Keshiyu Nakatani

Fish larvae from the upper Paraná River: do abiotic factors affect larval density?

The purpose of this study was to evaluate the role of abiotic factors on fish larvae occurrence. Samplings were carried out monthly at 12 stations (grouped in four areas) in the Amambai, Ivai and Parana rivers and in the Itaipu Reservoir (upper Parana River basin), from October 1994 to January 1995 (spawning season). Simultaneously, we obtained water temperature, pH, electrical conductivity, dissolved oxygen, water level, water velocity, and rainfall. Principal Component Analyses (PCA) and Detrended Correspondence Analyses (DCA) were applied to summarize abiotic and larvae density data, respectively. Amambai River differed significantly from the other areas in relation to abiotic factors. Itaipu Reservoir differed significantly from the other areas considering species composition, and the Ivai River also differed from the Parana River. The relationship among PCA and DCA axes were significant, indicating that abiotic factors do influence larva. For example: Leporinus elongatus prefered the Amambai River, Hypophthalmus edentatus, Plagioscion squamosissimus, and Hoplias aff. malabaricus the Itaipu Reservoir, and Pimelodus maculatus, Auchenipterus osteomystax and Iheringichthys labrosus the Ivai River. We suggest that species selected some abiotic factors characteristic to a given environment as spawning grounds.

Morphological description of the developmental stages of Parauchenipterus galeatus (Linnaeus, 1766) (Siluriformes, Auchenipteridae) on the floodplain of the upper Paraná River

We provide morphological and morphometric descriptions of the developmental stages of Parauchenipterus galeatus, from the floodplain of the Upper Parana River. Specimens were obtained by induced spawning. The species has large adhesive eggs with a double membrane. The incubation period is long, 65 hours at 27°C. The larvae are well developed at hatching, with relatively rapid larval development. Analysis of the morphometric data showed that the body parts of P. galeatus grow proportionately.

Ontogenetic shifts in digestive tract morphology and diet of fish larvae of the Itaipu Reservoir, Brazil

We analyzed the ontogenetic shifts in digestive tract morphology and diets of the young of Iheringichthys labrosus, Hypophthalmus edentatus and Plagioscion 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. In H. edentatus, the gill rakers developed more rapidly, and were longer and more numerous on the first arch, related to their planktivorous feeding habit. I. labrosus and P. squamosissimus had long gill rakers only on the first arch, they were short and thick on the rest. The stomach was defined only in P. squamosissimus, with pyloric caeca. Their diets were mainly zooplankton. I. labrosus fed particularly on cladocerans and rotifers; H. edentatus consumed essentially cladocerans; and P. squamosissimus fed basically on copepods. We observed greater similarity in diet between the young of I. labrosus and H. edentatus, especially for the first length classes. The diet of I. labrosus became more diversified at the end of the larval period, indicating a transition in the feeding habit and habitat for this species. P. squamosissimus showed 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.

Some aspects of the ecology of fish larvae in the floodplain of the high Paraná river, Brazil

The spatial and temporal distribution and nychthemeral variation of fish larvae in six stations (Ivinhema, Patos, Parana, Cortado, Baia and Guarana) in the floodplain of the high Parana river are provided. The paper also provides the relationship of this distribution to some environmental factors. From March 1992 to February 1993 ichthyoplanktonic samples were collected by conic cylindrical nets, with 0.5mm of mesh size and fluxometer attached, in 10-minute hauls at the surface and bottom during nychthemeral cycles. At the same time water samples were taken to determine environmental factors. During the above period 5,672 larvae were collected: 57,6% from Cortado station and 13,2% from Ivinhema and Parana stations. The greatest densities were recorded between October and February, chiefly at night at the surface and by day at the bottom.

Larval fish assemblage in the Baía River (Mato Grosso do Sul State, Brazil) : temporal and spatial patterns

SynopsisWe 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, Hoplias aff. malabaricus, Bryconamericus stramineus, Serrasalmus spp. and Catathyridium jenynsii. These taxa present distinct temporal and spatial occurrence patterns: H. edentatus, B. stramineus and C. jenynsii are abundant between September and March in lentic areas; H. aff. malabaricus and Serrasalmus spp. were caught between October and February in lotic areas; whereas P. squamosissimus occurs in all sampled areas, with peak of capture in January. Hypophthalmus edentatus, H. aff. malabaricus, Serrasalmus spp. and B. stramineus were the taxa that most contributed to structure the assemblages temporally and spatially, and their abundances were influenced by the interaction of several environmental variables.

Spatial and temporal distribution of larvae and juveniles of Hoplias aff. malabaricus (Characiformes, Erythrinidae) in the Upper Paraná River floodplain, Brazil

Spatial and temporal distribution of larvae and juveniles of trahira, Hoplias aff. malabaricus (Erythrinidae), and their relationship with environmental parameters in the Upper Paraná River floodplain were analyzed. Sampling of larvae and juveniles of H. aff. malabaricus has been conducted during the period from November 1991 through February 1995, with 42 sampling stations distributed in four sub-areas: Ivinhema I, Ivinhema II, Baía, and Paraná. During the same period, data were obtained for water temperature, dissolved oxygen, pH, electrical conductivity, river level, precipitation index, and photoperiod. The largest catches of larvae were in the Ivinhema I sub-area (47.06%), and of juveniles in the Paraná sub-area (54.55%). Larvae and juveniles were caught from October to February. Larvae were mainly collected at night and in all types of environments sampled (lotic, semi-lotic, and lentic). Principal Component Analysis of the environmental parameters and larval density showed that the largest catches were obtained in dry season months, with low values for temperature, electrical conductivity, river level, and photoperiod, and with high concentrations of dissolved oxygen and pH. This reproductive strategy may minimizes predation and maximizes food utilization, as it enables the fish to reach advanced developmental stages, while most other species are spawning.

Caracterização morfológica e distribuição temporal de larvas e juvenis de Apareiodon affinis (Steindachner) (Osteichthyes, Parodontidae) no alto rio Paraná, Paraná

With the purpose of characterizing morphologicaly the larvae and juveniles of Apareiodon affinis (Steindachner, 1879) and to verify their temporal distribution monthly samples were taken at Leopoldos Inlet, upper Parana River. The specimens were captured with a conic-cylindrical plankton net of mesh size 0,5mm from March 1991 to February 1992. Soon after identification, the specimens were separeted according to their development (prefle-xion, flexion, posflexion and juvenile) and then the moiphometric analyses were performed. The results showed that the larvae were captured from August 1991 to February 1992, with greatest densities in November 1991. The specimens occured in every timetable, however, larvae in pretlexion and flexion were captured during day time and, posflexion and juvenile, at night. According to series of morphological development, high body proportions variation were verifyed mainly in the head lenght, eye diameter and in height body. Moreover, the individuais showed little pigmentation and myomeres number changing between 39 to 42. The majority of morphometric characteristics have negative allometry with the cxception of head lenght with regard to standart lenght that have positive allometry.

Temporal distribution and composition of the ichthyoplankton from Leopoldo's Inlet on the Upper Paraná River floodplain (Brazil)

Univ Estadual Maringa, Dept Biol, Posgrad Ecol Ambientes Aquat Continentais, BR-87020900 Maringa, Parana, Brazil

Larval development of Plagioscion squamosissimus (Heckel) (Perciformes, Sciaenidae) of Itaipu reservoir (Paraná river, Brazil)

The aim of the present study was to characterize the larval development of Plagioscion squamosissimus (Heckel, 1840) morphometrically, collected at Itaipu reservoir from March 1988 to April 1990. It was obtained the samples monthly, with a conic-cylindrical plankton net with 0.5mm mesh. The morphological description of the larvae of P. squamosissimus was based on different stages of development. The specimens less than 6mm long present a moderate sized head and those that are larger than this length, present a large head. The pectoral fins are in an elevated position, near the operculum bones, and the ventral fins are in thoracic positions, the body has a moderate height, the eyes are small to moderate and the mouth is large with caniniform teeth. This species presents a proportional growth among the different parts of the body, as can be seen by the high correlation coefficient values (r>0.98; p<0.001).

The catfish, Rhinelepis aspera (Teleostei; Loricariidae), in the Guaíra region of the Paraná River: an example of population estimation from catch-effort and tagging data when emigration and immigration are high

Using the Leslie model, an estimate was made of the stock of the loricariid catfish, Rhinelepis aspera, in the fishing grounds in the Guaira region of the Parana River. The method was based on catch-effort and mark-recapture data collected over a 90 day period in 1986. The estimated initial population size, based on catch-effort, was 734 806 catfish with a biomass of 580 297 kg. During the experiment 2.372 million catfish entered the fishing area and 1.892 million catfish emigrated from it. A Petersen type estimate, based on the recapture ratio of tagged fish, was 812 359 catfish at the beginning of the experiment.