Selection and characterization of females of matrinxã,Brycon cephalus, for induced spawning

Abstract

Twenty-two (22) females of matrinxã, Brycon cephalus (Günther, 1869), in captivity, were selected by means of external features (swollen abdomen and enlarged urogenital papilla) and characterized in relation to the morphology of oocytes (percentual frequency distribution of oocytes, structural and ultrastructural observations) and to the relative condition factor (Kn) as an alternative method. This research was carried out in NUAP í  Fishery Institute, Apta, SAA, located in Pariquera-Açu, São Paulo State, from November/1994 to February/1996. The females were distributed into 3 groups. Ten (10) females, group A, presented high rate of fertilization and hatching of larvae, with a percentual frequency distribution of the oocyte diameter in the initial sample with two modes, 939.0 and 1001.6 µm, and with Kn >1.0. Other six (6), group B, ovulated but presented low rate of fertilization and hatching larvae, when compared with the previous group, and mean frequency diameter mode of 1001.6 µm, with Kn similar to 1.0. The females of group C (6) presented great number of the oocytes of the initial sample in degeneration and produced few larvae, abnormal in its majority, indicating regression of oocytes, and Kn < 1.0.