Rhythmic electromyographic activities of trunk muscles characterize the sexual behavior in the Him� salmon (landlocked sockeye salmon,Oncorhynchus nerka)

Vibrational and acoustic communication in fishes: The overlooked overlap between the underwater vibroscape and soundscape

Substrate-borne communication via mechanical waves is widespread throughout the animal kingdom but has not been intensively studied in fishes. Families such as the salmonids and sculpins have been documented to produce vibratory signals. However, it is likely that fish taxa on or close to the substrate that produce acoustic signals will also have a vibratory component to their signal due to their proximity to substrates and energy transfer between media. Fishes present an intriguing opportunity to study vibrational communication, particularly in the context of signal production and detection, detection range, and how vibratory signals may complement or replace acoustic signals. It is highly likely that the vibrational landscape, the vibroscape, is an important component of their sensory world, which certainly includes and overlaps with the soundscape. With the wide range of anthropogenic activities modifying underwater substrates, vibrational noise presents similar risks as acoustic noise pollution for fishes that depend on vibrational communication. However, in order to understand vibrational noise, more empirical studies are required to investigate the role of vibrations in the fish environment.

Behaviour of Arctic charr Salvelinus alpinus during an induced mating season in captivity: how male relative size influences male behavioural investment and female preference over time

The behaviour of sexually mature Arctic charr Salvelinus alpinus specimens (fifth farm generation) was observed in captivity for four consecutive days. Only agonistic interactions between males of different size were facilitated on the first 2 days, while both agonistic and courtship interactions were possible from the third day up to the end of the experiment. The reliability of behavioural analysis was assessed in order to reduce the possibility of observer errors within the generated datasets. The behavioural investment of big males, small males and females was analysed using general linear models (two-way repeated measures ANOVAs with time and male size as factors). A peak in the agonistic interactions between males occurred during the first day of interactions, where the agonistic investment of big males was significantly higher than that of small males. This resulted in an increased investment in submissive behaviour by the small males, who consistently performed submissive behaviours from the second day of interactions up to the end of the trial. Big males were found to invest significantly more than small males in courtship behaviours for the duration of the trial. Even though females performed inter-sexual behaviours towards both big and small males for the entire observation period, female interaction rate towards big males was higher than towards small males. This study suggests that both male investment in mating behaviour and female preference might be related to male characteristics such as body length and that S. alpinus behavioural patterns and mate choice cues might be strongly context-related and characterized by high levels of behavioural plasticity (i.e. presence-absence of certain behavioural units or potential reversal of a mate choice cue) within the same species. Finally, in light of this, some conservation measures are discussed. In particular, effective management plans should take into account the high level of behavioural plasticity likely to be occurring in this species.

Brainstem lateral line responses to sinusoidal wave stimuli in still and running water

The fish lateral line consists of superficial and canal neuromasts. In still water, afferent fibers from both types of neuromast respond equally well to a sinusoidally vibrating sphere. In running water, responses to a vibrating sphere of fibers innervating superficial neuromasts are masked. In contrast,responses of fibers innervating canal neuromasts are barely altered. It is not known whether this functional subdivision of the peripheral lateral line is maintained in the brain. We studied the effect of running water on the responses to a 50 Hz vibrating sphere of single units in the medial octavolateralis nucleus (MON) in goldfish Carassius auratus. The MON is the first site of central processing of lateral line information. Three types of units were distinguished. Type I units (N=27) were flow-sensitive; their ongoing discharge rates either increased or decreased in running water, and as a consequence, responses of these units to the vibrating sphere were masked in running water. Type II units (N=7) were not flow-sensitive; their ongoing discharge rates were comparable in still and running water, so their responses to the vibrating sphere were not masked in running water. Type III units (N=7) were also not flow-sensitive, but their responses to the vibrating sphere were nevertheless masked in running water. Although interactions between the superficial and canal neuromast system cannot be ruled out, our data indicate that the functional subdivision of the lateral line periphery is maintained to a large degree at the level of the medial octavolateralis nucleus.