Thought they are applicable to all fishes, more or less, the following terms refer specifically to fishes of the Family Poeciliidae which includes the familiar guppy, swordtail, platy and mollie. In most cases they are general terms that can be used for all fishes and many other organisms. In a few cases the definitions may have a slightly different meaning in other groups of fishes. Some fishes, for instance lack certain fins or have an extra one (such as the adipose fin of tetras, which is between the dorsal and caudal fins). When used in those cases the location information may not be entirely correct. The accompanying illustration should assist in locating many of the various parts (please note that it's of a goldfish which is NOT a livebearer and NOT in the family Pociliidae).

anal fin - single fin along ventral side, between caudal fin and pelvic fins.

anterior - the head end of an animal. When used as a direction refers to "in front of" as in "the eye is anterior of the anal fin."

caudal fin - the tail. Refers only to the actual fin rather than the whole of the posterior end of the fish.

caudal peduncle - section of body between the vent and the caudal fin. Supports the caudal fin.

dorsal - the top of an animal, toward the ceiling. When used as a direction refers to "above" as in "the dorsal fin is dorsal to the anal fin."

dorsal fin - the single fin along the back of a fish, between the head and caudal fin. Some other kinds of fishes have two dorsal fins, some have a dorsal fin and an adipose fin. Poeciliids only have a single dorsal fin.

eye - sight organ. One on each side of the head in Poeciliids.

gill slit - the opening at the posterior end of the operculum allowing water to flow out of the mouth, past the gills, for breathing.

gonpodium - modified stick-like anal fin. The male intromitant organ in some livebearers. Used to introduce sperm to the female.

gravid spot - dark area visible in most light-colored female livebearers above the anal fin. Internally it is where the developing embryos are located. Some livebearers have an actual spot on the skin in this location, that is NOT the same thing.

gular region - the area immediately under the mouth, in front of the throat. In humans, this is the bit between your chin and your neck.

head - the area of the fish in front of the gill slit.

lateral - the side of an animal. When used as a direction means "to the side of," as in "the eyes are lateral to the brain."

lateral line - sense organ running along the side of most fishes. Used for sensing motion in the water, it is extremely sensitive, and can even feel sound waves pushing on the water.

mouth - the opening into which food and water are taken. Located in the head.

operculum - bony plate covering the gill cavity in the head of a fish. Gill slit runs along the posterior edge of the operculum.

pectoral fin - one of the most anterior paired set of fins, in most livebearers located laterally immediately posterior to the gill slit, on the side of the body. Used for fine movement backward and forward.

pelvic fin - one of the most posterior paired set of fins, in most livebearers located ventrally, just anterior to the anal fin. Used for stability in the water (helps keep the fish from rolling)

posterior - the tail end. When used as a direction, refers to "toward the tail," as in "the caudal fin is posterior to the anal fin."

pupil - the dark portion of the eye through which light enters.

ray - a branched, relatively soft fin support structure, located in any fin, but posterior to any spines in that fin.

snout - the area of a fishes head anterior to the eye.

spine - an unbranched, relatively stiff fin support structure, may be located in any fin, but anterior to any rays in that fin.

standard length - the distance from the anterior tip of the snout to the base of the tail. Not including the caudal fin.

tail extension - elongated part of the tail, seen in species with "swords" and in lyretail forms.

total length - the distance from the anterior tip of the snout to the posterior edge of the tail. In species with a tail extension (such as swordtails) total length is measured without the tail extension, with the tail extension measurement given as well.

vent - the opening of the digestive and reproductive tracts, located just posterior to the anal fin.

ventral - the side of a fish opposite the dorsal side, usually facing toward the bottom of the tank.

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