Fisiologia do parto induzido por captura em Potamotrygon amandae (Elasmobranchii: Myliobatiformes: Potamotrygonidae)

Abstract

The stingrays of the order Myliobatiformes are considered viviparous, aplacental histotrophic. In this condition, they are considered more susceptible to capture-induced parturition. Although this phenomenon is a common consequence of fishing interactions with the group, it remains poorly studied. The aim of this study was to characterize the stress physiology in the freshwater stingray Potamotrygon amandae during induced parturition events by capture. Pregnant and non-pregnant females were collected from the Paraná River (UHE Engenheiro Souza Dias) using fish nets. Immediately after specimen capture, blood collection was performed, and the animals were placed in plastic boxes. In the case of pregnant females, the second blood collection was done at the time of induced parturition, and for non-pregnant females, it was done within a 60-minute interval. The specimens were transported alive to the Laboratório de Estudos em Fisiologia Animal (LEFISA) at UNESP for euthanasia and subsequent measurement of biometric data. Hematological (hematocrit), energetic (glucose and ketone bodies), respiratory (lactate), and endocrine (corticosterone) variables were measured and analyzed. The average time for fetal abortion was 57.5 ± 27.5 minutes. Body mass showed a significant difference when comparing pregnant and non-pregnant females, with higher values for pregnant females. Red blood cells are not responsive to capture stress, with an average amplitude of 15 to 38% of erythrocytes. Plasma lactate increases after a capture stress event, with an increased magnitude for pregnant females, making it a biomarker of the acute stress event in the species. Corticosterone shows high intra-specific variation and does not seem to increase after capture, and it does not differ between pregnant and non-pregnant females. Glucose was not responsive to capture, indicating that this substrate is not preferred during acute stress. Ketone bodies are the preferred energy source for acute stress events in the species, and their utilization occurs more slowly in pregnant females, with a lower decay rate in this group compared to non-pregnant females.