Burt and Tyrone have Different Smelly Brains!

Now that you know we also use pee and olfactory signals to communicate with each other, I want to tell you about another experiment designed to test how the neurons in our brain work to understand these smells.  The scientists put these little needles called electrodes in specific regions of our brain, and then pass water that contains different types of smells (or odors) over our noses to see how our brain responds.  When the neuron they’re recording from gets important information from our olfactory epithelium, it fires what’s called an ‘action potential’ (this is caused by ions like sodium and potassium crossing the cell membrane through channels). The researchers can then compare this firing activity after application of these different smells to determine which ones might be most important to us!

In the first experiments, they’re doing these recordings in us males.  Right now, I’m a dominant male, meaning that I successfully defend my territory, mate with the ladies, and sport this flashy bright coloration. But I wasn’t always dominant, and in fact, most of the other males in my home town, like Tyrone, are subordinate – they don’t have a territory or mate, look pretty faded, and get chased around a lot by dominant guys like me.  Not only do we behave and look differently, but there are also lots of physiological differences between me and Tyrone.  So, the scientists are asking whether the olfactory-sensitive neurons in our brains process smells differently when we’re dominant versus when we’re subordinate.  Some of the smells they’re testing are amino acids (found in food) and steroids (found in urine). But they’re also testing more complex mixtures of chemicals that might actually be released from us fish.  To get these fishy smell solutions, they place either a few ladies that are ready to mate, or a dominant male into some water and let them hang out for a while. Then they collect that water, which contains all of the smells released through the skin, gills, or through peeing!, and put them on our noses while they record from the brain.

Neuron action potential traces in Burt and Tyrone responding to water from females, males, and steroid hormone

What they found out is really cool! – it looks like us dominant males respond really well to lots of different smell types, but especially to the steroids and that water that held the females! When we’re dominant, our brains are more responsive to smells released from females, allowing us to better detect them and stimulate our courtship and mating dances. The subordinate males on the other hand are less responsive overall, but they did show more neurons that were responsive to the odors released from other males. This may help males like Tyrone to better distinguish the dominance status of the other males in the area.  Since Tyrone and the other subordinates are always looking for a chance to get a territory home and become dominant, this olfactory ability may help them better gauge which males are wimpy and which are macho. This is pretty cool and useful because it tells them which males to avoid (so they don’t get beat up) and which they should challenge with a higher probability of winning and getting a territory!

So, my brain and Tyrone’s brain are pretty different, but each one is perfectly-suited to perform all of the tasks we need to do when we’re dominant or subordinate.  This research is important because these types of brain differences may also exist in lots of other animals that also have dominance hierarchies, from bugs to even people!


Here’s the research article that explains the study details and results:

Nikonov, A. and K.P. Maruska. 2019. Male dominance status regulates odor-evoked processing in the forebrain of a cichlid fish. Scientific Reports 9:5083. Link

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I’ve got sickness on my mind…


Hey guys! It’s Burt again back with more fun science for you to explore. Last time I told you a little about smell and how it helps me communicate with Toni and other fish in my environment. We saw how the delivery and reception of chemical odorants dissolved in the water are important in mediating social interactions. Just as it’s important for me to communicate with Toni and other fish, it’s also important that systems throughout my body are able to communicate between each other, particularly the immune and nervous systems.

Just like you, my brain allows me to take in information from my environment, process it, and produce an appropriate response. Although this process takes a lot of energy, I’m able to do this fairly well, which is great because I need to perform a variety of behaviors like finding food, dancing for the ladies, defending my territory, and protecting myself from predators. But recently, I’ve been more concerned with how well I’ll be able to perform these basic functions in the future.


You see, some environmental changes like pollution and climate change, can negatively impact my normal physiology. This includes sustaining the factors that help me maintain homeostasis (keeping a constant & stable body environment) so that I can properly evaluate my surroundings and perform those behaviors I mentioned before. My immune system helps to keep me from getting sick in these changing times, but I worry that this stressful lifestyle may also have negative effects on my brain and body!


Because I’m a dominant macho male, hormones like testosterone circulate throughout my body, allowing me to properly perform crucial behaviors. Smaller, less dominant males have much lower levels of testosterone. So that this makes a little more sense, let me introduce you to my not so good friend, Tyrone. Tyrone is far less colorful than I, much smaller, and not nearly as attractive! I’m able to protect my territory from other males like Tyrone that might try to steal it, but whenever I leave to forage or find mates, Toni tells me that he quickly takes advantage of the opportunity by adapting my phenotype (i.e. bright coloration), but as soon as I return he becomes subordinate again. Pretty deceptive trick, Tyrone!

How might physiological differences between myself and Tyrone mediate different immune responses? I talked to Teisha, another graduate student in the Maruska Lab, about my concerns and she says she is on the move to investigate the interactions between the nervous system and mounting an immune response! She believes that addressing these types of questions would also be helpful in understanding immune interactions in other species, even humans! Fish and humans actually have many similarities in our immune responses, one being inflammation which is common in many diseases impacting humans today like Alzheimer’s, arthritis and even diabetes. I feel better already!

So, stay tuned for more information and if you’re interested in reading more about differences between Tyrone and I, check out these papers from the Maruska lab:

Maruska, K.P.and R.D. Fernald. 2018. Astatotilapia burtoni: A model system for analyzing the neurobiology of behavior. ACS Chemical Neuroscience. 9: 1951-1962. link

Maruska, K.P. 2015. Social transitions cause rapid behavioral and neuroendocrine changes. Integr Comp Biol. 55: 294-306. link

Maruska, K.P.  2014. Social regulation of reproduction in male cichlid fishes. Gen Comp Endocrinol207: 2-12. link

Maruska, K.P. and R.D. Fernald. 2014. Social regulation of gene expression in the African cichlid fish, Astatotilapia burtoni. pp. 52-78. Oxford Handbook of Molecular Psychology (Canli, T., ed). Oxford University Press. link



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OOOooh that smell! Can’t you smell that smell!?

olfactory epitheliumHello everyone! Today I want to tell you about how I smell my world! You see fish live in water (duh!), which means we constantly smell all of the dissolved odorants that are in the water around us while we swim around. In fact, we use smell for almost everything! I use it for finding food, avoiding becoming food (predator avoidance), navigating, and even finding mates or avoiding other males that may want to fight. Fishes have a sensitive “nose” comprised of an olfactory epithelium full of olfactory receptor neurons (ORNs) that detect all kinds of different smells. Each type of neuron detects a certain “type” of smell. For example, ones called ‘crypt neurons’ detect pheromones (which help me find my special friend Toni! ;)). Each of these different types of ORNs sends signals to a specific region in my olfactory bulb at the very front of my brain. You see, my olfactory bulb is a sorting center for all of these different kinds of smells. From there, the signals go on to other parts of my brain that help me decide how to behave. Should I try to eat this smell, should I do a pretty dance for this smell, or should I swim away from this smell??

PeeingNot only can I detect a whole lot of specific smells, but I also send a lot of smells! Especially to Toni, hehe. And Toni sends smells to me, too. You see one way that I communicate with Toni (and other male fish) is through my pee. That’s right! We all pee at each other! Our pee contains lots of molecules that have information on our species, sex, social status, and even reproductive state. So when I see that Toni is ready to spawn, I’ll pee at her more to let her know I am a big strong male with good qualities to pass on to our kids. And Toni pees at me to let me know that she’s ready to spawn. But my pee isn’t just for Toni. If another male wants to try to take over my territory (good luck, buddy!), we will pee at each other to show just how big and strong we are. This helps us assess one another and determine if it’s worth fighting. And Toni pees to other females, too! If she and another female start fighting, she will release pee towards her to show her strength.

So, as you might have gathered, smell is SUPER important for me. In fact, if I can only see Toni, and not smell her, I’m much less likely to dance for her, making her less likely to spawn with me. I need to smell her to be sure she’s ready for my dancing. This whole smelling each other thing is super handy in Lake Tanganyika too. Sometimes hippos or other giant wildlife can walk right through our homes, making things very murky and harder for me to see Toni or other males or even food. So having an excellent sense of smell really helps me out.

I hope you enjoyed learning about my awesome sense of smell and how I pee to communicate! If you want to know more, check out these papers on the lab website:

Field, K.E. and K.P. Maruska. (2017). Context-dependent chemosensory signaling, aggression, and neural activation patterns in reproductively-receptive female African cichlids. J Exp Biol. 220: 4689-4702. link

Nikonov, A.N., Butler, J.M., Field, K.E., Caprio, J., and K.P. Maruska. (2017). Reproductive and metabolic state differences in olfactory responses to amino acids in a mouth brooding African cichlid fish. J Exp Biol. 220: 2980-2992. link

Maruska, K.P. and R.D. Fernald. (2012). Contextual chemosensory urine signaling in an African cichlid fish. J Exp Biol 215: 68-74. link

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Looking on the bright side of a long snowy winter

Greetings from Minnesota! That’s right, Toni and I took a trip to the tundra! Why? Well we’re visiting some friends up here in Dr. Allen Mensinger’s lab at the University of Minnesota at Duluth. They’re helping Julie check our vision using this technique called electroretinograms (but more on that in a minute!).

If you haven’t already noticed, I’m pretty awesome and brightly colored. And I do this little dance for Toni when I’m trying to get her to spawn with me. Like a lot of animals, we primarily use visual signals during reproduction. When I’m ready to mate, orvisualsignals.png around Toni when she’s ready to mate, I produce A LOT more of these visual signals (check out some of them in this picture!). But what my humans are interested in testing is if Toni’s ability to detect my dance and colors changes with her reproductive state. We already know she can probably hear me better when she’s ready to mate (read about that here), but maybe she can see me better too!! How cool would that be?!?!

They’ve done a whole bunch of things to look at this, but the electroretinograms are the final step! We got shipped up here about a week before Julie so that we could acclimate to our new temporary home. And boy is it different! It’s all white outside. I overheard Julie talking excitedly about this thing called “snow”. Apparently, it’s really cold and wet and doesn’t really exist in south Louisiana. We African cichlids don’t know anything about cold. Or snow. Luckily they gave us some heaters so we can stay nice and toasty while the humans freeze.

But anyways, back to the science. So once Julie got here, we got to work! The first step was to make electrodes. They took these teeny tiny wires and soldered them to little metal rods. Once they have the electrodes, they’re ready to start! We get put in this dark room, and the electrodes get inserted into our retina. Then they let is sit in the dark for a long time so we become fully “dark-adapted”. You know how when you go outside to look at the stars it can take a while before your eyes adjust and you can see them? Adjusting to the dark can take a while. So we had to sit there in the dark for at least 30 minutes, but sometimes longer! After that, they flash our eyes with lights of differentquiver.png colors! The electrodes record the response of our retina to each of the wavelengths of light that they’re testing. So they’re comparing the responses of Toni and her friends at different reproductive states. I’m excited to hear about what they find!

We’re heading back to good ole Louisiana soon. While Dr. Mensinger and his lab are great, I miss my friends back in LA. Can’t wait to tell them about this magical thing called snow!

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Balancing Act

Hi everyone! It’s Toni again! Last time I talked about mouth brooding and how I carry my developing young in my mouth. As they develop and grow, they also increase in weight. This affects my buoyancy… Imagine having a weight strapped to just one side of your body! You’d probably walk a little crooked. Luckily, I have a way to fix this so my kids don’t bring me down (literally, and face-first)!

The humans took me on a field trip to the LSU Museum on Natural Science where they got to work with a really cool guy named Prosanta Chakrabarty (he’s an Ichthyologist, or scientist that studies fishes). Once there, they took x-ray images of me and my friends. Some of us were gravid (that means we have big eggs and are ready-to-reproduce). Others were mouth brooding, and some of my friends were in between (or recovering). When they looked at these pictures, they noticed that the swim bladder, an air-filled sac in the body, looked different depending on our reproductive state. The swim bladder helps us regulate buoyancy (or maintain position in the water column), so the humans thought it might change size or shape depending on if we were brooding or not.


After some fancy quantifications and morphometric analyses, they found out that my swim bladder does change size and shape depending on my reproductive state! My swim bladder has two compartments: the front/anterior compartment and the back/posterior compartment. There’s a small membrane separating the two compartments, and that membrane has a small hole that allows for air flow between the chambers.

When I’m holding the babies in my mouth, the front compartment of my swim bladder gets relatively bigger and more round in shape. This allows me to adjust my buoyancy so that I’m not swimming at a downward angle. It’s not easy or fun to swim with your head pointed down the whole time! As the babies grow inside my mouth, that front compartment gets bigger and bigger to compensate for their increasing weight.


Once my brood reaches full development and I release them, my buoyancy gets all messed up again. Immediately after I release the babies, I swim at an upward angle because there’s too much air in the front compartment of my swim bladder. Luckily, this air redistributes to the posterior compartment in ~5 minutes, and I’m able to regulate my buoyancy again.

If you want to know more about this, be sure to check out the article below or its feature in Inside JEB. I know you don’t need a swim bladder, but boy am I happy that I have one!

Butler, J.M., Whitlow, S.M., Gwan, A.P., Chakrabarty, P., and K.P. Maruska. 2017. Swim bladder morphology changes with female reproductive state in the mouth brooding African cichlid Astatotilapia burtoni. J Exp Biol. 220: 4463-4470. Link Here

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Extreme maternal care

Hey Y’ALL! (there’s that Louisiana vocab again!).  It’s Toni here, and in this post I want to share some more about some cool research looking at our maternal care behaviors.  Last time, I told you about how us females are mouth brooders, which means we hold our babies inside our mouths for ~2 weeks until they’re fully developed and can swim out on their own. BrooderNewDuring this time, we can’t really eat, so we’re pretty much starving and lose lots of weight, all to keep our babies happy and healthy! – this is extreme maternal care at its best!  Since we’re pretty hungry, we swim up to the food dropped in our tanks but stop ourselves before eating it when we remember those little guys already in our mouths.  As the babies get bigger, they get heavier too and to keep ourselves from doing a nosedive to the bottom, some adjustments are made in our swim bladders to keep us swimming straight (but that’s a story for another time!).  Anyway, once the babies are grown, we open our mouths and they swim out into the world –so proud!  While they explore their new surroundings, we watch over them for a couple of days, and let them swim back into our mouths if there’s danger like a big bully or predator around. After that, our parental duties are over and they’re on their own!; our new focus is now to eat, eat, eat – diet over!

So here’s the dilemma: how does our brain and body control these switches in motivation between feeding and maternal care? One minute we’re eating, and the next minute after we spawn and the eggs are in our mouth, we stop feeding, cold turkey, and need to start caring for the eggs by churning them around so they grow big and strong! To examine this question, the researchers are looking at which regions of our brain are ‘turned on’ or ‘activated’ in groups of us ladies that are either brooding, or starved or fed for ~ 2 weeks; the same time as a normal brood cycle. By comparing these groups, they can discover which brain regions might be involved in metabolism and feeding, versus those regions involved in our maternal care behaviors.  By doing some staining Stainingexperiments called double-labeling (see picture), they’re also looking at exactly what kind of neurons in the brain are turned on – this gives them insights on their function!  So far, they are unveiling some very interesting differences in brain activation patterns likely due to the starvation aspect of brooding compared to the maternal care aspect; stay tuned for more specific results in the future!  Since maternal care happens in lots of different animals, the researchers are interested in understanding how similar or different the brain mechanisms that help control these parental behaviors are, between, say, a fish like me, a frog, a bird, and a mammal. We love it when the scientists use us to discover new things that can be applied to other animals!

The nice folks at the National Science Foundation gave us some support to study some of these questions related to mouth brooding and maternal care. If you think about it, this research has important relevance to many other animals, including humans!  As fish, we are vertebrates (animals with backbones), as are amphibians, reptiles, birds, and mammals, and we all have very similar brain structures. If the scientists can better understand how the brain controls the conflicting motivations of feeding and maternal care in us fish, it could lead to insights into eating and metabolic disorders even in people!

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the lateral line – my superpower

Hi there! For this post, I want to talk about dancing. That’s right folks, I perform a little dance when I’m trying to get Toni or the other ladies to hang out with me. I also do this move called a “lateral display” where I make myself look really big and shake my body at other males to threaten them. When I fight with other males, we push around a lot of water at each other. If we can’t resolve our fight with these behaviors, then we go to the more dangerous behaviors, like biting each other.

See fish have this thing called the mechanosensory lateralNeuromast line. It’s composed of these little bundles, called neuromasts, that are on my skin or inside canals beneath my skin. These neuromasts have little hair cells on them that are covered by a jelly-like mass called the cupula. When something near me moves in the water, it creates water motion that deflects the cupula over these neuromasts and opens mechanically gated ion channels on the hair cells. This information then gets sent to my brain. This water-movement information helps me orient in a current, find things to eat, avoid things trying to eat me, and even communicate with my friends (and enemies!).

My humans are interested in how I use this sensory system for social communication. To look at my lateral line system, they placed me in a container of orange stuff they called DASPEI. This dye stains the hair cells of my neuromasts and makes them glow in the dark! Here’s a picture…. Think I’ll just use this as my Halloween costume this year!


They can also make my lateral line non-functional. They place me in a beaker of chemicals, either cobalt chloride or aminoglycoside antibiotics, for a few hours. This chemically disables my neuromasts. It’s a weird feeling. I can still feel it if they touch me, but I can’t feel any of the water movements from the other fish around me. Anyways, after this treatment, they let me recover overnight. Then they let me do my thing! I either get to court Toni or defend my territory from another dude. The humans then compare my behaviors when I have an intact functioning lateral line to when they’ve ablated it.

They found that when they knock out my lateral line, I have a hard time assessing the other male. Sure, I can see how big he is, but when we’re closely size-matched, that water movement information also helps me. Because we can’t feel the water we’re trying to push at each other without this functioning lateral line, we also escalate our fights a lot quicker. Man, that’s tiring! I’m happy I normally have use of my lateral line so I don’t have to do that all the time… They even looked in my brain to see where this information is processed!

Now my humans are trying to determine how we use our lateral line during reproduction. As I said, I perform a little dance called a “quiver” when courting Toni. My humans think that Toni uses the water information produced by this dance to help decide which male she wants (obviously I’m the only correct choice!). So they’re knocking out her lateral line system and seeing what it does to her receptiveness to me. I really hope my dancing still impresses her… Check back later to hear from Toni and how this impacts her!

Want to know more about the lateral line? Check out these papers from the Maruska lab:

  • Butler, J.M. and K.P. Maruska. 2016. Mechanosensory signaling as a potential mode of communication during social interactions in fishes. Invited Commentary, J Exp Biol 219: 2781-2789. link
  • Butler, J.M. and K.P. Maruska. 2016. The mechanosensory lateral line system mediates activation of socially-relevant brain regions during territorial interactions. Front Behav Neurosci 10:93. link
  • Butler, J.M. and K.P. Maruska. 2015. The mechanosensory lateral line is used to assess opponents and mediate aggressive behaviors during territorial interactions in an African cichlid fish. J Exp Biol. 218: 3284-3294. link
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Geaux girl fish power!

Hello everyone! I’m Burt’s friend Toni and I want to tell you a little more about us females – Geaux girl fish power! (a bit of Louisiana is creeping into my vocabulary!). While Burt and his other male territorial buddies are really colorful, us ladies are less flashy and we often hang out with the subordinate males (those without a territory). Burt and his macho friends often chase us around, and when the time is right, they also do all kinds of other crazy things in front of us! When our eggs grow large in our ovaries, our bellies get swollen, we have an urge to get rid of them, and we release some chemicals into the water that makes the males do awesome courtship dances. They get really bright GravidFemalecolors, quiver their bodies, and make grunt-like sounds in front of us, and then they turn around and wag their tails as they swim towards their territory shelter – they really want us to follow them! When one of us girls agrees to follow him, we go into his territory and lay some of our large yellow yolky eggs on the bottom of the lake (or the tank if we’re in the lab) and then we turn around and pick up the eggs in our mouth! The male then shows off his anal fin and shakes his body on the substrate. Since his anal fin has these big yellowy spots on them that look an awful lot like some of my eggs (see pictures of Burt’s fins in his previous posts), I swim down and start nipping at them. Then he does another crazy thing – he releases some sperm so that they can fertilize the real eggs already sitting in my mouth! Not all fishes reproduce this way, but many of our cichlid relatives in Africa certainly do, and it helps to ensure that our little guys survive.

BrooderNewWe do all of this because we are mouth brooders, meaning that we hold and care for our developing babies inside our mouths until they grow into little baby fish that can swim on their own. While the babies are growing, there’s lots of pretty amazing things that happen to our bodies!, and my human scientists are studying all sorts of cool things related to this (stay tuned for future posts on these different studies). You might now be wondering “But Toni, how do you eat with all those wriggling baby fish in your mouth?!”.  Great question!, and the answer is, we don’t! It takes ~ 2 weeks for the fertilized eggs to develop into little baby fish and we don’t eat during that time so that we can just focus on taking care of the little guys – this is maternal care to the extreme! Once they’re ready to make it on their own, we just open our mouths and let them swim out. But we do keep a sharp eye on them for a few days while they get used to life in the real world by letting them swim back into our mouths whenever something scary happens (like a big predator swims nearby looking for a snack) – this is no easy feat, since there can be up toBrooder ~50 babies that need to squeeze in there. After a few days though, they’re on their own!

Well, that’s a brief intro into the fish ladies – check back soon for more detailed stories about how the scientists are studying different aspects of our behavior and physiology!

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Hormones, brain, and behavior – A review of SBN 2017!

Hi there! I just got back from sunny California where I attended the Society for Behavioral Neuroendocrinology (SBN) meeting! There was a lot of great research and I had a great time. I was especially excited to learn about some of the research being presented about me and my family. Check out a quick synopsis about the cichlid research that was presented at SBN 2017.



Reproduction is really important. Neurons in my brain make sure that my reproductive system stays in tip-top shape. There’s this gene called tachykinin3 that helps regulate reproduction in mammals (like dogs, cats, and even humans!), but we don’t really know what it does in fish. Julie found that these neurons are located throughout my brain, not just in the one place that’s been so well studied in mammals. She also found that dominant males, like me, have more of these cells than subordinate guys. And she found that different groups of these cells are activated during different social behaviors. So when I chase off a subordinate, I use different sets of neurons than when I’m courting a female.


GravidFemaleYou could say I’m the cool kid on the block. Scientists love to study me and my reproductive behaviors, but they kinda ignore Toni and female reproductive behavior. I guess Scott felt bad for her, so he started looking at the neuroendocrine control of female spawning behavior. He found that there’s this hormone, called prostaglandinF2a, that acts in the brain to induce spawning behaviors. Using this cool technique called CRISPR/cas9 that basically acts like tiny molecular scissors, he got rid of the PGF2a receptor in our brains. When he did that, it didn’t matter how much I tried to get Toni to spawn with me, she never did. It was depressing. Check out Scott’s paper here if you want to know more.


Things that happen to us when we’re little can causes changes in our adult behavior and physiology. Tessa is one of the few people to study our kids – most people only study adults, like Toni and me. She found that the little guys don’t establish typical social structures. So they don’t hold territories like I do. By putting baby fish into different environments – raising them in either pairs or large groups of other fish – she found impacts on their adult behaviors. Now she’s looking at their brains and hormones to see what may be causing those behavior changes.


As you know, I’m really territorial. When I first got my home, I “ascended” in social rank (check out this paper for more on social ascent). Beau wanted to know how hormones called androgens, like testosterone, are used for behaviors during this ascent. He injected us with a compound that blocks these hormones from binding to their receptors. When he did this, I didn’t court Toni anymore, but I had no problems defending my territory from other dudes. So these hormones are needed for courtship but not aggressive behaviors during social ascent.


Nicole presented a poster about some of my cousins: these guys are weird. They’re from another African lake called Lake Malawi, which is just south of Lake Tanganyika where I’m from. If you want to know more, check out her research and the Streelman lab. Some of these guys are from rocky areas while others are in sandy areas, and they have different levels of aggression depending on where they’re from. Nicole made them fight their reflection in a mirror (idiots!, although I’m embarrassed to say I do this too!) to look at aggression, and found that the guys from rocky areas are a lot more aggressive than those from sandy areas. She also took the brains from these guys to look at neural activation in brain regions involved in social behaviors. Her goal is to use these guys to look at how genes lead to species differences in brain and behavior.

Here’s a picture of some of the amazing cichlid scientists! Scott skipped out on the picture (I guess he’s too fancy with his real, big kid job as an assistant professor for them!).


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Can you hear me now?

Hey everyone, thanks for coming back! Today I want to tell you about acoustic communication. Not only can fish hear, but a lot of us make sounds too!SoundProduction While we don’t actually ‘talk’, like seen in the movies, we do make sounds for a variety of reasons. Different fish produce sounds using different mechanisms, but the purpose is the same: to communicate with other nearby fish. My friend Todd the Toadfish does it to advertise his location and attract females. Like him, I produce sounds when courting the ladies1. I only make the sounds when performing a little dance, called a courtship quiver, in front of a female (click here for a video of me quivering and to hear the sounds I make). They like it. Actually, females prefer males that make sounds over those that don’t. So the more sounds I make, the more likely I am to get the ladies back to my pot! My human scientists don’t know exactly how I make sounds, but one of my cousins, Niles (a tilapia fish) makes sounds by shaking his body and compressing air within his swim bladder. My sounds are probably made in a similar manner. All I know is that the ladies like the sound, so I’m going to keep doing it!

So how do fish hear? While I don’t have an external ear that you can see, like you do, I have 2 inner ears that are similar to yours in a lot of ways! My inner ear contains three calcium structures, like bones, called otoliths. They’re surrounded by thin membranes that contain a sensory rich area called a ‘macula’ used to detect sounds. This sensory InnerEarmacula is made up of lots and lots of hair cells. Each hair cell has a hair bundle that sticks up towards the otolith. Because the otolith is denser than the rest of me and the water, it moves in response to a passing sound wave more slowly. This movement bends the hair bundles and opens mechanically-sensitive ion channels. This allows my ears to send information to my brain where it is processed and perceived as sound, which tells me something about the location, type, and source of the sound. While humans can hear frequencies from ~20-20,000 Hz, I hear best at lower frequencies (< ~2,000 Hz). But some fish species can also hear high frequencies really well. These fishes often have special structures that enhance detection of sound pressure waves.

The saccule, the largest of the three otolith organs and the main hearing structure in many fishes, also has steroid receptors that bind hormones like estrogen and testosterone. Levels of these receptors differs between me and my friends, depending on who is dominant or ready to mate2, and this may influence how well I can hear. In fact, AEPour human scientists can actually measure our hearing abilities! They stick these sharp things they call electrodes on top of our heads and play different sounds to us through underwater speakers. They can change the volume on the sound until we don’t hear it anymore, which they can tell because there’s no more brain activity picked up by the electrodes. Anyways, by doing this, they found out that dominant males (like me!) and subordinate males (my friends without a territory) have different hearing capabilities. Those lowly subordinate guys can hear better than me at higher frequencies, though. The scientists explanation is that this may help them sneak into the territories of the smaller dominant males and increase their chance of mating with the females. Female hearing varies with their reproductive state too! This is important for my lady friends like Toni, because when she and her friends are looking for males and ready to spawn, they can hear better at lower frequencies (the frequencies that I communicate in) than their other friends already holding developing babies in their mouths.

Thanks for learning about how we make and hear sounds! If you want more information about my acoustic communication and hearing capabilities, check out these papers on the Maruska Lab website:

  • Maruska, K.P., Ung, U., and R.D. Fernald. 2012. The African cichlid fish Astatotilapia burtoni uses acoustic communication for reproduction: sound production, hearing, and behavioral significance. PLoS One7(5): e37612
  • Maruska, K.P. and R.D. Fernald. 2010. Steroid receptor expression in the fish inner ear varies with sex, social status, and reproductive condition. BMC Neurosci11:58.
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