Per S. Enger

Hearing in herring.

Abstract 1. 1. A neurophysiological investigation of hearing in herring (Clupea harengus) has been undertaken. Gross nervous or multi-unit activity and single unit activity have been recorded from the acoustic region of the medulla oblongata, using 5–20 μ dia. metal electrodes and micropipettes, respectively. 2. 2. Nervous responses to pure tone stimulation were obtained for sound frequencies from 30 c/s to 4000 c/s at moderate intensities (up to 35 dB above 1μBar) and up to 8000 c/s at high sound pressure levels (50–60 dB). 3. 3. Single units can be divided into two groups (a) units responding to frequencies up to 500 c/s, (b) units responding to frequencies up to 2000 c/s or higher. The response of the first group consisted of an increase in discharge rate above the “spontaneous” level. In the last group acoustic stimulation caused either an increase in discharge rate for high sound frequencies and a decrease for low frequencies, or vice versa. 4. 4. The most sensitive single units had thresholds of −20 to −25 dB at their optimal sound frequency which for different units ranged from less than 100 to 1200 c/s. The threshold increased for higher frequencies. 5. 5. A tentative audiogram is suggested. This indicates that the herring has a uniformly low threshold of −20 to −25 dB for frequencies of 30–1200 c/s, with a sharp increase in threshold to +20 dB for 3000 c/s, +35 dB for 4000 c/s.

Frequency Discrimination in Teleosts—Central or Peripheral?

Pitch discrimination in fish is well established although the number of behavioral studies concerned with the topic is fairly limited. Table 12-1 lists some species investigated and the results obtained, including the value for Cottus scorpius which will be reported here. In such studies it is important to be aware of the complicated and unpredictable acoustics of small tanks (Parvulescu 1967). For example, when changing the frequency of the sound producing equipment, great fluctuations in sound pressure and particle displacement amplitude will occur as well. Moreover, the relation between sound pressure and particle displacement is not predictable, as it would be in a large body of water, like the open sea. It is generally agreed that particle displacement is the relevant stimulus for the auditory receptor cells. For a fish with a swimbladder, sound pressure is a relevant stimulus as well, since the swimbladder is then acting as a pressure to displacement transformer. This secondary displacement will be transmitted through the surrounding tissues to the inner ear, there stimulating the sensory hair cells. In the ostariophysine species, all of which have a bony connection between the swimbladder and the inner ear, the sense of hearing is particularly good. In nonostariophysine species there seems to be a relation between threshold and hearing range on the one hand, and the anatomical configuration of the peripheral auditory system and the swimbladder on the other (Coombs and Popper 1979).

Behavioral Investigations on the Functions of the Lateral Line and Inner Ear in Predation

The lateral line, comprising the canal organs and free neuromasts, is generally regarded as a sensory system for the detection of local water currents (Hofer 1908; Dijkgraaf 1934) and surface waves (Schwartz 1965; Bleckmann et al., Chapter 25). However, whether the lateral line responds to low-frequency sound as well has long remained an issue of debate. Dijkgraaf (1963, Chapter 2) strongly argued against an acoustic function of the lateral line, citing a lack of compelling behavioral evidence. Sand (1981, 1984) explained that the operation of the lateral line in free-moving fish is physically restricted to the immediate vicinity of the source. Kalmijn (1988a, Chapter 9) subsequently focused attention on the function of the inner ear in detecting the local flow fields of moving objects at distances beyond the limited range of the lateral line. The lowfrequency nature of the two sensory systems is consistent with the results of earlier physiological studies (Suckling and Suckling 1950; Harris and van Bergeijk 1962; Enger 1966; Kalmijn 1988a).

An electrophysiological field study of hearing in fish.

Abstract 1. 1. In order to study sound reception in fish in the acoustic far-field (propagated sound waves) saccular microphonic potentials have been recorded from codfish ( Gadus morhua ) and sculpin ( Cottus scorpius ) by means of implanted electrodes. The fish was held at distances of up to 10 m from an underwater loudspeaker delivering sinusoidal sound stimuli. The experiments were performed at sea where no reflections other than those naturally occurring from surface and bottom were present. 2. 2. In codfish—which possesses a swimbladder—the microphonic potential amplitude was a function of sound pressure only for distances of 0.7 m and more (smaller distances not tested) for frequencies above 200 c/s. For 200 c/s a small effect of the acoustic near-field was observed. Responses to sound of frequencies up to 800–1000 c/s were recorded. 3. 3. In sculpin—which lacks a swimbladder—the microphonic potential amplitude was dependent on both sound pressure and distance, but was not recorded at all at distances beyond 1 m. 4. 4. It is concluded that the swimbladder in teleosts is essential for hearing in the acoustic far-field, i.e. for hearing propagated sound waves. The swimbladder will generate near-field water displacements around itself, produced by compressions and rarefactions of the propagated sound wave. This local near-field effect can stimulate auditory receptors.

Acoustic threshold in goldfish and its relation to the sound source distance

Abstract 1. 1. Acoustic threshold levels have been obtained for goldfish in classical conditioning experiments, stimulating the fish with pure tones of different frequencies (50–5000 c/s). The threshold intensity for response has been established for different distances (0·1–2·0 m) between the fish and the underwater loudspeaker. 2. 2. Sound pressure thresholds (given in decibels re 1 μBar) for frequencies below 600–700 c/s are strongly dependent upon distance to the sound source, while no significant threshold differences were found for higher frequencies. Tests with an air loudspeaker gave thresholds similar to those obtained with the underwater loudspeaker at 2 m distance. 3. 3. Lowest threshold (−42 to −45 db) are in the 100–1500 c/s range, increasing to −10 db for 5000 c/s and to −6 db (at 2 m distance) or −38 db (at 0·1 m distance) for 50 c/s. 4. 4. The variation in threshold with distance is probably due to the physical characteristics of the sound stimulus. Close to the sound source, i.e. within a distance equal to the wavelength divided by 2π, the near-field water displacement amplitude is considerable. Calculated particle displacement at threshold is roughly the same for all distances for any given frequency and particle acceleration is the same for all distance and frequencies.

Effect of temperature on the discharge rates of the electric organ of some gymnotids

Abstract 1. 1. The discharge rates of the electric organs of six species of Gymnotidae, living in the Rio Negro, were between 60 and 1600/sec at 28°C—which was the surface temperature of the river—and had Q10-values of around 1·5. 2. 2. The lower and upper tolerated temperatures were 19–25° and 30–37°C, respectively.

Avoidance responses to infrasound in downstream migrating European silver eels, (Anguilla anguilla)

In an attempt to develop an efficient acoustic fish fence, we have designed an infrasound source able to generate large nearfield particle acceleration. The source generates water movements by means of two symmetrical pistons in an air-filled cylinder with 21 cm bore. The pistons are driven by eccentric coupling to an electric motor, with 5 cm p.p. amplitude. The piston movements are 180° out of phase. The piston reaction forces are thus opposed, leading to vibration free operation. The submergible infrasound source is operated freely suspended in the water mass. The emitted sound frequency is 11.8 Hz. The particle acceleration is about 0.01 m s−2 at a distance of 3 m, corresponding to the threshold intensity for deterring effects of infrasound on Atlantic salmon smolts. The sound source was employed to test the effect of intense infrasound on migrating European silver eels. Fish confined in a tank displayed startle behaviour and prolonged stress reactions, telemetrically monitored as tachycardia, in response to intense infrasound. The field tests were carried out in the River Imsa. A trap that catches all the descending eels is installed near the river mouth. The trap was separated in four equal sections. During the periods with infrasound exposure, the proportion of silver eels entering the section closest to the sound source was reduced to 43% of the control value. In the section closest to the opposite river bank, infrasound increased the proportion of trapped eels to 144% of the control values. This shift of the migrating eels away from the infrasound source was highly significant.

Microampullary organs and a submandibular sense organ in the fresh water ray,Potamotrygon

Summary1.Potamotrygon lacks ampullae of Lorenzini (defined by their long canals), otherwise general for elasmobranchs. There are present however microscopic ampullary organs with extremely short canals. A brief histologic description is provided, together with counts of their abundance in various parts of the body. They are chiefly concentrated ventrally in the head region.2.The skin has a relatively high resistance compared to marine rays. This is measured in the physiologically significant way, by measuring the potential distribution in and around a living ray placed in a homogenous electric field.3.The microscopical size of the ampullary organs and the high skin resistance are believed to be a specialization maintaining the electroreceptive function in the low conductivity, fresh water medium.4.These rays are shown to be responsive to d.c. and low-frequency a.c. electric fields. They give specific movements seemingly related to feeding. They seem to be less sensitive than marine sharks and rays. The threshold stimulus is probably less than 120 μV/cm (corresponding to 0.03 μA/cm2 with water resistivity of 4 kOhm · cm).5.Potamotrygon circularis appears to lack Savis vesicles. However, an organ which may be equivalent is a tubular, subcutaneous, receptor in the Submandibular region. It does not open to the outside or connect to the skin or to the skeleton. Its spontaneous background nerve impulses and the increases in firing with mechanical stimuli are described.

Ionic composition of the cranial and labyrinthine fluids and saccular D.C. potentials in fish

Abstract 1. 1. Saccular endolymph, cranial fluid and blood plasma of three species of teleosts and two of elasmobranchs were analysed for Cl, Na and K, and the saccular (endolymphatic) d.c. potential of Cottus scorpius (teleost) recorded. 2. 2. Average ionic concentrations in mM/1: Fluid Cl Na K Cranial 162 178 3·9 Teleosts Endolymph 162 131 65·5 Cranial 246 265 4·0 Elasmobranchs Endolymph 328 280 61·3 Blood plasma is similar to cranial fluid. 3. 3. The endolymph contains thirteen to twenty-three times as much K as the cranial fluid. In teleosts, the endolymph : cranial fluid ratio for Na is 0·7, for Cl 1·0; in elasmobranchs 1·05 and 1·3, respectively. 4. 4. The saccular potential is +8 to +11 mV, and has no obvious relationship to the ionic distribution.

Electrophysiological studies on the olfactory sense in char (Salmo alpinus L.)

Abstract 1. 1. Brain activity was recorded from the olfactory bulb and telecephalon of migratory and non-migratory chars, Salmo alpinus . 2. 2. Stimulation of the olfactory epithelium with water in which other fishes had been swimming elicited conspicuous responses. 3. 3. The activity evoked by stimulation with mucus of the skin was larger than those elicited by extracts from other organs and the stimulating properties of the mucus retained its potence after heating and storage. 4. 3. The possible role of pheromones in fish migration is discussed.