Question

Draw a diagram showing the external features of a fish and label any two parts.

Answer 1

Hint: Fish are cold-blooded animals, having fins and a backbone. Most fish breathe with gills and have scales. About 480 million years ago, 22,000 species of fish began to evolve. The largemouth bass shown above has the typical (fusiform) torpedo-like shape associated with many fish.

Complete answer:
Fins are appendages that the fish uses to retain its position, move, steer and stop.They are either single fins along the centerline of the fish, such as the dorsal (back) fins, caudal (tail) fin and anal fin, or paired fins that include the pectoral (chest) and pelvic (hip) fins. Behind the dorsal fin, fishes such as catfish have another fleshy lobe called an adipose (fat) fin .

The dorsal and anal fins mainly assist fish not to roll over on their sides. For propulsion to move the fish forward, the caudal fin is the primary fin. With steering, stopping and hovering, the paired fins help.

Most freshwater fish with ganoid scales other than gar and catfish with no scales are either ctenoid or cycloid scales in most bony fishes.Ctenoid scales have jagged edges, and smooth rounded edges have cycloid ones. Ctenoid scales composed of connective tissue covered with calcium are present in bass and most other fish with spines. Most fishes also have a very significant body-covering mucus layer that helps prevent infection.

The gills are the fish's breathing apparatus and are highly vascularized to give them a bright red cover. An operculum (gill cover) that protects the sensitive gills and is a flexible bony plate. Water is inhaled through the mouth, passes over the gills and from beneath the operculum is "exhaled"

Color can be detected by fish. Due to the refractive index of water, the eyes in fish are rounder than mammals and focus is achieved by moving the lens in and out, not reshaping the lens as in mammals.

To detect odors in water, paired nostrils, or nares, in fish are used and can be quite sensitive. Eels and catfish have senses of smell that are particularly well developed.

The shape of the mouth is a good clue to what fish are eating. The bigger it is, the greater the prey that it can consume. If they are not obvious prey items, fish have a sense of taste and can sample items before swallowing to taste them. The fish may or may not have teeth, depending on the species.

The lateral line is a sensory organ consisting of fluid-filled sacs that are open to the water through a series of pores with hair-like sensory devices (creating a line along the side of the fish). Water currents and pressure and movement in the water are primarily sensed by the lateral line.

The vent is the outer opening of the urinary and reproductive digestive tracts. It is immediately in front of the anal fin in most fish.

Note: The fins are supported in many freshwater fishes by spines that are rigid and may be quite sharp, thus playing a defensive role. In particular, catfish have hard, sharp fins, which anglers should be wary of. As are portions of other fins, the soft dorsal and caudal fins are composed of rays. Rays have less rigidity and are often branched.