Juveniles of mixed size and appearance. Several of the smaller ones (tending to follow the leaders) have slightly red bars on their tails and the caudal fins are "split" in the midline. It seems likely that that is a normal morphological marker for this species at this growth stage. The smaller ones also have slightly blotchy flanks, and that feature has been seen in some other inat observations, notably from the Whyalla area.
Two with similar markings.