Abstract
BackgroundData on sex-specific differences in sound production, acoustic behaviour and hearing abilities in fishes are rare. Representatives of numerous catfish families are known to produce sounds in agonistic contexts (intraspecific aggression and interspecific disturbance situations) using their pectoral fins. The present study investigates differences in agonistic behaviour, sound production and hearing abilities in males and females of a callichthyid catfish.Methodology/Principal FindingsEight males and nine females of the armoured catfish Megalechis thoracata were investigated. Agonistic behaviour displayed during male-male and female-female dyadic contests and sounds emitted were recorded, sound characteristics analysed and hearing thresholds measured using the auditory evoked potential (AEP) recording technique. Male pectoral spines were on average 1.7-fold longer than those of same-sized females. Visual and acoustic threat displays differed between sexes. Males produced low-frequency harmonic barks at longer distances and thumps at close distances, whereas females emitted broad-band pulsed crackles when close to each other. Female aggressive sounds were significantly shorter than those of males (167 ms versus 219 to 240 ms) and of higher dominant frequency (562 Hz versus 132 to 403 Hz). Sound duration and sound level were positively correlated with body and pectoral spine length, but dominant frequency was inversely correlated only to spine length. Both sexes showed a similar U-shaped hearing curve with lowest thresholds between 0.2 and 1 kHz and a drop in sensitivity above 1 kHz. The main energies of sounds were located at the most sensitive frequencies.Conclusions/SignificanceCurrent data demonstrate that both male and female M. thoracata produce aggressive sounds, but the behavioural contexts and sound characteristics differ between sexes. Sexes do not differ in hearing, but it remains to be clarified if this is a general pattern among fish. This is the first study to describe sex-specific differences in agonistic behaviour in fishes.
Highlights
A wealth of information is available on sound-generating mechanisms, sound production during agonistic and reproductive behaviour, and hearing in fishes
Kratochvil [12] found that pectoral sonic muscles and tendons were larger in male than female gouramis, and Pruzsinszky and Ladich [13] revealed that pectoral fin spines of male peppered corydoras Corydoras paleatus were relatively longer than those of females
Male M. thoracata possess relatively longer pectoral spines than females. This agrees with the general finding that males typically have larger sonic organs than females [2]. This sexual dimorphism was found in pectoral sonic organs in gouramis
Summary
A wealth of information is available on sound-generating mechanisms, sound production during agonistic and reproductive behaviour, and hearing in fishes (for reviews see [1,2,3,4,5]) Despite this knowledge, data on sex-specific differences in sonic organs, sound production and in hearing are very limited [6]. Swimbladder sonic muscles were typically larger in males than females in representatives of the families Batrachoididae (e.g. oyster toadfish Opsanus tau and midshipman Porichthys notatus; [14,15]), Sciaenidae (e.g. Japanese croaker Argyrosomus japonicus, [16]) and Gadidae (e.g. haddock Melanogrammus aeglefinus [7]). The present study investigates differences in agonistic behaviour, sound production and hearing abilities in males and females of a callichthyid catfish
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