Current Research
(I) Auditory sensitivity of
fish
(A) The psychoacoustic approach.
In order to know how well a fish can hear in terms of two
major physical properties of acoustic signals: frequency range
and sound pressure level, I have developed a computer-aided
automated system to measure psychophysical acoustic tuning curves
of fish. In this method, fish are trained by positive
reinforcement method, i.e., food reward to peck underwater
peddles to "inform" computer the acoustic signals
presented either are audible or beyond hearing range or below
threshold. The system also allows us to examine how well fish can
discriminate acoustical signals in terms of frequency and sound
pressure limits. A recently finished project shows that sympatric
bluegill and longear sunfish have almost identical auditory
tuning curves which may explain acoustic signals produced by
males of each species fail to serve as an ethological isolation
mechanism to prevent hybridization between these two species of
sunfish.
(B) The electrophysiological approach.
When acoustic stimuli are perceived evoked potentials
are generated along the ascending auditory neuronal pathway from
peripheral hearing organ, i,e., ear all the way up to auditory
cortex. These evoked potentials (auditory brainstem response,
ABR) can be measured by placing electrodes outside the skull of
the tested subject. This is a noninvasive recording methold and
is used to measure auditory sensitivity of fish. Our laboratory
has developed the ABR recording protocol to use on fish with the
assisatance from Professor Jeffrey Crowin of University of
Virginia. Because of its rapidity and noninvasive nature we have
been successfully using this technique to measure fish hearing
ability of more than 20 species of fish. We also demonstrated the
accessory auditory role of gas inside the suprabranchial chamber
of gouramis. The role of gasbladder in assisting underwater
hearing in fish has also been investigated with the aid of ABR
technique.
(II) Lateral line system as a
water pollution detection system
The lateral line system of fish is distributed along the
surface of fish body. Its main function is to detect vibrational
signals such as movement of conspecifics or heterospecifics. This
vibrational signals detection system is even more crucial for the
survival of fish in water bodies of high turbidity and low
visibility. Under such adverse condition, fish could use lateral
line system to engage a distance touch to detect either
approaching predators or to find preys. Because of its constant
and immediate contact with surrounding water, presence of any
pollutant in the water would have immediate impact on the
function of the lateral line system. I have been using
electrophysiological (extracellular) recording techniques to
measure compound action potentials generated by the lateral line
system of fathead minnow (Pimephales promelas) when
vibrational signals are given. After exposing experimental
subjects to cadmium chloride for 24 hours (at a concentration of
450 ug/l, no spikes could be recorded. When these cadmium-treated
fish are observed under complete darkness (with the aid of
infrared light and infrared camera), the lateral line mediated
schooling behavior is totally lost. The results showed that
electrophysiological activities of the lateral line system can be
used as a very sensitive probe for water pollution monitoring
purpose. Currently I am using immunocytochemical procedures to
examine how calcium channels of neuromasts are affected by the
exposure to cadmium ions. The finding may explain why
cadmium-affected neuromast cells fail to fire spikes when stimuli
are given.
(III) Role of visual and
mechanosensory systems on mate choice of swordtail fish
My ongoing collaborative work with Craig Sargent and Victor
Rush investigates how visual and lateral line sysem are used by
swordtail (a livebearer of Poecillidae) during mate choice. It
has been demonstrated that female swordtails could use visual cue
to favor males of longer tails. In the meantime when a male
reaches within 2-3 body lengths of female fish, lateral vibration
movement of male body can be observed. Presumably it has the
function of sending out vibrational signals to a female as an
indicator of strength of the male. In this collaborative project
we are trying to find the contribution of each sensory modality
(visual and mechanosensory) on the mate choice ability of female
swordtail. This research project is an unique sensory ecology
research which integrates techniques of sensory physiology and
evolutionary ecology.
(IV) Characteristics of sounds
produced by snapping shrimp
The snapping shrimps are known for the ability to generate
loud snapping sounds with the opening and closure of its big
chela. The function of the snapping sound is generally thought to
be used for acoustic communication. I am using Alpheus
heterochelus as study animals to investigate if sexual
dimorphism in acoustic signatures exists between each sex of the
species. Furthermore I am also instigating how growth (increase
of body size as well as chela) would affect the strength of the
signals produced. The ultimate goal of this project is to find
out how acoustic signals are used by these shrimps for
communication purpose.