A case of intersex occurrence in Steindachneridion parahybae (Steindachner, 1877) (Siluriformes: Pimelodidae) under captivity condition: a cytogenetic and morphological study

ABSTRACT Little is known about reproductive biology of endangered Steindachneridion parahybae , a gonochoristic teleost species inhabiting the Paraíba do Sul River Basin, and herein is the first description of intersex in S. parahybae juvenile. The normal appearance of ovaries and testes in juvenile from the same lot of breeding were also described for comparison, even as cytogenetic analysis was performed in these juveniles. One specimen was a priori classified as female due to the macroscopic characteristic of ovaries, with small yellow oocytes, without fringes (a main characteristic of catfish male), and larger than testes; however the microscopic analysis revealed the presence of ovotestes, including the complete spermatogenesis. S. parahybae had diploid number, 2n = 56 chromosomes with no evidence of differentiated sex chromosomes or supernumerary chromosomes among them. These findings may be due to the result of exposure to endocrine disrupting compounds or may also be influenced by environmental conditions. The possibility of intersexes might also happen spontaneously and it cannot be ruled out. Therefore, the functional significance and reproductive consequences of this anomaly remain to be determined, suggesting that this species may be susceptible to endocrine disruption. These results contribute to gain expertise about reproductive biology of an endangered species in captivity.

STATISTICAL THEORY OF AVALANCHE BREAKDOWN IN SILICON

The current flowing in silicon junctions under conditions of high electric field sufficient to cause avalanche breakdown consists of a sequence of pulses of constant magnitude and with randomly distributed spacing and duration. A statistical model is presented for this intermittent conduction mechanism in which the transition probabilities between the conducting and non-conducting states are Markoffian and depend on the excess of the applied voltage over the breakdown voltage; power-law and exponential dependences are considered and the precise form is shown not to be critical in deriving from these simple conditions a number of predictions about the macroscopic current–voltage characteristic, all of which have been confirmed by experiment.It is demonstrated generally that a randomly switched discharge of positive resistance has a macroscopic current–voltage characteristic which depends upon the d-c. source resistance and can have a region of negative slope. Only with a negligibly small source resistance is the true characteristic obtained.The observable fluctuations of current and their spectral distribution are derived and indicate the noisiness of silicon junctions under avalanche conditions.The influence of illumination on the breakdown statistics and macroscopic characteristic are briefly discussed.