Reef Fish, Colors, Vision, Development and Transexuality

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surgeonfish iin the Mladives

In the shallow reef as many 100 different species of fish may be found in one area. Tracking reef fish with transmitters implanted in the fish’s body indicates that the fish rarely venture outside their protected reef home.

Reef fish basically fall into two categories: 1) those that on algae and other food created by the reef; and 2) predators that feed on the aforementioned fish. Many species of reef fish such as surgeonfish and angelfish feed on algae in the coral and vigorously defend their territories against any intruders.┭

Many reef creatures have symbiotic relationships with other creatures in the reef community. Nearly-blind cleaner shrimp hang out with certain gobies and act as the "seeing eye" fish. Cardinalfish live with conches inside their shell and perform cleaning duties. Some sea anemones play host to several species of shrimp, each with a different role, as well as clownfish. As many as 16,000 small shrimps may live in a single wash-tub size loggerhead sponge.

Many of the world's coral have been depleted of large fish by overfishing. In the 1960's uneatable reef fish were hunted with spear guns explosive charges simply for the sport of it.

Some areas of the reef are characterized by low water flow and and thus low-oxygen, especially at night when photsenthesis stops but animals continue coming oxygen. Some fish that hang out among brahced coral fan themselves to increase ambient oxygen

Male mandarin fish flare their fins and display their full colrs of red, blue and green when are trying to attract smaller egg-filled femaes. They are popular aquarium fish, particularly the showy makes and there is some concern that the harvest of males is dentrmental to the species as a whole.

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase ; Encyclopedia of Life ; Smithsonian Oceans Portal ; Woods Hole Oceanographic Institute ; Cousteau Society ; Monterey Bay Aquarium ; MarineBio ; Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) ; International Coral Reef Initiative ; Wikipedia article Wikipedia ; Coral Reef Alliance ; Global Coral reef Alliance ;Global Coral Reef Monitoring Network

Reef Fish Colors

20120517-Reef_Fish_at_Lighthouse_site.jpg Reef fish and reef creatures often are brightly colored and have striking patterns that include bold stripes of contrasting color, chevrons of black and white, patches of color surrounded by a halo of another color. Even creatures that can not see themselves use color to suit their purposes. A small parasite that infects coral in Indonesia produced pink patches that attract fish. The fish feed on the pink patches and infect the fish who in turn spreads the parasite to other corals. When many kinds of reef fish are taken out of the water their dazzling colors turn quickly to grey.[Source: Les Kaufman, National Geographic, May 2005]

There are dozens of kinds of parrotfish and butterflyfish and other fish that look similar except they have different color patterns and other slight differences. Why is there such diversity for reason that don’t seem to offer an advantages? Marine ecologist David Bellwood, "The answer is that we really don't know. But I can tell you a lot of diversity within groups of tropical fish is a matter of historical accident. It may be that sea levels fell during the ice ages, ocean basins became isolated, and their populations evolved along separate lines, which we now regard as separate species. Later when the sea levels rose again, many migrated...and took up residence side by side."

Reef colors are especially bright when photographed with a strobe, which is what underwater photographers often use. When the light is turned off, especially tens of meters under the water, the reef is more of world of pale blues and greens and mottled yellows not bright red and orange. At the surface colors may look bright and distinct but as one goes deeper the world become bluer and bluer.

As one goes deeper into the water red colors tend to disappear the quickest because they are absorbed by water molecules, plankton and debris. To underwater animal reds may appear gray or black. It is not even clear why red exists in the underwater world. Blues and yellow blend in well in the pale blue world. The bright yellows and blues that light up angelfish and damselfish that appear so beautiful to humans provide useful camouflage in the blue world.

Other reef creatures use camouflage to stay clear of predators and catch prey. Cockatoo waspfish resemble dead leaves and trumpetfish look a drifting plant. Frog fish and scorpionfish pose as algae-covered rocks and seaweed and pounce an unsuspecting fish that wander their way. The sheer complexity of the reef produces its own camouflage. As a fish swims against the reef’s complex background predators have difficulty making out the details, outlines and contrasting colors of the fish especially as it retreats towards the reef where distance and motion add to the confusion.

Purpose of Reef Fish Colors

The bright colors of reef fish, serve several purposes: 1) to provide camouflage amongst the bright colored reef; 2) to confuse predators and prey; 3) to define territories; 4) to attract mates; 5) to warn predators of a foul taste or poison; and 6) advertise various services. [Source: Les Kaufman, National Geographic, May 2005]

Reef fish use color to advertise their sex, their sovereignty over a patch of reef, their willingness to mate, their readiness to fight and highlight a victory in a battle. Bright colors may be easy for predators to spot. Most bright colored fish hang close to the reef, where they can make a quick escape if a predator approaches.

mandarinfish (Synchiropus splendidus)

Markings and stripes are often intended to break up the outline, size and shape of a fish, which makes them difficult for predators to locate. Predators often lunge for reef fish in the direction they think the fish will go. To protect itself the soapfish changes the orientation of its stripes and the color of its eyes when threatened so that predators are not exactly sure which side is the front of soapfish and which is the back; consequently the predator has only a 50-50 chance anticipating which way the soapfish will flee. The soapfish can also coat itself with toxic slime to make itself unpalatable to predators.╆

Some species of gobies actually use their bright colors like a neon sign to attract large fish. The gobies are sought after by large fish because they eat parasites such as sea lice and copepods; in return the gobies get a free meal.╆

One reason reefs are so colorful is that color and vision are useful in water that is so clear and sunlight can can penetrate so easily. Creatures that live in the reef often have keen senses of vision. When the water is murky fish and other creatures tend to rely more on smell, taste, touch and sound.

Changing Colors and How Reef Fish Colors are Produced

"Fishes generate a rainbow of colors in somewhat the same way that human artists do by combining primary pigments — red, yellow, and blue — plus black and white. They do so by an ingenuous use of guanine, melanins and carotendois.” Black and shades of brown and gray are produced with the melanins, which are similar to the melanins in human skin. [Source: Natural History, September 1999]

Guanine, a common metabolic waste product produced by blood deposits in the skin, give some reef fish their shimmering iridescence. One of the most common organic compounds in nature, it manifests itself in pure form as tiny flattened crystals, each of which reflect light like a microscopic mirror." These crystals can be set up in different arrangements to reflect and absorb different bands of light that create different colors.

striated frogfish (Antennarius striatus)

Many fish can change their colors on and off in seconds (See wrasses, flasher wrasses). Many bright-colored reef fish change color to darker "pajama patterns" at night. The sand perch has stripes and bright colors during the daytime and dull, drab camouflaged splotches at night. Conversely, the five-inch-long squirrel fish looks brown and drab during the day but at night it turns brilliant red.╆

Colors and patterns change with age. Juveniles often have different pattens than adult. Studies have shown that fish that change color need their eyes. Those that have been blinded are unable to change color.

Marine creatures that change their colors quickly do so using chromatophores, skin cells with pigments that produce color and patterns by contracting and expanding with stimuluses from both neurons and hormones. Squid, octopus and squids use chromotophores. Pale colors are produced by specialized chromatophores called leucophores. Blue and iridescent colors are generated by iridophores, which manipulate crystals of guanine to scatter white light and then reflect specific wavelengths as needed.

Ultraviolet Light and Reef Fish Vision

Many fish are quite adept at seeing ultraviolet light which humans can not see. It was long thought that ultraviolet light could not penetrate water but is now known that it can reach depths below 100 meters. Some fish not only see ultraviolet light but also use ultraviolet light reflectors to send out different messages. Scientists use micro-spectrophotometry to analyze the colors that fish eyes can see.

Red fluorescence increases with depth in reef fishes supporting the theory that fluorescence is a visual function not ultra-violet light protection

Some fish such as the regal angelfish that are brilliant yellow, white and grey in visible light appear only black and white in ultraviolet but patterns on its fins that are nearly invisible in visible become more visible in the ultraviolet light. The phenomena is unusual in that the angelfish can not see ultraviolet light.

The azure damsel fish can see in both visible light and ultraviolet light. In visible light it is blue and yellow. In ultraviolet light the blue looks white and the yellow looks black. The male squaresport anthias produces a light blue patch on its side when it is trying to attract females. The patch is hard to see in natural light at 25 meters but is highly visible in ultraviolet light at that depth. It is not clear whether the fish can see in ultraviolet light.

Reef Fish Vision and Hearing

Diurnal reef fish can often more see colors than humans and parts of the spectrum that humans can't discern. Their eyes are generally small and usually have a thick layer of melanin that prevents light from bouncing around inside the eye, disrupting their visual images.

Nocturnal fishes often only see in black and white. Having evolved from species that once lived in deeper water, they often have big eyes with big pupils that can perceive a lot with only a little light. It is not clear how good reef fish vision. Some species have been observed feeding on diver's bubbles, apparently confusing them for small silvery fish.

Predator fish such as barracuda and groupers are most active at dawn and dusk and their eyes contains features found in both diurnal and nocturnal fish. Some sea creatures may react to contrasts rather than colors themselves. Shrimp that are bright red and white might actually look black and white to a reef fish, who respond to the contrast not the color.

Reef fish make quite a bit of noise underwater if you are tuned into the right frequency. Underwater noise includes groupers making a creaking door noise when they spot prey, cichlids emitting grunts, hamlet fish letting out loud squeals, the popping sound made by pistol shrimps, the crunching sound of feeding parrotfish and the grunts of damsel fish.

Cleaning Stations

20120517-cleaning station Humphead_wrassemelb_aquarium.jpg
small wrasse cleaning a large Humphead wrasse
“Cleaning stations” are places on the reef where cleaner wrasses, cleaner shrimp and other creatures clean fish that visit the station. Some fish return every few days. Even thought the cleaners can deal with up to 50 customers an hour, sometimes lines form. The fang-toothed belly is a fish that mimic wrasses. It enters the mouth of a victia fish's mouth and bites off a piece and quickly darts away.

Some 26 species of fish and six shrimps are known as cleaners. In places with no wrasses, cleaning is often done young fish. The most commonly removed organisms are fish-lice, specialized crustaceans that survive by eating the tissue and sucking the blood of their hosts. Some fish-lice burrow so speedily into their hosts the only parts of their body that are visible are their tails.

Cleaners wrasses are small slim fish, about 7.5 centimeters (three inches) long, with blue and white stripes that play an important role in the reef community by feeding on parasites that feed on other fish. They also eat dead skin and mucus. The wrasses set up cleaning stations at well defined areas. Fish signal they are ready to be cleaned by assuming a relaxed pose with their fins erect. The fish line up for their turn. One scientist observed 300 fish get cleaned by a single wrasse at a single station in a six hour period.

Reef Fish Development

According to Animal Diversity Web: Recently, researchers of coral reef fishes (mostly of the order Perciformes) have made significant advances concerning the life history of larvae. Nearly all bony coral reef fishes produce pelagic (living in the open ocean, far from land) young (meaning they live in the water column for a period of time before settling on reefs), and the length of the stage is highly variable, from only a week in some damselfishes to greater than 64 weeks in some porcupine fishes. [Source: Nicholas White, Animal Diversity Web (ADW) /=]

Initially, researchers made relatively simplistic assumptions about the pelagic (living in the open ocean, far from land) phase, "portray[ing] larvae as little more than passive tracers of water movement that 'go with the flow,' doing nothing much until they bump into a reef by chance and settle at once". Actually, the larvae of most coral reef fishes are endowed with good swimming abilities, good sensory systems, and sophisticated behavior that is quite flexible. And, while mortality rates are quite high at this stage (as with many other ray-finned larvae), many larvae are able to detect predators at a considerable distance, and they are often transparent (usually larvae) or cryptically colored (many juveniles).

It is important to note that the young of reef fishes develop quite differently from most temperate fishes that have been studied. While the eggs of most temperate fishes hatch from three to 20 days after laying, the eggs of most coral reef species hatch within only a day. Also, at any given size, the larvae of reef fishes are more developed than most temperate, non-perciform fish: they have "more complete fins, develop scales at smaller size, [have] seemingly better sensory apparatus at any size, and are morphologically equipped for effective feeding within a few days of hatching". Finally, the settling habitat for reef fishes (coral reefs) tends to be relatively fragmented and, therefore, much more difficult to locate, unlike the habitat of temperate fishes, which tends to have large expanses suitable for settling. This brief glimpse into the pelagic (living in the open ocean, far from land) stage of reef fishes reveals the diversity and complexity of development in ray-finned fish. /=\

Transsexual Fish

Reefs and oceans are filled with transsexual sea creatures. Among them are hooked sipper snails, which are born male, grow up on the backs of their mothers as males until they mature and become females themselves, who carry males on their back; and sea hares, which carry both eggs and sperm, can mate as a male or female or both, and often form long orgy chains of individuals fertilizing and being fertilized.

Conies are another species of fish which change from females into males, and visa-versa. The purple fridmani does them one better by changing its color and its sex. After spending part of their life as orange and gold female it is transformed into a purple and red male.

Scalefish also change color and sex. They are born as orange-red females. As the they get older some turn into purple males. These schooling fish are organized into a hierarchy with the males at the top and large females and small females respectively underneath. The hierarchy stays intact when a school is stable, but if some males die off then females, no body know quite how, change into males with a couple of weeks.

Blue-gilled wrasse society is made up of “normal” males and “feminized” males — fish that look like females but have mate gametes — who reproduce by help dominant males to mate with females and in doing so they get more chances themselves to reproduce. When a male fairy basslet suddenly disappears for good. Often with hours, the dominant female begin showing male characteristics. Within a few days she is a male.

See Wrasses, Sea slugs

Reality of ‘Finding Nemo’s’ Marine Life

20120521-NOAA fish skipjack_100.jpg
Juliet Eilperin wrote in the Washington Post: The underwater world on display in Disney’s “Finding Nemo” is teeming with a dizzying array of cheery creatures, from sea turtles to seahorses and mackerel to sharks. So a team of Canadian and U.S. scientists decided to assess the mythical ecosystem inhabited by the small clownfish and his friends to see how their real-world counterparts were faring. It turns out that when it comes to surviving in a non-Pixar sea, being adorable isn’t enough. Sixteen percent of the species associated with characters in “Finding Nemo” that have been evaluated face the threat of extinction, according to the study, which was conducted by the International Union for Conservation of Nature (IUCN) and Canada’s Simon Fraser University.[Source: Juliet Eilperin, Washington Post, December 12 2011]

The analysis of 1,568 species is not just a whimsical look at American popular culture and its cartoon characters. It reveals how humans treat some of the ocean’s most charismatic inhabitants. “These are species that should be doing better because they are the ones we care about,” said Loren McClenachan, a post-doctoral fellow at Simon Fraser University. She said that highly migratory species such as turtles, sharks and rays are particularly vulnerable to fisheries and other human pressures. “They’ve got life histories that cause them to interact with people wherever they go,” McClenachan said.

“The Oscar-winning 2003 Disney-Pixar movie, which details how the clownfish Marlin defies all odds to save his son from the aquarium trade, has a conservation message. But the film actually inspired a booming aquarium trade in the bright orange fish with white stripes, significantly reducing native clownfish populations on coral reefs in Australia and elsewhere. While the International Union for Conservation of Nature (IUCN) classifies clownfish as a “species of least concern,” meaning it does not face an imminent extinction risk, 18 percent of the evaluated species that are related to Nemo — those of the scientific family Pomacentridae — are at risk of extinction. There have been few formal scientific assessments of coral reef fish populations that are sought by the aquarium trade, McClenachan said, so “it’s very hard to know the true extent of the aquarium, live reef and curio trade.” Disney officials could not be reached for comment.

20110307-NOAA goldensmooth_100.jpg
golden smoothfish
Boris Worm, a marine biologist at Canada’s Dalhousie University who has reviewed the study, which is being published in the journal Conservation Letters, said the clownfish boomlet underscores the complex relationship humans have with marine species.“When people see a beautiful film about tigers, they don’t go out and shoot a tiger. They don’t go out and purchase a tiger,” Worm said in an interview. “In the case of things in the ocean, they think, ‘I care about them, so I’d like to have them,’ or, ‘I care about them, that’s why I’d like to fish them.’ ”

The survey of the animals with speaking parts in “Finding Nemo” gives a decent sense of how these species are doing. More than half of all hammerhead sharks (personified by “Anchor” in the movie) face a threat of extinction, according to the IUCN, along with all species of marine turtles (“Squirt” and “Crush”). Those species, McClenachan said, “are more threatened than the most threatened vertebrates on land.” Neil Hammerschlag, a research assistant professor at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science who studies sharks, said many people are unaware that sharks are under such pressure.“They are truly the celebrities of the ocean,” Hammerschlag wrote in an e-mail. “Despite their legendary status, most people are unaware that sharks are literally being fished to extinction.”

Fish Farms for Reef Fish

Juliet Eilperin wrote in the Washington Post: SeaWorld Parks & Entertainment in Orlando has launched the Rising Tide Conservation program, which aims to promote captive breeding of ornamental saltwater fish to ease pressure on the world’s coral reefs. Many of the saltwater fish sold in the aquarium trade are wild-caught, collected through destructive practices such as dynamite and cyanide fishing, because it is cheaper and easier than raising them. [Source: Juliet Eilperin, Washington Post April 15, 2012]

“The program, which started collecting eggs from 20 species in large reef displays in U.S. zoos and aquariums in 2010 and 2011, has raised six species. Working with the University of Florida’s Tropical Aquaculture Laboratory, the program aims to teach what it’s learned to commercial fish-farming operations so they can raise those species, such as semicircle angelfish and smallmouth grunt.

“Judy St. Leger, who oversees the program and serves as SeaWorld’s director of pathology and research, said many commercial operators stopped researching once they mastered the art of raising clown fish and other popular species. She and her collaborators, by contrast, “realize that this is not a problemthat can be resolved in one or two years. We’re prepared to be working on it for 10 or 20 years...We’re prepared to keep going in order to make a difference for the reefs.”

Although ornamental-fish farmers face many obstacles such as figuring out what tiny live food the microscopic ornamental larvae will eat, they both face the challenge of competing in an open marketplace. U.S. hobbyists are willing to buy farm-raised fish, but they can cost four to five times as much. Dustin Dorton, who works with Rising Tide and sells farmed saltwater fish as president of Oceans, Reefs & Aquariums, said he remains optimistic the price differential will narrow with a few big breakthroughs. “There’s just no way the hobby trade is going to be able to continue harvesting fish at whatever pace they desire in the future,” Dorton said.

Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

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