| Summary: | Field trials were conducted at three British Columbian Atlantic salmon
farms to test the performance of a fish image capturing and sizing system
(FICASS) against the presently used seine/dip netting technique. FICASS
consisted of underwater video camera equipment combined with an S-VHS videorecorder
and image processing equipment. Salmon farmers require a new, noninvasive,
sampling method to obtain population average fish weight (kg) (AFWIKE)
and standard deviation (kg) (SDWIK), because the current level of accuracy is +/-
20% of actual mean fish weight and is very invasive to the fish. Environmental,
husbandry (i.e. grading, sorting, feeding histories), swimming and stocking
characteristics were recorded and, whenever possible, related to the sizing
results. FICASS was developed by a research group at Dr. Petrell's Fish Imaging
Laboratory, Chemical and Bio-Resource Engineering Department, University of
British Columbia.
In the three cages of one kg-sized fish of low stocking density that formed
uncompacted types of aggregations and had not been previously size sorted, the
AFWIKEs obtained by FICASS changed with sampling position. In 13 out of 15
cages of fish (> 3 kg) which had been size sorted, the AFWIKEs obtained by
FICASS did not significantly change with position. In cages of harvest-sized fish
and size-sorted three kg-sized fish, AFWIKEs by FICASS varied with position if
the fish were unfed. When 3 kg-sized fish had been previously size sorted,
FICASS results agreed with seine/dip netting results in 11 out of 13 cages. When 1 kg-sized fish were tightly schooling together, FICASS results was agreed with
seine/dip netting results in 4 out of 6 cages sampled. Generally FICASS results
agreed with seine/dip netting results when size un-sorted and unfed fish were
videotaped at the top of aggregation (4 of 5 positions). FICASS results agreed
with harvest data either when fish had been previously size sorted or fed as
scheduled, and when sized-unsorted and unfed fish were videotaped in the middle
or bottom of a loose, swimming aggregation.
In general, different feeding and sorting schedules, and stocking conditions
appeared to promote the incidence of sub-populations characterized by size within
a sea cage. Ideally fish sizing should occur when the population size is
randomized. FICASS can be used as an effective sizing tool because it can be
used to non-invasively detect subpopulations, and if detected, the fish sizing could
be repeated at a latter date when fish conditions become more randomized. === Applied Science, Faculty of === Chemical and Biological Engineering, Department of === Graduate
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