Individual behavioural variation in adaptation to a novel environment in female broodstock prawns (Penaeus monodon)

Welfare concerns are now increasingly being applied to aquatic species, including decapod crustaceans raised in aquaculture. A key consideration in measuring the behaviour and welfare of animals, is the impact of individual variation for interpreting and improving welfare status but research in decapods is limited. The black tiger prawn ( Penaeus monodon ) is the most prominent aquaculture industry in Australia, using wild-caught broodstock in hatcheries. Assessing animals in experimental contexts is important for building the knowledge on, for example, resource preferences, as well as individual behavioural variation. The study aims were to understand the variation in locomotory movement between individual adult female broodstock prawns across an approximately 21-hour period following placement into a novel observation tank and to observe changes in behaviour across time as an indication of adaptation to the testing context. Forty-seven adult female prawns were individually placed into observation aquaria and video recorded. Scan sampling behavioural observations were conducted every 10 min for a period of 20 h 40 mins. The location of the prawns (left, middle, right tank third), and behaviours of ‘inactivity’, ‘swimming’, ‘walking’, ‘aquarium wall exploration’ (contact with the walls), and ‘stationary activity’ were recorded. The locations of the prawns at each sample were converted to a binary ‘transition score’. Prawns showed fewer transitions following placement compared to later observed time periods ( p < 0.0001). Hierarchical clustering separated prawns into low (mean ± SEM 0.13 ± 0.01, medium (0.25 ± 0.008), and higher (0.44 ± 0.03) degrees of transitioning activity. Prawns were predominantly inactive (time proportion: 0.66 ± 0.01), with all observed behaviours showing changes across time (all p ≤ 0.03). There were significant positive relationships between mean transition score and ‘aquarium wall exploration’ ( p = 0.0009) as well as ‘walking’ ( p = 0.0004). More locomotory movement as well as aquarium wall exploration may indicate anxiety-like behaviour in those individuals rather than boldness. Further work could determine the repeatability of individual differences in exploration across time, and across different contexts. Confirmation of personality in P. monodon could inform the potential for domestication selection on desired traits. Animals were still engaging with the aquarium wall at the end of the observation period suggesting they may still be acclimating to their new environment. A longer observation period would be needed to conclude on the duration needed for these prawns to adapt to a testing environment, or the potential limitations for interpreting behaviours under these individual testing contexts. • Female broodstock prawns showed individual variation in exploration behaviour • Clustering analysis grouped prawns into low, medium, and high location transitioning • Location transitions positively correlated with walking and aquarium wall exploration • Wall exploration suggests prawns were still adapting to the test aquarium after 21 h • Individual variation could be used to inform on traits during breeding selection