The isotopic composition ( δ13C and δ 15N) of muscle, carapace and claw was determined from six wild individuals of Phrynops geoffroanus (Schweigger, 1812) in order to verify the variation between those tissues. The mean values of δ13C e δ 15N were, respectively, -19.48 ± 0.81‰ (-20.8 - -18.64‰) and 7.23 ± 0.67‰ (6.49 - 8.3‰) for muscle, -16.52 ± 0.98‰ (-17.88 - -15.43‰) and 7.29 ± 0.54‰ (6.74 - 7.97‰) for carapace and -18.57 ± 0.97‰ (-19.97 - -17.26‰) and 4.36 ± 0.33‰ (3.93 - 4.79‰) for claw. We found a significant difference for the tissues evaluated for both δ13C and δ15N. Muscle and claw were statistically similar and more depleted in 13C than the carapace. Nonetheless, claw was more depleted in 15N than muscle and carapace tissues. These results are likely related to differences in metabolic processes involved on each tissue formation. The description of the isotopic signatures variation in P. geoffroanus tissues provides a baseline for future investigations on the diet reconstruction of this species when more than one tissue is involved.

The innate immune activity of the freshwater turtle Phrynops geoffroanus (Schweigger, 1812) was investigated, using a sheep-red-blood cell hemolysis assay. The time- and concentration-dependent hemolytic activity of the turtle plasma was low compared to that reported for other reptiles. However the plasma of P. geoffroanus exhibited higher activity at elevated temperatures, resulting in temperature-dependent hemolysis. The sensitivity of turtle plasma to temperature could be interpreted as a mechanism by which freshwater turtles use basking behavior to elevate body temperature, thus enhancing the innate immune response. However, we cannot discard the possibility that environmental contaminants could be affecting the turtle's immune response, since the animals in this investigation were captured in a polluted watercourse.

Phrynops geoffroanus (Schweigger, 1812) is the freshwater turtle with the widest geographical distribution in South America. During 2006, physical examination and hematological evaluation were performed on free-ranging turtles from two polluted rivers, the Piracicaba River (n = 51) and its tributary Piracicamirim (n = 42), in southeastern Brazil. Red blood cell and thrombocyte counts, mean corpuscular volume and mean corpuscular hemoglobin levels differed in turtles from the two water courses. Although free-ranging turtles showed ectoparasites and boat propeler lesions, animals apparently had no signs of clinical disease. In spite of our results, further monitoring of the demography and health status of Phrynops geoffroanus in anthropogenically altered environments is recommended.