Cooperation/Koji Yamazaki

first

This time we will introduce Orygias mekonensis (hereinafter referred to as Mekonensis), a member of the medaka family. It belongs to the same genus Origias as the Japanese killifish, but it is an extremely small species with a total length of about 2 cm. Let's take a closer look at the charm and breeding of this adorable tiny medaka.

About the genus Orysias

Before introducing Mekonensis, let's briefly touch on the genus Orygias. The genus Origias is a group of fish belonging to the order Medaka, family Medaka, and subfamily Medaka. genus nameOryziasis derived from the ancient Greek word Oryza, meaning rice or rice, and is thought to have been named because this fish was often found in rice fields and surrounding waters. By the way, the plant genus also comes from the ancient Greek wordOryzaIt is said that

In addition, guppies and platies are called ovoviviparous medaka, so they are called medaka, but they belong to the order Kadayata. Origias used to belong to the order Kadayas, but due to reclassification, it became part of the order Acariformes. In other words, medaka such as guppies and medaka of the genus Orygias are classified as different fish at the order level. This can be clearly understood by their English names; fish of the genus Orygias are called Ricefish or Medaka, while fish of the Order Origiformes, such as guppies, are distinguished as Killifish.

Killifish of the genus Origias are widely distributed from South Asia to East Asia and Southeast Asia, and currently more than 30 species have been described. This genus also includes killifish (Kitanomedaka, Minamimedaka) that are distributed in Japan. Famous species that have been distributed as tropical fish for a long time include the Celebes killifish from the Indonesian island of Sulawesi (Sulawesi was formerly called Celebes Island) and the Java killifish, which is widely distributed from the southern part of the Malay Peninsula to Indonesia. Around the year 2000, when killifish from Sulawesi Island attracted attention, endemic species such as black-colored Nigrimas and Nebrosus, yellow Profundicola, Marmoratus, and Matanensis began to be distributed. The author also had the experience of collecting and reporting on these killifish twice in the early 2000s at Lake Poso, Lake Matano, and Lake Tootee on Sulawesi Island, and I found that these beautiful killifish live in unique environments. I remember being moved by it.

Further research in Sulawesi Island and surrounding areas revealed that a beautiful species called Wowolae, whose entire body shines in metallic blue, began to be distributed in 2010. In addition to these, members of the Origias family are sometimes imported from countries such as India and Thailand, and if you pay attention to these members, you will find that they are quite interesting.

mekonensis and the ultra-small orysias from Thailand

Now, Mekonensis (Oryzias mekongensis) However, this species is a particularly small species in the Origias genus, with a total length of less than 2 cm even when it grows. It is characterized by the fact that the upper and lower ends of its tail fin are colored vermilion red, and the inside of the red color turns black depending on the state of the male, especially when excited, making it a truly beautiful medaka. This ultra-small medaka is distributed in the basin of the Mekong River, which flows through the Indochina Peninsula. Yes, the species name is the Mekong River.mekongensis(Mekonensis) is the origin. Its distribution area is the area from Nong Khai province in northeastern Thailand to Ubon Ratchathani province, which borders the Mekong River, which is the border with Laos, and its inland areas. Even now, habitats have been discovered in various parts of the Tohoku region, and the detailed distribution area is still unclear. We may even be able to find its habitat in Laos on the opposite coast, and its distribution range is very interesting.

In fact, in Thailand, Orygias, which is as small as Mekonensis, is distributed. Minutilus (Oryzias minutillus) and Songkramensis (Oryzias songkhramensis)is. The former is a small species with a total length of less than 2 cm, and is widely distributed mainly from eastern to central to southern Thailand, and is phylogenetically included in the Java medaka group ( Sakaizumi, 2020). On the other hand, the latter is a relatively new species that was described in 2010, and is also an extremely small species with a total length of about 2 cm. The species name originates from the Songkhram River, which is a tributary of the Mekong River and flows through the northern part of northeastern Thailand, and can be found in various provinces in the basin of this river, such as Nong Khai Province, as well as on the Laos side. This species is phylogenetically close to Mekonensis and is included in the Minami medaka group, which includes Japanese medaka. However, this is not the case for any of the species in terms of distribution range; the author has collected Minutilus in southern Cambodia, and it has also been confirmed to live in Maha Sarakham Province in the northeastern region of Thailand. I also have experience collecting Songkramensis in Savannakhet Province in southern Laos, so I can say that its actual distribution area is still unknown. Please refer to the table below, which summarizes the various characteristics and distribution areas that will be used to determine identification.

As shown in the table, if you know the difference between Minutilus and Songkramensis, it will be easier to distinguish them from Mekonensis. Minutilus has a black spot near the cloaca, but this is not seen in other species, and there is no black spot at the base of the pectoral fin. Mekonensis and Songklamensis have black spots on their pectoral fins, but Songkramensis does not have red spots on their caudal fins. It is difficult to see the true color of mekonensis immediately after import or when it is frightened, but if you look closely you can see the red color, so it should be easy to identify. In addition, black markings can appear even when the natural body color is not showing, so if you understand these characteristics, you should be able to use them as material for identification.

Ecology and sex differences

Mekonensis can be observed searching for food while swimming just below the water surface, like the Japanese killifish. Due to their timid nature, they usually live in groups in the aquarium, but during breeding and feeding, excited and strong males can become aggressive and drive away other individuals.

The head is flat and the mouth is angled upwards, making it effective for eating food floating on the surface of the water. Their eyes are large and have good vision, and they respond quickly to the appearance of their handlers.

Mekonensis has a remarkable color difference in sex compared to Minutilus and Songcramensis. Males have a stronger and more vivid coloring on the upper and lower ends of their caudal fins than females, and depending on their condition, the inside of the tail fins often turn black. Some individuals also have reddish dorsal fins. Males also have more developed dorsal and anal fins than females, and when they mature, the fins often elongate and become comb-shaped.

On the other hand, females' caudal fins are not as colored as males, but the red color at the base of their caudal fins is a characteristic of females. Many individuals have reddish dorsal fins. In addition, the dorsal and anal fins do not stretch and become comb-shaped, making it easy to distinguish them from males. Mature females have plump bellies, so you can easily tell that they are females at first glance. However, the sex difference is often not clear in young or sub-adult fish, so if the fish you are selling is a sub-adult fish and you want to get a male or female from it, it is better to buy a larger quantity.

The male's coloration is highly ornamental.

The body color of males often becomes more beautiful when they are excited, such as when fighting or feeding. I think they are probably beautiful when they breed, but the females lay eggs early in the morning, so the breeders are often asleep, so it's a shame that it's hard to find a good time to admire them. Please check it if you have a chance, such as when you wake up early. When a male is excited, the vermilion-red color at the top and bottom of his tail fin becomes darker, and the inside becomes black, making it very impressive to see. Furthermore, when fighting, the dorsal and anal fins become blackish, and depending on the angle of light, they can appear gray. The male at this time is so cool!

Mature males sometimes fight violently with each other. They frequently spread their fins to show off their bodies, and can sometimes be seen colliding with each other. Males who are competing in strength may engage in fierce battles that may cause you to worry, but it is unlikely that they will kill the other. Once the battle is over, the losing male often becomes lighter in color and becomes more docile. The winning male becomes more colorful and may relentlessly chase other individuals. When it spreads its fins, it looks like little butterflies dancing and I never get tired of watching it.

Regional differences are interesting!

When a male matures, the upper and lower ends of his tail fin turn red, but in healthy or strong individuals, the inside of the red part turns black, making them even more beautiful. This color pattern is known to vary depending on local populations. Among the recently discovered populations, the one collected in the wetlands of Udon Thani province has become a hot topic for its beauty. The author also collected this, and I think it is a very beautiful population with a clear vermilion red color. When examining multiple males, we were able to see individual differences, such as some having yellow at the upper and lower ends of their caudal fins.

Furthermore, the population in Sang, Bueng Kan Province, where its habitat was discovered last year, not only has a vermilion red color, but the black inside is darker than other populations, creating a clear contrast. The individual in the photo posted at the beginning is one of them, and it can be said to be a very beautiful population that is highly regarded among enthusiasts.

Mekonensis can have different colors depending on their habitat, so I think it would be interesting to collect them by regional population. It's a very small species, only about 2cm long, so I think it would be fun to keep populations from different regions in multiple small aquariums and compare the differences in color expression.

mekonensis habitat

Mekonensis is often found in wetlands, lakes, and still waters without strong water currents, such as wetlands, lakes, and river wands in the northeastern region of Thailand. The water in its habitat is clean, and there are no muddy or sludge-filled areas. In their habitat, they can be seen moving in groups of dozens near the water surface, looking for food. The water temperature just below the surface during the day can reach over 30 degrees Celsius, but they live there without any problems. Other common species in the northeastern region of Thailand, such as Rasbora spirocerica, Boraras micros, and three-striped cloaking gourami, can also be seen in the habitat, and in some places Betta smaragdina may also be found. In large wetlands, there are many predators such as snakeheads such as Nandus nebrosus and plachon, catfish such as Clarias, Malayan goby, and knifefish, which I think poses a threat to small Mekonensis. They swim through the aquatic plants that grow under the water to hide from predators.

Mekonensis inhabits a large wetland in Udon Thani province that I visited in 2016, and I saw many schools swimming under the water. The water depth here is over 150cm at its deepest points. In the deep water, the water temperature was low and stable, and there were many Boraras micros. Places where Mekonensis and Micros can be seen together are often wetlands with stable water quality. We have measured the water quality of the habitat, so please refer to it. It is interesting to note that the TDS (total dissolved solids) value was much lower; in another wetland across the farm road, the pH was 6.3 and the TDS was 268 ppm, with almost no mekonensis or Boraras micros seen, but a solid・The environment was inhabited by many Smaragdina and Cloaking Gourami. What's interesting is that they seem to live differently depending on subtle changes in water quality.

Mekonensis was also collected from Lake Bung Kong Long in the neighboring Bung Kan province. We also shoot underwater videos, so please take a look. Habitat data is as follows. It is also characterized by low TDS. Even within the same lake, TDS is higher in areas close to human living areas, and Mekonensis seems to be less likely to be seen in such areas. Mekonensis is often found in areas with abundant vegetation, which has the advantage of clean water and the ability to hide.

In the habitat, I interviewed a Thai friend of mine who works as a fish shipper (exporter), and he showed me how he collects the fish. You might think that since it's a killifish, it would be fine to just scoop it up quickly, but that's not enough to transport it in good condition. If Mekonensis is collected with a net and handled roughly, it will often be damaged by abrasions and become weak or even die. Careful care is essential when collecting. Instead of rattling the net, fix a large net and gently drive the flock away. Instead of lifting the net out of the water, they repeat the steady process of scooping out several fish in the water with a large spoon or spoon and transferring them to a bag. Mekonensis collected in this way is cured at a shipper's stockyard in Thailand before being exported. This kind of hard work is necessary because it is small. Of course, not only small fish but also fish, the quality of the imported fish greatly affects the subsequent breeding, so handling them in a shipper is very important. Knowing this behind-the-scenes story makes me even more attached to Mekonensis, which comes all the way from Thailand.

Distribution and acquisition

Most of the specimens currently in circulation are wild specimens collected locally. In the past, it was sometimes imported mixed with ultra-small carp such as Golden Rasbora, Rasbora rubrodosaris, and even ultra-small carp such as Rasbora spirocerica and Boraras micros, but it is still rare. However, recently, individuals with so-called locality, which have a clear name of the place where they were collected, have come into circulation. For enthusiasts, being able to obtain specimens with clear locality is a great way to enjoy this hobby. As I mentioned earlier, if you can obtain individuals with multiple localities, we recommend breeding them separately for each locality. However, currently, Mekonensis is not a fish that is distributed in large quantities, so it is important to keep your antenna up by checking frequently for information on arrivals from shops that specialize in rare small fish or shops that have a sales history.

Key points of breeding

There is nothing difficult about breeding them if you can obtain them in good condition, but if you want to enjoy their beautiful appearance and aim to breed them, it is important to keep in mind a few points.

◆Example of breeding Mekonensis
Here, we use a small aquarium with a width of 23cm to raise 10 Mekonensis. Since Mekonensis prefers slightly acidic water quality, we used soil-based sand for the substrate. Although Mekonensis is a gentle species, males often fight with each other and often chase females around. Therefore, a large amount of aquatic plants are used so that chased individuals can escape. The Vietnamese sprite leaves are placed near the water surface. Another point is that the leaves and roots of sprites serve as spawning grounds for mekonensis.

■Aquarium data
Aquarium: width 230 x depth 150 x height 250mm/approx. 7.3L
filter:Suisaku bottom filter mini/Air pumpSuishin SSPP-7Suse
Filter media: Same as substrate
Substrate: Soil type
illumination:light up 150 white(Lights on for about 1 hours a day using a timer)
timer:LED smart timer
Water temperature: 23-26℃/controlled by air conditioner (water temperature gauge isPaste balance Muse)
Water quality: pH6.2, TDS73
Food: Granule food or flake food for medaka in the morning and afternoon, brine shrimp larvae hatched in the evening
Breeding organisms: Orygias mekonensis (10 animals)
Aquatic plants: Vietnam sprite, Microsolum “trident”, willow moss
*Aquarium isGlass garden N230use

●Number of animals and aquarium
If you can get 5 or moreIt is recommended to keep them in groups of 10.It is best to let them live in groups, just like in their native habitat. If you keep them in large numbers, they will often appear at the front of the aquarium, making it easier to aim for breeding and enjoying the charm of this species. If you keep a small number of animals, they may hide and not come out easily, or weaker individuals may be chased intensively and become stressed. If you have a cube aquarium with a width of 20 cm, you can easily keep about 10 fish by placing plenty of aquatic plants. If you want to keep a large number of fish or mix them with other fish, increase the size of the tank according to the number of fish you keep. You could also use a larger aquarium and have many of them swimming around like a habitat.

●Place to place the aquarium
Ultra-small medaka such as Mekonensis are quite timid.Every time a person stands in front of the aquarium, I see them running away in surprise. It is important to avoid stress as much as possible, and avoid placing the aquarium close to the flow line of the room, such as near the door.It is best to keep them in a quiet place..

●Water quality and breeding style
The water quality in its habitat is generally slightly acidic and soft with a pH of around 6.In actual breeding, it is easier to keep the pH at around 5 to 6.5.However, as long as the water is clean, it is possible to raise them near neutrality. The water quality data of the habitat showed a low TDS value, but as long as the value is not extremely high, there will be no problem in rearing it, and you should be able to raise it by adjusting the pH of the tap water. However, they do not like alkaline water, so avoid using sand, filter media, accessories, etc. that will raise the pH. By using soil-based bottom sand, you can maintain stable slightly acidic water quality over a long period of time. In addition, because it is an ultra-small species, the amount of food and feces it feeds is small, and if water quality can be maintained properly, it can be kept in bare tanks without using sand. In any caseNew water allows for better rearing than old water.Therefore, even if the dirt in the tank is not noticeable, it is a good idea to change the water from time to time to maintain the water quality.

●Filter (filtration)
Mekonensis does not like strong water currents.So you can use any filter as long as you keep that in mind. In this breeding example, the bottom type filter (Suisaku bottom filter mini)using. By using soil as the substrate material, it acts as a filter and maintains the water quality at a slightly acidic level, making it a filtration system that kills two birds with one stone. The key is to set the water outlet higher than the water surface. This will reduce strong water currents and allow fresh air to enter the water, maintaining the environment that Mekonensis prefers.

●Filter material
Avoid using filter media that makes the water alkaline.Use something that is weakly acidic or one that does not affect water quality.

●Bottom sand
Soil-based sand is recommended because it is easy to use and maintains suitable water quality. Of course, you can also use gravel-based bottom sand that does not affect water quality.

●Water temperature
Breeding is easy if you maintain the temperature around 25℃.is not it. There is no particular problem if the water temperature is between 23 and 30 degrees Celsius, but please be careful as sudden changes in water temperature can lead to illness.

●Lighting
Necessary for growing aquatic plants and observing Mekonensis. The area around the eyes and abdomen of Mekonensis shines depending on the angle of the light. If you turn off the lights in the aquarium and observe the fish under indoor lighting, you'll find that they sparkle and give you a completely different look. In addition, in this breeding exampleLED smart timerI use it to irradiate for about 1 hours a day.

●Bait
Feed for medaka and artificial feed for small fish are easy to use and recommended.is. In particular, there are many high-quality feeds available for medaka fish these days, and feeding them frequently will help them gain weight and reproduce. Baby food for medaka fish is also small and easy to eat, so they eat it well. Flake food is also a good bait as it does not pollute the water. However, if the food is large, there may be some leftover food, so it's best to rub it with your fingers to make it very fine before giving it to them. They also love and often eat hatched brine shrimp larvae. It is also recommended if you are aiming for breeding, and I feed it once a day.Feeding twice a day, preferably three times a day, is effective for spawning..Feed enough to eat.By the way, Mekonensis sometimes eats soft roots of aquatic plants such as moss and water sprite that grow in the aquarium.

●Layout inside the aquarium
They prefer places with abundant waterside plants and aquatic plants, so it is a good idea to add a lot of aquatic plants.Probably. Aquatic plants are also convenient when males fight with each other or chased females run away, as weaker individuals can quickly hide. We recommend hardy aquatic plants such as Microsolum, but it is also a good idea to arrange your garden with your favorite species. In this breeding example, Vietnam Sprite was not planted on the substrate, but placed so that its leaves grow near the water surface.If you lay out the area so that the area near the water surface is covered with aquatic plants, Mekonensis will settle down more easily.I think it would be a good idea to float floating plants such as salvinia as a habitat.

- Mixed swimming with other fish
mekonensis isYou can also enjoy swimming with other small species and gentle fish.Compatible with them are gentle, ultra-small species such as Boraras and Deep Red Firefly Tetra. As long as the fish do not attack or eat Mekonensis, you can basically swim with them. However, in mixed aquariums with other species, the eggs laid by Mekonensis are often eaten, soIf you are aiming for breeding, it is better to keep only Mekonensis.is. Otocinculus and shrimp, which are often used as moss removers, will also eat eggs, so be careful.

Fish suitable for mixed swimming
・Medaka friends: It is possible to swim with smaller species, but it can be stressful because their living areas overlap. Look at the situation.
・Small characin: Gentle, ultra-small species such as deep red firefly tetra
・Small carp: Ultra-small species such as Boraras and Rasboras
・Anabantid: Possible for small species such as licorice gourami and pygmy gourami.
・Gentle catfish: Small species that do not eat other fish such as Otocinculus and Corydoras
・Loach: Gentle species such as coolie roach
・Small crustaceans such as shrimp：Small species such as Yamato Numa shrimp and Minami Numa shrimp

●Daily management
As I mentioned earlier, new water can be managed better than old water, soIt is a good idea to change the water by 1/2 to 1/4 of the total water volume once every 1 to 2 weeks.Probably. At this timemaintenance goodsYou can maintain a good environment by removing moss from the glass surface and cleaning the bottom floor.If aquatic plants grow vigorously, it will be a good environment for mekonensis.It can be said.

●About illness
If you can obtain a specimen in good condition, diseases will not occur, but if there are major environmental changes after purchase, the water becomes old due to long-term maintenance, or the filtration function deteriorates and the water becomes dirty and the environment worsens. Pepper disease and columnaris disease are more likely to occur. Also, be careful as white spot disease may appear when the water temperature drops suddenly, such as in early autumn. Because fish are small, if they get sick, they often get sick quickly and die, so the first thing to do is to keep the environment in good condition to prevent the disease from spreading. If your fish becomes sick, bathe it as soon as possible using a fish medicine suitable for the condition.

Also, although he is not sick, he has surprisingly good jumping ability,To prevent jumping accidents, it is also effective to place a glass lid firmly or lower the water level.is. Mekonensis may jump when scooping, so be careful.

●About breeding
Once you have a mature male and female, spawning is not difficult. If you keep them in good condition, you can see the female swimming with eggs on her stomach. However, in a mixed aquarium, eggs and young fish are often eaten, so preparation is necessary if you are aiming for breeding.I would like to explain the details of breeding in the next time, so please refer to it.

in conclusion

Mekonensis is a very small species that is closely related to the Japanese killifish, but is only about 2cm long as an adult. It is an attractive killifish that can be collected by enthusiasts as it has different colors depending on the region.
It can be kept in a small aquarium, so if you have the opportunity, please enjoy its adorable appearance.
see you!