Acoustic signalling in female fish: factors influencing sound characteristics in croaking gouramis

Abstract

The characteristics of sounds produced by fishes are influenced by several factors such as size. The current study analyses factors affecting structural properties of acoustic signals produced by female croaking gouramis Trichopsis vittata during agonistic interactions. Female sounds (although seldom analysed separately from male sounds) can equally be used to investigate factors affecting the sound characteristics in fish. Sound structure, dominant frequency and sound pressure levels (SPL) were determined and correlated to body size and the order in which sounds were emitted. Croaking sounds consisted of series of single-pulsed or double-pulsed bursts, each burst produced by one pectoral fin. Main energies were concentrated between 1.3 and 1.5 kHz. The dominant frequency decreased with size, as did the percentage of single-pulsed bursts within croaking sounds. The SPL and the number of bursts within a sound were independent of size but decreased significantly with the order of their production. Thus, acoustic signals produced at the beginning of agonistic interactions were louder and consisted of more bursts than subsequent ones. Our data indicate that body size affects the dominant frequency and structure of sounds. The increase in the percentage of double-pulsed bursts with size may be due to stronger pectoral muscles in larger fish. In contrast, ongoing fights apparently result in muscle fatigue and subsequently in a decline in the number of bursts and SPL. The factor 'order of sound production' points to an intra-individual variability of sounds and should be considered in future studies.

Sound production in femaleTrichopsis schalleri(Labyrinth fishes): comparison to males and evolutionary considerations

“…In catfish species, a size-SPL relationship was observed when both sexes and several species were pooled (Knight and Ladich 2014;Hadjiaghai and Ladich 2015). No such a relationship was evident in both sexes of the longsnout seahorse Hippocampus reidi or in both sexes of adult T. vittata (Ladich et al 1992;Oliveira et al 2014;Ladich and Maiditsch 2018). Interestingly, a strong positive correlation is reported in female T. schalleri in the present study, but not in the prior study on males (Ladich et al 1992).…”

“…The burst number is furthermore positively correlated to the SPL in females. This correlation resembles the positive relationship between number of bursts in agonistic sounds and SPL in female T. vittata (Ladich and Maiditsch 2018). One potential explanation is that the maximum tension of enhanced pectoral fin tendons may only be reached in longer sounds, which are subsequently louder.…”

“…This relationship may be important in assessing potential mates or the fighting ability of opponents (Myrberg et al 1986;Ladich 1998). A negative correlation is given in males of all species of the genus Trichopsis and in females of T. vittata and T. schalleri (Ladich et al 1992;Ladich and Maiditsch 2018;present study). Such a relationship has further been shown in females of the drum Pogonias cromis (Tellechea et al 2010), potentially the skunk clownfish Amphiprion akallopisos (Colleye et al 2009) and can be expected in many more species.…”

“…Ladich (1997) and Pruzsinszky and Ladich (1998) showed that sound duration depended on the length of the pectoral spines in several catfish species. In the genus Trichopsis no correlations were found between temporal characteristics and size in both sexes of T. vittata and male T. schalleri (Ladich et al 1992;Ladich and Maiditsch 2018). This contrasted to female T. schalleri, in which burst period and body weight showed a strong positive correlation.…”

“…The few descriptions of female sounds in general and of statistically significant differences between sexes do not accurately reflect the vocal activity of female fish (Ladich 2007;Fine and Waybright 2015;Ladich and Maiditsch 2018). We can assume that in all fish species having sound-generating mechanisms, both sexes are vocal during agonistic interactions such as during territorial defence and when being disturbed by con-or heterospecifics (Ladich 2015a;Casaretto et al 2016).…”