Stiphodon alcedo

Overview

A Ryukyu stream goby, Stiphodon alcedo combines a pointed, nonfilamentous male first dorsal with metallic turquoise on the head during courtship. Breeding males may become black or orange. Its care depends on a continuing supply of edible biofilm and oxygen, not simply on bringing out those colors.

Distribution & habitat

Records cover four streams on Okinawa and two on Iriomote, Japan. It is less common there than Stiphodon percnopterygionus. Transport of larvae from farther south by the Kuroshio Current remains a possible explanation rather than a confirmed extension of its range.

This species occupies the gentler-gradient type of stream: broader channels with slow to moderate runs, riffles, pools, and small cascades. Typical habitats of the genus have rock beds, rounded stones, clear oxygenated water, and rich biofilm. Bankside vegetation and fallen leaves are common; submerged plants are much less so.

Aquarium setup

Use an established aquarium with sand or gravel, rounded stones of different sizes, shelters, and interrupted sight lines. These gobies may burrow to sleep or spawn, so support heavy rocks on the aquarium base rather than loose sediment.

Maintain filtration and aeration continuously. Circulation of 10–15 tank volumes hourly is one workable arrangement; 5–10 can suffice with strong oxygenation. A violent current throughout the tank is unnecessary. Strong lighting sustains grazing surfaces. Aged wood is suitable, whereas fresh wood can stain the water and reduce light penetration. Hardy Microsorum, Crinum, or Anubias provide cover and additional surfaces for algae.

Replace 30–50% of the water weekly, leaving growth on surfaces other than the viewing glass. Fit a close cover because these fish can climb glass. A newly established tank without stable biofilm is unsuitable.

Diet & feeding

The feeding specialization of Stiphodon is scraping benthic algae and associated microorganisms. Protrusible mouthparts, replaceable teeth, and the pelvic disc work together during grazing. Some sinking foods or bloodworms may be eaten, but they are occasional supplements rather than substitutes for productive surfaces.

Grow algae on spare rocks in a separate brightly lit container if the main tank cannot keep pace with consumption. Outdoor cultivation is possible in suitable weather. Diatoms, cyanobacterial films, and softer green growth are more useful than tough black brush algae. Severely thin newcomers need immediate access to food without competitors; clean water alone will not reverse starvation.

Behaviour & compatibility

Community arrangements should follow experience with the genus: choose small, peaceful stream fishes for the upper water and unassertive bottom dwellers. Large fishes, aggressive feeding loaches, and territorial bottom-dwelling cichlids are poor choices.

Males defend loose areas, particularly during breeding. Several require ample room, food, and cover. Females form loose groups, making one male with at least two females a useful starting combination. Similar females may group across species, so association is not an identification test.

Sexual dimorphism

Outside courtship, males are pale brown with reddish tones on the head and back, a dark flank stripe, a blue-gold mark above the pectoral base, and white markings on several fins. Nuptial males develop turquoise lips and head sides, a black crown, and often black bodies with turquoise bars. Orange flanks or fins can occur, especially in small males. Brown striped coloration can return quickly between displays.

Females are creamy with widely separated lateral stripes: the upper one is thin and pale, and the lower consists of blotches. They lack the male's conspicuous white fin pattern. A single dark or pale moment is therefore an unreliable sexing criterion.

Breeding

The genus has an amphidromous cycle. Adults spawn beneath rocks in freshwater, males guard the eggs, larvae drift to sea, and developing juveniles eventually return upstream. Studied congeners produce thousands of attached eggs, sometimes around 10,000, approximately 0.5 mm across. Hatching can occur within a day. The poorly developed larvae must reach the sea before their yolk is exhausted after roughly three to four days.

Spawning in freshwater is consequently only the beginning. A study of Stiphodon percnopterygionus found a pelagic phase of 78–146 days, longer in colder conditions; that is a comparison, not an established rearing timetable for this species. Returning juveniles use the pelvic disc to negotiate obstacles, and migration can take months.

On Okinawa, nuptial males of S. alcedo were observed only from October through December. A short breeding season is inferred from that pattern rather than demonstrated as a fixed spawning schedule.

Notes

Elongated fourth and fifth dorsal spines, without threadlike extensions, help distinguish males. The metallic pectoral-base mark and the widely separated female stripes are also useful. Dependable collection locality and intact fin structure are stronger clues than one photograph of a displaying fish.