Walter Norbis

Hábitos de alimentación del lenguado Paralichtys orbignyanus (Valenciennes, 1842) en una lagunacostera somera del Atlántico Sur: Rocha, Uruguay

A total of 293 stomachs of adult flounders, Paralichthys orbignyanus, were analyzed from the catch of artisanal fisheries that operate in Rocha Lagoon, Uruguay. Flounders between 25 and 64 cm total length showed that 119 individuals (40.61%) had content in their stomachs, the silverside Odontesthes argentinensis being the main prey item. Significant variations were observed between size classes. Cannibalism was less than 3% of total prey items and occurred within the 46–56 cm size class. Significant and positive trends were observed between the length of the silverside and the total length of the flounder, but a low percentage of the variability in prey size (<47%) was explained by the predator size. The specialized and selective diet of P. orbignyanus adults is considered to be typical of active piscivore predators and visual fish feeders. The state of prey digestion (in relatively fresh condition or in the beginning of digestion), the moment of catch and the low feeding index could indicate that the species acts as an active predator during the night.

Length-weight relationships and condition factor of two Sciaenid species Micropogonias furnieri and Cynoscion guatucupa from the Rio de la Plata and Uruguayan ocean coast, Southwestern Atlantic

espanolEn este trabajo se analizaron las relaciones longitud-peso y el factor de condicion de Micropogonias furnieri y Cynoscion guatucupa en diferentes epocas [verano; otono; invierno, primavera y anos (2006, 2007 y 2011)] a partir de muestreos mensuales de desembarques de la flota costera uruguaya que opero en el Rio de la Plata y costa oceanica uruguaya. Fueron analizados 9.146 individuos de M. furnieri (entre 15-69 cm de longitud total) y 5.285 individuos de C. guatucupa, (entre 21-54 cm de longitud total). Para ambas especies, el coeficiente de alometria fue negativo (b 3). Para M. furnieri, las pendientes no mostraron diferencias significativas entre el 2006 y 2007, mientras que el 2011 presento diferencias significativas con ambos anos. Para C. guatucupa no se encontraron diferencias significativas entre el 2007 y 2011, pero si cuando ambos anos fueron comparados con el 2006. Los mayores valores del factor de condicion fueron obtenidos en verano de 2006 y durante el verano y otono del 2007 para M. furnieri, mientras que para C. guatucupa fueron en invierno 2006 y otono 2007. Para ambas especies el factor de condicion mostro diferencias significativas estacionales y anuales. Este trabajo presenta la primera referencia del factor de condicion para estas especies de Sciaenidos en el area de estudio. EnglishThe present study analyses the seasonal (summer: January, February, March; autumn: April, May, June; winter: July, August, September and spring: October, November, December) and annual (2006, 2007 and 2011) length-weight relationships and condition factors of Micropogonias furnieri and Cynoscion guatucupa from Rio de la Plata and the Uruguayan ocean coast from data collected throught monthly landings by the Uruguayan coastal fleet in the Montevideo port (Uruguay). A total of 9,146 individuals of M. furnieri ranging from 15 to 69 cm total length (L T); and 5,285 individuals of C. guatucupa, ranging from 21 to 54 cm L T were analyzed. For both species, the allometry coefficients showed that growth in the majority of seasons were negative (b 3). For M. furnieri, no significant differences among slopes were found between 2006 and 2007 whereas 2011 showed significant differences compared to 2006 and 2007. For C. guatucupa no significant differences among slopes were found between 2007 and 2011, whereas 2006 showed significant differences with other years. The highest values for the condition factor in M. furnieri were recorded in summer 2006, and during the summer and autumn 2007 and for C. guatucupa in winter 2006 and autumn 2007. Significant seasonal and annual differences for condition factors were found for both species. This work provides the first reference regarding condition factor for both sciaenid species in the study area.