Bull Shark (Carcharhinus leucas)

It’s been quite a while since I’ve written about a shark, which is a shame, because sharks are awesome. Not all sharks are created equal, however, so I thought end my shark drought by writing about a particularly fearsome species, the bull shark. Bull sharks go by a number of different names, including Zambezi sharks, Nicaragua Sharks, and cub sharks. I’m going to stick with bull shark, for simplicity’s sake.

Bull sharks have a wide range, in tropical and subtropical areas. They are mainly found in coastal areas in the world’s oceans, though they will enter estuaries, deltas, rivers and lakes. In the United Sates, bull sharks have travelled up the Mississippi River as far as Alton, Illinois. Bull sharks don’t like to swim very deep, rarely being found at depths beyond 30 meters.

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A map showing the distribution of bull sharks worldwide. Looks like I’m safe here in Canada! Image source: Wikipedia

Bull sharks have earned their name, being large, chunky, and aggressive. Female sharks are bigger than males, reaching average lengths of 2.4 m, with the largest recorded specimen measuring in at a whopping 4.0 m long. Bull sharks have short snouts, and mouths that are filled with large (and terrifying) triangular teeth. There’s good reason to stay away from a bull shark’s mouth: they have the highest bite force of all sharks, relative to body size.

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Look at those teeth! I don’t think being bitten by those would be very much fun… Image credit: D Ross Robertson via Wikipedia

There’s another reason you probably shouldn’t get into water with a bull shark — as mentioned, they are very aggressive. Along with tiger sharks and great whites, bull sharks make up the three most dangerous shark species to humans. Bull sharks are particularly deadly thanks to the wide variety of habitats they live in, as well as their penchant for hanging around in shallow waters. Because people also like to swim in shallow areas, bull sharks run into people more often than other species do. What fun!

Though bull sharks do readily attack humans, they don’t make regular meals out of them. Instead, bull sharks prefer to feed on various fish and small sharks, but will also eat turtles, birds, mammals and stingrays. They have excellent senses of smell and hearing, which they use to navigate the often murky waters they hunt in.

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I don’t know who got close enough to take this picture, but I wouldn’t want to be them! Image source: Wikipedia

Reproduction in bulls sharks occurs in summer and autumn, when the sharks swim into estuaries and river deltas to mate. Males will often bite female sharks during copulation, leaving nasty scars on their bodies. Female bull sharks give birth to live young, after almost a year’s gestation. Litters range in size from four to ten pups. The young are born in freshwater lagoons, rivers, and estuaries, and stay there until they mature.

Bull sharks are unique among sharks for being able to survive in both salt and freshwater habitats. This gives their young a distinct advantage — the little ones can hang around in the relatively predator-free freshwater areas until they’re big enough to protect themselves. Bull sharks are able to move between salt and freshwater thanks to their kidneys, liver, rectal glands and gills, all which help regulate the salinity of blood in the sharks’ bodies.

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I drew this for a special project I’m working on… hopefully you’ll hear more about it soon! 

Unfortunately, though breeding in fresh, shallow water protects the young sharks from animal predators, these areas are also those that are most affected by human development. In recent years, the number of bull sharks in estuaries has been declining, and the species is now listed as near threatened. I know bull sharks are scary and they attack people, but those attacks are quite rare, and they’re not evil enough to deserve extinction. But do be careful when swimming in shallow waters!

Cover image credit: Pterantula via Wikipedia

Filefish (Family Monacanthidae)

I’d never heard of filefish before I started writing this post. But I was browsing one of the websites I use to get ideas for posts, and the name filefish caught my eye. I always like it when fish are named after other animals or objects because I get to picture a cross between a fish and whatever that fish is named after. Today I thought of a metal file with fins and great big googly eyes, and got a good chuckle out of it. So let’s learn about filefish today, and though you may be disappointed to learn that filefish are not actually a file/fish hybrid, they are pretty cool.

Filefish belong to the family Monacanthidae, which has 27 genera and 102 species. They are fairly widespread, being found in the Atlantic, Pacific and Indian Oceans. Australia is a particularly abundant area for filefish, with over half of all filefish species living in Australian waters. They prefer shallow areas, rarely venturing below depths of 30 meters. Filefish are commonly found in lagoons, reefs, and seagrass beds.

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Aluterus scriptus is the biggest species of filefish, and can grow to over 110cm. Image credit: Choo Tee Yong Vincent

Filefish range in size from below 60 cm to 110 cm, depending on the species. They are laterally compressed (meaning their bodies are tall and thin, like they’ve been put in a press and squished), and are shaped a bit like rhomboids. Filefish have two spines on their heads, one of which is much larger than the other. The spines are retractable, and the second, smaller spine holds the bigger spine up when it is erect. Filefish are coloured in a range of hues and patterns, mostly to blend in to their environment.

This type of colouration is vey important to filefish. They have small fins, and so are pretty bad swimmers. This means they can’t easily get away from predators, so camouflaging among corals and sea grass is super important. For filefish that eat invertebrates (some species subsist solely on algae, seagrass, or coral), cryptic colouration also helps hide them from their prey. Some filefish hide out in rock crevices, and use their spines to stay lodged inside if a predator tries to eat them.

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Filefish come in such an array of beautiful colours. Image credit: Julian Finn via Wikipedia

Filefish lay eggs on the ocean floor, in nests prepared by the males. Species differ in terms of parental care; in some species both parents guard the nest, while in others that task is left solely to the male. Once the young filefish hatch, they simply drift in the open ocean, often living within Sargassum seaweed species.

I’ve told you a lot about filefish, but I’ve left out the most important fact: why filefish are called filefish. Unfortunately, the reason is fairly mundane. They are thin and have rough skin, which I guess reminded people of files. In fact, it’s said that dried filefish skin was used as a tool to sand wooden boats. In any case, I’m going to leave you with a picture of what a real filefish should look like. Enjoy!

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This is what a true filefish should look like. It would use the file part of its body to file open clams and mussels and things. Evolutionarily it is the most perfect of fish. 

Cover image source: Diver Vincent via Wikipedia

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