Meta-analytic assessment of physiological markers for decapod crustacean welfare

Decapod crustacean welfare is not only an ethical consideration for legislative purposes. Under culture and fishery settings, poor environmental conditions and operator practices can cause stress, which compromises the immune system and increases the risk of disease. For finfish, there are established environmental and animal (group, individual) welfare indicators. This is not the case for crabs, lobsters or shrimp. While environment-based indicators like temperature, pH and oxygen levels are easily transferable, there is no consensus for a common measure of stress to monitor welfare in decapod crustaceans. To address this shortcoming, we conducted a meta-analysis of the primary literature to test for relationships between haemolymph (blood) condition, for example, levels of glucose, _L-lactate, haemocytes (n = 8), and sources of physical stress, for example, handling, trawling, emersion and transport (n = 12). Despite variations in effect sizes (n = 459), generalised linear mixed models repeatedly ranked _L-lactate (followed by urea and glucose) as the most significant physiological predictor of stress in the haemolymph, with trawling followed closely by emersion as the most impactful stressors. Duration post (stress) exposure, sex (male, female), water temperature and moult stage (pre-, inter-, post-moult) were not associated significantly with stress prediction using the selected biochemical and cellular parameters, however, moult status was undefined in ~48% of literature sources and should be interpreted with caution. We present evidence that quantitating _L-lactate levels in the haemolymph represents a physiologic operational welfare indicator of decapod crustaceans, which complements existing condition/vigour indices.