THE ULTIMATE ANGLING BUCKET LIST

Working in conjunction with these in the skates and rays, on each side of the head close to the eye, is a
small hole known as a spiracle through which water is drawn in to oxygenate the gills over which it is
passed before exiting the respiratory system through the gill slits.
Were skates and rays to take water in through their mouths like bony fish, they would run the risk of
also taking in sand and other unwanted particulate material from the bottom they are resting on.
Spiracles vary in size, though evolution has seen to it
that some of the larger free swimming shark species,
and in particular the mackerel sharks and thresher
sharks, have managed to do away with them altogether,
passing water over their gills via the open mouth
passively while swimming.
Thornback spiracles
One feature however all round bodied cartilaginous
fishes other than angel sharks or monkfishes share is
uneven tail lobes, with the upper lobe always being
longer than the lower, which in conjunction with large
pectoral fins in many open water shark species helps
produce lift when swimming as they are negatively
buoyant and would otherwise sink.
Characteristically, they all also lack traditional scales, having instead opted for small sharp edged overlapping
back pointing denticles for aqua-dynamic stream-lining, which is the reason why they have
such a rough feel when brushed against the grain from tail to head.
Less obvious will be the many tiny pores dotted around the nose and mouth. Dependant on species,
these relay information of varying quality back to one of the most amazing and sensitive natural
detection adaptations known to science, the ampullae of lorenzini. Special jelly filled pores which act
as electro-receptors capable of locating weak electrical impulses from the blood circulatory system of
potential prey items.
This feature is not entirely unique to sharks and rays, all of which have them, as they can also be found
in some non-cartilaginous fishes such as reed fish and sturgeon.
Sharks and rays are also able to pick up subtle pressure
changes using their lateral line. But arguably, the sense
they are perhaps best known for is their legendary ability
to detect minute quantities of blood and other lost body
fluids in seemingly vast volumes of surrounding water.
Smell is the main detection sense acting at long range on
organic traces such as blood, though it is actually tuned in
to a whole range of odours of the type released typically by
injured or distressed prey species.
This is facilitated by the extraordinarily large size of the
Pores – ampullae of lorenzini olfactory lobes of the brain, which when water containing
an odour enters the nostrils, the information provided is
analysed specifically by these lobes, which can be as much as two thirds of the weight of the entire
brain, a level of development unique to sharks and rays.
Having nostrils placed wide apart on either side of the head also allows for directional swimming along
the greatest line of concentration of an odour back to its source, aided by side to side movement of the
head to keep the fish on track. Taste only comes into play once an item of potential interest is located.
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