| Abstrakt: |
The anadromous Geotria australis , one of only three lamprey species representing the early agnathan (jawless) stage of vertebrate evolution in Australia and New Zealand, is declining in abundance. Its adults were caught soon after they had entered rivers on their non-trophic upstream migration and maintained in laboratory tanks for 13–15 months through to spawning. As adult G. australis are susceptible to haemorrhagic septicaemia, they were treated prophylactically and maintained in 3-m3 aquaria supplied with a flow-through charcoal filtration system and UV steriliser. Air temperature and the light : dark regime were constantly adjusted to parallel those in the environment. Males developed the very large suctorial disc and gular pouch characteristic of maturity and both sexes matured at the same time as in the wild. While males frequently showed aggressive behaviour towards each other, the same male and female mated on several occasions. The male coiled around the female and, with his urogenital papilla close to the female's cloaca, twisted and vibrated, leading to egg release. These eggs formed coagulated clusters as in the wild, with many progressing through to the eight-cell stage. Remarkably, numerous G. australis were still alive 95–392 days after the end of the short spawning period, and one male after a further 119 days. Postspawning survival would be facilitated inter alia by extensive proteolysis, reflected in a shortening of the body. The data in this paper emphasise that G. australis is a highly atypical lamprey and provides invaluable information for conserving this declining species. The lamprey Geotria australis , when provided with appropriate conditions, can be maintained in laboratory tanks for many months from the commencement of the upstream migration through to spawning. Successful maintenance requires, however, the provision of conditions that overcome the potential for this species to succumb to haemorrhagic septicaemia. Spawning, which occurs at the same time as in their natural environment, is described. The prolonged period during which G. australis survive after spawning parallels that recorded for this species in its riverine environment and is unique among lampreys. [ABSTRACT FROM AUTHOR] |
