternetzi in Sinhá Mariana lagoon, and a strong negative correlation at Chacororé lagoon, although some very consumed preys were numerically abundant in the environment. Despite the intake of insect and shrimp, P. ternetzi was piscivorous since immature stages. A correlation between each item and the size classes of P. ternetzi was tested by means of Pearson correlation that showed that the changes in the use of resources over ontogenetic development have been represented by increased intake of P. curviventris in Mariana lagoon, and S. borellii at Chacororé lagoon, accompanying the increase in the size of the predator. In this way, the results suggest that several factors can be involved in the use of food resources by P. ternezi, among them the abundance, the size and morphological characteristics of the prey. Peixe foi o principal alimento, porém camarões e insetos também foram consumidos. A dieta de P. ternetzi foi significativamente diferente entre as lagoas, mas não diferiu entre os períodos de cheia e seca. Na lagoa Mariana, Psectrogaster curviventris foi a presa mais consumida em ambos os períodos. Na lagoa Chacororé, peixes dominaram a dieta (principalmente Astyanax spp., Leporinus spp. and Schizodon borellii) na cheia, e camarão e Eigenmannia spp. na seca. Uma correlação de Spearman mostrou que não existe correlação entre a abundância das espécies de peixes capturadas e suas abundâncias na dieta de P. ternetzi na lagoa Mariana, e que há uma correlação negativa na lagoa Chacororé, embora algumas presas importantes na dieta tenham sido numericamente importantes nas capturas. Embora tenha consumido camarões e insetos, P. ternetzi foi piscívora desde imatura. A correlação entre os itens alimentares e as classes de tamanho de P. ternetzi (Correlação de Pearson) evidenciou que as mudanças no uso do alimento durante a ontogenia estiveram associadas ao incremento no consumo de P. curviventris na lagoa Mariana, e de S. borellii na lagoa Chacororé, acompanhando o aumento de tamanho do predador. Assim, os resultados sugerem que vários fatores podem estar envolvidos no uso dos re...
The feeding selectivity of laboratory-reared larvae of Rhamdia voulezi was assessed to investigate the preferred preys in early life stages. Three experiments were conducted at different larval development stages, starting soon after the absorption of the yolk sac (on fourth day after hatching -DAH), using zooplankton from fish ponds as food. Differences were detected in the patterns of prey selection among development stages. At first, the larvae prefer small preys, such as rotifers and cladocerans. Later, when they are more developed, they prefer to feed on large preys, such as copepods. On the fourth DAH, larvae in the preflexion and initial flexion stage strongly selected rotifers and cladocerans (Diaphanosoma spinulosum, D. brevireme, Moina sp., M. micrura and M. minuta). At the other stages, cladocerans continued to be strongly selected. However, on the eighth DAH, larvae in flexion stage selected less strongly copepods Argyrodiaptomus azevedoi, Metacyclops mendocinus and Termocyclops decipiens. On the tenth DAH, larvae in postflexion stage selected more strongly copepods Argyrodiaptomus furcatus, Notodiaptomus cf. spinuliferus and M. mendocinus. As larvae grow, they tend to specialize in feeding of a particular prey. Prey selection of R. voulezi larvae was based both on species and zooplankton size. The size of the zooplankton ingested was related to the mouth gape size of larvae.
ABSTRACT. Morphological shifts in digestive tract and diet composition of larvae and juveniles of flounder Catathyridium jenynsii from Itaipu Reservoir, Paraná River, Brazil. The objective of this study was to characterize the diet and digestive tract morphology of flounder, Catathyridium jenynsii (Günther, 1862) (Achiridae), in its early stages of life. For analysis of the digestive tract, we used a specimen of each larval stage, pre-flexion to post-flexion, and juvenile. A total of 256 larvae and 16 juveniles, belonging to five classes of standard length was analyzed for diet. Data were collected in the Itaipu Reservoir, Paraná River, Brazil, from September, 2001 to March, 2002, and from September, 2002 to February, 2003. The occurrence and numerical methods were applied for determining the occurrence frequency and numerical frequency of each food item in different standard length (SL) classes. The anterior digestive tract of C. jenynsii began to differentiate into the stomach at 4.70 mm SL (not presented pyloric caeca). Since the stage of pre-flexion, there are three intestinal folds and a lot of grooves in the digestive tract. The dietary analysis showed that the smaller larvae (class 1) had a distinct diet, with dominance of cladocerans (mainly Bosmina hagmanni and Bosminopsis deitersi). For class 2, the copepod Notodiaptomus sp. was important both in number and occurrence, however B. hagmanni also had significant importance in the diet. Already the largest larvae (classes 3 and 4) and juveniles (class 5) showed a similar diet, consuming mainly copepods (Notodiaptomus sp.). Therefore, in this study, larvae of C. jenynsii can be considered zooplanktivore, since in all stages of development, copedods and cladocerans dominated the diet. Changes in diet followed the morphological changes of the early stages of C. jenynsii.
This study aimed to identify potential sources of organic matter in sediment, using stable isotopes of carbon (δ 13 C) and nitrogen (δ 15 N). Sediment samples were gathered from the margin and in center of three subsystems: Ivinheima, Paraná and Baia, in August/2001. The samples were fractionated granulometrically and separated by size (< 200 μm; 70-200 μm; > 70 μm), prepared and sent to CENA / USP, for identifying the isotopes proportions. Significant differences were detected in the isotopic ratios of the sediment only between sampling stations. The Baía channel presented the lowest δ 13 C values, while the highest ones were recorded in Paraná river. At this last, δ 15 N values were negative (-14.41‰). We did not verify significant difference in isotopic composition between the particle sizes of sediment, and between the sampling points. The main sources of carbon for the sediment were C 3 macrophytes, periphyton and particulate organic carbon (POC).
ABSTRACT. This work aims to investigate the hypothesis that sedimentary organic matter presents concentration variations in accordance to the size of sediment particles and to proximity with the river's margin. This organic matter is known as a feeding source for benthonic fishes. Sampling of the sediment was carried out in dry and rainy periods, at three Paraná River floodplain subsystems. Three sampling points were established: right margin, center and left margin. The samples (n=88) were submitted to granulometric fractionation (< 70µm; between 70 and 200µm; > 200µm). Low variability in organic matter concentration was observed for samples from the center of the subsystems. Particles, smaller than 70µm, had high variability in organic matter concentration. The rainy period was shown to affect concentration of organic matter adhered to the sediment fractions in transversal section at the sampled environments. With support of literature, the experiment lead to the conclusion that fish species which ingest particles of detritus < 70µm obtain more organic matter of sediment. RESUMO. Disponibilidade de matéria orgânica sedimentar para peixes benticos da planície de inundação do rio Paraná. O presente trabalho teve por objetivo investigar a hipótese de que o material orgânico sedimentar, conhecida fonte de alimento para espécies de peixes exploradores de fundo, apresenta variações na concentração de acordo com o tamanho das partículas do sedimento e proximidade com a margem do rio. A obtenção das amostras de sedimento foi realizada no período de seca e de chuva em três subsistemas da planície de inundação do rio Paraná, sendo estabelecidos três pontos de coleta: margem direita, centro e margem esquerda. As amostras (n=88) foram submetidas ao fracionamento granulométrico (< 70µm; entre 70 e 200µm; > 200µm). Observou-se menor variabilidade na concentração de matéria orgânica para as amostras do centro e maior para partículas menores que 70µm. Identificou-se o efeito do período de chuvas sobre a concentração de matéria orgânica aderida as frações de sedimento das secções transversais e nos ambientes amostrados. Concluiu-se, com base na literatura, que as espécies de peixes que ingerem detrito com partículas < 70µm, obtêm mais matéria orgânica do sedimento.Palavras-chave: planície de inundação, rio Paraná, sedimento, matéria orgânica.
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