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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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

Candiru (Vandellia cirrhosa)

There are some nasty things that lurk in bodies of water. Whether you’re in a lake, river, or ocean, there’s always something you should look out for, always something swimming quietly in the depths to make you just that little bit nervous while you’re paddling around. Today’s animal, the candiru, is a particularly nasty critter.

Luckily, candirus are only found in the Amazon River Basin, so you don’t have to worry about them unless you’re swimming in the Amazon. Candirus have been found in Bolivia, Brazil, Colombia, Ecuador and Peru. They like slow moving, shallow areas, particularly those with muddy bottoms.

Candirus are quite small, only growing to maximum lengths of 17cm. They are not very noticeable fish, as they are translucent except after feeding. They are long and thin, with large eyes on top of their heads. The most interesting part about candirus is the backwards-facing spines that project from their gill covers. These have quite a sinister purpose, I assure you.


It used to be thought that candirus were attracted to urea released from their hosts’ gills, but this is untrue. They hunt using visual cues, hence the large eyes. Image source

You see, candirus have a taste for blood, and the way they get it is definitely creepy. They lodge themselves into a fish’s gills, where their spines pierce the thin gill membranes, letting blood flow right into the candirus’ mouths. It used to be thought that Candirus were attracted to urea released from their hosts’ gills, but this is untrue; they hunt using visual cues, The spines also keep the candirus stuck under their hosts’ gills; the backwards-facing nature of the spines means these parasites are incredibly difficult to dislodge.

Sounds pretty nasty, right? Well that’s not the worst thing about candirus, according to prevalent rumours. You see, it’s said that sometimes when people are urinating in the river, a candiru gets a little confused and swims right into a person’s urethra. And because of those spines, they are extremely hard to remove. Not pleasant experience I’m sure.


Some recently fed candirus. Image source

So yes, candirus are horrible fish. But the accounts of candirus swimming into peoples’ urethras are rare, and are not terribly reliable. The only modern case occurred in 1997, and has a few inconsistent details that makes it unlikely that a candiru did actually lodge itself in a man’s urethra. Still, I’m not going to be the one to go in the Amazon to test whether or not the tales are true.

Manylight Viperfish (Chauliodus sloani)

Finding an interesting fish to blog about isn’t too difficult. All I have to do is plunge into the depths of the sea, and the deeper I go, the weirder and more bloggable the creatures become. Today’s fish is one of the stranger ones, and is known as the manylight viperfish, or Sloane’s viperfish.

Manylight viperfish live in deep waters (which is why they are so bizarre), in the bathypelagic region of the ocean. This ranges from 1000 to 2000 meters in depth, though viperfish have been found as deep as 2800 meters. They migrate daily, coming to the mesopelagic zone (200 to 1000 meters deep) at nighttime. Viperfish are found in all subtropical and tropical oceans, and have also been found in the Mediterranean Sea.


Finding good pictures of deep sea creatures is a bit of a challenge. Image source

Sloane’s viperfish don’t get very big, only reaching lengths of 20 to 35 cm. They are long and thin, and have iridescent blue, green, black or silver scales. Viperfish have rows of photophores that produce light running along their sides and bellies, hence the name ‘manylight’.

So why are they called viperfish? Well you see, viperfish have massive teeth coming out of both their upper and lower jaws. In fact, these fish have the largest teeth relative to head size of any fish in the world. The teeth are hinged, so they can rotate into viperfish’s mouths, preventing prey from swimming away once they’re caught. Manylight viperfish also have a hinged connection between their skulls and backbones, which allows them to swallow big prey — up to 63% of their body length!


A nice close up of a viperfish with its lovely teeth. Image source: Wikipedia

The problem with writing about deep sea creatures is that they are very hard to study in the wild. Which often means we don’t know all that much about them. Such is the case with the manylight viperfish, at least in regards to their mating habits. What we can guess is that these fish use their photophores to communicate with each other, but that’s about it. Otherwise these fish (or at least how they breed) are a mystery to us.

Still, what we do know about these creatures is pretty amazing. Hopefully with some more deep sea exploring we can discover even more crazy facts about these guys!