Cod, Gadus morhua - Gadiformes.
An important food fish for over 1000 years, cod have been overfished
and the previous enormous stocks have collapsed, recently cod farming
has been successful.
Photo: Hans-Petter Fjeld
Creative Commons Attribution
ShareAlike 3.0 License
A Coral Grouper or vermillion Seabass,
Cephalopholis miniata (Perciformes) - a carnivore of about
of a Sea Lamprey - Cyclostomata - a jawless fish.
Lampreys are parasitic on larger fish, they attach themselves to
their host and rasp at tissue with the teeth and/or feed on blood,
letting go when they have had enough.
Lion fish, Pterois sp. (Scorpaeniformes)
- A reef fish with poisonous spines, predatory on small fish and
invertebrates, can often be seen at night near to lights by the
sea that draw its prey. If diving or snorkeling towards dusk they
can emerge in surprising numbers from nooks and crevices, sometimes
rather shockingly appearing if flushed out by another fish diving
for cover with its spines erect as defence.
A Parrotfish, the group is considered to be a subfamily
of the Wrasses. These fish have a particular arrangement
of their teeth that looks like a parrots beak. They feed on algae
that grows on coral and when diving or snorkeling can be heard grinding
and rasping away at the coral underwater. The coral passes through
them and is deposited as coral sand which helps build reefs and
islands over time. Most parrotfish start off life as females, and
then become male later in life.
Hammerhead Shark - Elasmobranchii - a cartilaginous
fish. Two of the defining characters can be seen clearly, the heterocercal
(asymmetrical) tail and the row of gill slits just in front of the
Copyleft: This work of art published according
to terms of the Free Art License
A puffer fish or blowfish - Tetraodontiformes
- amongst many other names. When threatened, these fish are
able to take in a large volume of water to blow themselves up to
nearly spherical at which point the spines point outwards. These
fish are also amongst the most poisonous vertebrates in the world
having enough toxin to kill a human if the fish is not prepared
correctly for the table.
A file fish - Tetraodontiformes
- Found usually in shallow water of 30m or less and frequently
in or around coral reefs. Not great distance swimmers but very maneuverable as
the pair I watched shredding a large jellyfish while snorkeling
in the Red Sea demonstrated.
A Manta Ray, Manta Birostris
- Elasmobranchii. The largest of the rays, mantas
can be over 6m (20 feet) across and weigh more than a tonne. They
are plankton feeders, gentle and harmless despite their appearance
and alternative name of devilfish.
Pisces is a Class in the Subphylum
Vertebrata of the Phylum
Chordata, so they have all of the characteristics of both of these
groups in addition to the following:
Kingdom - Animalia
- Skin covered in scales
- Soft shelled eggs
that must be laid in water
- External fertilization
- All members are fully aquatic
- Limbs modified into fins
- Gas exchange through gills
Phylum - Chordata
Subphylum - Vertebrata
Class - Pisces
The group includes:
The status of fish groups, whether they are Classes, Orders,
infraorders, subclasses etc. is something that is currently changing
and somewhat confusing as to what they should be called. I have
named some of the major groups without saying which level the group
is (class, order, etc.) as doubtless the hierarchy will change whereas
the names are relatively constant. The following list is representative
but not complete.
- Agnatha - jawless fish
- Cyclostomata - no jaw so
the mouth cannot close, retractable teeth -
hagfish and lampreys
- Chondrichthyes - cartilaginous fish,
skeleton made of cartilage rather than bone, gill slits at the
side of the head, urea retained in the blood for osmotic balance.
- Elasmobranchii - no swim
bladder, teeth in several series, heterocercal (vertically
asymmetrical) tail - sharks and rays
- Osteichthyes - bony fish
- Sarcopterygii - fleshy finned
fishes (ancestors of tetrapods) - Coelocanths,
- Actinopterygii - ray finned
fishes, fins are skin supported by a number of bony spines
- Teleostei - moveable
lower and upper jaw, homcercal (symmetrical) tails -
Most living fishes are members
of this group
reduced fin number, dorsal, anal and caudal fin
often fused to make a ribbon running much of the
upper and lower length of the body -
the true eels
- Clupeiformes, include
many important food fish, usually silvery schooling
plankton-eating and pelagic-
herrings, sardines, anchovies
- Cypriniformes, mostly
fresh-water - carp, goldfish,
- Siluriformes, prominent
barbels around the mouth which resemble the whiskers
of a cat - catfish
all members spawn in fresh water, though many
spend much of their lives in the sea -
salmon, trout, char, graylings
mainly ambush predators and highly adapted as
such - pike
- Lampriformes, oceanic pelagic feeders -
oarfish, opah and ribbonfishes
a fleshy growth on the head of the fish is used
a lure - anglerfish
- Gadiformes - cod, burbot,
identifiable as they have two dorsal fins and
no lateral line, detritivores -
includes the flying fish
which have greatly developed pectoral fins into
wings for gliding
mostly found in the sea around coral reefs,
many departures from the normal streamlined
fish shape - file fish,
puffer fish, box fish, oceanic sunfish
flatfish, asymmetrical fish, both eyes lie on
one side of the head -
halibut, flounders, plaice, sole
- Scorpaeniformes, -
lion fish, scorpionfish, stone fish
- Perciformes 40% of
all fish - bass,
cichlids, gobies, gouramis, mackerel, perch,
tuna, bonito, whiting, wrasse
What do fish eat?
As in many animal groups, between them all fish eat a whole range
of different foods. Some fish are specialists on just a few sorts
while others are generalists. The specialists often have very highly
adapted mouths and teeth to enable them to feed more efficiently
on their particular types of food. Here are some examples amongst
the variety of carnivores, omnivores and herbivores:
- Sharks - mainly carnivorous on other fish,
often have several series of teeth that move forwards to take
the place of damaged or missing ones.
- Plankton feeders - Plankton are tiny, often
microscopic plants and animals of many different groups that
live in the upper levels of waters, particularly seas. They
are the basis of many marine food chains and many fish are specialized
to sieve them out of the water. Such fish include anchovies,
mackerel, sardines and the largest of all fish, the whale shark
(a shark but not a whale). Many other fish feed on plankton
when they are in the larval stage and many kinds of fish make
up part of the plankton themselves while they are larvae.
- Detritus and algae in mud and sand - fish
such as mullet feed in this way, they have highly adapted digestive
systems to separate out the organic food matter from the sediments.
- Anything that fits in their mouth and is edible
- some fish are not at all fussy about what they eat and end
up being pretty successful as a result. Cod
in particular fit into this category, they will eat detritus,
shrimps, worms and other invertebrates, smaller fish and even
birds if they are big enough and get the chance. Fish that do
this tend to be demersal - feeding at the bottom the water.
- Ambush predators - These fish feed on other
fish or crustaceans such as shrimps, crabs, worms etc. They
may lie on the bottom of the water as do flatfish such as
flounders, sole, turbot and halibut. These
fish are highly unusual in that they are asymmetrical with both
eyes on the same side of the face and a twist to the mouth.
The Anglerfish take ambush to another level
by having a lure that has evolved from the first three spines
of the anterior dorsal fin. They may lie in wait camouflaged
against the sea bottom, or may float in the water column in
the dark depths with a bioluminescent lure that attracts smaller
fish or invertebrates that see it as prey, in the last instant
the anglerfish opens its usually enormous mouth and swallows
the would-be predator.
- Shell crushers - many rays and skates have
their teeth adapted to crush shelled organisms such as snails,
oysters, mussels, clams, shrimps and crabs.
- Cleaning stations - Some small reef fish,
particularly wrasses and gobies make their
living by cleaning larger fish or turtles. The larger fish come
to the site of the cleaning station and often a number of the
cleaners will remove parasites from the skin and even inside
the mouth and the gills of the fish which refrain from making
a meal of the cleaner fish which they might do in the normal
course of things.
What eats fish?
Fish are an important part of many food chains and webs. Many
terrestrial or partly terrestrial animals such as birds, bears,
reptiles etc. also feed on fish so their food webs stretch beyond
The biggest natural consumers of fish are other fish.
Most fish are not cared for by the parents, the eggs are fertilized
externally and often left to drift in the water, particularly at
sea, though may stick to rocks where in some cases the parents may
waft water over them to ensure they survive and hatch. At hatching
the care of even this small number of fish mainly stops and the
young larval fish are on their own.
As fish start off so small, in large quantities (Atlantic cod
lay around 5 million eggs in a single spawning for example) and
are on their own, this means that they are eaten by all manner of
other fish and invertebrates of all sizes with a huge mortality
in the early larval stages particularly when they are part of the
Fish are a major source of protein for people too, wherever there
is a body of water near where people live it will be fished for
food (or was in the historical past).
The total world fisheries for human food, marine and freshwater
is around 80 million tonnes per year! With another 13 million tonnes
of invertebrate fishery.
Some of the groups of fish caught are:
||Annual catch, millions of tonnes
|Salmon, trout, smelts
|Sharks, rays, chimeras
Pelagic - fish that live in the water column or near the surface,
Demersal - fish that live on or near the bottom of the water
including coral reefs.