Physiological Biomarkers of Hypoxic Stress in Red Swamp Crayfish

Crayfish harvested from the Atchafalaya River Basin (ARB) represent the majority of Louisiana wild crayfish landings.  However, ARB sedimentation and anthropogenic activities have altered the historic river-floodplain connection, causing reduced water circulation and flow patterns that prompt the formation of hypoxic conditions (dissolved oxygen ≤ 2 mg/L) during the annual flood pulse.  Physiological stress caused by chronic hypoxia exposure may lead to detrimental population effects such as reduced survival, growth, and fecundity.  The purpose of our study was to determine if ARB hypoxia causes physiological stress in red swamp crayfish Procambarus clarkii by examining hemolymph lactate, protein, and glucose concentrations in individuals captured from hypoxic and normoxic sites throughout the annual ARB flood pulse.  Adult P. clarkii hemolymph was collected by pericardial cavity puncture and serum protein, lactate, and glucose concentrations were spectrophotometrically determined.  Mean crayfish hemolymph glucose concentrations were not dissimilar in individuals captured from hypoxic and normoxic areas.  However, crayfish from hypoxic sites displayed a significantly higher (P = 0.0458) mean hemolymph lactate concentration and a significantly lower (P = 0.0147) mean hemolymph protein concentration when compared to individuals from normoxic sites.  Additionally, the disparity in hemolymph protein concentrations between crayfish from hypoxic and normoxic areas appears to intensify during the latter stages of the flood pulse.  Hemolymph lactate and protein concentrations appear to be good physiological biomarkers of hypoxic stress in P. clarkii.  Although not seen in the field, results of laboratory experiments indicate rapid changes in glucose concentrations under hypoxic conditions.  These changes suggest an additional acute response to hypoxia, possibly dampened by various biotic and abiotic factors.