Few fish have the untapped potential to captivate and amuse aquarists, as do the flying gurnards, of which only one species - Dactyloptena orientalis, the oriental flying or helmet gurnard - seems ever to be traded. Yet few aquarists ever attempt their care. These cute and interesting fish do not belong to any of the major clades or 'families' of marine aquarium fishes, though they somewhat resemble the mandarinfishes, to which they are, actually, quite related. D. orientalis can reach 40 centimeters, or 16 inches long; but more commonly they are half this length. It is a benthic species, native to sandy bottoms in shallow, Indo-Pacific waters, and all the way from East Africa to the distant Hawaiian and Pitcairn archipelagos.
The name 'gurnard' originally applied to triglid scorpionfishes, which through convergent evolution, have evolved a few traits shared with flying gurnards. Formerly, the two clades were assumed to be related in the sense of evolutionary kinship, though this is due to the wonders of convergent evolution; flying gurnards are not scorpionfishes at all. Another early misconception surrounds the supposed flight of the flying gurnards; earlier naturalists had assumed the large pectoral fins, which have a different shape to those of the exocets and freshwater hatchetfishes, were actually aerofoils.
Although flying gurnards possess wing-like pectoral fins, they do not swim close to the water surface, and therefore they are unable to escape dangerous predators by gliding through the air. Like the true gurnards, they have achieved the ability to walk by making use of their paired fins; unlike the kind of skeleton that exists in the limbs of four footed vertebrates, both kinds of gurnard have evolved a series of jointed limbs that are modified from the bony rays of ordinary pectoral fins, and thus resemble human digits. Indeed, it is amusing to watch flying gurnards forage, using their anterior limbs to sense nearby food. These structures constitute true, jointed legs, and these fish can truly walk on the seabed, and they walk more often than they choose to swim.
Both, unrelated, types of gurnard also have expanded, wing-like pectoral fins, that are used for display; and pelvic fins that support the body from underneath, allowing the fish to move along the seabed. They also share the ability to communicate by making grunting sounds. Such an ability has evolved a number of times in the history of the fishes, and aquarists find it characterful; unsuspecting aquarists can also be puzzled by the sounds made by 'talking fish'! These noises are produced in the swim bladder of these fishes; unlike certain bottom living fishes, both true and flying gurnards have not reduced or lost their swim bladders - structures for which they have a use; not only for sound production, but because they walk with their bellies held off the seabed, which means the fishes benefit from some bouyancy.
However it is the paired fins of both types of gurnards, that is the most striking; and to most people, the notion of a walking fish is more wonderful than even a talking fish. Flying gurnards have so modified their paired fins, that their pelvic fins apparatus is not even visible from above, when the pectoral fins are outstretched. In their typical walking gait, the flying gurnards employ their pelvic fins, with extra thrust from their tail ends; at higher speeds, the pectoral fins are unfurled like great wings, which provides them extra lift; therefore,the expanded fins are not simply useful for display. (But when the fish swims, the reverse is true; the pectoral fins are folded during high speed swimming, so as to reduce drag.) The ordinary walking gait of flying gurnards, is bipedal, explaining why they have re-oriented their mai walking legs,to give the fish support beneath their bodies.
One of the amazing things about flying gurnards, is their adaptation to use the anterior portion of their pectoral fins, when procuring food beneath sand. Each pectoral fin has two distinct sections, that are articulated separately on the pectoral girdle, where the fin meets the torso of the fish. Thus the anterior portion is functionally distinct from the 'wing' behind; the anterior fin is itself composed, mainly, of jointed fin rays, that are tactile and used for both feeling and non-bipedal walking. But these legs or digits are preceded by a robust and unjointed anterior ray, that the fish uses to unearth food by digging. Is there nothing a flying gurnard cannot do?
Flying gurnards are found associated with seagrasses, and in other inshore habitats where the bottom is suitably soft and sandy, for them to dig up food. Their dietary niche is as foraging benthivorous carnivores, consuming mainly small arthropods, as well as similar items, such as small fishes, burrowing annelids, and bivalve molluscs. Flying gurnards strictly feed from the seabed, and not up in open water at all. Although they are entirely carnivorous, they can hardly be considered as hunters, and their entire anatomy and behavior is geared to suit a life looking for food lying just below the sand surface. For protection whilst they are foraging, flying gurnards possess body armor.
Although flying gurnards do not have enormous mouths, and are neither fast persuit hunters, nor are they ambush predators, they can and will eat small fishes and other motile animals. Similarly, their natural diet tis composed of the sorts of helpful creatures, that people want in flourish in their sandbeds. However flying gurnards are entirely benign to larger animals they will not see as food, as well as to plants and corals. Their own diet in the aquarium, ought to be meaty, defrosted fare.
Because they are genuine walking fish, flying gurnards require an aquarium with an appropriately large and unobstructed area of substrate. They do not make use of the rockwork that is available in an aquascaped reef tank, and their need is for a soft substrate of sand. Flying gurnards are more active than are some other benthic fishes, therefore they do need more space in the aquarium, so that they can roam around, and in doing so, they will be sure to entertain.
