Abstract
Optimal stocking density allows shrimp farmers to maximise profit while maintaining animal welfare. To date, holistic assessments of chronic crowding stress effect on Litopenaeus vannamei are lacking regarding biological impairments, stress-related behaviors, and recovery capacity. Twelve tanks of a recirculation aquaculture systems were maintained at three stocking densities: 1 kg/m(2) (low density-Low), 2 kg/m(2), (standard density-Standard) and 4 kg/m(2) (high density-High). The experiment was divided into phase 1 (21 days stress) and phase 2 (21 days recovery). After stress, shrimp at Low treatment exhibited the highest survival rate, best growth performance, antennae and uropods quality. Stress behavior included more frequent abnormal swimming patterns and loss of balance. Hemolymph analysis suggested homeostatic mechanisms for the mobilization of energy from storage organs. Mild upregulation of specific markers indicated cellular/oxidative stress. Limited immune system effects indicate low correlation with crowding or distress. During the recovery phase, mortalities ceased and partial compensatory growth was recorded. Shrimp recovered from injuries, while abnormal behaviors frequency also decreased. Oxidative stress marker expression returned to baseline levels for unstressed shrimp. Morphological and behavioral observations can be used industrially to assess crowding stress or as tools for developing welfare indices or monitoring systems.