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

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