How do Angelfish Sense their World? A Presentation for The Angelfish Society March 16, 2008 Meeting By Tamar Stephens

Have you ever wondered…? If you live in the water, is it better to be warm blooded or cold blooded? Do angelfish have ears? What is the lateral line? Do angelfish see color? Do angelfish have noses? This presentation will give you an overview of how angelfish sense the world around them.

If you feel cold… If you feel cold, your body responds by producing more heat to keep the body temperature at a fairly constant temperature right around 98.6°F. If you regulate your temperature internally, you are what we call an “endotherm” – or warm-blooded.

If an angelfish feels cold… If an angelfish feels colder surroundings, its body does not generate heat to keep it warm. Instead its body temperature will drop to the surrounding temperature. Angelfish are “ectotherms.” (Huh? What’s an ectotherm?) If the body temperature is regulated by the surrounding environment a creature is an “ectotherm” – more familiarly called cold blooded..

It doesn’t take much energy to heat air! Your body stays very close to 98.6°F regardless of the surrounding temperature. If you stand in 70°F air, it doesn’t take much to heat the air that is close to your body. With a light jacket to capture a thin layer of air, you can be comfortable in a wide range of temperatures. A polar bear’s coat allows it to maintain its body heat in temperatures down to -50°F and colder!

Is it better to be warm blooded or cold blooded if you live in the water? It takes a lot more energy to heat water than air. If you jump into cold water, you lose body heat very rapidly. Most creatures that live in the water have their body temperature regulated by the surrounding water. It takes tremendous energy to generate the heat to warm up the water or to maintain a body temperature higher than the surrounding water! So except for large marine mammals and a few types of large fish, water-dwelling animals are adapted to adjust to their environment’s temperature. One consequence is that most fish live in a fairly small temperature range. Angelfish generally do best between about 75 to 85 degrees F, and they don’t do well with sudden temperature changes!

Do angelfish have ears?

Well, yes they do! You won’t see their ears, because angelfish do not have external ears. Their ears are internal! Sound travels very well through water – much better than through air. Sound vibrations in the water will transmit through the fish’s body to the ear.

Ear structure The upper section of the ear (called the pars superior) has three semicircular canals that give fish its sense of balance. The canals are filled with fluid and have sensory hairs that are stimulated by rotational motion of the fluid. The lower section (called the utriculus) senses sound. Vibrations of the utriculus stimulate surrounding hair cells to vibrate, a lot like our ears.

Fish ear structure Pars superior – sense of balance. Utriculus – sense of sound Figure is a diagram of a gourami inner ear. Source: http://www.life.umd.edu/biology/popperlab/background/index.htm

What is the lateral line?

Have you ever noticed a curved row of dots on your angelfish? Yellow arrow points to the lateral line. (Photo is of a black crossover female, courtesy of Gil Repetto)

Here’s another example Lateral Line (Wild angelfish photo from Bob Barone)

And one more Lateral line (Photo from phenotype library. Sorry, name of contributor not known.)

The lateral line is sort of a cross between hearing and feeling. The lateral line consists of a series of fluid-filled ducts that sense pressure or vibrations. As the ducts are stimulated in sequence, the angelfish can sense the direction of the stimulus. This allows it to sense the motion of another fish and the direction from which it is coming.

Do angelfish see color? Photo of leopard male from Gil Repetto

Vision in fish Sorry, I don’t have information specific to angelfish. So this is general information about fish vision. Fish in general have a good sense of vision, on a par with human vision. Many fish can see color. A fish’s eyes are different from ours. We have a convex lens. A fish’s lens is spherical. The spherical shape has a higher refractive index, which enables them to see better under water. They focus by moving the lens in and out, instead of changing its shape like we do. But do angelfish see color?

Anecdotal evidence that angelfish see color I read on a forum some time ago someone describing letting her fish select which kind of food they wanted. She would hold up the different containers, each a different color, and the angelfish would gather by the food container that they selected. I have observed my fish act startled if they see me appear in new clothing in a color they aren’t accustomed to seeing me in. So, based on these anecdotal bits of information, I think angelfish do see color. (Maybe in a future presentation we can look at how researchers investigate the ability of fish to distinguish colors – and you can do a study on color vision in angelfish!)

Do Angelfish have noses? Fish in general have a a well-developed sense of smell. They don’t have noses, but they do have two nostrils - “olfactory rosettes” - one on each side of the head. They are not connected to the throat as in humans. They are not obvious in angelfish to the casual observer. (Sorry, no photos. You would need a good close up photo to see the nostrils.)

Do they have a sense of taste? Yes! Fish have taste buds on their lips, tongue and mouth.

“Feeler” Fins Every now and then someone new to angelfish will ask a question on a forum about the “feeler” fins. Of course, those of us who are more experienced know these are more properly called “ventral” fins, or ventrals for short. But there is a nugget of truth to in referring to them as “feeler” fins.

Ventral fins allow the angelfish to “feel” things below them. Angelfish can feel the contours of the bottom of their environment (pond, river, aquarium) as the tips of the ventrals brush against sediments, rocks, or vegetation. This can be very useful in the dark. Photo from phenotype library. Contributor not known.

The End I hope you enjoyed this presentation! Now back to the meeting chat room for discussion!