Acoustic Signalling in Female Fish

Abstract

Sound production in female fish has only seldom been mentioned, which is in contrast to the vast literature on male sound production. This lack of information is surprising because sound-generating mechanisms are present in females of (almost) all vocal species. Typically, female sonic organs are smaller than those of the males, for example in batrachoidids or callichthyids. Moreover, female sonic muscles do not hypertrophy during the reproductive season, such as they do in male gadids and sciaenids. The sexual dimorphism in sonic organs indicates that males are more active sound producers than females. In most species, males emit advertisement and mating sounds. The exceptions are one osphronemid species in which only females vocalise prior to spawning, and seahorses in which both sexes produce courtship sounds. At the same time, agonistic behaviour and aggressive sounds are rather similar in males and females, indicating that both sexes defend feeding and breeding sites. In numerous cichlids, females are even the more aggressive sex while defending their brood. This resembles the situation in hermaphroditic clownfish, in which females are the larger sex and primarily defend their host sea anemones. Sounds have very rarely been recorded under standardised conditions in both sexes, and sound characteristics have therefore seldom been analysed and compared in detail. Female agonistic sounds may differ in frequency and sound level from male sounds, reflecting differences in body and sonic organ size between sexes. Furthermore, sex-specific differences in pulse length and number of pulses have been described. Differences between female mating and female agonistic sounds have been described in one species. Overall, the assumption is that sex-specific differences in acoustic signalling during agonistic behaviour are minor in vocal species. These differences seem to depend on morphological differences. Furthermore, a more detailed analysis of reproductive behaviour in fish is expected to show more teleost species in which females are vocal during courtship and spawning.