Discovery Of Eudontomyzon Sp. (Petromyzontidae) Larvae In Lakes And A Characterisation Of Their Habitats

The extended freshwater life of Petromyzontiformes larvae (ammocoetes) takes place mainly in lotic waters where it has been studied in detail. Information on ammocoetes in lentic habitats is extremely limited, with few data on the occurrence of specimens in ponds or large lakes. The area of the Smolenskoye Poozerye National Park has a dense network of lakes and rivers, with streams abundantly populated by lamprey larvae of the genera Lampetra and Eudontomyzon. In this paper, we evaluate the habitability of lakes belonging to such systems and the manner in which they are populated by lamprey. Larval habitat identification and documentation (bed analysis where ammocoetes exist, including ground composition and biotic and abiotic habitat characteristics) were carried out, resulting in the first documentation of larvae and metamorphic specimens of Eudontomyzon sp. inhabiting littoral areas of small lakes. These specimens were found in the fringe biotopes between the river mouth and lakes. One peculiarity that distinguishes the lentic habitats from the typical river ones is the absence of distinct currents. Freshwater flows diffusely into lakes, mixing continuously at the sites we studied. Preferred habitats for Eudontomyzon sp. consisted of swales filled with debris carried from inflowing streams and deposited as current diminished. In ammocoete beds of this type, the examined larvae had a good trophic position. Such habitats can be both permanent and ephemeral as tributary water levels changes. During flood events, elevated velocity can flush debris and ammocoetes away from these fringe habitats and further into a lake. No accentuated active decomposition was found in the areas where the ammocoetes were present. The results of the study indicate that Petromyzontiformes larvae may be more common in lentic habitats than is currently documented.