There has been further discussion on the yahoo site regarding stationary boats and moving fish with SI
This first image is of an Australian barramundi moving fast through the SI beam. We know the fish is traveling fast because the fish image is squat and obviously not in normal proportion.
Here is another shot with stationary boat and moving fish, same species. This time the fish is not speeding through and its image is in proportion.
These images also show how important chart speed can be to obtain proportionally correct images.