Ricardo Ferriz

Dieta y ecomorfología de la ictiofauna del arroyo Manantiales, provincia de Buenos Aires, Argentina

Diet and ecomorphology of the ichthyofauna of Manantiales stream, Buenos Aires prov- ince, Argentina . The present study addresses the correlation between diet and morphology of 19 fish species that inhabit the Manantiales stream at the headwaters of the Samborombon river, Buenos Aires province, Argentina. The species were classified into four trophic groups: carnivores, omnivores, insectivores and detritivores-alguivores. Twelve ecomorfologic attributes related to habitat use and feeding patterns were analyzed to distinguish ecomor- phologic groups of species with the food consumed. Univariate and multivariate analysis techniques were used to determine groups of species using the ecomorfologic and diet attributes as descriptors. Carnivores were associated with well developed head, mouth, pectoral and caudal fins and usually presenting compressed bodies. Omnivores were a more heterogeneous group. Nektonic forms of this group were associated with a compressed body, lateral eyes and relatively small size of the pectoral fins and caudal fins; nektobentonic forms were associated with small mouth, fusiform body and long caudal peduncle; benthic forms were related to depressed body, dorsal eyes, ventral mouth and long digestive tract. The only nektonic species consuming insects on the surface is characterized by a strongly compressed body, lateral eyes, tail and big wide mouth facing up. The detritus-alguivores had a long digestive tract, mouth ventral or terminal and long caudal fin. The significant relationship between diet and ecomorphology allows to sustain that fish with similar diets converge towards common ecomorfologicic attributes.

Reproducción y dinámica poblacional de Cheirodon interruptus (Ostariophysi: Characidae) en el arroyo El Portugués, alta cuenca del río Samborombón, Argentina

The reproductive period of Cheirodon interruptus was determined by analyzing 1658 individuals collected monthly in the stream El Portugues, Argentina, from May 2004 to April 2005. Two prolonged spawning seasons, one in spring and another in autumn, were observed based on the maturity stages and gonadosomatic index (GSI) of female specimens. The mean monthly GSI of males was significantly correlated with depth. In females, the GSI exhibited a significant correlation with photoperiod and depth. The remaining environmental variables, including temperature, pH, conductivity, and monthly rainfall, did not show a correlation with the mean monthly GSI. The first sexual maturity in females and males was reached within the 24-26 mm standard length class. The mean absolute fecundity was 448 oocytes (SD = 217.8), and the mean relative fecundity was 0.33 (SD = 0.097) oocytes per milligram of body weight; this species is a multiple spawner. The oocyte diameter ranged from 0.05 to 0.70 mm, with a mean of 0.48 mm (SD = 0.16).

Alimentación de Gymnotus omarorum (Gymnotiformes: Gymnotidae) en Laguna Blanca (Parque Nacional Río Pilcomayo), Formosa, Argentina

Se describe la dieta de la morena, Gymnotus omarorum, en Laguna Blanca Parque Nacional Rio Pilcomayo, Formosa. Se realizaron 8 muestreos desde septiembre de 2012 hasta julio de 2013. Para el analisis de los contenidos estomacales se utilizaron metodos de frecuencia, porcentaje volumetrico, porcentaje numerico e indice de abundancia (IA). Las presas ingeridas pertenecen generalmente a invertebrados y peces que viven al amparo de las plantas flotantes. Los ejemplares de tallas menores a 200 mm de longitud total (LT) presentaron una dieta carnivora con mayor especializacion mientras que en tallas mayores a 201 mm de LT la dieta fue carnivora del tipo generalista. Se observo un aumento del consumo de peces y decapodos con el incremento del LT. Los insectos en general, y en particular las ninfas de Odonata, dominan en las tallas pequenas y medias. Se observaron diferencias significativas en la dieta de esta especie a lo largo del periodo considerado, relacionandose la misma con los cambios de biomasa de las plantas flotantes. Los resultados permiten caracterizar a la dieta de Gymnotus omarorum como una especie carnivora generalista

Algunos aspectos biológicos de Bryconamericus iheringii (Ostariophysi: Characidae) en dos arroyos de la alta cuenca del río Samborombón, Argentina

Some aspects of biology of Bryconamericus Iheringii (Ostariophysi: Characidae) in two streams in the high basin of the Samborombon river, Argentina. This study analyzed the following aspects of the Bryconamericus iheringii population structure: abundance patterns, condition factor, male-female sex ratio, relation between weight and length, and reproductive period. Samples were made monthly from May 2004 to April 2005 using small trawling nets, in the Manantiales and El Portugues streams. The highest values of biomass for the Manantiales stream corresponded to May, July and March, the highest values of biomass for El Portugues stream were for May, September and March. In the Manantiales stream, both for males and females, the set of individuals < 25 mm Lst dominated during the spring. Individuals included among the 26-40 mm Lst predominated in the warmer months, while those between 41-60 mm Lst abounded at the end of the summer, autumn and winter. In the Portuguese stream, individuals males < 25 mm Lst, were present in the summer, the rest of the year was dominated by sizes between 26-40 mm Lst during the warmer months. Sizes between 41-60 mm Lst dominated in colder months. The relationship between the sexes differed significantly from the 1:1 reason with predominance of females in almost every month. Higher values of K factor were recorded at the end of the spring and summer for both streams. This species has a slightly allometric growth and differences between males and females in this factor may be due to the greater size of females. The largest number of females in maturation and mature was observed in the months of August, September and November in both streams and during the post-spawning period in February-May in the Manantiales stream and in March-May in the Portuguese stream. This would indicate that the spawning period would be between the months of August and November.

Alimentación de Pseudocorynopoma doriai (Pisces: Characidae) en el arroyo El Portugués, provincia de Buenos Aires, Argentina

Feeding of Pseudocorynopoma doriai (Pisces: Characidae) in “El Portugues” stream, Buenos Aires province, Argentina. We describe the diet of dragonfin tetra, Pseudocorynopoma doriai, in the El Portugues stream (58° 26’ 30’’ S - 35° 04’ 24’’ W) belonging to the high Samborombon river basin, Buenos Aires province. To achieve this aim, samples were taken monthly from May 2004 until April 2005. The methods used for the analysis of stomach contents were, frequency, volumetric percentage, numerical percentage and index of relative importance (IRI). The results obtained indicate a diet with no significant differences throughout the year, consisting mainly of aquatic insects, allochthonous insects and spiders. The analysis shows that while there were no significant differences in diet at differents range length of this species, individuals less than 42 mm standard length, consumed a greater number of insects of terrestrial origin. The results allow to characterize Pseudocorynopoma doriai as a generalist insectivorous species for this stream of Pampasia.