ANATOMY OF FISHES
MEASUREMENTS OF A "TYPICAL" FISH
.---_ __ __ _ _ _ T L - - - - - - - - - - - - - - ,
~-------- F L ----------__,
1--_____________
SL - -------------,
BO
body depth
FL
fork length
SNL snout length
CL
caudal fin length
HL
head length
TL
total length
CPO caudal peduncle depth
PL
pectoral fin length
UJL upper jaw length
EO
eye orbit diameter
SL
standard length (snout to base of caudal fin)
VL
pelvic (ventral) fin length
rays. Fin spines are usually stiff and have a sharply pointed
tip, but some fishes (e .g. blennies) have soft, flexible
spines. Soft-rays, as the name implies, are generally soft
(flexible), always segmented (articulated) and, in most
fishes, branched. The cross-striations (articulations) of the
soft-rays are best seen if the fin is held up to a light.
The scales of most fishes are either cycloid or ctenoid.
Cycloid scales are smooth, but the rear margin of ctenoid
scales is provided with small, tooth-like prickles (called
ctenii) which give ctenoid scales their rough texture when
the fish is stroked from the tail towards the head. In some
kingfishes (Family No. 210: Carangidae) the posterior lateral-line scales are modified to form scutes: thick, bony
scales with a median ridge ending posteriorly in a sharp
spine. Most clupeid fishes (pilchards , sardines, etc.) and
some trachichthyid and zeid fishes (Families Nos. 127 and
A
B
A. Cycloid scale from right side of fish. B. Ctenoid scale from right side of fish.
128) have scutes along the ventral midline of the belly.
The gills of fishes bear numerous soft gill filaments along
their outer (posterior) edge. The bright red colour ofthe gill
filaments of a fresh fish is from the abundant blood capillaries in each filament. The gills absorb oxygen from the
water and release carbon dioxide from the fish's respiration. On the inner (anterior) edge of the first gill arch are
the gill-rakers. These gill-rakers may be long, slender and
numerous, as in the plankton-feeding fishes whose gillrakers form a sieve to filter out their microscopic food from the
water passing through the gills. Most fishes have a few gillrakers, but some lack them completely . When counting the
gill-rakers always count those on the first arch unless otherwise stated, and the raker in the angle of the gill arch is
counted with the lower rakers (see illustration).
gill arch
upper gill-rakers
....
I ,
lower gill-rakers
I
I
gill filaments
Gill arch from left side of fish. Gill-raker counts = 3 + 7. i.e. 3 on the upper limb
and 7 on the lower limb.
3
MEASUREMENTS OF A "TYPICAL" FISH
.---_ __ __ _ _ _ T L - - - - - - - - - - - - - - ,
~-------- F L ----------__,
1--_____________
SL - -------------,
BO
body depth
FL
fork length
SNL snout length
CL
caudal fin length
HL
head length
TL
total length
CPO caudal peduncle depth
PL
pectoral fin length
UJL upper jaw length
EO
eye orbit diameter
SL
standard length (snout to base of caudal fin)
VL
pelvic (ventral) fin length
rays. Fin spines are usually stiff and have a sharply pointed
tip, but some fishes (e .g. blennies) have soft, flexible
spines. Soft-rays, as the name implies, are generally soft
(flexible), always segmented (articulated) and, in most
fishes, branched. The cross-striations (articulations) of the
soft-rays are best seen if the fin is held up to a light.
The scales of most fishes are either cycloid or ctenoid.
Cycloid scales are smooth, but the rear margin of ctenoid
scales is provided with small, tooth-like prickles (called
ctenii) which give ctenoid scales their rough texture when
the fish is stroked from the tail towards the head. In some
kingfishes (Family No. 210: Carangidae) the posterior lateral-line scales are modified to form scutes: thick, bony
scales with a median ridge ending posteriorly in a sharp
spine. Most clupeid fishes (pilchards , sardines, etc.) and
some trachichthyid and zeid fishes (Families Nos. 127 and
A
B
A. Cycloid scale from right side of fish. B. Ctenoid scale from right side of fish.
128) have scutes along the ventral midline of the belly.
The gills of fishes bear numerous soft gill filaments along
their outer (posterior) edge. The bright red colour ofthe gill
filaments of a fresh fish is from the abundant blood capillaries in each filament. The gills absorb oxygen from the
water and release carbon dioxide from the fish's respiration. On the inner (anterior) edge of the first gill arch are
the gill-rakers. These gill-rakers may be long, slender and
numerous, as in the plankton-feeding fishes whose gillrakers form a sieve to filter out their microscopic food from the
water passing through the gills. Most fishes have a few gillrakers, but some lack them completely . When counting the
gill-rakers always count those on the first arch unless otherwise stated, and the raker in the angle of the gill arch is
counted with the lower rakers (see illustration).
gill arch
upper gill-rakers
....
I ,
lower gill-rakers
I
I
gill filaments
Gill arch from left side of fish. Gill-raker counts = 3 + 7. i.e. 3 on the upper limb
and 7 on the lower limb.
3