Ecological Constraints on Sound Communication in Fishes

Animals communicate under ecological conditions which may hinder signal transmission or may even be dangerous for the sender. The aim of the project is to investigate acoustic communication in fishes in the presence of two major ecological factors namely noise and predators. It is assumed that fishes modify their behaviour and sound production to optimize acoustic communication. Noise reduces the ability to hear sounds and communicate acoustically. While the effects of noise on hearing have been described in several freshwater and marine species possessing different hearing abilities it is almost unknown if noise affects sound production. So far, only a single study on a small freshwater minnow indicates that fish may be able to modify sounds in response to noise. Signaling represents a major risk for animals because signals may be detected by predators. Prey fish may modify their foraging, fighting and courtship behaviour in the presence of predators but it is unknown if and how they change sound production. This project will be the first one investigating to what degree major ecological constraints influence acoustic communication in fishes. It is planned to investigate sound production during aggressive interactions in the croaking gourami, a small tropical freshwater fish belonging to the labyrinth fishes. Sounds, acoustic behaviour and hearing have been investigated by the project leader in several prior studies. The behavioural part of the project focuses on the changes in aggressive behaviour and sound production in the presence of white noise at typical ambient noise levels encountered in the habitat of fishes and in the presence of a moving artificial predator outside the tank. The following variables will be determined and compared between different experiments: occurrence and number of different behaviours such as fin erecting, circling and number, pitch and intensity of sounds produced. The physiological part will investigate the decrease in hearing abilities in the presence of noise by recording acoustically elicited electric potentials noninvasively from the head of the fish. The stress response of the fish during aggressive behaviour and in the presence of a predator will be measured noninvasively by determining cortisol in the fish holding water. The work will be supervised by the project leader and carried out by the Ph.D. student Isabelle Maiditsch. Isabelle has successfully investigated the effects of temperature on hearing in fishes in the course of her master thesis and sound production and acoustic behaviour in several courses.

Ecological Constraints on Sound Communication in Fishes This project aimed to investigate the influence of major ecological factors - predators, noise and temperature - on sound communication in fishes. The research was carried out in the course of a Ph.D. thesis by Isabelle Maiditsch from 2018 to 2022 on croaking gouramis from Southeast Asia (closely related to Siamese fighting fish) and in South American long-whiskered Pictus catfish at the bioacoustics lab at the University of Vienna. The results demonstrate that croaking gouramis reduce aggressive behaviour in the presence of a predator, in particular fin spreading and production of croaking sounds. This indicates that fish try to be less conspicuous and increase their vigilance (Maiditsch & Ladich 2022a). Research on the effects of noise demonstrates that croaking gouramis do not increase the level of their sounds. Hearing of sounds by conspecifics will thus be hindered by ambient noise (Maiditsch & Ladich 2022b). Measuring the hearing abilities in croaking gouramis shows that hearing declines in the presence of noise. This decrease in hearing sensitivity limits the detection of conspecific croaking sounds (Maiditsch & Ladich 2022c). The influence of temperature on sound production was investigated in the Pictus catfish when hand held. These catfish possess rapidly contracting muscles that vibrate the swimbladder and subsequently produce low-frequency drumming sounds; they can also rub their pectoral spine in the shoulder girdle, which results in the emission of high-frequency chirping sounds. Underwater sound recordings at 22 and 30C show that the duration of sounds is shorter at the higher temperature, but the number of sounds is not affected by temperature. The pitch of drumming sounds increases with temperature, but this is not the case with chirping sounds. The data demonstrate that temperature affects properties of vocalizations in fishes (Ladich & Maiditsch 2020). Results of the project reveal that ecological factors, in particular noise, impair sound communication in fishes. This is relevant in aquatic environments that are increasingly affected by anthropogenic noise. Freely available articles published within the framework of the project: Maiditsch, I.P. & Ladich, F. (2022a) Acoustic and visual adaptations to predation risk: A predator affects communication in vocal female fish. Current Zoology 68, 149-157. Maiditsch , I.P. & F. Ladich (2020b). Effects of noise on acoustic and visual signalling in the croaking gourami: Differences in adaptation strategies in fish. Bioacoustics. https://doi.org/10.1080/09524622.09522022.02086174 Maiditsch , I.P. & F. Ladich (2022c). Noise-induced masking of hearing in a labyrinth fish: effects on sound detection in croaking gouramis. PeerJ 10: e14230. Ladich, F. & Maiditsch, I. P. (2020). Temperature affects sound production in fish with two sets of sonic organs: the Pictus cat. Comparative Biochemistry and Physiology, Part A 240, 110589.