Although the discoloration is beautiful, your master may have scared shi.

"Joker Lantern", "Milk Lantern", "Crystal Lamp", "Baolian Lantern", "Green Lotus Lantern" …... At first glance, when you hear these names with "lights", you may think it is the product list of which lamps and lanterns wholesale market. In fact, they are the trade names of ornamental fish.

Lanterns do not belong to a unified taxon. They come from different taxa, including several families of the order Cyprinidae in general, as well as some species of Cyprinidae, medaka ng and Carpiidae, most of which are small and colorful. Today's protagonist, neon carp Paracheirodon innesi, is also a member of the lantern fish gang, which has a nickname that makes drivers' friends respect-"traffic lights".

Neon carp. Photo: H. Krisp / wikimedia

Home on the other side of the world

Although neon carps are frequent visitors to the domestic aquarium market, their real hometown is a tributary of the Solim?es River River in South America, which is almost farthest from us on earth.

Map of the Amazon and its major tributaries. Photo: Park E, Latrubesse E M / Remote Sensing of Environment (2014)

The Solimoise River, where neon carps live, flows through eastern Peru, southeastern Colombia and Brazil, where Manaus meets the Negro River River. At the confluence, there is a clear distinction between the black Negro and the yellow Solimonis, which is covered with a lot of sediment. The black Negro River is the home of neon fat carp (green lotus lamp) P. simulans and South American neon fat carp (red lotus lantern) P. axelrodi.

The Negro River and the Solimonis River meet in Manaus, Brazil. The black river is the Negro River, and the more muddy one is the Solimonis River. Picture: NASA (2008)

In the Solimonis River, some small tributaries often show a strong tea-like brown because the tannins decomposed by humus dissolve in water, and the water here is weakly acidic because of humus. Such rivers are often called Blackwater, and neon carps like to live in such an environment.

A Blackwater river in Florida, which is dyed brown with tannins. Picture: Tim Ross / wikimedia

Neon carp often swim in small groups in the water layer near the surface of the water. They hunt for small insects such as Chironomus near the surface of the water, or they look for wrigglers [jieju é] or water fleas to satisfy their hunger in the water.

Perform a beautiful "double skating"

The Solimonis River is located in the tropics, where the temperature is suitable all the year round, and neon carp can breed within a year. Although neon carp are fertilized in vitro, their reproduction does not expel gametes as hastily as some other fish fertilized in vitro, but has a pursuit of beauty and interest. If I have to describe it, it feels like two figure skaters dancing on the ice.

The pair figure skating began in the morning. The male fish first appeared on the stage, and the female fish appeared later. after a few laps around the "field", they began to show the "scoring action". The male fish uses the mouth and nose against the Gill cover and abdomen of the female, and then bends the body side by side with the female. Then, the female and male fish fan one side of the pectoral fin and caudal fin respectively, and the male fish and the female fish circle in the field. One lap, two laps, they completed the most critical action. Just as the action was completed, the female and male fish each discharged their gametes, and a wonderful double performance came to an end.

This is the pair of South American neon fat carp (red lotus lantern) P. axelrodi. Picture: Varna Malsyangal / youtube

After a perfect pair performance, female and male fish will leave 36,190 "trophies". These fertilized eggs, with a diameter of 0.9mm, hatch for about 24 to 36 hours at 24 to 25 ℃, and then develop after 5 days of embryo development, and the newborn fish can live freely in the water.

The neon carp, which has a maximum body length of only 20mm to 30mm, also grows rapidly. If all goes well, these new creatures, who have just acquired the ability to swim, will mature in another 6 to 7 months, and they will join the breeding army of neon carp as a new force.

Neon carp in the family aquarium. Picture: Tan Meng Yoe / wikimedia

How does the traffic light change color?

Neon carp are slender, with teeth in their mouths and small fat fins on the back of their bodies, proclaiming their identity as Cyprinidae. If there is anything special, it is the extended blue-green metallic band on the side of the body, and the dazzling red band below the bright band. This is the origin of the name "traffic light".

Two ribbons on the side of the neon carp. Photo: J. de lange

But the color of the "traffic light" is not that simple. If you have the experience of raising neon carp, you may find that the color of these bands does not seem to be the same under different conditions-the color of the bright band on the side of the body will change when the light changes or is frightened. This is because the blue or green presented by the bright band is actually a structural color.

The biological colors we see are actually divided into two categories. One is pigment, also known as chemical color. They are produced by pigments in the organism. Fish skin generally has melanin, yellow pigment and red pigment cells, which show the color of the pigment itself.

The other is structural color, also known as physical color. They are formed by the reflection, refraction and final interference of light in the medium. The colors of CD discs, oil films on the water, and the wings of some birds are all structural colors.

The different colors shown by a bird from different angles are actually a structural color. Picture: Seyed Morteza Kamaly / github

The color of neon fat carp belongs to structural color. The skin in the bright band on the side of their body is closely lined with many layers of glossy cells containing guanine crystals. The guanine crystals in these lustrous cells form a layer of sparse-dense-sparse-dense arrangement with the cytoplasm. When the light hits the skin of the neon carp, it constantly reflects and refracts through the cascading structure, and the corresponding structural color is produced.

Not only that, when neon carp feel pressure or light changes, they can change the cell permeability, so that luster cells absorb water and swell. Within the expanded cells, the guanine crystals are looser, so a different structural color can be produced. This is how the discoloration of neon carp is done.

Neon fat carp produces structural color through luminous cells and changes structural color by means of lustrous cell permeability. Picture: Cong Hjell et al./Optics express (2011); Sinicization: species calendar

Don't let them be alone.

The discoloration skill of neon fat carp is a response to pressure or a change in light intensity. Therefore, for neon fat carp, a relatively timid fish, it is not a good thing to observe the discoloration of the bright band on the side of the body. In order to take good care of your neon carp master and make him less worried, you have to do something.

In addition to adding the necessary shelter such as aquatic plants in the aquarium tank, can you also add friends to them? Well, the answer is yes.

Neon carp need companions. Picture: Corpse89 / wikimedia

Several British scientists have studied the animal welfare of raising neon fat carp in family aquarium tanks. They divided the neon fat carp into 1, 2, 5 and 10 tails and put them into aquarium tanks to study the restlessness, aggression, closeness and feeding behavior of neon fat carps under different group sizes. In general, when the population is the largest (10 carps), the neon carp appear calmer, have the least aggressive behavior, are more willing to come into contact with their own kind, and have a shorter time to start feeding. This result is generally valid in some clustered small fish. So, in order to make your little fish happy, you might as well find more company for them.

A group of buddies are the happiest. Photo: Myfishroom / youtube

The beautiful neon carp has won the love of lovers all over the world since it first entered the ornamental fish market. In the 1950s, the breakthrough of neon fat carp breeding technology made them one of the most popular ornamental fish.

In the 1990s, the United States imported about 1.8 million neon carps worth 175000 US dollars from all over the world almost every month. Most of the fish come from aquaculture plants in Southeast Asia, while a few come from wild populations of origin in Colombia, Peru and Brazil. Even today, people's love for neon fat carp is only increasing.

A stamp issued by Hungary in 1962 with the design of neon carp. Picture: Darjac / wikimedia

In the past few decades, about hundreds of millions of neon carps have come out of the breeding grounds and traveled across the ocean to all parts of the world. These neon carps should not have seen the Blackwater River, a tributary of the Mengis River, and their memories of their hometown are only written in their genes.

People try their best to create a hometown-like environment for these little guys wandering in a foreign land-the right temperature, PH value, water hardness. Perhaps as long as the water flowing through the Gill filaments is still the smell written in the memory, they will not be homesick.

This is the 245th article in the fourth year of the species calendar, from the author of the species calendar @ Sundayhao.