Page 338 - (DK) Ocean - The Definitive Visual Guide

336 ANIMAL LIFE

Bony Fishes

BONY FISHES EXCEED ALL OTHER VERTEBRATE groups both in HUMAN IMPACT
DOMAIN Eucarya
number of living species and in their abundance. They have FISH FARMING
KINGDOM Animalia
evolved into myriad shapes and sizes, suiting every aquatic
PHYLUM Chordata Many important bony fish stocks
lifestyle and habitat and range from the shore to the deepest
CLASSES Actinopterygii are fished at unsustainable levels.
depths and from polar seas to hot deep-sea vents. Bony fishes Relieving the pressure by fish
Sarcopterygii farming is not easy as species such
have an internal skeleton of bone, although that of a few
ORDERS 48 as cod are difficult to rear on a large
primitive groups is part cartilage. The bony skeleton supports scale. In contrast, almost all Atlantic
SPECIES 31,290 salmon come from aquaculture.
flexible fins that allow them to move with far greater precision Many farmed fish eat feed prepared
than do the stiff fins of cartilaginous fishes. About one-third of bony fishes live only from other wild-caught fish.
in fresh water, while the remainder lives in the oceans or migrates between the two.
forward
Anatomy movement
Like other vertebrate animals, bony fishes have a skull, backbone, and ribs, but
the skeleton also extends out into the fins as a series of flexible rays. Bony fishes,
unlike sharks, can use their paired pectoral and pelvic fins for maneuvering,
braking, and even swimming backward. Spiny-rayed fishes, a group that
includes most bony fishes, also have sharp spines in the front portion of their
dorsal, anal, and pelvic fins. A bony flap called SALMON FARM
the operculum covers the gills of bony fishes. It SWIMMING Salmon farms, such as this one in Tasmania,
are a common sight in temperate seas.
can be opened to regulate the flow of water in The sideways force and backward However, there are problems with fish lice
through the mouth and out over the gills. A force exerted when a fish moves its (see p.346) and with dilution of the wild gene
covering of overlapping, flexible scales made tail from side to side results in a pool by escapees.
of thin bone protects most bony fishes. Some thrust at an angle between the two.
The resultant thrusts on left and right
primitive bony fishes, such as sturgeon, are produce a net backward thrust and so
armored with thick, inflexible scales or plates. the fish is propelled forward. movement of tail
sideways force
BONY SKELETON first dorsal fin
Flexible rays and hard spines support all the fins resultant thrust
in bony fish, such as this cod. The fins connect to vertebrae linked into a backward force
spines extending from the vertebrae. flexible vertebral column
The fish can precisely adjust the spine extends from
position of each fin. vertebra to fin
second dorsal fin
skull
third dorsal fin
orbit (eye
socket)

rib
pectoral
fin
first second
bony gill
hinged covering anal fin anal fin
jaw (operculum) pelvic fin tail (caudal)
fin
surface
esophagus concealed
under adjacent
gill filaments
scale
oral valve
annual growth ring
mouth
exposed surface

exposed surfaces
overlap to create
direction of smooth covering
water movement
OCEAN LIFE GILLS, VIEWED FROM ABOVE SCALES
gill arch, attachment
point for filaments
As water passes over the gill filaments, gases are
Bony fishes can be aged by their
exchanged. Oxygen passes into the blood and carbon
scales. Slow winter growth
dioxide passes out into the water. Within the filaments,
produces dark rings on the scales,
the blood flows in reverse relative to the water
so each dark ring indicates one
outside, so the concentration of gases in the fluids
year of life. The system works best
is opposed, which speeds the gases’ transfer.
for temperate-water fish such as cod.