This study aims to test the influence of size grading on self-feeding behaviour, social
structure (measured by the percentage of triggering acts per individual), growth
performances, and blood physiological variables of individually passive integrated
transponder (PIT)-tagged sea bass juveniles, using a computerized on-demand feeding system
coupled with a PIT tag monitoring device. Three consecutive periods of 27 days each were
compared: a first period (P1) before grading (6 tanks of 100 fish; 40.2
± 8.9 g) followed by a second period (P2) after grading. The protocol
applied aimed to create two groups of fish of similar mean weight but with either a low or
a high coefficient of variation of weight
(CVw) corresponding to an imposed
difference in social disruption (Tlow:
CVw ~ 10%, 3 tanks of 60 fish each with
social disruption;
Thigh:CVw ~20%,
3 tanks of 60 fish each, without social disruption). Tlow and
Thigh groups were studied over P2, and an
additional 27-day period under identical conditions (P3). The grading
protocol used and/or time modified the social structure when comparing P1
and P2. Thereafter, during P2 and P3,
no difference could be observed in growth performances, feed demand, or physiological
variables between Tlow and
Thighgroups. Feeding rhythms and social structures were
similar in both groups. In conclusion, such grading practice only transiently modifies
feed demand behaviour and social structure built around the self-feeder, without further
improvement in individual growth performances in sea bass.