A comparison of underwater speakers for fish playback studiesa).

Acoustic playback is a key method used to determine the behavioral significance of animal sounds, including fishes. This study presents the first comparison of the acoustic quality of underwater speakers for the playback of fish sounds. Seven underwater acoustic playback systems were tested for their ability to accurately reproduce the low frequency, pulsed, courtship sounds of a small fish, Tramitichromis intermedius (Cichlidae). Results indicated that in an aquarium with low ambient noise and at low amplitude playback levels (<120 dB re 1 µPa), the Clark Synthesis speakers were the best choice for playback at moderate distances (>20 cm), and that the Electro-Voice UW30 was the best speaker for short distance (<20 cm) playback of low frequency fish sounds. However, in aquaria with higher levels of ambient noise and at higher amplitude playback levels, the Clark Synthesis speakers performed best. However, none of these speaker systems reproduced a high-fidelity quality fish sound. It is important when using underwater speakers for behavioral studies that there is a careful assessment of the played back sound and comparison to the original sound.

Lack of mitochondrial genetic structure in hamlets (Hypoplectrus spp.): recent speciation or ongoing hybridization?

Species in the genus Hypoplectrus (hamlet fish) have been recognized primarily on the basis of colour morphology, which varies substantially. Limited differentiation in other morphological characters, however, has led to ongoing debate about their taxonomy. Our analysis of mtDNA sequences demonstrates neither reciprocal monophyly nor significant genetic differentiation among hamlet colour morphs. These data are potentially consistent with a model of recent speciation due to sexual selection on colour morphology. The presence within hamlets of two divergent mtDNA clades, however, suggests a longer history during which hybridization and gene flow have prevented the differentiation of hamlet colour morphs, at least in neutral genetic markers.

Enzyme activities of pharyngeal jaw musculature in the cichlid Tramitichromis intermedius: implications for sound production in cichlid fishes.

Owing to its high degree of complexity and plasticity, the cichlid pharyngeal jaw apparatus has often been described as a key evolutionary innovation. The majority of studies investigating pharyngeal muscle behavior and function have done so in the context of feeding. Analysis of enzyme activities (citrate synthase, 3-hydroxyacyl-CoA dehydrogenase and L-lactate dehydrogenase) of pharyngeal muscles in the Lake Malawi cichlid Tramitichromis intermedius revealed differences between pharyngeal jaw muscles and between males and females. Therefore, these muscles have different performance characteristics, resulting in different functional characteristics of the muscles within the complex. Furthermore, the differences between muscles of males and females represent fundamental differences in muscular metabolic processes between sexes. This study is the first to demonstrate that the pharyngeal anatomy is not only used for food processing but is possibly responsible for sound production, in turn influencing sexual selection in cichlid fish.