Comparison of embryological development in the threatened Australian lungfish Neoceratodus forsteri from two sites in a Queensland river system

Abstract

Lungfish are a relict group of basal fishes, survivors of an extensive fossil fauna that first appeared in the Devonian era. The Australian lungfish Neoceratodus forsteri is the only survivor of this fossil fauna in Australia, and is now confined to only 3 natural environments in southeast Queensland, as well as a few lakes and rivers to which the species has been introduced, all in southeast Queensland. The lungfish is under threat from many aspects of human activity in this highly populated part of the state, notably from conversion of the natural riverine environment into large reservoirs for water conservation where conditions are not ideal for adults or for eggs, embryos and hatchling lungfish. Food in reservoir environments is limited for all stages of the life cycle, and refuges for young fish do not exist because the water level fluctuates, especially in spring when lungfish are spawning. Lack of refuges for small fish has been identified as a possible danger to recruitment of young lungfish to the adult population. Comparison of embryological development between eggs and embryos found in unaltered reaches of the Brisbane River to eggs and embryos from a spawning event in Lake Wivenhoe, where lungfish were trapped when the reservoir was built over the Brisbane River in 1984, suggests that lungfish may face more problems than lack of shelter for the young. None of the material collected from Lake Wivenhoe developed normally, possibly because the level of nutrition for parent fish in this lake was so poor that they were unable to produce viable young.