Aba aba: Hunting

Summary: How does the Aba aba find its food? Join Kiersten to find out!

 

For my hearing impaired followers, a complete transcript of this podcast follows the show notes on Podbean

 

Show Notes:

“The Mechanism of Object Location in Gymnarchus niloticus and Similar Fish,” by H. W. Lissman and K. E. Machin. Journal of Experimental Biology (1958) 35 (2): 451-486.

Music written and performed by Katherine Camp

 

Transcript

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Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

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Kiersten - Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

I know I left you with a cliffhanger last week and we will remedy that now! This is week seven of Aba abas and the seventh thing I like about this super cool fish is the way they hunt. 

We know that Aba abas are carnivores and that they eat aquatic insects, small fish, and fresh water crustaceans. We also know that they have tiny eyes and relatively poor eyesight. There is not much discussion of olfactory functions in animals that live underwater, and I found no mention of the sense of smell when deep diving the Aba aba. Sooo…we can rule out Aba abas using sight or smell to help them find their prey. What does that leave them with for hunting? Let’s find out!

Something I haven’t mentioned about Gymnarchus niloticus, yet, is that they are an electric fish. This little quirk was discovered by Hans Lissman in 1950 when he received a living specimen as a wedding gift. As he watched the Aba aba swimming in the aquarium he noticed that they could swim backwards and forwards equally well. It never ran into the sides of the tank or into anything placed inside. He wondered how it was navigating so well, thus began some of the first European studies into electroreception in fish. 

Electroreception is the biological ability to detect electrical stimuli. Electrogenesis is the ability to create electrical fields. Both of these abilities are important to the Aba aba. There are two types of electrolocation. I know, there’s a lot of electric words here, bare with me. One type of electrolocation is passive. When using passive electrolocation the predator senes the electric field that the prey item creates. On the other hand, or fin shall we say, is active electrolocation. Here, the predator creates its own electric field and uses the distortions other objects create in its field to target prey or notice obstacles.

Active electrolocation is practiced by three types of fish that we currently know of including Order Gymnotiformes, the knifefishes, Family Mormyridae, the elephantfishes, and our friend Gymnarchus niloticus. All of these fish are considered weakly electrical fish because they do not use their electric fields to stun their prey. Electroreception and electrogenesis are more common in aquatic animals as water conducts electricity more easily than air. 

An electric fish creates an electric field with an electric organ modified from muscles in the tail. The tissue of these modified muscles are called electrocytes and they have evolved at least six times among various fish species. These organs are used for everything from prey detection to communication, mating, and even stunning prey items. The electric field created by this tissue can emanate in short bursts, as in the elephantfishes, or as a continuous wave, as with the knifefishes.

To detect electric fields generated by other creatures, our Aba aba, elephantfishes and knifefishes use sense organs called Ampullae of Lorenzini. They are electroreceptors that form a network of mucus-filled pores in the skin of various fishes. They evolved from the mechanosensory lateral line organs for early vertebrates. Most modern fish and mammals have lost this adaptation.

How does this work in the Aba aba? This is truly amazing! The Aba aba makes its tail negatively charged while its head will stay positively charged creating a symmetrical electric field around its body. To keep this field present its back must remain straight. That’s why it has the long dorsal fin that they use to swim. This fin structure allows it to keep its body completely straight when in motion. 

This electrical field it has created allows the Aba aba to navigate around obstacles and underwater features it cannot see. It also allows it to find nearby prey items. It can sense the distortions that these objects or prey items create in its own electric field. It can actually sense this distortion on its skin with the Ampullae of Lorenzini organs. The Aba aba’s brain is larger than other species of fish, this is true of all electric fish, so they can process the data provided by their various electroreceptive organs. 

If nothing else about the Aba aba has convinced you of their absolute awesomeness, this is it! This is one of the most amazing ways to interact with your surroundings and to hunt for prey that I have ever come across.

In my personal experience, I never felt any electrical shocks when working with my Aba aba at the zoo. They do not use their fields to stun prey, so they never send it out from their body. It is not something that humans can feel. I am not sure if other small fish can sense it either since that would make hunting with it extremely difficult. You’d never catch anything to eat if your food could tell you coming.

They do have to be cautious about other species of electric fish that use this method of hunting because if their electric fields are similar they can interfere with the Aba aba’s detection. Most fish that use this form of perception can create a jamming avoidance response. If two electric fish with very similar wave discharges meet, each fish will shift its discharge frequency to increase the difference between the two. This prevents them from jamming each others perception. My mind was just blown! Can you believe that?

This one snuck up on you didn’t it? This is probably the coolest adaptation of the Aba aba. That’s why the way Gymnarchus niloticus hunts is my seventh favorite thing about them. 

 

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Join me next week for another exciting episode about the Aba aba.  

    

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This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.