The effect of two olfactory cues on the behaviour of habitat-seeking river lamprey (Lampetra fluviatilis) larvae

Abstract

While olfaction-related behaviour in adult lampreys has been extensively studied, less is known when it comes to their larval counterparts. This study aimed to increase knowledge by investigating the behaviour of larval river lampreys (Lampetra fluviatilis), who typically live in underwater sand burrows. The primary focus was on their choice of habitat and how this could be affected by two different olfactory cues: the smell of conspecifics and the conspecific alarm cue. First, a set of quick-choice experiments were conducted where the lampreys got to choose between habitat substrates with or without the addition of a cue in an experimental tank. Second, the larvae were distributed evenly between the substrates in the tank and then given the choice to switch substrates in a set of overnight experiments. While the overnight experiments yielded too few results for analysis, the quick-choice ones provided more substantially. These results showed the lampreys picked a substrate randomly, meaning neither cue was able to attract nor repulse the lampreys enough for them to actively seek out or avoid it. However, strong evidence was found that the larvae burrowed faster when doing so in substrate with the conspecific smell compared to substrate without. Additionally, some evidence was found that presence of the conspecific alarm cue in the tank made the lampreys burrow slower overall. The results suggest that larval lampreys are encouraged to burrow by the smell of conspecifics, and that stress induced by the conspecific alarm cue may disrupt the burrowing behaviour. Also, stress due to a perceived threat of predation is likely behind the lacking results and the lampreys choosing a substrate randomly. Hopefully, the results of this study may contribute to conservation work regarding threatened lamprey populations.