| Summary: | Spray marking of fish, using fluorescent pigment propelled by compressed air, is a mass
marking technique, and is useful in the studies of fishery management. This method
typically uses a conveyor system to transport fish into a marking unit that dispenses the
powdered pigment through a nozzle with the aid of compressed air. The marked juvenile
fish are then released to continue their life cycle, and may be subsequently caught for
the purpose of experimental investigation. The previous design of the marking machine
(MK-5) had many shortcomings. In particular, the pigment dust caused worker discomfort
and possible environmental pollution, overlapping of fish on the conveyor resulted in
poor marking quality, and improper feeding and conveying caused injury and mortality
in fish during marking. Due to these, the marking machine MK-5 was not widely used. In
the present work, a new prototype of the automated spray marking machine was designed
and built in the Industrial Automation Laboratory at the University of British Columbia.
The new design was based on studies related to pigment emulsion, compressed air pressure,
zig-zag shaped feeder channel, conveyor belt compartmentalization and pigment
recycling. Image processing for assessing the retention of fluorescent pigment mark on
fish body was investigated by first developing retention indices, and subsequently using
appropriate image processing techniques such as the dilation and erosion of mark density,
in order to recover an aged mark. Our design developments have led to a fast, accurate,
reliable, low-cost and environmentally friendly system for marking fish. The prototype
has been tested at several hatchery sites in British Columbia and has thus far exhibited
good performance.
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