This report presents a culmination of different research projects on two species of tilapia (Oreochromis mossambicus and Tilapia mariae) and provides recommendations for the future management and research of these pest fish. Feral populations of O. mossambicus and T. mariae are now widely distributed in tropical northeastern Queensland, with O. mossambicus also occurring in southeastern Queensland and river systems of Western Australia. O. mossambicus is known to have existed in impoundments in southeastern Queensland, as well as urban drains and ornamental ponds in the Townsville region of north Queensland from about the late 1970s, while T. mariae became established in some easternflowing tropical streams by the early 1990s. In Australia, feral stocks of tilapia are widely regarded as pests that potentially threaten both native fish stocks and biodiversity.
In the first section of this report we describe a study of feral populations of both O. mossambicus and T. mariae from five locations within a 67 km radius, showing a wide diversity and plasticity in their reproductive and growth parameters. It is thought that this inherent variability is partly responsible for their capacity to quickly and efficiently invade new and sometimes marginal areas, such as the Kewarra Beach drain examined during this study. A high level of parental care ensuring that a relatively high proportion of eggs and larvae are recruited as juveniles, and the ability to spawn multiple broods over a year-round reproductive season gives tilapia a significant competitive advantage over native fishes.
In both species of tilapia, males grew faster than females and there was evidence of considerable variability in the growth characteristic of O. mossambicus between study sites. In Tinaroo Falls Dam, the O. mossambicus population grew faster than the population in the Kewarra Beach drain, probably because the effects of harsher environmental conditions at
the latter site. Ageing studies indicate that Tinaroo Falls Dam was more recently colonised by T. mariae than the Mulgrave River suggesting that invasion of north Queensland habitats by this species ongoing.
The CARPSIM model was successfully adapted for use with O. mossambicus and T. mariae. Some of the simulations completed suggest that it is possible to drive tilapia populations to pseudo-extinction using very high levels of fishing pressure or a combination of fishing pressure and recruitment failure. However, simulations that used more realistic estimates of fishing effort, levels of spawning disruption and other interventions, suggested that while it was possible to drive tilapia abundance down to low levels, populations would not become pseudo-extinct and would quickly recover to previous levels once interventions ceased.
An ongoing control experiment in the Herberton Weir using monthly physical removal of Mozambique tilapia via electrofishing has resulted in a substantial reduction in their relative abundance. However, fish abundance has now stabilised with the current challenge being to implement effective strategies to eliminate the remaining fish from the weir.
|Secondary title:||PestSmart toolkit - tilapia|
|Author:||Russell DJ, Thuesen PA and Small FE|
|Publisher:||Invasive Animals Cooperative Research Centre|
|Institution:||Invasive Animals CRC|
|Department:||Freshwater Products and Strategies|
|ISBN/ISSN:||Web ISBN: 978-1-921777-50-9|
|Region:||Australia - national|
|Documents:||Tilapia in Australia [2Mb PDF]|