Wamberal Lagoon Catchment Aquatic Survey Final Report (PDF ...

5.2. Fish Species
5.2.1. Poeciliidae
Large numbers of Mosquito Fish Gambusia holbrooki were captured at most sites and
this species represents the main species with the widest distribution and largest biomass
in the catchment. Gambusia holbrooki are an introduced species that is a major pest
and is having devastating repercussions on our native species. They are live bearers
protecting their eggs and young and an exceptionally robust species, surviving in
conditions that will kill most native species. They eat the eggs and larvae of our native
species and survive in both fresh and marine environments.
Gambusia were captured along the full length of Forresters creek from the lake to the
upper most regions and from all drains and feeder streams. Gambusia numbers were
exceptionally high with densities of 12 to 112 per cubic mtr of water. In May as a flood
conditions survey, inflowing water from roadside drains were common and this obviously
attracted Gambusia and other native species.
In June with reduced water levels and flows, the Gambusia numbers were still
exceptionally high. One small box trap capturing 108 Gambusia, a frighteningly high
number. The overwhelming numbers of Gambusia is considered a concern, though they
are a food source for native species like the Flatheaded Gudgeons (stomach contents
indicated Gambusia and shrimp as the main foodsource) and birds, etc., they do eat
native fish eggs and larvae, dramatically reducing native species numbers in the area.
Other pest and exotic fish species like swordtails, guppies, mollies, carp & goldfish were
all absent from the catchment. Much of eastern NSW is impacted by these pest
species and their absence in the catchment was fantastic news and very encouraging for
the future health of the local environment and prosperity of the native aquatic fauna.
Figure 20. Gambusia holbrooki “a typical scoop”
Wamberal Lagoon Catchment Report Australian Aquatic Biological P/L 22