Category: Fish

Eels of the Ribbon Sort

ribbon eel

A ribbon eel, also called a ribbon moray. Image taken at the California Academy of Sciences.

This interesting looking fish is a ribbon eel. Those big membranes on its face are its nostrils, which also act as a lure to attract prey to their sharp-toothed jaws. When it snaps its jaw shut, it recoils into its burrow. They will also use their burrows to hide when they are threatened. I can tell that this is a juvenile or a small adult male because of its coloration. Adult males will have a yellow snout and females are yellow, with a little white and black on their fins. Females are comparatively rare and not seen often. None of these fish are born females-all of them are born as males. This is another sex changing fish that changes from male to female.

ribbon eel

A ribbon eel. Image taken at the California Academy of Sciences.

Now You See Me, Now You Don’t

Flashlight fish

This is what it looks like when you take a picture of a flashlight fish without using your flash. Image taken at the California Academy of Sciences.

This little stripe of light you’re looking at is coming from a flashlight fish-a small, nocturnal fish that lives in warm oceans, along steep drop offs and caves. They’re usually only spotted by humans in the shallows on moonless nights. So, what causes that beautiful glow? And how does the fish use it?

The light is coming from what’s called a photophore, which is an organ located under their eyes:

flashlight fish

A flashlight fish specimen. The arrow is pointing to the photophore, an organ just below their eyes. Image taken at the California Academy of Sciences.

This organ contains a bio-luminescent bacteria, which casts a greenish glow that can be seen as far away as 100 feet. Some flashlight fish have a photophore cover that can be raised and lowered to expose or hide their special lights. Other flashlight fish can rotate their photophore back into their head to hide their lights. This flashlight fish has a cover:

flashlight fish

A flashlight fish specimen, partially covering its photophore. Image taken at the California Academy of Sciences.

This gives the fish the appearance of blinking and the photophores seem like eerie, glowing eyes.

At any rate, this special bacteria sack brings a lot of special advantages to the fish. For instance, small prey, such as plankton, small fish, crabs and shrimp, are attracted to the green glow and the light helps the fish see to catch them. They also use their glow to communicate. These fish will normally “blink” 2-3 times per minute, but when they are in danger, they’ll blink up to 75 times per minute. If there is an intruder in a couple’s territory, the larger females will “turn off” their light, get close to the intruder and then turn their light back on, which is meant to scare them. They’ll also use their light to confuse a potential predator. They will “flash and run,” exposing their photophore and then darting in a zigzag motion. Apparently this works pretty well, because these fish are very rarely found in the stomach contents of larger fish.

Of course, this doesn’t stop humans from catching them. Some fishers will catch these fish and then remove their photophore to use as a fishing lure.

Imitation Scallop, A.K.A. Skates



A small skate shows off its camouflage. Image taken at the Monterey Bay Aquarium.

This flat sandy colored fish is one of many types of skates. Sometimes these fish bury themselves in the sand, with just their eyes and spiracles sticking out. Spiracles are the holes behind their eyes that pull in water to push across their gills so they can breath while sitting still. Several species of skates have been found to have electrical tissue in their tail. So they can produce electrical energy (much more than is required for simple muscle movement), but no one has ever been shocked by a skate and at the moment, we don’t really know what they have this ability for, although it is thought that it might be for reproductive and social interactions.



This skate swims over us in a large tunnel at the Aquarium of the Bay.

Skates are closely related to rays and sharks. Just like rays and sharks, their skeleton is made of cartilage, which is more flexible and lighter weight, instead of bones. They have several gill slits visible instead of a gill cover. You can tell the males from the females the same way (by looking for claspers-long, thin protrusions on their underside). And the coolest similarity, is that they can detect electricity. If you look closely at the last picture, you can see small golden spots on the underside of the skate’s body. In this picture, you can see them most clearly around its mouth. These spots are the ampullae of Lorenzini. These spots can pick up very small electrical pulses, so if the skate is hunting and there’s an animal buried in the sand but the skate can’t see it, or smell it, or hear it, it can still detect the electrical pulses from its heart beat. But then what? Well, notice the two holes above its mouth that look like the eyes of a happy face? Well, their eyes are actually on top of their head and these holes are its nostrils. They can actually shoot jets of water out of their nostrils to push sand away and find food living underneath, such as clams. Another trick they have is to cup their wings toward the sand creating a suction cup to pull the sand away. This little trick has led to many disappointed fishers, because the great force required to dislodge this fish when it’s suctioned to the ground makes them think they are getting a much bigger fish than they actually are.

Although skates have a flattened body shape similar to a ray and are closely related to rays, they have their own separate order. A couple of major differences help to distinguish them. One is that skates will never possess a venomous barb, while many rays do (manta rays have lost their barb). The other is that skates lay eggs, while rays give live birth.

Skate eggs are particularly cool. They are often called mermaids purses. One cool trick aquariums like to do is replace part of this leathery egg with clear plastic so that we can watch the embryo develop. Here is a video of a skate embryo, inside its flat sea weed-looking egg:

Is that cute or what? That little yellow ball in the middle of its chest is the yolk, which is giving the embryo nutrition. When that ball is gone, the embryo will make its escape through the sides of the egg and emerge as a miniature version of the adults. Some skate eggs can have as many as 7 embryos in them! That’s pretty cramped.

While watching these embryos develop, scientists noticed that they go through a number of stages very similar to shark embryo development before continuing on to a skate shape. Also, they discovered many malformed skates, where their embryonic development was arrested and they looked like a cross between a shark and a skate. Based on this, they believed that rays and skates evolved from a shark ancestor. However, the molecular studies now show that they share a common ancestor with sharks rather than evolved directly from an ancient shark species, so they are not modified sharks.

If you are interested in learning more about skates, the Florida Museum of Natural History has two great pages filled with ray and skate information here and here.

Lastly, skates are not a sustainable seafood, as they are overfished and frequently caught with high amounts of by-catch. Read more about this here. Are you eating imitation scallop? Imitation scallop is just one of the common market names for skates. The rest can be found at the aforementioned site. How is this vertebrate being misidentified as a shellfish? Well, if you can’t sell skate to consumers, use a cookie cutter to cut out chunks of a skate’s wings and call it scallop. Apparently, it works.

Red-bellied piranha

A red-bellied piranha. Image taken at the California Academy of Sciences.

Of all of the fish in the Amazon, the piranhas are probably the ones with the most recognized name. Everybody has heard of piranhas. But what have they heard? What were your first impressions of piranha? Do you think they were accurate? Were they something like this:


Yes, that is a real movie (having been New World Picture’s most profitable movie, there is actually a part 2, Piranha 2: The Spawning. Not joking) .

So, this is the part where I tell you that piranhas are just misunderstood and they really aren’t dangerous and they are really beneficial and we should all love our piranha, right?

Well…not quite.

But I will talk about some of the things that science has discovered about them and some of the things that are myth, or at least lack authenticated records.

There are over 20 species of piranha each with a unique way of making a living. They are generally small animals, but there are at least 3 that are comparatively larger and could potentially kill or hurt a large animal or person. These are the black piranhas, the red-bellied piranhas and the pirayas. The largest of these are the pirayas. They can grow to be at least 20 inches long or more as adults. The black piranha’s bite is strong enough to remove a person’s finger or toe (more on this later). The red-bellied piranhas live mostly in lakes and are one of the most colorful piranhas. They have a bright red stomach and throat that becomes lighter as the fish gets older. In Brazil however, their bellies are yellow.

Red-bellied piranha

See the shiny red scales, belly and lower fins of a red-bellied piranha. Image taken at the California Academy of Sciences.

So, those are the 3 that are considered the most dangerous. However, to give this a little perspective, there are no verified, recorded human deaths from piranha attacks. Zero. So, why the reputation as people eaters? If you still doubt this reputation, from 1978 I give you:


So awesome. Anyway, there is probably a lot of reasons for the people eating fears. One of them is definitely the razor sharp jagged teeth that they have. They have triangular shaped, serrated teeth from birth. The lower part of their jaw juts out farther than the upper part of their jaw, so when they open their mouth, the teeth on their lower jaw point out. Their upper and lower teeth fit together like a puzzle, interlocking so no area is left unscathed from a piranha bite. And they are really sharp. They can bite through thin steel fishing hooks and fishing nets, and if they are flopping around on a boat with fishers who aren’t being careful, some can bite through a toe or a finger. (Despite this, they are heavily fished and eaten in the Amazon.) People in the Amazon sometimes use piranha jaws as cutting tools.

To make sure these weapons stay in tact, piranha species are known to shed and replace their teeth after a relatively short time compared to the functional life of the teeth. And to make sure that they can always eat, they replace their teeth on one side of their jaw at a time.

They use these sharp teeth to take small bites out of their prey’s bodies. They don’t chew, but swallow their food whole. Tiny but strong jaws mean that they literally nibble their prey to death. They will often take bites out of living animals, eating fins, tails and toes off of them while they swim. They will even bite off pieces of other piranhas’ fins. But, another interesting thing about them is that they’ll grow their fins back! Cichlids have actually developed a behavior that is specifically anti-piranha because of this. They will form a circle, with their tails pointing inward, so the piranha can’t easily bite their tails off.

There’s a few other reasons they might be cast as people eaters. What? Still not convinced they are unfairly cast in this role? Well then, from 2010 I give you:


Keep in mind, this is classified as sci-fi, horror and action, not humor. And that is at least 4 Piranhas-are-coming-to-kill you movies that I have found, and they are actually getting worse as they go.

Alright, so reason number 2 that they are considered people eaters is that…they…sort of…are. But not living people. Piranhas actually have a wide variety of feeding habits. In general, they are really not that picky. They’ll eat meat, fruits, nuts, seeds and sometimes plants that grow in the water. Young will eat insects. And while they will hunt (predominantly fish), they are also very likely to try to scavenge. A few researchers believe that people who have died in the water are scavenged upon by the fish, and when they are found, people attribute the cause of death to the piranhas. And the corpses that have been found can definitely be cause for fear or at least extreme respect. When researchers went to investigate, they found 3 cases to follow and they were all pretty gruesome. All of them had post-mortems where the people were found to have other causes of death (2 drowning, 1 heart attack) but were scavenged upon by the piranha. This is thought to fuel the piranha-as-man-eater image.

They are really efficient scavengers. One of the reasons why is that they have 4 nostrils and an amazing sense of smell. They can actually smell the blood of an injured animal (or human corpse) and are attracted to it. However, they’ll also scavenge for left over plant remains, such as leaves and seeds that other animals have left behind. This is an important job for the rain forest, as they will keep the rivers and lakes clean by eating dead animals and they will spread the seeds that they eat to new areas.

If reasons 1 and 2 weren’t terrifying enough, these fish scare humans one other way-they are often found traveling in schools, sometimes with over 100 fish swimming side by side. (They will not get too close to one another and they don’t like fish swimming directly behind them, probably because of the aforementioned fin and tail biting. If a fish gets too close, the offended fish might chase it or wag its body from side to side to tell it to get lost.) One piranha with pointy sharp teeth is scary enough, but over 100 piranhas with pointy sharp teeth is bone chilling.

So, a little bit about piranhas’ schooling behavior. First of all, not all piranhas are always in a school. Sometimes solitary piranhas do fine on their own and in fact make a handsome living as ambush predators as opposed to “pack hunters.” They will sometimes hunt together in their schools, using techniques such as having one piranha scatter a group of fish and then each piranha in the school can grab one for themselves. However, it is likely that they also school for protection. These animals are eaten by birds, people, snakes and crocodiles, so they have their own lives to worry about as well. (In fact, they also have a special type of scales called scutes along their belly, which when looked at closely form a saw-edge, which acts as extra armor against all of their potential predators.)

Another thing about their schooling behavior is that their school size is inversely proportional to the amount of water available. During droughts, when water levels drop, these fish “school” or gather in much larger groups wherever they can to survive. It is during this time that they have the hardest time getting food as well, and in this time when they are considered the most dangerous.

Sea Dragons

Leafy sea dragon

A close up view of a leafy sea dragon. Image taken at the Monterey Bay Aquarium.

Sea dragons are these beautiful and bizarre fish that live off of the coast of Australia and are closely related to seahorses. There are two types of sea dragons-leafy sea dragons (shown above) and weedy sea dragons (shown below).

Weedy sea dragon

A weedy sea dragon floats by. Image taken at the Monterey Bay Aquarium.

As you can see, the leafy and weedy sea dragons have camouflage to match seaweed. I like to think of them as the vertebrate versions of  stick insects in the ocean. Just like stick insects matching the movement of branches in the wind, sea dragons will gently float in the water in a manner that matches the movement of the swaying seaweed.  The long leaf-looking branches coming off of their bodies are actually skin growths.

It’s a good thing their camouflage is so effective; these fish rely heavily on their ability to hide for protection. Sea dragons and their relatives, seahorses and pipefish, are incredibly slow swimmers. They are some of the slowest fish in the ocean. Some seahorses would take more than an hour just to swim across a swimming pool.

There’s a couple of reasons why the animals in this family are such slow swimmers. As you can see, it’s tail is not one that will help much when its trying to swim. No, instead of using their tails to push them along like most other fish, these animals have a so-thin-its-see-through fin on their back that ripples and moves them along slowly. In the picture below, you can actually see the rays of this fin.

Leafy Sea Dragon

A full view of a leafy sea dragon. Note the nearly invisible fins. Image taken at the Monterey Bay Aquarium.

But that’s not the only reason they’re so slow. Unlike other fish, sea dragons don’t have scales. Instead they have an armor-like skeleton made of plates and rings, covered in skin. This armor, while tough, bony and often unappealing to potential predators, is not very flexible.  So, getting away is no easy task for the sea dragons. While they do have a few spines they can protect themselves with, they’re better off just not being seen in the first place, and they are very good at that.

leafy sea dragon

A leafy sea dragon. Image taken at the Monterey Bay Aquarium.

I suppose aside from their camouflage, the one thing sea dragons and relatives are most known for is how they produce young sea dragons. That is, in this family, it’s the males that get pregnant and carry the eggs. For sea dragons, the females will stick tiny pink eggs along the underside of the male’s tail (an area called the brood patch). He fertilizes them and then a cup forms around each of the eggs, through which oxygen is transmitted. By doing this, the males ensure paternity, thus eliminated a common problem for males in the animal kingdom. (I suppose it’s better than the stick insect’s way of just riding on top of the females for hours at a time.) Multiple females will attach their eggs to a male until his brood patch is completely full. When these eggs hatch, the young come out tail first and are just miniature versions of the adult.

I have been using images of the same leafy sea dragon, so I wanted to include at least one other, so you can see the variation. Individual sea dragons can change color as well. Here’s another one below:

leafy sea dragons

A different leafy sea dragon. Image taken at the Monterey Bay Aquarium.

The patterns on their face are actually unique to each animal, so researchers and aquarists can use these markings to identify individuals. So look closely at this face. You’ll never see another one like it.

Magnificent Large Finned

Canary Rockfish

A Canary Rockfish. Image taken at the California Academy of Sciences.

This pretty fish is called a canary rockfish (or Sebastes pinniger, literally translated to magnificent large finned, hence the title). All along its back, those fin spines are actually venomous, although not as venomous as some of its relatives. Its a great defense, but its first defense is, well, to be a rock. It sits really still along rocky bottoms, on kelp leaves or along piers and man made structures. Since predators eyes are attracted to motion, sitting still really helps keep them from being noticed. But, failing that, venomous spines. Win! I suppose its major defense against humans is that it is really high in mercury and PCB’s, poisons that in excess can cause anything from numbness, memory loss and irritability to circulatory failure and permanent damage to the kidneys and the brain. And that’s in adults. Children or developing fetuses have even more health risks to worry about. Mercury accumulates in fish that live for a very long time, or are top predators because they accumulate mercury from all of the fish that they eat.  San Francisco Bay is particularly bad for mercury contamination in fish as well, because the gold miners used to use mercury to separate the gold from the rock and all of that mercury has come down the river into our estuary.

Despite containing human poison in its flesh, this animal is listed as threatened and protected under the ESA because of overfishing. Rockfish live for a very long time. From the many species of rockfish, scientists have estimated life spans from between 100 and 200 years! (This species lives to be around 75 years old) Like most animals that live a long time, these animals are late to mature and reproduce, so often they are fished before they ever have young. Which, by the way, are born alive, in a larval form, and not from eggs released into the water column. The females of this species actually have a lot more eggs than the other rockfish and can have up to 1.9 million eggs inside of them at a time. Coo-ool. Of course, many of the larva don’t survive, assuming the female even lives to reproduce.

So, if eating poisonous, threatened, protected fish doesn’t appeal to you, then you want to look out for Rock cod, Pacific snapper, red snapper and Pacific Ocean perch, all of which are just different market names for rockfish. (There aren’t even any snapper on the U.S. west coast.) And once again, kudos to Safeway for taking red snapper out of their stores.

Canary rockfish

Look me in the eye when I'm talking to you! And please don't eat me. Canary rockfish image taken at the California Academy of Sciences.

You Can’t See Me, I’m Hiding

bay pipefish

A bay pipefish hidden in a bed of eel grass. Image taken at Aquarium of the Bay.

Pipefish are hardly visible when they’re hanging out in a bed of eel grass. They will even sway gently with the current like the blades of their home to complete the camouflage. If you think they look similar to sea horses, that’s because they are closely related. They have that same face shape and slurp up their food like a vacuum cleaner, since they have no teeth, just like sea horses and sea dragons.

And just like sea horses, in pipefish it is the males that carry the eggs and give birth. The females deposit the eggs on the male. In different species of this family, the males will either carry them in a pouch or just have the eggs stuck to them. In the bay pipefish, the females lay the eggs between flaps on the males abdomen and a protect layer of tissue covers them. When the eggs hatch, little miniature versions of these adorable fish pop out. Here is a MUST SEE video of a pipefish giving birth.

Upside-down Catfish

Upside down catfish

An upside-down catfish swimming along belly up. Image taken at the California Academy of Sciences.

These fish will often be found relaxing and swimming with their belly’s upward and their dorsal fin pointing downward. And so the question of the day is… Why? Well one thought has to do with the food that these fish eat, such as algae off of floating logs and under leaves and branches and insects floating along the surface of the water. Rather than flipping over every time they are getting a meal, they eventually evolved to just stay upside-down.

upside-down catfish

An upside-down catfish using a leaf to anchor itself and rest. Image taken at the California Academy of Sciences.

False Clownfish: AKA the Nemo fish

Clownfish in anemone

False clownfish in anemone. Image taken at the California Academy of Sciences.

I’m a big fan of the movie Finding Nemo, so the first fish on my blog is Nemo, AKA the false clownfish.  In the picture above, Nemo is carefully tending to his home anemone. In general, false clownfish live in groups with one dominant female, which is the largest fish, a dominant male (the second largest) and then a few male underlings. Just like in the movie, they seldom stray far from the protective arms of the anemone, which is also where they lay their eggs. They will care for their eggs by fanning and guarding them. There’s a lot more to the relationship between Nemo and the anemone, but I will discuss that in depth in a later post.

So the movie certainly got some things right about the life of an anemonefish. However, it did miss one important part of their life history. (Yes, I know it’s a cartoon. What’s your point?) Anyway, in the movie, you might recall that Nemo has a dad but he doesn’t have a mom. But in real life, this would never happen because Nemo, like all false clownfish, is a sex-changing fish. So in real life, if Nemo’s mom died, then Nemo’s dad would turn into Nemo’s mom.  Maybe they’ll make a part 2 and Marlin will be Marla! Yeah, okay, probably not, but my inner nerd loves the thought of scientifically accurate cartoons.

BTW, one thing that’s seriously hurting Nemo’s home in the coral reef right now is that a lot of people like to have brightly colored tropical fish for their home aquariums, and divers don’t always use environmentally friendly ways of getting these fish.  They use dynamite and poisons, for example, to stun the fish to collect them. So, if you’re considering a Nemo for your home aquarium, you can help by asking if your Nemo was raised in captivity and avoiding Nemos that came from the wild.