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.