The Waikato River is the longest river in New Zealand and is exposed to range of anthropogenic stressors. This study investigated the effects of three major point‐source discharges on resident shortfin eels Anguilla australis along the river. Shortfin eels were caught from sites upstream and downstream of discharges of bleached kraft mill effluent (BKME) from pulp and paper manufacture, sewage, and a thermal power plant. At ea...

We investigated the effects of native common bully ( Gobiomorphus cotidianus ) and non‐native western mosquitofish ( Gambusia affinis ) on zooplankton assemblages in an outdoor mesocosm experiment. Twenty‐one 100 L mesocosms containing zooplankton were assigned either four G. cotidianus , four G. affinis , or were left as a control group (i.e. with no fish) and monitored for 14 days. Zooplankton community composition in the fi...

The common bully ( Gobiomorphus cotidianus ) was used as a bioindicator to assess the impacts of geothermal, bleached kraft mill effluent (BKME), sewage, and thermal discharges in the Waikato River, Northern New Zealand. A range of morphological and physiological parameters were measured to assess fitness in fish sampled upstream and downstream from these point sources. Isotopic signatures gave evidence that fish were resident...

Introduced common carp ( Cyprinus carpio ) are a recognised threat to New Zealand’s freshwater ecosystems. In 2011, an invasive fish removal programme was undertaken in 16.8 ha Lake Ohinewai, a Waikato riverine lake. Active fish removal using netting and boat electrofishing was supported by installation of a one‐way exclusion barrier on the outflow to Lake Ohinewai. The barrier was designed to allow fish passage downstream out...

Previous research has identified distinct genetic, life‐history and reproductive differences between populationsof common bully ( Gobiomorphus cotidianus ) upstream and downstream of a pulp and paper mill outfall on the Tarawera River in the Bay of Plenty, New Zealand. This study investigated the distribution of common bully in the Tarawera River by examining fish collected from upstream (37 km inland) and downstream (20 km in...

A total of 566 koi carp ( Cyprinus carpio ) from the lower Waikato region were aged from scales and opercular bones, and growth was modelled with the von Bertalanffy growth function. There was no difference in growth rate between male and female carp. Growth of koi carp between zero and 3 years of age was lower than that of common carp in Europe and Australia. However, after 5 years of age the growth of koi carp was higher tha...

The potential for western mosquitofish, Gambusia affinis, to negatively affect populations of black mudfish in New Zealand wetlands was investigated with annual fishing surveys of the Whangamarino wetland and by laboratory experiments evaluating competition and predation of mosquitofish on mudfish adults and larvae. Abundance of mudfish juveniles was reduced in the presence of mosquitofish at marginal wetland sites close to pe...

The acute lethality of low dissolved oxygen (DO) was examined in laboratory studies using several New Zealand freshwater fish and two invertebrates at 15°C. The 48‐h LC50 value was used as the endpoint for acute DO sensitivity as, owing to rapid mortality, this was found to best approximate the threshold lethal concentration. Median lethal time to death did not provide a reliable endpoint for comparing sensitivities. Fish LC 5...

Mosquitofish ( Gambusia spp.) have been spread throughout most of the temperate world during the 20th Century as biological control agents for mosquitoes. However, in many areas of introduction these small aggressive fish have been implicated in the displacement or exclusion of native species of fish and amphibians. Those species most affected are small, surface‐feeding, littoral‐zone fishes and the egg and larval stages of am...

The natural incidence of deformities in the larval head capsules of Chironomus zealandicus was investigated at four lake sites in the central North Island, New Zealand, in summer (December 1994) and winter (June 1995). Significant differences were observed between sites and seasons. Individuals from the peat lakes Ngaroto and Hamilton (Rotoroa) had the highest incidence of deformities during summer (78 and 48%, respectively) a...