Abnormalities in flatfishes of the south-west Atlantic Ocean.

Five adult paralichthyid specimens with various kinds of abnormalities are reported from the south-west Atlantic Ocean. These abnormal flatfish specimens represent the first records of wholly ambicoloured Paralichthys orbignyanus specimens having a deep notch between the eye and dorsal fin and a partially albinistic specimen having skeletal deformities and only the second record of an almost totally ambicoloured specimen. We also report the first observation of reversal in Paralichthys patagonicus and an almost totally ambicoloured, reversed Xystreurys rasile.

Diet and food selection by Ramnogaster arcuata (Osteichthyes, Clupeidae).

The goals of this study were to describe the diet and estimate the trophic level and food selection of Jenyns's sprat Ramnogaster arcuata, one of the common fishes in the Bahía Blanca estuary in Argentina. The copepods Acartia tonsa [53·7% index of relative importance (I(RI))] and Eurytemora americana (13·4% I(RI)), the mysid Arthromysis magellanica (13·9%I(RI)) and the small shrimp Peisos petrunkevitchi (8·2% I(RI)) were the most important food items for this species, and its diet exhibited monthly variability with respect to the principal prey categories. The zooplankton species in the study area consisted of 32 taxa. Acartia tonsa was the most abundant species [54% individuals (N) m(-3)], followed by Balanus glandula (13·8% N m(-3)) and E. americana (10·1% N m(-3)). The rest of the zooplankton groups represented <3% N m(-3). The most preferred items throughout the year were A. magellanica and Idotea sp. The trophic level value estimated was 3·1.

Ovarian folliculogenesis in the smallnose fanskate sympterygia bonapartii (Müller & Henle, 1841) (Chondrichthyes, Rajidae) / Foliculogénesis ovárica en la raya marmorada, sympterygia bonapartii (Müller & Henle, 1841) (Chondrichthyes, Rajidae)

Chondrichthyes have become an important economic resource in the last decades, with Argentina as one of the countries that exploits more sharks and skates, even at levels that exceed de limits of many species. However, there is a scarce knowledge of the reproductive biology of this group, particularly from species inhabiting the Southern hemisphere. This work shows the most relevant facts during folliculogenesis in Sympterygia bonapartii. Results show that germinal cells are present in immature and maturing females. The most important facts that vary along de follicular development are the number of types and layers of follicular cells, the establishment of thin projections from the follicular cells and the degree of development of the thecae. Follicular cells are, at least, of two different types and both of them emit projections that break through the zona pellucida. The outer theca shows signs of synthetic activity. Atretic follicles of different sizes are present in exemplars of all the reproductive stages. These results are discussed in a physiological and adaptive context.

Los Condrictios se han convertido en un recurso económico importante en las últimas décadas, siendo Argentina uno de los países que más explota tiburones y rayas, incluso a niveles que exceden los límites de varias especies. A pesar de esto, es poco lo que se conoce sobre la biología reproductiva de este grupo, particularmente en especies del Hemisferio Sur. En este trabajo se estudian los estadios más relevantes de la foliculogénesis en Sympterygia bonapartii. Los resultados muestran que las ovogonias están presentes tanto en ejemplares inmaduros como subadultos. Las características más importantes que varían a lo largo del desarrollo folicular son el número de capas y tipos celulares que constituyen el epitelio folicular, el desarrollo de proyecciones de las células de la granulosa y el grado de desarrollo de las tecas. Las células foliculares son, al menos, de dos tipos y ambos emiten proyecciones que atraviesan la zona pelúcida. La teca externa presenta características compatibles con la actividad sintética. Folículos atrésicos de distintos tamaños están presentes en ejemplares de todos los estadios de madurez sexual. Estos resultados se discuten en un marco fisiológico y adaptativo.