WFSC 448 – Fish Ecophysiology
(Week 6 – 2 Oct 2017)
Sensory biology 2:
Objectives
· Understand unique transmission properties of sound and vibration in water.
· Understand the diversity of relevant acoustic and pressure wave sensory apparatuses in fishes.
· Know the case studies (e.g. water striders, herring, midshipmen, nurseryfish, drums, rheotaxis, complex schooling, predator-prey detection, etc.)
· Be able to construct a novel hypothesis about pressure wave use in the ecology of fishes and design a critical test of the hypothesis (including statistical analysis)
· Be able to envision a practical use or problem in fisheries biology regarding pressure wave sensitivities in fishes.
ACOUSTIC (sound) AND PRESSURE WAVE (vibration) DETECTION
Demonstration (simulated): fish have highly sensitive senses regarding slight vibrations in water: https://www.youtube.com/watch?v=Q13VQa2Q_KA
Many aspects of life such as prey or food location, predator detection, species and mating cue assessment, and communication depend on acoustic and pressure wave detection.
Stim Wilcox deciphered the pressure wave signaling system of water striders. He suspended a broad hemispheric glass tank of water by elastic cords from the ceiling, to isolate the water from building vibrations, installed a high density pipe in the center of the tank with a magnet float which sat in the meniscus. He surrounded the tank with copper wire coils and attached an electronic bridge to the wires. He could use this device to record pressure waves. How?
Physics of waves—
Energy traveling through matter is shifted when alternative densities are encountered. Reflect on this. Recall that as light passes through alternative density media (e.g. a glass wedge, or air laden with moisture). Liken this process to pressure waves passing through a fish’s body.
Most biological tissue is very similar in density to water (it is mostly water). What parts of the fish body has density vastly unlike water?
1.
2.
What is sound?
Two components: pressure and fluid motion, each of which is more or less important in sensory biology at differing distances from the sound source.
Also: Course page link (pw molec)
web link (animation of fork)
Learn to picture this phenomenon in full 2D then into 3D (forces you to exercise a different modality than normal lecture matter)… Imagine this pressure wave propagating just under the air-water interface. Keep picturing things until you see why surface waves propagate as an epiphenomenon of the pressure wave passing, all in response to the vibration.
Also imagine a raindrop on the surface of the water:
When a pressure gradient exists, molecules will rush from areas of high pressure to areas of low pressure. Thus when a pressure wave passes water moves aside when the high pressure part passes, then back when the low pressure passes. Water is temporarily displaced but put back in order as if nothing happened once the wave passes. Think of a bobber on the water’s surface as a wave passes—the bobber moves in a circle normal to the passing wave, but experiences no net movement (neglecting friction).
Since water is heavy, inertial forces dampen the fluid motion component pretty quickly. We refer to the fluid motion rich component of sound as the near-field.
Thus, near-field effects are the fluid motion components and are important relatively close to the source. Far-field effects are pressure variations and may be felt approximately 5× farther from the source than near-field effects.
In air, both near- and far-field effects are far less extensive. Why?
Acoustico-lateralis system
Fish hear with ears bones, often attached to a drum. Fish sense vibration (fluid motion) with their lateral line.
Fish ear:
The brain cannot sense pressure directly, much like Stim Wilcox could not directly record surface waves. Recall that Stim transduced pressure waves into fluid motion, and measured that motion with a magnet moving with the fluid (on a float inside a monitored magnetic field). Fish evolved a similar innovation: they evolved ways to transduce pressure waves into fluid motion. They sense fluid motion in fine canals using hair cells.
A neuromast consists of hair cells in a cupula projecting into the fluid filled canal of the lateral line. When the fluid moves due to near-field effects, the cupula is bent. Inside the cupula are sensory villi (hair cells) that when bent release an action potential, triggering nerve impulses to the brain via CN
The labyrinths are lined with hair cells and were evolutionarily coopted for positional acceleration (equilibrium) sensing.
Lateral line
Generally a dermal channel, often broken into many bits as it runs across the fishes body in varied ways; sometimes singular pores. To be dermal this means the scales must have holes and the epidermis must be pored:
(note line of holes in scales)
Here is a typical teleost with prominent lateral line:
Note the fin-avoidance positioning.
Why might this be so?
What else do you know about drums?
Here is a shark snout. Why so profligate with pores here?
Aripaima. What elements of it’s ecology can you infer from this picture?
In case you are interested, these fish are very cool: link
What ecological “public information” are fish grabbing with these lateral line systems?
Consider the three fish just pictured. Consider also herrings… (e.g. anchovies; what are the defining features of herring life?)
Course page link (animation)
Herring farts
http://news.nationalgeographic.com/news/2003/11/1110_031110_herringfarts_2.html
https://www.youtube.com/watch?feature=player_embedded&v=OcwCYIfm6eA
(critique the arguments made in the video)
Rheotaxis—see Mongomery et al. (1997) on course page
Special adaptations:
Nurseryfish—see Carpenter et al (2004) on course page
Note the unique adaptations and argument style in the paper. Reflect on how the adaptations they describe are conceptually related to hearing in minnows and drums.