Page 19 - Encyclopedia of Aquarium and Pond Fish, 3rd Edition

WHAT IS A FISH? 17

The shape of the fins identifies the sexes in species Some cichlids, such as the Chessboard Cichlid The elaborate fins of the domesticated male
like Trichogaster Gouramis (see pp.112–113). Males (see p.144) pictured here, display lyre-tailed Siamese Fighting Fish (see pp.104–106) are larger and
have longer and more tapering dorsal and ventral extensions on their caudal fins. The function of more flamboyant than in its wild counterparts. Fish
fins than females. this elaborate tail is to attract and select mates. have been bred selectively for this characteristic.

requires considerable muscular effort, and the main thrust the fish can support themselves or even walk around.
for swimming is provided by the caudal fin at the rear of Sometimes the pectoral fins are equipped with spines for
the body; this starts the rippling movement that spreads defense. In gouramis, the pectoral fins may be transformed
through the fish’s body. The dorsal fin, which runs down into hairlike structures that help the fish locate food by
the center of the back, helps to keep the fish moving in a detecting scents in the water.
straight line and is counterbalanced on the underside of Some fish, notably characoids, have an additional smaller
the body by the anal fin. fin behind the dorsal fin. This is known as the adipose fin, and
Paired ventral (or pelvic) fins are set on either side of the as its name suggests, it acts as a store of adipose (fatty) tissue
midline in front of the anal fin on the underside of the body. and has only a minor role in locomotion.
They act like stabilizers, keeping the fish upright, and in some
species, such as corydoras catfish, they are used to hold the Fin variants
eggs during spawning. The pectoral fins, located farther The shape and position of the fins vary between species and
forward, close to the gills on each side of the body, also provide valuable clues to their lifestyle. For example, shoaling
help the fish to maneuver. In bottom-dwelling species, fish that live in areas of open water have forked caudal fins,
these fins may be adapted for use as props, or legs on which which provide them with good propulsive power. The
open V-shaped structure gives little drag but does
not have the power to provide rapid propulsion
from a stationary position. Sit-and-wait
MOUTH SHAPES predators that catch their prey in a sudden
The shape, size, and position of a fish’s mouth give a good insight burst of speed tend to have rounded,
into its feeding habits. Predators tend to have much larger mouths paddle-shaped caudal fins—ideal
than omnivores. Some species have obvious canine-shaped teeth; in for fast acceleration. To move
others, teeth are absent or less clearly visible. quickly from a standing start,
some fish rapidly expel a stream
of water from their gills in an
aquatic form of jet propulsion.

The bladelike teeth of the
piranha enable the fish to bite
Surface feeders, Mid-water feeders, Bottom-feeding fish, chunks out of its quarry. Fish
such as hatchetfish, such as tetras, have like the plecos, have teeth can be found in a variety of
have a relatively short slightly protrusive jaws suckerlike mouths for places. Some species have them
upper jaw, which so they can catch scraping food and algae on their jaw bones or on the
enables them to grab passing food particles. from rocks, and bones of the roof of the mouth;
invertebrates at the This is the most common scavenging from the others have patches of teeth on
water’s surface easily. mouth design. bottom of the tank. the tongue or pads of teeth on
the gill arches in the throat.

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