TECHNICAL TERMS
Adipose fin: an unpaired, membranous non-rayed fin, commonly found on the dorsal midline of the caudal peduncle of, e.g.,
catfishes.
Anal fin: an unpaired rayed fin, on the ventral midline of thebody just behind the anus.
Anus: like that in human beings; in fishes, it usually appears as
a minute hole on the ventral midline just before the anal fin (butwell separated from the anal fin in some fishes).
Barbel: a thread-like cutaneous (rarely bony) structure, which
is developed around the mouth. Four categories of barbels arecommonly recognized: 1) nasal barbel, a kind of barbel associatedwith the nostril; 2) maxillary barbel, a kind of barbel associatedwith the upper jaw or lip; 3) rostral barbel, a kind of barbel on theanteroventral part of snout before jaws; 4) mandibular barbel, akind of barbel at the ventral surface of lower jaw.
Belly: an anteroventral part of the body around the abdominal
cavity.
Branchiostegal ray: a thread- or blade-like laminar bone, supporting the gill membrane (branchiostegal membrane).
Caudal fin: an unpaired rayed fin at the posteriormost regionof the body. It is sometimes minute, absent, or continuous withthe dorsal and/or anal fins.
Caudal peduncle: a posterior part of the body behind the verticalline through the end of the anal-fin base.
Cheek: a small area in the lateral part of the head between theoperculum and the infraorbital region.
Chin: an anteriormost part of the ventral surface of the lower jaw.
Dorsal fin: an unpaired rayed fin on the dorsal midline. In many
spiny-finned fishes, the dorsal fin is divided into two parts; insuch case, the anterior and posterior parts are called "1st (first)
dorsal fin" and "2nd (second) dorsal fin", respectively.
Filamentous ray (or filament): an elongated, thread-like fin
ray (or spine), entirely or largely free from the fin membrane.
Fin: a membranous structure developed on the body, which
is used in swimming and/or maintaining the body position.
In many fishes, 2 kinds of paired fins (viz. pectoral and pelvicfins) and 3–4 unpaired fins (dorsal, anal, adipose, and caudalfins) are recognized.
Finlet: one or more posterior rays of the dorsal and/or anal fin,separate from the main part of the respective fins.
Gill opening: a slit or pore-like opening for water discharge at
the posteriormost of head.
Gill raker: usually an element of the comb-like structure, developed along anterior margin of each gill arch. When the rakers on
the upper and lower limbs of the gill arch are counted separately,a raker straddled the angle of the arch, if present, is included inthose of the lower limb.
Infraorbital region: a small area in the lateral part of the headjust below the eye (not including the jaws).
Isthmus: narrow midventral interspace between right and left
sides of the gill membranes.
Keel: sharp-edged, linearized cutaneous or bony structure, looks
like a keel along the bottom of a boat. Clupeids, engraulidids
and some cyprinids have a long "keel" along the ventral midlineof the body.

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Lateral line: an external organ of the sensory system (exposed
terminal region of nerves) on the head and body; hereinindicated in particular is the one found on the body (i.e., notincluding the cephalic lateral-line system), unless otherwise
noted. In many fishes, the lateral line(s) forms as a linearlyarranged canal structure (lateral-line canals), and they appear
as longitudinal "line(s)" on the body. There are no lateral-line
canals on the body in several fishes (e.g., clupeids, engraulidids, and gobiids).
Nape: a dorsoanterior part of the body just behind the occipitalregion.
Nostril [or naris (pl. nares)]: a nasal opening; frequently foundat the tip of a short tube. In many fishes, there are two pairs of
the nostrils on the snout.
Nuptial color: a particular coloration, which appears chiefly
in the reproductive season; usually this color is more vivid inmale than in female (with a few exceptions).
Occiput (or occipital region): a dorsoposterior part of the headjust behind the eyes (superior to the skull).
Operculum: a posteriormost part of side of the head behind thepreopercle, and covering the gill chamber.
Pectoral fin: a paired rayed fin, which is developed on thelateral or ventrolateral side of the body just behind the head.
Amongst the Mekong fishes, swamp eels usually lack this fin (aswell as the pelvic fin).
Preopercle: a lunate bone at the boundary between the cheekand the operculum.
Pelvic fin: a paired rayed fin, which is developed on the ventral
surface of the body before the anal fin. Several fishes lack
this fin (e.g., phallostethids); in the gobies, the pelvic fins areusually fused medially, forming a sucking-disc.
Ray (or segmented ray): a type of fin rays, having segments (atleast in distal part). In many cases, segmented rays are soft andbranched distally (called "branched rays"); some simple rays
are often hardened and form a spine-like structure (found in e.g.
some cyprinids and catfishes). Actually each ray represents alaterally-paired structure.
Spine (or spinous ray): a type of fin rays, lacking segments.
In many cases, spines are bony and pungent, but sometimes
flexible (in e.g. dragonets and gobies). Actually each spine
represents a laterally-unpaired structure. See also "Ray (orsegmented ray)".
Scute: a type of modified scale with a sharp bony keel at its midline. Commonly found on the pre-anal midline in the clupeid
and engraulidid fishes (see right figure).
Snout: an anterior part of the head before the eye (not including jaws).
Swim bladder (or air bladder): an internal balloon-like organ,
which is developed beneath the vertebral column.
Tail: a posterior part of the body behind a level of anus.
Trunk: a middle part of the body between the head and the tail.
Thorax: an anteroventral part of the body before the belly;
usually points toward the area ventral and anteroventral to thepectoral-fin base.

dorsal fin

gill opening
operculumocciputeyecaudal fin

caudal peduncle

napelateral line

nostril(s)
snout
chin
barbel(maxillarybarbel)

cheek

preopercle

thoraxgill membraneanal fin

anus
belly
pectoral fin

pelvic fin

filamentous ray

nasal
barbeladipose fin

maxillary barbel
mandibular barbels
1st dorsal finscutesunbranched (or simple) rays
[longest one with serrated
hind margin in this example]

2nd dorsal fin※pelvic fins of gobies areusually fused medially,
forming a sucking-discspinesrays(branched rays)

branchedrays

soft portionof dorsal fin

spinous portionof dorsal fin

gill archgill rakers

Types of mouth

Types of caudal fin

superior

terminal

forkedsubinferior

inferior

lanceolate (or pointed)

emarginate

truncategill filaments
rounded9