Tilting Behaviour, a Fear Response to Frightening Stimuli, as a Possible Predictive Index for Stocking Effectiveness in the Juveniles of Red Sea Bream Pagrus major

Abstract

Some individuals of the red sea bream released in an experimental tank aggregated and tilted their bodies on the bottom, exhibiting dark stripes and stretching their fins. Such “tilting behaviour” was observed for longer times and higher ratios in larger fish groups (40 mm in total length) than in smaller ones (12 mm and 20 mm TL). The recovery time from tilting behaviour was different among individuals in the same size group (80 mm TL). The fish with a strong tendency to exhibit tilting behaviour, which exhibited tilting behaviour for longer times, were not eaten by 3 +red sea bream (340–390 mm TL), while the quicker recovering fish (with a weak tendency to exhibit the tilting behaviour) were eaten. A fish group with a stronger tendency to exhibit tilting behaviour in an experimental tank showed a higher rerapture rate (15.1%) when released in the field than fish with the weak tendency (8.9%). Tilting behaviour is regarded as a fear response to frightening stimuli and might be a predictive index for estimating fish quality and the stocking effectiveness of red sea bream juveniles. © 1993, The Japanese Society of Fisheries Science. All rights reserved.