About Zacco platypus (Temminck & Schlegel, 1846)
Zacco platypus, commonly called the pale chub, has a moderately large head with moderately large eyes positioned on the upper side of the head. It has a large mouth, where the posterior end of the jaw reaches the anterior part of the eye. The species has an elongated body that is more compressed toward the posterior end, and bears a black longitudinal band. Its maximum recorded total length is 20 cm (7.9 in), while the average length is 13 cm (5.1 in). It has moderately large cycloid scales, which are much larger on the sides of the body than on other parts of the fish, and it has a complete lateral line. The caudal fin is forked, and its upper edge is shorter than the lower edge. The pelvic fins are bright yellow, while the pectoral and caudal fins are dull in color. The dorsal region of the body is grayish, and the rest of the body is silvery. Zacco platypus has 7 dorsal fin rays, and the dorsal fin is positioned near the midpoint between the tip of the snout and the end of the caudal peduncle. Each spine of the first dorsal fin is slightly extended, and the first spine of male individuals is extended in a thread-like shape; the edge of the second dorsal fin is straight, and all of its rays are branched. The anal fin rays are elongated, with the longest ray reaching the caudal peduncle, and there are 8 to 10 anal fin rays and 7 to 9 pelvic fin rays. The single lateral line has 42 to 46 lateral line scales, with 6.5 to 8.5 scales above the lateral line and 3 scales below it. A transverse lateral line is present in the occipital area, connecting the lateral lines on the two sides of the body. No scales are present on the head. The top of the body is quite rounded toward both sides, and the muzzle narrows noticeably in front of the nostrils, ending in a fairly short, conical, but rounded tip. The mouth is oblique, and the posterior end of the upper jaw reaches the anterior margin of the eye. The pharyngeal teeth have a dental formula of 1,4,4-4,4,3; these teeth are conical with curved tips. Zacco platypus also has oral folds at the bottom of the oral cavity, which gradually develop and increase in number as the fish grows. Two distinct low ridges are present in the occipital region. When spawning, males develop 10 or more bluish vertical strips. This species can live for 6 or more years. Pale chub primarily live in freshwater habitats. Adult pale chub prefer shallow waters with rapid flow, and tend to hide in cracks between rocks to stay in areas with high food availability and low predation. They do not favor deep, stagnant water. They inhabit waters with an average temperature of 23–24 °C (73–75 °F). Adult individuals mostly stay near the bottom, where their food source is found. Due to environmental changes and pollution, the population of pale chub is shrinking in many regions. Pale chub are widely distributed in northern China, Korea, northern Vietnam, Japan, and the northwestern part of Taiwan. They are mostly found in climates with temperatures ranging from 10–22 °C (50–72 °F). All species in the genus Zacco share similar mating patterns, and have two main mating seasons: one in spring from February to April, and another in summer from June to August. In natural environments, males develop brighter coloration around breeding time to attract females for mating. While reproduction in aquariums is possible, there have been no reported cases of successful breeding in captivity. Compared to values recorded in summer, higher gonadosomatic index (GSI) and higher yolk counts in spring confirm that Zacco platypus has an evolved reproductive strategy where it invests more energy into spring mating to avoid damage from summer floods. At the start of the mating ritual, several males will chase a single female at a time, occasionally displaying their dorsal and anal fins to threaten competitors, and will also swim aggressively and fight one another. After some time, the female rests on the sandy riverbed, and a male will press against her belly to make her tilt, positioning her anus closer to the male. The male then vibrates its body and stirs the riverbed while releasing sperm, and the vibration causes the female to scatter her eggs. Subordinate males often join the spawning event to attempt to fertilize some of the eggs. During the breeding season, male pale chubs undergo sexual dimorphism, growing numerous sharp, colorful nuptial tubercles on the head, especially the jaws, and on the fins. The body shape also changes during this season: the anal fin becomes longer, and body depth increases for both sexes. Zacco platypus are free spawners; after spawning, both males and females cover their eggs with sand by vibrating their anal fins and digging up sand. No parental care is provided to the eggs after spawning. Zacco platypus is used as bait for sport-fishing targeting larger fish. It is popular with fly fishers, and is caught for human consumption. Males are kept in aquariums because of their vibrant coloring.
