Typical Fish
Atlantic
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
published under
Creative
Commons Attribution ShareAlike 3.0 License
A Coral Grouper or vermillion Seabass,
Cephalopholis miniata (Perciformes) - a carnivore of
about 30-40cm length
Mouth 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.
A
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 pectoral fins.
Phot: National
Geographic
Copyleft: This work of art published according to
terms of the Free Art License
Cool Fish
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 a 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.
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Basic Features:
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:
- Skin covered in scales
- Ectothermic
, cold blooded-
Soft shelled eggs that must be laid
in water
- External fertilization
- All members are fully aquatic
- Limbs modified into fins
- Gas exchange through gills
Kingdom - Animalia
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
decided to name 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, lungfishes
- Actinopterygii - ray finned
fishes, fins are skin supported by a number of bony
spines or rays
- Teleostei -
moveable lower and upper jaw,
homcercal (symmetrical) tails -
Most living fishes are
members of this group
- Anguilliformes,
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, minnows
- Siluriformes,
prominent barbels around the mouth which
resemble the whiskers of a cat -
catfish
- Protacanthopterygii
- Salmoniformes,
all members spawn in fresh water, though
many spend much of their lives in the sea -
salmon, trout, char,
graylings
- Esociformes,
mainly ambush predators
and highly adapted as such
- pike
- Lampridiomorpha
- Lampriformes, oceanic pelagic feeders -
oarfish, opah and ribbonfishes
- Paracanthopterygii
- Lophiiformes,
a fleshy growth on the head of the fish is
used a lure -
anglerfish
- Gadiformes - cod,
burbot, hake
- Acanthopterygii
- Mugiliformes,
identifiable as they have two dorsal fins
and no lateral line, detritivores -
mullet
- Beloniformes, includes
the flying fish which
have greatly developed pectoral fins into
wings for gliding
- Tetraodontiformes,
mostly found in the sea around coral reefs,
many departures from the normal streamlined
fish shape - file fish, puffer fish,
box fish, oceanic sunfish
- Pleuronectiformes,
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. 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 water too.
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 plankton.
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:
| Fish group |
Annual catch, millions of tonnes |
Freshwater fish:
Miscellaneous |
6.80 |
| Salmon, trout, smelts |
1.03 |
Marine demersal:
Cod,
hake, haddock |
8.96 |
Marine pelagic:
herrings,
sardines, anchovies |
22.40 |
Marine pelagic:
Tunas,
bonito, billfishes |
6.24 |
Marine pelagic:
Miscellaneous |
11.18 |
| Sharks, rays, chimeras |
0.77 |
| Other marine |
9.56 |
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