Most deep sea possess bioluminescent organs that are normally dependent on bacteria, maintained in special cells, for the production of the light.
The bacterial light is usually produced as a result of an enzyme (often luciferase) mediated oxidation reaction in which a molecule (often luciferan) changes its shape and emits a single photon of light in the process. Luciferan is a large complex molecule that can later be returned to its original shape through a reduction reaction during which it gains an amount of energy equivalent to the single photon of light it emitted earlier. Because the essential reaction is an oxidation reaction the host organism, in this case the fish, can control the amount of light emitted by controlling the blood flow, and hence the oxygen supply, to the cells containing the bacteria.
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Archerfish are renowned for their amazing ability to shoot water at prey. The fish have a narrow grove on the roof of its mouth, which the fish presses its tongue against to form a channel. It then contracts its gill covers to force water through the channel to form a jet up to 5m long.
An adult archerfish can reliably shoot prey up to 2m away. If the first jet does not knock the prey into the water, the fish will quickly fire a second shot. Accuracy is gained through experience, with young fish hunting in small schools to increase the chance that the prey is hit.
It’s rough living in the deep sea. It’s super cold, rather scary, and absolutely pitch black. Luckily for the Flashlight Fish (Photoblepharon palpebratus) they never have to worry about the latter. Flashlight fish are aptly named for their large bean-shaped bioluminescent organs (a.k.a. photophores) under their eyes. To get that rockin’ glowing effect, luminous bacteria actually live in the organ create the light! It’s a symbiotic relationship in that the photophores glow in the dark, attracting zooplankton and small fish, on which the flashlight fish feed and the bacteria get the leftovers, so to speak. The light is also used for predator avoidance and for communication.
Pictured above is a very peculiar fish that lives in a few North American caves. It looks very much like other fish, except in one respect: it has no eyes. The story of its adaptation to life in pitch blackness is one of the weirdest stories in evolutionary history.
Mutations vs. Cryptic Variation:
When people think about how evolution occurs, the classical model generally comes to mind. According to this view, species experience random genetic mutations that confer novel traits when they move to a new environment. The most beneficial traits — those that help individuals better adapt to their new habitat — get passed along to subsequent generations and eventually spread throughout the population.
It’s a relatively simple, easy-to-digest model, but it’s not able to explain all cases of evolution. “Imagine if you had a quick change in the environment,” said Nicolas Rohner, a geneticist at Harvard Medical School in Boston, Massachusetts. “This evolutionary process would take too long.” To rapidly adapt to a sudden shift in environment, a population would have to have some kind of standing genetic variation already available, which nature then selects for.
But how can this “cryptic variation” be maintained and accumulate in a species without actually affecting individuals before the environmental shift occurs? Scientists proposed that something must keep the genetic variation silent under normal conditions; then, when a species relocates to a new, life-threatening environment, it becomes physiologically stressed and that silencing mechanism stops or breaks down somehow…
Mudskipper is a fish which spend more time on land than in water. In fact, a mudskipper will drown if it’s never able to reach the water’s surface! Like other fish, mudskippers breathe through gills, but in addition they absorb oxygen through their skin and the linings of their mouths and throats. They are able to move over land by using their pectoral fins to pull themselves forward, or they perform a series of skips or jumps. Pokemon “Mudkip” is based on this fish.