1 Yes it is possible using Tracker but within error limits that the fish are moving perpendicular to the line of sight. this can provide you an estimate of the fish swimming speed in the wild in meters/second (you need a unit of measure in the video at the position of fishes) or bodylength/sec (perhaps you do not need a ruler of sorts).

2 i recommend you use something in the video as a unit of measure to calibrate against the fishes body length. If so , tracker can give estimates of fish size as well as speed

http://weelookang.blogspot.sg/2015/06/tracker-motion-of-person-progressive.html

use ruler to calibrate length

3 for a moving camera reference frame, you need to tell Tracker what is constant, a rock that is to be used as origin (0,0) or else nothing can help in completely different/ or no points of reference in terms of habitat for measuring distance?

http://weelookang.blogspot.sg/2015/06/tracker-constant-acceleration-of-050.html

use a fixed object as reference origin (0,0)

In summary, you need to be scientific (reference length, fixed camera point, fixed object to be used as origin(0,0) ) about your video taken in order for the results to be scientific (repeatable and accurate). else, it is not going to yield data on the speed of fish correctly in the wild.

Post edited June 24, 2015 at 11:57 PM EST.

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