The Cryptic Life of Ghost Pipefishes

Author: Francesco Ricciardi

A marine biologist explores the lifestyles of the mysterious and elusive ghost pipefish.

Mysterious Ghost Pipefishes

Masters in the art of mimicry, ghost pipefishes are still poorly known to science, but their incredible abilities and life history make them among the most amazing fishes you can find in the whole animal world.

The very small family of ghost pipefishes—Solenostomidae—includes very few species, all belonging to the genus Solenostomus. Some species are still waiting to be officially described. They are close relatives of seahorses and pipefishes, live in tropical waters of the Indo-Pacific area, and have been successfully maintained in public aquaria, where on at least one occasion a captive mating and successful breeding have been recorded.

Tricky Biology

Even marine scientists still very poorly know the biology of the ghost pipefishes. Juveniles are planktonic and almost transparent; they move with the oceanic currents and if they survive long enough to find a proper reef, they settle in the proximity of crinoids, gorgonians, or other favorable areas. After that they find a partner, reproduce, and vanish again. Most likely they die after the release of the larvae. Unlike as in their relatives, the seahorses and pipefishes, the female of the ghost pipefishes, carrying the eggs in a brood sac formed by two fused pelvic fins until the hatching and the release of the small embryos in the open sea, is bigger than the male..

Camouflage

Ghost pipefishes are masters in the art of camouflage. The most common ghost pipefish is the ornate—also called harlequin—ghost pipefish (Solenostomus paradoxus), which can easily blend in with the natural background (normally crinoids or gorgonians), thanks to the patchwork coloration and the position of the body, normally with the mouth facing downwardsand the body oscillating with the waves. Even other ghost pipefish species use the same strategy; for example, the robust ghost pipefish (Solenostomus cyanopterus) looks like a leaf or algae, and the recently discovered halimeda ghost pipefish (Solenostomus halimeda) looks very similar to the macroalgaHalimeda.

Other species, such as the hairy ghost pipefish (Solenostomus paegnius) and the delicate ghost pipefish (Solenostomus leptosomus), are quite rare and can easily remain unspotted due to the filaments covering their body.

Coloring

The coloring of ghost pipefshes can vary between individuals; the ornate ghost pipefish, for example, is able to change its coloration depending on the area it occupies. It’s not a sudden change like the change we can observe in octopuses and cuttlefishes; the change may take some hours. When found in pairs, ornate ghost pipefish males and females always have the same color. It appears that they make an extra effort to assume the same color as the partner; the advantage of this behavior is not yet very clear to us. In other species, as in the robust ghost pipefish, on the contrary, it is quite common to find a pair with different body colors.

Hunting and Defense

Ghost pipefishes use their capacity for camouflage as both a defensive measure (to avoid being spotted by predators) and as a way to easily approach their prey. Their ability to catch their food (normally tiny crustaceans, like small shrimps or other invertebrates) is based on the anatomy of the mouth, which is tube-shaped as in seahorses and pipefish, with some muscles that can increase the diameter of the tube very quickly, creating a depression that basically “sucks” the prey directly inside the mouth of the fish.

Sexual Plasticity

Juvenile ghost pipefishes also have revealed an unusual “sexual plasticity.” Male individuals placed into an aquarium with other males have demonstrated the ability to change sex. It is possible that juvenile ghost pipefishes can change not only sex but also color, depending on the surrounding environment and the presence of potential partners. We don’t know yet whether this kind of hermaphroditism is common in nature or happens only in aquaria.

Rare but Beautiful

Called “ghosts” for their ability to appear and disappear, these fishes are not very common, but they appear for short periods of time and become relatively easy to spot if you know how to look for them. Like every other proper ghost, they don’t like to show up for everyone.

See the full article on TFH Digital http://www.tfhdigital.com/tfh/august_2014#pg79