Abstract
BackgroundThe fish family Sciaenidae has numerous species that produce sounds with superfast muscles that vibrate the swimbladder. These muscles form post embryonically and undergo seasonal hypertrophy-atrophy cycles. The family has been the focus of numerous passive acoustic studies to localize spatial and temporal occurrence of spawning aggregations. Fishes produce disturbance calls when hand-held, and males form aggregations in late afternoon and produce advertisement calls to attract females for mating. Previous studies on five continents have been confined to temperate species. Here we examine the calls of the silver croaker Plagioscion squamosissimus, a freshwater equatorial species, which experiences constant photoperiod, minimal temperature variation but seasonal changes in water depth and color, pH and conductivity.Methods and Principal FindingsDissections indicate that sonic muscles are present exclusively in males and that muscles are thicker and redder during the mating season. Disturbance calls were recorded in hand-held fish during the low-water mating season and high-water period outside of the mating season. Advertisement calls were recorded from wild fish that formed aggregations in both periods but only during the mating season from fish in large cages. Disturbance calls consist of a series of short individual pulses in mature males. Advertisement calls start with single and paired pulses followed by greater amplitude multi-pulse bursts with higher peak frequencies than in disturbance calls. Advertisement-like calls also occur in aggregations during the off season, but bursts are shorter with fewer pulses.Conclusions and SignificanceSilver croaker produce complex advertisement calls that vary in amplitude, number of cycles per burst and burst duration of their calls. Unlike temperate sciaenids, which only call during the spawning season, silver croaker produce advertisement calls in both seasons. Sonic muscles are thinner, and bursts are shorter than at the spawning peak, but males still produce complex calls outside of the mating season.
Highlights
Sciaenid fishes, with common names such as croakers and drums, produce advertisement calls during the reproductive season [1,2,3,4,5,6]
Silver croaker produce complex advertisement calls that vary in amplitude, number of cycles per burst and burst duration of their calls
Unlike temperate sciaenids, which only call during the spawning season, silver croaker produce advertisement calls in both seasons
Summary
With common names such as croakers and drums, produce advertisement calls during the reproductive season [1,2,3,4,5,6]. The sounds are produced by contraction of a pair of sonic muscles typically present in males or occasionally in both sexes [7]. Under androgenic control [13], the sonic muscles progress through a yearly hypertrophy-atrophy cycle in which the muscles increase in mass, thickness and fiber diameter to a peak for the mating season and atrophy afterward [14]. The fish family Sciaenidae has numerous species that produce sounds with superfast muscles that vibrate the swimbladder. These muscles form post embryonically and undergo seasonal hypertrophy-atrophy cycles. We examine the calls of the silver croaker Plagioscion squamosissimus, a freshwater equatorial species, which experiences constant photoperiod, minimal temperature variation but seasonal changes in water depth and color, pH and conductivity
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