Der Einfluss der Temperatur auf das Hörvermögen des Karpfens Cyprinus carpio und des Welses Silurus glanis

Studien belegen den Einfluss der Umgebungstemperatur auf die physiologischen Prozesse im Körper von ektothermen Tieren. In der aktuellen Studie wurde der Einfluss der Außentemperatur auf das Hörvermögen von ektothermen Otophysen untersucht. Hierfür wurden der Karpfen Cyprinus carpio (Familie Cyprinidae) und der Welse Silurus glanis (Familie Siluridae) herangezogen. Die Versuchstiere wurden mindestens drei Wochen auf die zu testenden Temperaturen akklimatisiert. Zuerst wurden sie auf 15 °C akklimiert, dann auf 25 °C und anschließend wieder auf 15 °C zurückakklimiert. Mittels der Ableitung Auditorisch Evozierter Potentiale (AEP – Methode) wurde die Hörempfindlichkeit bei insgesamt sieben verschiedenen Frequenzen zwischen 100 bis 4000 Hz getestet. Weiters wurden die Latenzen der Antwort als Verzögerungen auf einen Klick-Stimulus gemessen. Die Latenz wurde als die Zeit definiert, welche zwischen dem Einsetzen des Klick-Stimulus und der ersten konstanten und höchsten Spitze des AEP (P2) registriert wurde. P2 zeigte sich als eindeutige Antworten auf den Klick-Stimulus in allen Temperaturen. Bei der höheren Temperatur verbesserte sich das Hörvermögen bei den Karpfen zwischen 300 und 2000 Hz und bei den Welsen zwischen 300 und 4000 Hz. Die P2-Latenzen der AEPs nahmen bei 25°C im Vergleich zu 15°C bei beiden Arten um 0.37 ms ab. Diese Daten lassen erkennen, dass die Hörempfindlichkeit mit zunehmender Temperatur bei eurythermen Otophysen steigt.Background: Ectothermic animals, such as fish, are affected by ambient water temperature. Their body temperature depends on environmental heat sources, which influence the physiological and metabolic processes, including sensory systems such as the auditory system. In this study I investigated how the ambient water temperature affects the auditory system in two eurythermal otophysan fish species representing two different orders. Methodology/Principal Findings: In order to investigate possible effects of temperature on the auditory sensitivity I utilized the auditory evoked potentials (AEP) recording technique. Auditory sensitivity and temporal resolution were measured in the common carp Cyprinus carpio (order Cypriniformes) and the Wels catfish Silurus glanis (order Siluriformes) after acclimating fish for at least three weeks to two different water temperatures (15°C, 25°C and again 15°C). Hearing sensitivity increased with temperature in both species. In C. carpio best hearing was detected at 1 kHz at both temperatures and the maximum increase was found at 0.8 kHz (7.8 dB). S. glanis showed highest sensitivity between 0.5 – 1 kHz and largest increase at 0.5 kHz (10.3 dB). The improvement in hearing abilities differed between species in particular at 4 kHz. The temporal resolution was measured by determining the latency in response to single clicks from the onset of the sound stimulus to the highest positive peak of the AEP. The latency decreased at the higher temperature in both species by 0.37 ms on average. Conclusions/Significance: The current study showed that an increase in temperature results in an improvement of hearing (lower thresholds, shorter latencies) in eurythermal species representing different orders of otophysines. The increase in sensitivity seems to be more pronounced in eurythermal than stenothermal (tropical) species

Auditory chain reaction: Effects of sound pressure and particle motion on auditory structures in fishes

Despite the diversity in fish auditory structures, it remains elusive how otolith morphology and swim bladder-inner ear (= otophysic) connections affect otolith motion and inner ear stimulation. A recent study visualized sound-induced otolith motion;but tank acoustics revealed a complex mixture of sound pressure and particle motion. To separate sound pressure and sound-induced particle motion, we constructed a transparent standing wave tubelike tank equipped with an inertial shaker at each end while using X-ray phase contrast imaging. Driving the shakers in phase resulted in maximised sound pressure at the tank centre, whereas particle motion was maximised when shakers were driven out of phase (180 degrees). We studied the effects of two types of otophysic connections-i.e. the Weberian apparatus (Carassius auratus) and anterior swim bladder extensions contacting the inner ears (Etroplus canarensis)-on otolith motion when fish were subjected to a 200 Hz stimulus. Saccular otolith motion was more pronounced when the swim bladder walls oscillated under the maximised sound pressure condition. The otolith motion patterns mainly matched the orientation patterns of ciliary bundles on the sensory epithelia. Our setup enabled the characterization of the interplay between the auditory structures and provided first experimental evidence of how different types of otophysic connections affect otolith motion

Effects of temperature on auditory sensitivity in eurythermal fishes: common carp Cyprinus carpio (Family Cyprinidae) versus Wels catfish Silurus glanis (family Siluridae).

In ectothermal animals such as fish, -temperature affects physiological and metabolic processes. This includes sensory organs such as the auditory system. The reported effects of temperature on hearing in eurythermal otophysines are contradictory. We therefore investigated the effect on the auditory system in species representing two different orders.Hearing sensitivity was determined using the auditory evoked potentials (AEP) recording technique. Auditory sensitivity and latency in response to clicks were measured in the common carp Cyprinus carpio (order Cypriniformes) and the Wels catfish Silurus glanis (order Siluriformes) after acclimating fish for at least three weeks to two different water temperatures (15°C, 25°C and again 15°C). Hearing sensitivity increased with temperature in both species. Best hearing was detected between 0.3 and 1 kHz at both temperatures. The maximum increase occurred at 0.8 kHz (7.8 dB) in C. carpio and at 0.5 kHz (10.3 dB) in S. glanis. The improvement differed between species and was in particular more pronounced in the catfish at 4 kHz. The latency in response to single clicks was measured from the onset of the sound stimulus to the most constant positive peak of the AEP. The latency decreased at the higher temperature in both species by 0.37 ms on average.The current study shows that higher temperature improves hearing (lower thresholds, shorter latencies) in eurythermal species from different orders of otophysines. Differences in threshold shifts between eurythermal species seem to reflect differences in absolute sensitivity at higher frequencies and they furthermore indicate differences to stenothermal (tropical) species

Mean differences in hearing sensitivity of <i>C. carpio</i> and <i>S. glanis,</i> between the two tested temperatures (mean of 15°C and 15°C repeated) and 25°C.

<p>The last column gives the difference in threshold changes between <i>S. glanis</i> and <i>C. carpio</i>. Asterisks indicate significant differences between species.</p><p>Mean differences in hearing sensitivity of <i>C. carpio</i> and <i>S. glanis,</i> between the two tested temperatures (mean of 15°C and 15°C repeated) and 25°C.</p

AEPs of one specimen of <i>C. carpio</i> in response to a single-click stimulus.

<p>Click stimulus presented 28 dB above hearing thresholds at both temperatures. Arrows indicate onset. The vertical dashed line indicates the position of the P2 peak at 25°C relative to the P2 peak at 15°C and 15°C repeated.</p

Mean (± S.E.) latency of the second positive peaks (P2) of <i>C. carpio</i> and <i>S. glanis</i> measured at 15°C, 25°C and 15°C repeated calculated as the time period between the onset of a single click stimulus and the second positive peak.

<p>Mean (± S.E.) latency of the second positive peaks (P2) of <i>C. carpio</i> and <i>S. glanis</i> measured at 15°C, 25°C and 15°C repeated calculated as the time period between the onset of a single click stimulus and the second positive peak.</p