The Stomiiformes are small to moderate in size, ranging from 0.6 in (15 mm) to 20 in (508 mm). Most species are mesopelagic (residing between 660 and 3,300 ft [200 and 1,000 m] deep), while some others are bathypelagic (residing below 3,300 ft [1,000 m] deep). Stomiiform fishes have been recorded to a depth of more than 14,000 ft (4,270 m).
One of the trademark physical features of many stomiiformes fishes is their fearsome dentition; their large mouths are filled with enormous fang-like teeth. This allows them to efficiently capture relatively large prey that are infrequently encountered. On average, fishes possessing these huge fangs take prey about a third their own size. This would be equivalent to an adult human eating more than 100 hamburgers in a single sitting—and such an equivalent would be an average meal for these fishes! In some cases, the weight of their prey has been known to exceed that of the predator. These fishes have a suite of other adaptations for this type of diet: long, sac-like stomachs; reduced ossification of the anterior vertebrae, allowing the mouth to expand dramatically; and a lack of gill rakers in adults.
Bioluminescence results from an oxidative reaction in which an organic molecule, called a luciferin, is raised to a chemically excited state in the presence of the enzyme luciferase. The excited luciferin then decays to the stable state by releasing light (most oxidations release heat). This energy can also be transferred to a fluorescent molecule, which releases light of its own color. Some fishes (e.g., deep-sea anglerfishes) rely on bacterial symbionts for light production. The stomiiformes, however, rely on self-generated, self-regulated luciferin/luciferase reactions occurring within their photophores for light production. The bodies of most stomiiformes species bear two serial rows of photophores along each flank. The majority of stomiiformes species also bear barbels on their chin. At the end of these barbels are often elaborate, bulb-like bioluminescent organs, thought to serve as "fishing lures." These chin-barbels range in size from less than the head length to as much as 10 times the length of the fish. Many species, particularly those of the genus Eustomias, are differentiated solely on the form of the barbel.
Stomiiformes generally lay eggs in deep seas, but the eggs are light and float towards the ocean surface, so they hatch in surface waters. When the larvae have completed their metamorphosis and look like the adult Stomiiformes, they descend to join the adults. Like a lot of benthic fish species, certain members of the order — especially in families Gonostoma and Cyclothone — change their sex during their life. They are born as males, then "transform" into females. Some species spawn several times, while others spawn once and die. Some species have separate sexes, while others mature into males, produce sperm to fertilize eggs, and then later develop into females, producing eggs that are fertilized by younger males. In species with separate sexes, males often have greatly developed olfactory (smell) organs to help in locating females.
During the day, Stomiiformes stay in deeper waters and measure the intensity of the light that reaches them. While doing this, they manage to stay in the region that always has the same light intensity. When the sun sets, the Stomiiformes follow the dimming sunlight up to near-surface waters. The upper regions are richer in animal life: small fishes, and planktonic invertebrates. The Stomiiformes hunt and feed on these organisms all night long and swim back to deeper waters as soon as the sun rises. This daily migration is well observed of Stomiiformes. Most species are mesopelagic (residing between 660 and 3,300 ft [200 and 1,000 m] deep), while some others are bathypelagic (residing below 3,300 ft [1,000 m] deep). Stomiiformes fishes have been recorded to a depth of more than 14,000 ft (4,270 m). Most species undertake a daily vertical migration, swimming from a daytime depth of 1,600 to 3,300 ft (490 to 1,000 m) to near the surface at night, and then back down again before sunrise. This upward migration is thought to be mainly for feeding—food in the form of plankton, fish, and other invertebrates is much more plentiful near the surface. Daytime depths, on the other hand, provide refuge from visual predators as well as an energy savings in the colder deep water. This vertical migration, undertaken by most mesopelagic fishes, shrimp, and squid, is the largest animal migration on Earth, and it happens every day in the deep sea.
All members of the Stomiiformes order but one have bioluminescent organs (photophores), whose structure is characteristic of the order. The gleam emitted can be more or less strong and its color can be light yellow, white, violet or red. The lighting mechanism can be very simple - consisting of small gleaming points on the fish body - or very elaborate, involving lens and refractors.
The most common example is 1 or 2 photophore rows on the lower part of each side of the body. The rows run from the head down to the tip of the tail. Photophores are also present at the tip of chin barbels. The Stomiiformes order does not seem to utilize bacteria as a lighting source; however, recent researches have found that a piece of bacterium-like DNA in one photophore, which suggests that these contain bacteria that must have been largely modified.
The light coming from these fish are generally invisible to their prey.
- Stomiiformes by Wikipedia
- Stomiiformes by Answers
- Order Summary for Stomiiformes by Froese, R. and D. Pauly Editors; 2006, FishBase