The effects of acute oxygen changes on heart rate in the freshwater crab Poppiana dentata (Randall, 1840)

Heart rate is a key physiological feature that can be used to assess the response of organisms to changing environmental conditions in aquatic habitats, such as acute fluctuations in oxygen levels and hypoxic conditions. This experiment, therefore, investigated cardiac responses in a freshwater brachyuran species, Poppiana dentata, exposed to low oxygen levels. Heart rate was derived from beats per minute (bpm) signals (n = 576) using an infrared, non-invasive technique over a 96 h period, under different dissolved oxygen (DO) conditions. These involved three regimes: normoxic (6.8 ± 0.1 mg L-1), decreasing DO to hypoxic levels (6.2 to 1.7 mg L-1), and recovery with normoxic levels (6.3 ± 0.1 mg L-1). Changes in heart rates among the three regimes were significant (P < 0.05); reflecting the shift in heart rate during different conditions of oxygen availability, normoxic (59 to 61 bpm), declining DO (54 to 62 bpm) and recovery DO (53 to 64 bpm). Additionally, the normal rhythmicity of heart rates under the normoxic condition was not maintained throughout most of the declining DO and recovery periods. P. dentata has demonstrated cardiac compensations in heart rate during low oxygen levels, providing insight into the species cardiac physiology.