Family : Solenostomidae
Text © Giuseppe Mazza
English translation by Mario Beltramini
Mimicry is at home in the order of the Syngnathiformes.
As an example, let us look at gorgonians, so frequent in the multi-coloured world of the corals. On these live some tiny seahorses, such as the 2 cm Hippocampus bargibanti, that escape predators perfectly imitating their polyps, and thanks to its changeable camouflaging livery even their 80 cm greedy relative, Aulostomus chinensis, literally disappears vertically close to the big fans of these Alyonacea ready to surprise the unfortunate passing by fishes.
Then stand those imitating the green world. Master in this regard is undoubtedly the Leafy seadragon (Phycodurus eques) who when swimming calmly, predating without being predates, seems a tuft of drifting seaweeds, but in this strategy, in its own small way, also shines the Robust ghost pipefish (Solenostomus cyanopterus Bleeker, 1854), quite similar to a leaf fragment.
With the Ornate ghost pipefish (Solenostomus paradoxus) it belongs to Solenostomidae, a small family, counting nowadays only this genus and 5 species with characters intermediate between the seahorses and the needlefishes.
Unlike these, however, the eggs are not incubated by the males but protected by the females in a showy ventral pouch born from the merging of the pelvic fins.
The genus Solenostomus, created by Lacépède in 1803, derives, composed and Latinized, from the old Greek “σωλήν” (solen) = channel, and “στόμα” (stóma), mouth, due to the united to form a tube, as indeed happens in all Syngnathiformes but the adults of the genus Bulbonaricus who lose it like Bulbonaricus brauni while growing.
The specific term cyanopterus also originates from old Greek “κύανος” (kúanos), blue, and “πτερόν” (pteron), wing, with reference to the dark black-bluish spots present among the spiny rays of the first dorsal fin.
Solenostomus cyanopterus lives in the tropical waters of the western Indo-Pacific. Indicatively, starting from the Red Sea, is present along the coasts of Tanzania, in Mozambique, South Africa, Madagascar and adjacent islands, Comoros, Mayotte, Réunion and Mauritius. To the north, it reaches the Maldives Islands, India and Sri Lanka.
Then, eastwards, we find it in the Andaman Islands, in the waters of Thailand, Indonesia, Timor-Leste, Papua New Guinea and Australia up to New Caledonia.
Present in Palau, it has colonized northwards, Taiwan and Japan, and eastwards, after Guam and the Northern Marianas, Micronesia, Marshall Islands and finally Fiji Islands.
It must however be added that presently, in 2022, in this vast range under the name of Solenostomus cyanopterus circulate various species that are quite similar. Some of them have already been separated, and it is possible that with molecular biology new ones will be discovered.
For instance, Solenostomus paegnius Jordan & Thompson, 1914, differs only for the presence of thin flaps of skin that confer it a hairy look, and Solenostomus halimeda Orr, Fritzsche & Randall, 2002, specialized, as the name suggests, in reproducing in the least details the seaweeds of the genus Halimeda, has only added some camouflaging tuft.
Solenostomus cyanopterus is not a common and easy to observe fish. As a matter of fact, it spends most of its life in the pelagic state and reaches the bottom only when it has become adult, reproducing only once and thus concluding its existence.
Monogamous and always coupled, it may be then seen up to the depth of 25 m close to the corals or cliffs rich in seaweeds, in the submerged prairies of phanerogams and on the sandy bottom among colonizing plants and dead leaves that it imitates even in their wave motion in vertical position head down. It loves the calm waters of the lagoons and of the harbours, but ventures out also in the brackish ones of the deep and clear estuaries.
The Robust ghost pipefish, as its vulgar name states, is the biggest among the ghost fishes with a long and thin body that may reach the length of 17 cm.
It is scale less but is protected by 25-35 bony starred plates.
It may change its look within 36 hours to imitate the environment where it lives. Its livery, covered by small white and black spots imitating the foliar encrustations, can present in fact, depending on the circumstances, with green, yellow, red, brown or blackish shades.
The head, with its tubular snout and small curved spines close to the mouth, occupies about one third of its total length, and with this long tool Solenostomus cyanopterus aspirates lightning fast, like the seahorses and the seadragons, all the small crustaceans it sees around showing a marked predilection for the microscopic shrimps of the order Mysida and the larvae of the fishes that often arrive carried in mass by the currents.
There are two dorsal fins. The first, relatively big with 5 spiny rays is aligned with the pelvic ones, whilst the second, equal to the anal, is low and transparent with 17-22 unarmed rays. The only way for seeing these last, is to observe with a lot of attention their attachment point, on the two large tubercle swellings placed just before the caudal peduncle.
Also the pectoral fins, close to the head, are tiny and transparent with 25-27 soft rays. Conversely, showy is the caudal fin with its 16 rays, often truncated rectangular in shape, supported by a short and thin peduncle well visible in the young males, but at times almost non-existent in the females.
The operculum, like in the Ornate ghost pipefish, has an unusual checkerboard design.
The sexual dimorphism is evident because the females are for about one third bigger than the males, not to forget their showy pelvic 7 rayed fins, merged at the belly to form a big pouch that may accomodate even 350 eggs. The males, slenderer, often have small ramified outgrowths on the snout.
The biology of this species is little known.
After fecundation the eggs are glued on the inner side of the female pelvic fins in the ventral brood pouch where they receive feeding from the yolk and from the maternal vascularized walls. They are less than 1 mm broad, and they hatch in about 3 weeks.
Like the seahorse males, to reduce the risks linked to the dispersion, the transparent larvae are expelled in small groups staggered over time by means of successive contractions.
The newborns are transparent and like in the Ornate ghost pipefish the rays of the fins are proportionally very long compared to the adults, more suitable for swimming during their ling pelagic life.
They measure about 3 mm and come to life with the eyes already pigmented, the backbone visible and a small aspirating tube
The Robust ghost pipefish is not hunted by man and does not interest even the aquarists because of the difficulty in nourishing it and the short duration of its life. The fishing vulnerability risk, very low, marks only 10 in a scale of 100 and in the Red List Solenostomus cyanopterus appears presently low risk (Least Concern, LC).
Solenostomus bleekerii Duméril, 1870; Solenostomatichthys bleekeri (Duméril, 1870); Solenichthys raceki Whitley, 1955.