Agonistic interactions between Gambusia affinis and Galaxias maculatus: implications for whitebait fisheries in New Zealand rivers

Abstract

Laboratory tank studies were used to identify the outcome of behavioural interactions between Gambusia affinis (gambusia) and Galaxias maculatus (inanga), whereas field data on spatial distribution were used to determine whether gambusia could be affecting inanga populations in the wild. Mortality rates for juvenile inanga (mean length 42 mm) exposed to gambusia (mean length 32 mm) for 15 days at 10°C were low (<10%) and no greater than those for control fish. However, at temperatures between 15 and 25°C, gambusia nipped the fins of juvenile inanga, resulting in immobilisation and death. Cumulative mortality rates over 15 days at these temperatures were over 60%. The survival of larger (mean length 58 mm) adult inanga was also reduced by gambusia. Adult inanga occurred in 15% of shallow (<0.5 m) sites where gambusia was present compared with 33% of shallow sites where it was absent. Furthermore, the mean depth of sites containing inanga in swamps and wetlands where agonistic interactions would be greatest was 1.8 m where gambusia was present compared with 1.0 m where it was absent. Displacement of inanga into deeper waters is therefore likely to be occurring as a consequence of gambusia aggression. The spread of Gambusia in New Zealand has the potential to reduce the use of shallow-water habitats by inanga. This would further exacerbate the historic decline of these galaxiid fisheries related to land-use changes.

Temperature-Specific Competition between Invasive Mosquitofish and an Endangered Cyprinodontid Fish

“…Although interference competition is often more influential and clearer than exploitative competition [41], both types of competition can occur concurrently and interactively and may be difficult to distinguish [42]. G. affinis and G. holbrooki are well known to produce severe fin damage through nips, which can result in several adverse effects on recipient species [43], [44]. For example, swimming performance is likely to be reduced with potential consequent reduction in reproductive success and increased predation risk.…”

“…The influence of temperature on interactions with mosquitofish has been examined in relation to several native species. For example, G. holbrooki aggression towards two Iberian toothcarp species ( A. iberus and Valencia hispanica ) increased at higher temperatures [23] and increased aggression with temperature has been shown by the closely related G. affinis towards Galaxias maculatus in New Zealand [43] and the least chub, Iothichthys phlegethontis in the USA [31], with effects on the survival of these native fish. In the current study, mosquitofish aggression may have immediate, medium and longer term consequences for toothcarp.…”

“…In the current study, mosquitofish aggression may have immediate, medium and longer term consequences for toothcarp. In addition to disrupting normal conspecific interactions, mosquitofish can cause considerable fin damage [43], [44] and mortality, especially of juveniles [23], [43]. Injury, along with decreased food intake [24] and reduced growth rates [47] can lead to increased stress and susceptibility to illness [45], [46].…”

Experimental evidence indicates that native freshwater fish outperform introduced Gambusia in mosquito suppression when water temperature is below 25°C

“…Secondly, in temperate climates, G. holbrooki abundance decreases markedly during the cooler months, then rapidly increases after reproduction peaks in mid-summer (Melden, 1951;Brown & Fox, 1966;Penn & Potter, 1991). Consequently, G. holbrooki is typically only abundant at water temperatures above 20°C (Rowe et al, 2007). However, in south-western Australia mosquito larvae begin to hatch in spring, when water temperatures are around 10-15°C, well before the peak in G. holbrooki reproduction occurs.…”

Baseline survey of the fish fauna of a highly eutrophic estuary and evidence for its colonisation by Goldfish (Carassius auratus)

“…Such a finding is important as introduced fish have been identified by the Australian Federal Government as a key threat to the ecological character of the Vasse-Wonnerup Wetland System (Australian Government 2011). The poeciliid G. holbrooki, for example, is known to behave in a highly antagonistic manner to other small fishes, causing damage to their fins and even death (Schoenherr 1981;Rowe et al 2007), and to predate on the eggs and larvae of fish and amphibians (Ivantsoff and Aarn 1999;Pyke 2005). As this species is highly tolerant of changes in salinity, water temperature, dissolved oxygen and turbidity (Cherry et al 1976;Hubbs 2000) and is extremely abundant in disturbed habitats near urban areas (Lloyd et al 1986), it is likely to be able to survive in the Vasse Estuary despite the large seasonal changes in hydrology.…”