''Sicyopterus lagocephalus'', the red-tailed goby or blue stream goby, is a species of goby native to islands of the Indian Ocean from the

Comoros The Comoros,, ' officially the Union of the Comoros,; ar, الاتحاد القمري ' is an independent country made up of three islands in southeastern Africa, located at the northern end of the Mozambique Channel in the Indian Ocean. It ...

to the Mascarene Islands to the Pacific Ocean where it reaches

French Polynesia )Territorial motto: ( en, "Great Tahiti of the Golden Haze") , anthem = , song_type = Regional anthem , song = " Ia Ora 'O Tahiti Nui" , image_map = French Polynesia on the globe (French Polynesia centered).svg , map_alt = Location of Frenc ...

and can be found as far north as

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. It is an

amphidromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousan ...

species: adults can be found in swift-flowing streams with rocky beds but the eggs hatch at sea and the larval stage remains in marine waters, migrating to freshwaters when they reach the postlarval stage. This species can reach a total length of . In some places it is an important species for local consumption with the post-larvae being caught as they mass in estuaries.

Description

Male ''Sicyopterus lagocephalus'' can grow to a total length of about while females can reach . The dorsal fin is divided in two and has 6 to 7 spines and 9 to 10 soft rays. The anal fin has a single spine and 10 soft rays. The pectoral fin has about 19 soft rays. During the rainy season, males become very colourful; the sides are metallic bluish-green, the tail is orange-red and there are about seven dark, saddle-shaped markings on the back. Females are grey or brown with dark saddle markings, a pale belly and a black and white band at the base of the tail.

Distribution and habitat

This species has a wide distribution in the tropical Pacific. Its range extends from Sri Lanka and the Mascarene Islands to Japan, Taiwan, the Philippines, Papua New Guinea, Australia, the Marshall Islands and French Polynesia. Adults live in fast-flowing streams with rocky beds while the larvae live in the ocean.

Ecology

The female ''S. lagocephalus'' lays its eggs in fresh water. After hatching, the larvae repeatedly rise towards the surface of the stream and then sink down again; this helps them to get carried along by the current. They consume their yolk sacs and will die if they do not reach the sea within about seven days. On arrival in the marine environment they are between long, and start to feed on plankton. They are translucent at this stage and remain at sea for somewhere between 133 and 256 days before getting the urge to migrate back into fresh water. The post-larval stage starts as they enter estuaries. They have already developed suction discs, but now they undergo

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

, their mouths move from the tip of the snout to the underneath of the head, they begin to develop pigment, the pectoral fins transform, the tail loses its fork, they grow teeth on the premaxillae bone, changes occur in the cranium and changes in osmoregulation take place. As the rake-like teeth push through, they start to feed on

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s and

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

that they scrape off the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

. After two days in the estuary, the juvenile fish move upstream, overcoming small waterfalls with the aid of their suction discs, and after about three or four weeks of migration start to take up territories in the fast-flowing streams where they will breed.

References

{{Taxonbar, from=Q644014 Sicyopterus Freshwater fish of Sri Lanka Taxa named by Peter Simon Pallas Fish described in 1770 Taxonomy articles created by Polbot