The objective of this study was to evaluate the effectiveness of estradiol valerate in an attempt to feminize the male Astyanax altiparanae. One thousand newly-hatched larvae were randomly distributed in four incubators. During a period of 30 days, estradiol valerate was administered in different dosages (20, 40, and 80 mg/kg of diet); the control group did not receive hormone in the diet. After 161 days of hatching, biometry was performed on 50 fishes per treatment group, and the gonads were analyzed. The hormone treatments were effective in feminizing A. altiparanae, achieving 70-76% of the desired sex, while the control treatment had 44% females. The hormone did not affect the growth of fish.

Neste trabalho está descrito o cariótipo detalhado de Pattonella intermutans. Esta espécie apresenta 2n = 12 cromossomos: três pares de autossômos metacêntricos e dois submetacêntricos e um par de cromossomos sexuais XX/XY. Os autossomos são caracterizados pela presença de bandas C nas regiões pericentroméricas e os cromossomos sexuais são totalmente heterocromáticos. A técnica de FISH detectou a NOR no autossomo IV.

Pattonella intermutans has 2n = 12 chromosomes including three metacentric and two submetacentric pairs of autosomes and an XX/XY sex chromosome pair. The autosomes are characterized by the presence of a C band in the pericentromeric region while sex chromosomes are totally heterochromatic. The FISH technique showed a nucleolar organizer region (NOR) in autosome IV.