fish

Calls emitted by the brown meagre Sciaena umbra (L., fam. Sciaenidae) were recorded at the Natural Marine Reserve of Miramare (Trieste, Italy) in seven nocturnal surveys (12-h continuous sampling) during the summer of 2009. Calls consist of pulses, with the main energy content below 2 kHz and mean peak frequency of c. 270 Hz. Pulses were short, with an average duration of 20 ms and a pulse period of 100 ms. Sounds lasted approximately 500 ms. Three types of sound patterns were recognized: irregular (I), regular (R) and the chorus (C). Their acoustic parameters are described showing that I, R and C differ in pulse duration, pulse peak frequency and pulse period. Occurrence of the three call types changes throughout the night: the R pattern occurred mainly at dawn and dusk, C predominated after nightfall, while I calls were produced sporadically during the whole nocturnal period. Our results indicate that S. umbra has a pronounced nocturnal rhythm in vocalizing behaviour and highlight how the diagnostic time–frequency pattern of S. umbra calls can be used to identify the species in the field. Considering that the abundance of S. umbra is currently declining, the information presented here will be relevant in developing non-invasive and low-cost monitoring acoustic systems for managing S. umbra conservation and fishery along the Mediterranean Sea.

Darters in the sub-genus Catonotus are small benthic fish that adopt a reproductive strategy in which a male establishes a cavity and recruits multiple females to lay eggs within his shelter. These nest guarding males have been shown to be vocal and acoustic communication is thought to be critical in allowing these males to recruit females (courtship vocalizations) and also ward off other males (aggressive vocalizations). One such species, Ethesotoma crossopterum is known to produce, three types of vocalizations including knocks and purrs which consist of pulses as well as a harmonic component previously termed a ‘drum’. Although these vocalizations have been previously studied, little is known about individual differences between males and how these differences are related to the size of the male, or the physiological effect of these vocalizations on other conspecifics. We examined the behaviours of the fish associated with each of these vocalizations and examined the inter-individual differences in call components. Recordings were conducted in the laboratory, using nest guarding males which were exposed to both gravid females, and intruder males. This poster will examine the specific use of each of these vocalizations as well as associated behaviours, in both aggressive and courtship contexts. Future planned research includes an investigation of possible hormone modulation in response to playbacks of conspecific vocalizations.

Many teleosts emit sounds from crevices, holes or cavities beneath stones and other types of submerged objects. Yet, the acoustical properties of fish shelters are virtually unexplored. This study investigates the resonance properties of shelters commonly used by Mediterranean gobies as hiding places and/or nest sites in the field, i.e., flat stones, shells belonging to five bivalve species (Tapes philippinarum, Crassostrea gigas, Mytilus galloprovincialis, Scapharca inaequivalvis, Cerastoderma edule) or within aquarium tanks (PVC tubes, concrete blocks, clay flower-pots cut in halves). Both natural and artificial shelters were stimulated using a small underwater buzzer as sound source, placed inside or around the shelter to mimic a fish calling from the nest site (source levels comparable to the those of the goby sounds emitted under similar circumstances), and different types of driving stimuli (white noise, pure tones and artificial pulse-trains). Results showed the presence of remarkable amplitude gains (3-15 dB) at lower frequencies (100-150 Hz) in all types of natural shelters but one (Mytilus), and in terracotta flowerpots and concrete blocks. Gain was higher for stones and artificial shelters than for shells. The experimental piling of sand on the shelter (mimicking a nest-related activity common in sand gobies) increased gain in all types of shelter. Conclusions were verified by performing analogous acoustical tests on natural shelters in the field. The enhancement of low frequencies by stones and shells may explain the widespread use of low-frequencies for acoustic communication by many teleosts calling from enclosures. Results draw attention to the use of suitable shelters for the recording of sounds by fishes kept within laboratory aquaria.

The Canestrini’s goby Pomatoschistus canestrinii (Ninni) is an endemic sand goby occurring in lagoons and estuaries of the northern Adriatic Sea. Likewise as in other sand gobies, reproduction implies nest acquisition and defence, mate attraction, and repulsion of other male intruders that may try to penetrate the nest and perform sneaking fertilisations of the eggs. Furthermore, sound production has been documented in this species by previous work, occurring both in reproductive and aggressive behavioural contexts. In this paper, sound production and associated behaviours were assessed and compared in pairs spawning in two different experimental situations: 1) Isolated resident males 2) Resident males paired with a smaller male, and therefore exposed to possible nest intrusions. The simultaneous video- and acoustical recording of the spawning behaviour allowed to quantify the intensity of sound production and associated behaviours, that were then compared between the groups of males. Results indicated that the spawning behaviour of the nest-holding male was affected by the presence of a male intruder, as the spawning sequence was repeatedly interrupted by the intrusion attempts. This was reflected in an intense aggression and associated sound production of the nestholding male towards the intruder male, but also in a significant increase of aggressive sounds and aggressive visual displays towards the female. Furthermore, the frequency of a female visual display increased significantly when the male was exposed to nest intruders. By contrast, the overall frequency of pre-spawning sounds did not change between the two situations, although the mean duration of the burst containing the highest number of sounds was higher in the group of males exposed to male intruders that in the isolated spawning males. On the whole, these results indicate that parasitic nest intrusions affect significantly the spawning patterns of the nest-holding males, even in terms of sound rate.

Male Lusitanian toadfish, Halobatrachus didactylus, are territorial and have a wide acoustic repertoire. The sound production apparatus consists of a pair of intrinsic large sonic muscles on the two lobes of the swimbladder. Sonic muscle activity and the variability of the vocalizations were related using electromyograms (EMGs). EMG electrodes were surgically implanted on the sonic muscles of several territorial males. After recovery, the subjects were released into an experimental tank with an available nest. Sonic muscle activity was registered and the vocalizations were simultaneously recorded using a hydrophone. Social context was manipulated by releasing different kinds of intruders (male(s) or female(s)). This action elicited the production of boatwhistles, while grunts were generated during fish disturbance. Preliminary analysis shows that, unlike previously reported, the bilateral sonic muscles contract simultaneously during the generation of both signals. The muscle contraction period is halved during the production of the grunt relative to the boatwhistle. The EMG period matches the sound pulse period and determines the fundamental sound frequency.

During the breeding season, Lusitanian toadfish males become territorial and emit an advertisement call (the boatwhistle, BW) to attract mates. We test the hypothesis that boatwhistles can convey information on individual quality by relating calling activity and signal parameters with male physical features, namely male total length, gonadosomatic index, sonic muscle index and male condition, measured by the condition factor and muscle lipid content. We recorded 22 males in the Tagus River estuary (Portugal) during the breeding season (2006 and 2007) for up to eight days and for an average of 35h. Single males were kept inside closed artificial nests and groups of 6-8 individuals maintained a normal chorus activity. Acoustic activity varied greatly among subject males. All males produced boatwhistles during the study period but calling rate varied markedly among them. Average calling rate varied from 0.1 to 361.7 BWh-1 (overall mean = 39.9 BWh-1) and the majority of time was spent in silence (72.4% of the recorded hours). Boatwhistle emission rate and the fundamental frequency of boatwhistles (equivalent to the sonic muscle contraction frequency during sound production) were correlated with male condition (somatic and lipid content). Boatwhistle emission rate was also correlated with sonic muscle index, i.e. with sonic muscle hypertrophy. Calling rate variability also decreased with increased sonic muscle and gonadosomatic indexes. These results suggest that only males with higher somatic and reproductive condition and with higher sonic muscle mass were able to sustain elevated acoustic activity and sonic muscle contraction rates during sound production. In conclusion, boatwhistles seem to be able to signal male quality during social interactions.

As with other African great lakes, Lake Malawi exhibits an explosive radiation of several hundred cichlid species, most of which are endemics. Although visual communication is widely considered the predominant force driving species recognition and mate choice in this radiation, recent studies highlighted a potential role for acoustic signals. To corroborate this proposition, we are analyzing internal and external constraints on acoustic communication in several species from different tribes. Here we focus on the correlation between characteristics of species-specific vocalizations, auditory sensitivity, and eco-acoustical constraints shaping this communication system. Ambient noise in Lake Malawi is characterized by a steep increase to 800 Hz and a slow decline up to several kilohertz. This increase is particularly pronounced during windy conditions creating a low frequency sound window. Interestingly, hearing sensitivity in Melanochromis johanni and Metriaclima callainos revealed by auditory evoked potential measurements, is maximally sensitive at 150-200 Hz and lowest at 800-1000 Hz. Moreover, this is true whether sensitivity is measured in terms of acoustic pressure or particle acceleration. All genera investigated to date produce pulsed sounds during agonistic and reproductive interactions with energies concentrated between 200-300 Hz. Thus, the main frequencies for sound communication are concentrated both at the maximum auditory sensitivity, and within the ambient noise window of the lake. These results indicate that sound communication in Lake Malawi cichlids is facilitated by both internal sensory and eco-acoustical conditions in the lake, and could play a major role in speciation.