Dragonet (family Callionymidae)

I’ve loved dragons ever since I can remember loving anything. I think they’ve always been my favourite mythical creature. So any real-life animal that is named after dragons always sparks my interest. Which is how I came across today’s group of animals, the dragonets.

Dragonets belong to the family Callionymidae, which consists of 139 fish species in nineteen genera. They live in the Indian and Pacific Oceans, and enjoy hanging around in warm, tropical waters. Dragonets are bottom dwelling fish, residing on the sandy ocean floors at depths of up to 200 meters.

Dragonets, as their name implies, are not overly large fish. The largest species of dragonet reaches lengths of only 30 cm. Many species of dragonet are brightly coloured, and have wonderful patterns along their bodies. Males and females have different colour patterns, and although the fins of all dragonets are large, males are known for having particularly impressive dorsal fins.

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A very colourful mandarin fish, look for a post on these guys in the future, they’re super cool! Image source

They may look pretty, but dragonets are not friendly fish, and males are especially aggressive during courtship and mating. They will charge each another, biting the other fish’s mouth, and twist around one another. Both their large spines and bright colours are required to achieve dominance, and thus gain access to mates. Unfortunately, this comes at a cost: males are more likely to die than females, both from fights with one another and from predation, since they are easier to find, thanks to their bright and beautiful colouration.

Reproduction in dragonets begins with courtship, with both sexes (though more commonly males) displaying to one another. Displays include spreading of the fins, as well as swimming around one another. Males will also open and close their mouths, and position themselves on top of females and rub them. Once a pair has been formed, the two prepare to spawn.

To spawn, dragonets swim upwards, rising together in a semicircular pattern. They don’t move very quickly, and have to take a rest after rising about fifteen centimetres. Once they proceed to the second part of their rising swim, the dragonets start to spawn, with both sexes releasing their gametes into the water. The buoyant eggs stay floating in the water, and travel away with the current. Once spawning is done, male dragonets go back to the depths and look for more females to mate with.

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A picturesque dragonet, looking spotty and colourful. Image source

Dragonets feed on benthic organisms, primarily small invertebrates. They have large mouths, and can extend their jaws towards their prey, sucking the unfortunate victim into their mouth. When dragonets themselves are threatened, they will bury themselves in the sand, so that only their eyes are visible. Other defences depend on the species; some spines on dragonets have been reported to be venomous, while many species are able to secrete nasty tasting substances that deter predators.

Though I picked these fish as my animal for the week because of their name, they turned out to be a lot of fun to draw too. Their bright colours and pretty patterns made a lovely subject to paint. Isn’t it nice when things work out like that?

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My watercolour painting of an oscillated dragonet. I decided to highlight the splash of colour on its dorsal fin by keeping the rest monochrome.

Spotted Ratfish (Hydrolagus colliei)

A lot of fish are named after land animals — catfish, dogfish, rabbitfish, porcupine fish, kangaroo fish (that last one does’t actually exist, but I wish it did).  Today’s animal, the ratfish, seems to have gotten the short end of the naming stick. I like rats, but I don’t think I’d want to be named after them.

Ratfish belong to the family Chimaeridae, otherwise known as shortnose chimaeras. Chimaeras are an odd group of fish that have cartilaginous skeletons like those of sharks and rays. In fact, their closest relatives are sharks. Almost all chimaeras are deep water fish, and are therefore difficult to find and to study. So today I’m going to focus on one of the few chimaera species that hangs around in shallow waters, the spotted ratfish.

Spotted ratfish live in the Pacific Ocean, from Alaska to Baja California. They have been found at depths of up to 913 m, but are much more common in areas between 50 and 400 m deep. In the spring and autumn spotted ratfish tend to hang out in shallower waters, moving to deeper areas in the summer and winter. They prefer to live on the ocean floor, particularly on sandy, muddy or rocky reefs.

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These guys are a little strange looking…     Image source

Spotted ratfish are named for their spots, and for their long, ratlike tails. They can grow to be up to a meter in length, and females are much larger than males. Ratfish tails can make up almost half of the fish’s length, and are long and thin. Spotted ratfish have silvery-bronze skin, and are covered in fun white spots. They have big huge adorable eyes, which reflect light like those of a cat or dog.

Spotted ratfish hunt during the night, using their sense of smell to locate prey. They swim slowly above the ocean floor, looking for shrimp, worms, fish, crustaceans and sea stars. Ratfish particularly enjoy foods with some crunch to them, such as crabs and clams. They have incisor like teeth that act as grinders to help break up their yummy diet.

Spotted ratfish may be hunters, but they themselves fall victim to predators. Sharks, halibut, pinnipeds and pigeon guillemots are all known to consume spotted ratfish. Eating a ratfish is not always a pleasant experience, however. They are equipped with a venomous spine on their dorsal fin, which can cause painful wounds. The spine can also be deadly if ingested: harbour seals have died after a ratfish spine penetrated the stomach or esophagus. The lesson here: don’t eat ratfish, unless you posses spine-removal tools.

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A spotted ratfish egg sack. Image source

Breeding season in spotted ratfish occurs from spring to autumn. Female ratfish lay one or two fertilized eggs into sandy or muddy areas every two weeks or so. Egg laying can last for four to six days, which is a long time, but is necessary, considering the size of the egg sacks. Each sack is twelve centimetres long, and is basically a leather pouch. The eggs take a long time to develop and hatch, sometimes staying inside the egg case for up to a year.

Unfortunately for spotted ratfish, the appearance of their eggs, and the extensive time it takes for the eggs to hatch means that the eggs are sometimes mistaken as inanimate objects by divers. But the news isn’t all bad: the overall population of spotted ratfish is doing just fine, in part because they don’t taste that good. I guess the key to surviving in the modern world is to taste bad, and not look too pretty.

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A quick sketch of a spotted ratfish, emphasizing its big cute eye. 

Cover image credit: Clark Anderson via Wikipedia

Bluespotted Fantail Ray (Taeniura lymma)

There’s something so graceful and beautiful about rays that I can’t help admiring them. I think it’s the way they move through the water, with their undulating ‘wings’ — they are such marvellous but strange creatures. I’ve written about a few rays before: the manta ray and the giant freshwater stingray, and today I’m going to talk about the bluespotted ribbontail, or fantail, ray.

Bluespotted ribbontail rays live in the Indian and western Pacific Oceans. They are found in shallow coastal waters, rarely venturing beyond 25 meters in depth. Bluespotted rays prefer to live in and around coral reefs and sandy flats, so they have places to hide during the day. The rays will also venture into intertidal zones and tidal pools.

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Aren’t these guys amazingly beautiful? Image credit: Jens Petersen via Wikipedia

These stingrays are easily recognized by the bright blue spots that cover their bodies, though they are not the only species of ray known as bluespotted stingrays. They are, however, quite distinctive, as they have more and brighter spots than other species, as well as having two bright blue stripes on their tails. Bluespotted fantail rays do not get overly large, reaching maximum widths of 35 cm. They are oval in shape, with a smooth, yellowish-green disc.

Bluespotted fantail rays are nocturnal, spending the day hidden in caves, shipwrecks, or coral reefs. At night, these guys emerge and head to the shallows, following the high tide into tidal flats in search of tasty meals. They feed on a wide variety of animals, including crabs, shrimp, fish, and sand worms. They detect their prey using electroreceptors, and trap them by pressing their discs into the ocean floor. Once the prey is caught, the rays move around until their meal is directed into their mouths, which are located on the underside of their bodies. Bluespotted rays have 15-24 rows of teeth arranged into plates, which can easily crush the shells of molluscs.

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A close up of a bluespotted ray’s eyes, which makes it look pretty creepy. Image credit: Nick Hobgood via Wikipedia

Bluespotted rays themselves are targeted as prey; both hammerhead sharks and bottlenose dolphins are known to feed on these rays. When threatened, bluespotted rays prefer to run away, swimming in zigzags to try and confuse predators. These rays have another method of defence, however — they have lovely venomous spines at the tips of their tails, which can deliver a nasty sting to anyone foolish enough to get close to them. Hammerhead sharks get around this by using their hammer-shaped heads to pin the stingrays down while they eat them.

Bluespotted rays mate in the spring and summer, when males start to follow females around. They eventually start nipping at the females’ discs, and then hold on while the pair copulate. The exact gestation period of bluespotted fantails is uncertain, but after four to twelve months females give birth to up to seven pups, which look like miniature versions of their parents.

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A quick sketch of a bluespotted fantail ray.

Bluespotted fantail rays are popular in home aquaria, in spite of their dangerous spines. They are also very difficult to keep in captivity, with many refusing to eat or dying for unknown reasons. But people still try and keep them for some reason, and the rays are also suffering from degradation of their natural habitat. They are still fairly abundant in the wild, but have been assessed as Near Threatened by the International Union for Conservation of Nature (IUCN). Hopefully these beautiful creatures can stick around for a while.

Cover image credit: Jon Hanson via Wikipedia

Zebrafish (Danio rerio)

Usually I pick animals for this blog because they look funny, or they have a silly name, or because there’s something really super special awesome about them. Today’s animal is a bit different, because although it is quite an incredible creature on its own, many of the most amazing things about it are the results of human experimentation.

Zebrafish are found in parts of India, Pakistan, Bangladesh, Myanmar and Nepal. They have also been introduced to some areas of the US and Colombia, inadvertently and on purpose. They are freshwater fish, and are generally found in slow-moving, shallow waters. They can live in rivers, streams, floodplains, and rice fields.

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A wild-type zebrafish. Image source

Human disturbance is detrimental to many species of animals, but there are always a few that can cope or even benefit from human-changed habitats. Zebrafish are one of these lucky species, as they don’t seem to mind areas that have been altered because of rice cultivation. Growing rice often means waterways are dammed and irrigation systems are created, and zebrafish can be found in both of these altered ecosystems.

Zebrafish are quite small, innocuous fish. They can reach massive lengths of 6.4 cm, though sizes are more commonly a much more reasonable 2.5 cm. Zebrafish get their name from the stripes that run down their sides; each fish has five to seven blue stripes. Male zebrafish have gold colouring between their blue stripes, while females are silver-coloured.

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I decided to try something a bit different for this post. Not sure how I feel about the fish, but I like the way the background turned out! 

Breeding in zebrafish occurs during the monsoon season, from April to August. The fish get pretty excited about the chance to mate, rising at dawn to start courting one another. Male zebrafish follow a female around, each of them trying to lead her to a spawning site. They do this by nudging her and swimming in circles around her, which must get extremely annoying. Once a pair has reached an appropriate site, they line up their genital pores and the female releases her eggs, and the male releases his sperm.

The fertilized eggs hatch after two to three days, with all hatchlings being female. Differentiation between the two genders starts to occur at five to seven weeks of age, though males need about three months for their testes to develop completely. What causes fish to become female or male is not yet known, though it is thought that food supply and growth rates influence gender. Slow-growing zebrafish grow up to be males, while faster growing ones become females.

Zebrafish, while seemingly simple and nondescript fish, have incredible regenerative powers. While they are still larvae, zebrafish can grow back their fins, heart, brains, and retinas. These abilities have been the subject of intense research, with possible applications in human medicine being explored.

Regeneration isn’t the only trait that makes zebrafish useful research subjects. They are hardy fish, with short lifespans and large clutch sizes, making them ideal for genetic studies. They were one of the first vertebrates to be cloned, and many mutated strains of zebrafish have been created. Among the more bizarre is a strain of transparent zebrafish that glows when the brain is undergoing strong activity, and a zebrafish that turns green in waters polluted by oestrogen.

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Some GloFish… look how many colours they come in! Image source

Zebrafish aren’t just popular research animals — they are also extremely common in aquaria, especially since they come in many colours. They have even made florescent zebrafish, because why would you want a natural looking fish when you can have a GloFish®? And yes, they are actually called that.

Cover image source: Azul via Wikipedia

Crocodile Icefish (family Channichthyidae)

Almost by definition, animals that live in and around Antarctica have to be bizarre. After all, you have to be pretty strange to want to live in frigid temperatures year round. Today’s group of animals, the crocodile icefish, are specialist fish that are particularly fond of cold waters.

There are sixteen species of crocodile icefish, all of which are found in the Southern Ocean. They range from Antarctica to southern South America, staying in waters that stay between -1.8 to 2.0 degrees Celsius year round. Because of the increased oxygen content in cold water, lower temperatures are key to icefish survival.

Icefish can reach lengths of 25 to 50 centimetres, so they get to be reasonably sized. They have protruding snouts and distinctive spiny dorsal fins. Crocodile icefish don’t have super flashy colouration; they are light coloured with darker patterns, such as stripes or blotches covering their bodies.

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A crocodile icefish – they look a little funny, don’t they? Image credit: marrabbio2 via Wikipedia

One of the strangest things about crocodile icefish is the lack of hemoglobin and red blood cells in their blood. Because of this, icefish have colourless blood, which must look very strange. They are the only known vertebrates that lack hemoglobin.

So how to these fish survive without the oxygen-carrying protein hemoglobin? Well, they have much larger blood vessels and bigger hearts than other fish. Crocodile icefish have blood volumes that are four times as large as other fish, and their hearts’ outputs are five times greater. Icefish also have very spongy ventricles in their hearts, which means the organ can absorb oxygen from the blood they pump. All these adaptations means blood flows in large quantities at low pressures, allowing oxygen dissolved in the blood plasma to be absorbed by the body.

You may think, then, that icefish have evolved a more efficient way of living without haemoglobin, but that is not the case. In fact, although icefish can live without hemoglobin, the lack of it is not adaptive. The reason these traits evolved when they were not adaptive is that crocodile icefish evolved in a very unique environment.

The steadily cold waters of the Antarctic allow for very high concentrations of oxygen in the water. There is also limited competition in Antarctic waters — many species of fish went extinct millions of years ago, and ocean trenches and current keep icefish populations relatively isolated.  Thus, a deleterious trait that would have resulted in the extinction of the species anywhere else has been able to persist in crocodile icefish, and this unique species is the end result.

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My drawing of a crocodile icefish. I haven’t worked in pencil for a very long time, so this was fun! 

I love writing about animals that live in extreme environments; they are always some of the coolest creatures around. The fact that icefish can survive without one of the most important proteins in our bodies is crazy. The world is truly full of amazing creatures.

Mexican Tetra (Astyanax mexicanus)

The vast variety of environments on Earth gives rise to an incredibly diverse array of species, all which have adapted to live in specific ecosystems. Today’s animal is an excellent example of how environments influence species’ characteristics, as different forms of the Mexican tetra are radically different, depending on where they live.

Mexican tetras are found in Mexico (what a surprise!), but also occur in Texas. They live in the Rio Grande and the Neueces and Pecos Rivers, as well as in caves in northeastern Mexico. They are freshwater fish that like warm waters with temperatures of 20 to 25 degrees Celsius. In winter these fish migrate, moving to find warmer waters.

Mexican tetras can get as large as twelve centimeters in length (terrifying, I know). They are fairly normal-looking fish, and are somewhat compressed laterally. They don’t come in any particularly flashy colours, being silver with reddish fins.

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Mexican tetras, looking pretty normal and boring. Image credit: haplochromis via Wikipedia

So what is so exciting about this little fish? Why am I blogging about it? So far the most exciting thing about it is that lives in Mexico, which is a pretty awesome place, or so I’ve heard. Well, Mexican tetras have two distinct forms, a normal form and a blind cave form. Both of them are members of the same species, but they have one very important difference.

You see, it’s not very helpful to be able to see in caves, because there isn’t much light underground. So Mexican tetras that live in caves have lost their sight. Some populations do retain some sight, while other cave tetras are completely blind, and have even lost their eyes.

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The blind form of the Mexican tetra – doesn’t it look creepy? Image credit: JohnstonDJ via Wikipedia

There are other differences between cave tetras and normal tetras. Cave dwellers have taste buds on their heads, which lets them smell better, and they can store four times as much fat in their bodies. As food sources in caves aren’t particularly reliable, extra storage helps these fish survive long term. Cave tetras also are albino, having lost all the pigmentation in their skin.

The result is a two very different animals: one fish that is perfectly normal and perfectly bland, and one fish that looks like it is some kind of freak from a horror movie. Don’t worry though, both forms of the species are still the same species and so they can breed and produce fertile offspring.

Because of the weird differences between surface-dwelling and cave-dwelling tetras, scientists use these guys as a model to study different kinds of evolution. They are also popular aquarium fish, especially in their blind form. I don’t know if I’d want a blind cave tetra in my house, I think they look really creepy. But that’s just me!

Cover image source