SEA LAMPREY, Petromyzon marinus, AMMOCOETE MOVEMENTS IN THE SUBSTRATE

consequently submitted to an intense fishery during upstream reproductive migration in the rivers were natural populations still subsist. Sea lamprey life cycle is well documented, but it is comprehensible that the knowledge about ammocoete behaviour during the burrowing phase is scarce (see Hardisty and Potter, 1971; Hardisty, 1979). Habitat destruction (water pollution and sand extraction) is pointed out as a major factor affecting the sea lamprey populations by its effect on the ammocoete fraction of the populations. Such threats might be specially negative for sea lamprey populations if we consider the length of the ammocoete burrowing phase. Consequently the understanding of the ammocoete behaviour during the burrowing phase is of enormous interest both in a management and in conservation perspective. As referred by Hardisty and Potter (1971) the study of the larval behaviour is difficult except when thin section aquaria or artificial substrates are used. But even using thin section aquaria we have found that the amount o