Dissection of a Blue Mackerel
Scientific name: Scomber australasicus
The species was chosen because of the cost and because it has a large swim bladder which is easy to find.
The Blue Mackerel is a schooling fish found right around the Australian coastline. Adults live in deep offshore
waters, whereas young fish occur in coastal bays and estuaries.
It is a plankton feeder, which filters small crustaceans from the water. Adults also eat small fishes and
squids.
The Blue Mackerel can be recognised by the pattern of narrow dark bars dorsally and spots ventrally. It
grows to 65 cm in length and is often referred to as the Slimy Mackerel.
Incision at Anus/ Cloacae
The dissection begins by inserting a fine scalpel blade into the anus (also called the vent) of the fish.
The Blue Mackerel's anus is located just anterior to (in front of) the anal fin, on the ventral (lower)
side of the fish. This is also the case for most fishes, but some, for example the pearlfishes (family
Carapidae), the anus is located well forward on the throat.
Cut anteriorly between pelvic fins
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•
The incision passes anteriorly between the pelvic (ventral) fins. Depending on the type of fish, these paired fins
are used to stabilise the fish when swimming and also for braking. The pelvic fins of the Blue Mackerel are located
ventral to (under) the pectoral fins.
The pelvic fins are supported by the bones of the pelvic girdle which are anchored in the belly muscles. Other
fishes such as the herrings, family Clupeidae, have pelvic fins located abdominally. The eels have lost their pelvic
fins entirely. Male sharks and rays have their pelvic fins modified into claspers, organs used for internal
fertilisation. The Eastern Cleaner Clingfish has its pelvic fins modified into a sucking disc.
Continue cut to Isthmus
Use scissors to cut anteriorly through the bones attached to the pelvic
fins. Cut forward along the isthmus, the narrow, fleshy space
beneath the head and between the gill covers. The gill covers (also
known as operculae) are flaps which lie along both sides of the head
and protect the underlying gills.
Open body cavity
• Pull apart the two walls of the body cavity and expose
the internal organs (see next image for names).
• The neat incision now runs from the anus forward
between the two pelvic fins and along the isthmus.
Internal Organs
Some of the ventrally located internal organs.
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heart
•
liver
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pyloric caecae
•
adipose (fatty) tissue
Pull aside gut
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•
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Here the the adipose tissue (1) and gut (2) are pulled aside to expose the swim bladder (3),
gonads (4) and kidneys (5).
As a general rule, carnivorous fishes like the Blue Mackerel have relatively short guts.
Herbivorous fishes have much longer guts. View an image that shows the long gut of a Carp.
The gonads and kidneys are paired. One of each can be seen on both sides of the swim bladder.
Cut posterior end of gut & pull gut
forward for greater exposure
Pulling the gut forward exposes the swim bladder
(1), gonads (2) and kidneys (3) in position
dorsally (at the top) in the body cavity. A larger
portion of the liver is now visible (4).
Removing operculum
• Here, the right gill cover (operculum) is being removed to expose the
underlying gills.
• The Blue Mackerel shares the usual bony fish character of having a
single opening behind each operculum (the branchial aperture).
Water passes in through the mouth, over the gills and out through
the branchial aperture. In contrast, the sharks and rays have five to
seven branchial apertures on each side of the head.
Gills exposed
The gills of the Blue Mackerel.
• Gill filaments - the site of gas exchange
• Gill rakers - appendages along the front edge of the gill arch
• Gill arches - support the gills
Cut upwards from anus to
backbone
Cut upwards behind operculum
Remove fillet
Remove all organs exposing Swim
bladder
The other organs have been removed to expose
the swim bladder at the top of the body cavity.