Detailed Explanation of the Morphological Characteristics and Living Habits of the Giant Mudskipper

Mudskippers are the collective name for fish in the family Gobiidae, commonly known as jumping sharks, mud hoppers, jumping fish, etc. They are warm-water and warm-temperate nearshore small fish, widely distributed along the west coast of Africa, India, the Pacific waters, and the tropical and subtropical nearshore shallow waters of the New Hebrides (not found in the Americas), and are found along the entire coast of China. There are not many species of mudskippers; along the coast of China there are mainly 3 genera and 6 species. Along the coast of Zhejiang there are a total of 3 genera and 4 species, namely the mudskipper, the giant mudskipper, the blue-spotted mudskipper, and the large blue-spotted mudskipper. Mudskippers are small edible fish with delicious meat, a short food chain, low breeding costs, low investment costs, few fish diseases, easy to raise, live fish tolerate long-distance transport, and are rich in nutrients with nourishing properties. They are widely regarded by the people of Zhejiang, Fujian, Taiwan, China, and Guangdong as an excellent tonic food, and are in great demand both internationally and domestically. The giant mudskipper is the most important species in mudskipper aquaculture.

I. Morphological Characteristics of the Giant Mudskipper

The giant mudskipper BoleophthalmnsPectinirostris (Linnaeus) has an elongated body, with the anterior part nearly cylindrical, the tail laterally compressed, and the dorsal and ventral margins straight. The head is medium-large and slightly laterally compressed. The snout is short and blunt, larger than the eye. The eyes are high-set, close to each other, protruding from the dorsal surface of the head, with the lower eyelid free, and the interorbital space rather narrow, resembling a longitudinal groove. The mouth is large, subterminal, and horizontally cleft; the upper jaw is longer, with the maxilla extending below the posterior margin of the eye. The teeth in both jaws are in a single row; the upper jaw teeth are fine, with 2 to 4 canine teeth at the front; the lower jaw teeth are large, horizontal, with obliquely truncate tips, and a pair of canine teeth at the symphysis. There are no teeth on the vomer, palatines, or tongue. The tongue is large and thick, round, and not free. The upper lip fold is well developed, nearly reaching the center; the lower lip fold is short, located at the corners of the mouth. The gill opening is medium-large, the gill membrane is connected to the isthmus, the isthmus is wide, and the gill rakers are pointed and short.

The body and head are covered with cycloid scales; the scales on the anterior part are small, while those on the posterior part are larger; the base of the pectoral fin is also covered with fine cycloid scales, and there is no lateral line.

There are two dorsal fins; the first dorsal fin is high, with the fin spines filiform and elongated; the second dorsal fin is low, with an elongated base, and its tip extends beyond the base of the caudal fin. The anal fin is low and elongated, with the last several fin rays elongated; the pectoral fins are long and slightly pointed; the pelvic fins are united into a suction disc with an entire margin; the caudal fin is rounded. The dorsolateral side is olive-brown, the ventrolateral side is lighter; the first dorsal fin is dark blue with irregular small white spots; the second dorsal fin is blue with 4 longitudinal rows of small white spots; the anal, pectoral, and pelvic fins are light gray; the caudal fin is greenish-black, sometimes with small white spots.

II. Living Habits

(1) Habitat Habits

Mudskippers can use their pectoral and caudal fins to crawl or jump on the water surface, sandy beaches, and rocks. The giant mudskipper can use the inner gill cavity, skin, and tail as auxiliary respiratory organs. As long as the body is moist, it can live out of water for a relatively long time. It is a warm-water fish with broad temperature and salinity tolerance. Mudskippers kept in fresh water for more than ten days will die. They grow relatively fast at water temperatures of 14 to 30°C; below 14°C they retreat into burrows, feed little, and grow slowly.

Mudskippers tolerate poor water quality better than ordinary fish, and have habits similar to freshwater @#@236@#, being able to burrow into tunnels for shelter; numerous openings can be seen scattered across the tidal flats. Generally, a tunnel must have more than 2 openings: one is the main opening, and the other is the rear opening (commonly known as the rear bubble hole). The main opening is the main passage for entering and exiting, while the rear opening allows smooth water flow and air circulation. The tunnel passages are not very regular, generally often Y-shaped or U-shaped. The depth and length of the passages vary depending on the nature of the substrate. In soft mud, they are relatively deep and long, reaching 50 to 70 cm. The burrows are generally exclusive. However, during the breeding season, males and females often share the same burrow. The mudskipper's tunnel also serves as a spawning chamber.

(2) Feeding Habits of the Giant Mudskipper

Mudskippers live on tidal flats below the high tide zone along nearshore coasts and estuaries. On sunny days they come out of their burrows and move about on the mudflats in search of food, feeding on benthic algae, small insects, and other small organisms on the tidal flats. Analysis of stomach contents shows that mudskippers mainly feed on attached diatoms. At low tide or on the bottom of drained ponds, mudskippers are often seen feeding on benthic algae, that is, with the lower jaw touching the surface of the tidal flat, like plowing a field, swinging the head left and right while crawling forward to seek benthic algae. Mudskippers do not have the bad habit of cannibalism. In artificial breeding, fertilization is often used to cultivate basic bait organisms to promote the growth of mudskippers.

(3) Reproduction and Growth

Sexually mature giant mudskippers are 12 to 15 cm in body length and 30 to 40 g in body weight. The breeding season is from April to September, with the peak from May to July. In nature, they spawn in burrows on tidal flats, laying eggs within, deeply hiding the fertilized eggs, which hatch naturally. When sexually mature, the female's genital pore is red and swollen, large and round; the male's genital pore is narrow and small, elongated and pointed. The ovary is yellow, and the eggs produced are demersal-adhesive, spherical, pale yellow, and transparent. A female carries 10,000 to 25,000 eggs. One end of the egg membrane has a cluster of adhesive filaments that can attach to other objects. The egg diameter is 0.51 to 0.61 mm. Fertilized eggs hatch into larvae after 87 hours at a water temperature of 26.5 to 29.0°C and a salinity of 25‰ to 27‰, and after one month they can grow to 13 mm. The male has 2 seminal vesicles, appearing as pale red thin strips on the side of the abdomen.

The giant mudskipper grows very fast. Under good environmental conditions and in areas rich in benthic algae, early larvae can grow to 12 to 13 cm in the same year, reaching commercial size. Generally, they can also reach commercial size after two years. Mudskippers generally live 3 to 5 years, with a maximum age of 7 years.