External Anatomy

Word Roots and Origins operculum from the Latin operculum, meaning "cover"

figure 39-10

The external features of the yellow perch, Perca flavescens, are representative of bony fishes. Note the growth rings on the scales shown in the inset. They indicate the fish's approximate age.

Figure 39-10 shows the external anatomy of a yellow perch, a bony fish common in freshwater lakes of the eastern United States and Canada. The yellow perch, like all bony fishes, has distinct head, trunk, and tail regions. On each side of the head is the operculum (oh-PUHR-kyoo-LUHM), a hard plate that opens at the rear and covers and protects the gills.

Fins

The fins of the yellow perch are adapted for swimming and navigating through the water. The caudal fin extends from the tail. It moves from side to side and amplifies the swimming motion of the body. Two dorsal fins, one anterior and one posterior, and a ventral anal fin help keep the fish upright and moving in a straight line. The fish uses paired pelvic fins and pectoral fins to navigate, stop, move up and down, and even back up. The pelvic fins also orient the body when the fish is at rest. The fins are supported by either rays or spines. Rays are bony yet flexible, while spines are bony and rigid.

Skin

The skin of the yellow perch is covered with scales. Scales are thin, round disks of a bonelike material that grow from pockets in the skin. As Figure 39-10 shows, scales overlap like roof shingles. They all point toward the tail to minimize friction as the fish swims. Scales grow throughout the life of the fish, adjusting their growth pattern to the food supply. The scales grow quickly when food is abundant and slowly when it is scarce.

Posterior dorsal fin

Anterior dorsal fin

The external features of the yellow perch, Perca flavescens, are representative of bony fishes. Note the growth rings on the scales shown in the inset. They indicate the fish's approximate age.

Posterior dorsal fin

Anterior dorsal fin

Operculum

Nostril Mouth

Anal fin

Pelvic fin '

Pectoral fin

Operculum

Nostril Mouth

Anal fin

Pelvic fin '

Pectoral fin

Tubarao Osseos

figure 39-11

The skeleton of Perca flavescens is similar to that of other bony fishes. The general structure of the vertebrae, rib cage, and fins is found in many fishes.

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