The observation of fish swimming into rubber rings is not restricted
to freshwater or sturgeons. I have seen a number of specimens of
small sharks (mainly Mustelus lenticulatus) "wearing" rubber rings.
In several cases these were the rubber gaskets that seal disposable
car oil filters. Sometimes the gasket lodges ahead of the pectoral
fins and wears through the skin to produce an open wound. But I have
also seen a M. lenticulatus with a gasket embedded halfway back
through the first dorsal fin - it had evidently passed the pectorals
and worn its way into the dorsal fin. The fin had then healed
anteriorly to the gasket, which was moving its way posteriorly under
the pressure of water, and would presumably have eventually dropped
off the tail! This animal appeared quite healthy. M. lenticulatus
is a bottom feeder and may have picked up the gaskets while burrowing
in the seabed mud. I have also seen M. lenticulatus with sections of
nylon monofilament mesh embedded in the gill area - in one case
completely encircling the gills but embedded so deeply that only the
broken tips of the meshes emerged.


Malcolm Francis
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Malcolm Francis
National Institute of Water and Atmospheric Research
P. O. Box 14-901, Kilbirnie, Wellington, New Zealand
Phone: ++64 4 386 0300
Fax:   ++64 4 386 0574
Email: [log in to unmask]
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