Halimeda Ghost Pipefish is More Unusual Than You Can Imagine

We’ve been quite busy the last few weeks, setting up coral nurseries all around the island of Bali, Indonesia. One of our reef restoration sites which is an Ocean Gardener project in Amed, North Bali is starting to attract more and more interesting reef creatures and critters. The last one we were lucky enough to spot and observe was a trio of Halimeda Ghost Pipefish, Solenostomus halimeda.

This fish is so well camouflaged, that only the young eyes of our last female Ocean Gardener instructor could spot it. And even with someone pointing it to me underwater, my weary eyes took a long time to actually be able to make out the fish in its habitat. It has only been than 20 years since the halimeda ghost pipefish was described, although it was known by divers for a lot longer than that.

Description:

Here is a close up of the fish face, note the same growing invertebrates that can be found on the Halimeda algae

The specialty of Solenostemus halimeda is to mimic perfectly Halimeda algae leaves. And this very distinctive fish is so good at camouflage that it’s almost impossible to distinguish from the Halimeda algae within which it lives. This level of specialization pushes the level of mimicry to also harbor the same invertebrates that grow on the algae. The different body proportion and ray fin count separates it from the other members of this genus which includes the Ornate (Solenostomus paradoxus), Robust (Solenostomus cyanopterus) Ghost Pipefish.

A Female Halimeda Ghost Pipefish with its large pelvic fins, designed to incubate eggs

In this Genus, females differ from male by having large, fused pelvic fins designed to incubate their eggs, unlike Syngnathids like other seahorses and pipefish in which males brood the eggs.

Female ghost pipefish, Solenostomus halimeda

Embryos, enclosed in egg envelopes, are attached to epidermal stalks, termed cotylephores, that occur only in brooding females. Cotylephores are cellular outgrowths of the epithelium on the inside surface of the pelvic fins. This particularity makes this genus really special.

Adjacent calyces of the same cotylephore establish attachments with the envelope of a single egg. Cotylephores are composed of a surface epithelium that is continuous with the skin and a fibrous connective tissue core that contains blood vessels that ramify into an apical capillary plexus. The plexus may function in maternal-embryonic metabolic exchange.

The cotylephores of Solenostomus closely resemble the epidermal stalks (cotylephores) that are the sites of egg attachment in the skin-brooding South American catfish, Platystacus cotylephorus. Based on similarity in structure and probable function, cotylephores in the two groups of fishes are an example of evolutionary convergence. (Wetzel, J., Wourms, J.P. Adaptations for reproduction and development in the skin-brooding ghost pipefishes,Solenostomus . Environ Biol Fish 44, 363–384 (1995). https://doi.org/10.1007/BF00008252)

Here is a picture of the pelvic fins of a male.

The females carry multiple ages of eggs/larvae in their ventral fin “pouch”. So they release larvae every day once they are mature. This also explaining why there are often multiple males hanging around a female.

Habitat:

These fish are skinny, and as thick as the algae itself.

Obviously the habitat is Halimeda algae beds, where it blends perfectly. Halimeda is a genus of green macroalgae which has a body that is composed of calcareous green segments and most herbivorous fish avoid it. This species produces extensive algae beds, and reefs, that can harbor a wide diversity of flora and fauna.

Here is the Halimeda bad it was found in. Believe it or not, but it's seating right in the middle of the poor quality picture. — DCIM\100GOPRO\GOPR8381.JPG

Life Cycle:

The life cycle of this amazing critters, is short. They spend most of their live hanging in the water column among plankton. They are small and mostly transparent during all these stages, until they settle on the reef, color up, mature, and reproduce. They then die off. That’s why, we can only observe them on the reef for only a few weeks. We start seeing transparent newly settled larvae then they mature and gather together for breeding purposes, get some eggs, and age quickly before disappearing.

This fish is truly unique and mesmerizing.

This genus was successfully spawned and bred few times already. But the challenge is to keep genetically viable broodstock out of each cycle. Needing a regular input of new genetics into the loop. Thanks to Matt Wandell and Richard Ross for many of these informations.

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Vincent Chalias

Vincent is a coral passionate aquarist with extensive experience in the industry, travelling the world to learn about corals. His background is a master degree in Marine Aquaculture. He set up the first Indonesian Coral mariculture farms at the beginning of the century and spent over 20 years in Indonesia running them. He's been extensively diving and documenting corals all over the Indo-Pacific.