Varying numbers of adult desert pupfish (Cyprinodon macularius) and mosquitofish (Gambusia affinis) were introduced separately into experimental habitats open to egress to determine resource requirements for each species and the relation between numbers and resources. Laboratory environments in which "voluntary" colonization was achieved, were created for both species. Results indicated that both species have the innate ability to regulate numbers in their respective populations to available resources via emigration. The number of resident fish varied directly with experimental reductions of cover. When adult mosquitofish were introduced into open tanks with established populations of adult desert pupfish in habitats containing constant resources, there was no significant change in population size for either species as compared to single species populations over a 5-day period. Adult desert pupfish and mosquitofish are able to coexist successfully in habitats open to egress for 5 days because they utilize available resources in very different ways and the number of fish that become residents do not go beyond resource limits. These data suggest that replacement of desert pupfish by mosquitofish in the American Southwest is a phenomenon that is the result of more long-term interactions between all life stages of the species and may be more likely to occur in environments of low complexity and closed to egress.

Thesis (M.S.)--Humboldt State University, 2008. / Includes bibliographical references (leaves 63-68). Also available via Humboldt Digital Scholar.

Thesis--Catholic University of America. / Bibliography: p. 25-29.

A research study was conducted to examine the relationship between speciation of heavy metals (Zn, Cd, Pb, Cu) and their biotoxicity. Therefore, static bioassay experiments were designed to determine LC-50 values for those metals on mosquitofish, Gambusia affinis. The standard bioassay scheme consisted of twelve 16-liter all-glass aquaria that provided duplicates of five different metal concentrations and a control for each run. Deionized tap water and filtered retention/detention water from Maitland Pond were used for bioassays. The effects of various physiochemical parameters such as pH, alkalinity, hardness and organic complexation on metal toxicity were determined. Also, synergistic and antagonistic effects resulting from metal mixtures were examined. It was concluded that metals in pond water were considerably less toxic than in deionized water for mosquitofish. Also, copper was consistently the most toxic metal tested for both deionized water and pond water.

The association of olfactory information with a resource is broadly known as olfactory-based associative learning. From an ecological perspective, associative learning can reduce search time for resources and fine tune responses to changing biotic and abiotic factors in a variable environment, which in mosquitoes has implications for pathogen transmission and vector control strategies. The purpose of this dissertation was to examine the ability for olfactory-based associative learning across the major life history domains of mosquitoes. Six different experiments comprise this dissertation. The first was to evaluate the response of mosquitoes following conditioning to 5, 10 or 50% sucrose concentrations with individual level mosquito conditioning and testing and introduction of statistical analysis with binary logistic regression. Mosquitoes did not respond in a dose dependent manner with respect to positive response to target odors following conditioning. This effect appears to be related to the mosquitoes' prior exposure to sugar as those exposed to 10% sucrose before conditioning did not prefer 50% sucrose but significantly fewer chose 5% sucrose. In an evaluation of host associated odors and second blood meal choice by females using a dual-choice olfactometer no significant effects were observed. The lack of significance may have been due to insufficient sample sizes, problems with odor collection or physiological state of mosquitoes. Effects of predatory mosquitofish on larval development and female oviposition choice were evaluated by rearing in separated habitats under three different treatments followed by an oviposition choice assay. Females did not prefer their natal habitat or avoid predators but chose substrate that had contained mosquitofish fed conspecific larvae. Mosquitofish affected larval development with acceleration in treatments with mosquitofish fed Tetramin® and delayed pupation in treatments with mosquitofish fed conspecific larvae. Mosquito memory length was evaluated by conditioning and testing at six time intervals from colony and field populations at two ages. Younger mosquitoes showed higher levels of positive response after conditioning at all time intervals except the longest (24h). Finally the olfactory-based associative learning ability of Anopheles cracens was evaluated. Significant evidence for learning was observed in males but not females at a memory length interval of 24h.

Without an adequate understanding of complex interactions between native and non-native species, management of invasive species can result in unforeseen detrimental impacts. I used both field and laboratory experiments to study reciprocal species interactions between the endangered Mohave tui chub (Siphateles bicolor mohavensis) and invasive western mosquitofish (Gambusia affinis). I also examined the impacts of both fish species on the aquatic invertebrate communities in desert springs. I demonstrate a case of intraguild predation (IGP) as a mechanism facilitating co-persistence of the endangered Mohave tui chub with invasive mosquitofish using field mesocosm experiments. In this case of IGP, adult tui chub prey on adult and juvenile mosquitofish, while adult mosquitofish prey on tui chub eggs and/or larvae. I conducted laboratory predation trials to assess if IGP was size-structured due to predator gape-limitation. I explored sex specific differences in gape-size limitation in mosquitofish, because mosquitofish are sexually dimorphic. Larval tui chubs had lower survival in the presence of female mosquitofish than in the presence of males. Reciprocally, male mosquitofish had lower survival than the females in the presence of Mohave tui chub. These results combined with vulnerability modeling supported that IGP in this system is size structured based on gape-size limitation. These results collectively suggest size-structured IGP may facilitate the co-persistence of these two fish species. My findings also suggest that mosquitofish may not be a limiting factor for the persistence of the endangered Mohave tui chub. Further, habitats currently harboring mosquitofish were considered as future refuge habitats for Mohave tui chub, a management option previously un-available. In addition to such reciprocal interactions between fish species, recently established fish populations may impact unique invertebrate communities. Mesocosm experiments with sympatric and allopatric populations of tui chub and mosquitofish showed negative impacts of both fish species on changes of invertebrate community structure. Specifically, fish caused population declines and, in some cases, extirpations of various invertebrate taxa. These results suggest important conservation implications of invasive fish as well as protected fish transplants into fishless desert springs. Overall my research emphasizes the complexity of ecological interactions between native and non-native fish species in desert aquatic systems.

Establishing historical water velocities is a goal of Everglades restoration because of their role maintaining landscape topographic relief. However, flows may also change the trophic state of marshes by phosphorus loading. I used fatty acid (FA) and stoichiometric data to quantify how increased sheet flow altered the relative heterotrophic and autotrophic contributions to aquatic consumers in a field experiment that introduced flowing water to an Everglades marsh in November, 2014. Algal taxonomic composition was different between pre-flow and flow sampling, marked by increases in the nutrient exploiting Mougeotia species (green algae) during flow sampling. Dietary tracer FAs in consumers reflected changes in algal resources, including an increase in green algae-derived and a decrease in bacteria-derived FAs. These food web responses indicate that establishing historic water velocity in degraded wetlands can shift the origins of organic matter from a more detrital to more algal supported web.

Niche separation may be the key to promoting the long-term coexistence of introduced and native species. Physical alterations to the environment (habitat manipulation) or re-introducing native species to former habitats can exploit the maladapted traits of introduced species to create a refuge for native species. No two species have identical niches because evolutionary constraints differ between species with different evolutionary histories. Our objectives were to determine if cold temperatures could promote coexistence between native least chub and introduced western mosquitofish. We used individual scale and population scale experiments to test four hypotheses: 1) colder temperatures would reduce the aggressive behavior and predatory effects of western mosquitofish on least chub, 2) colder temperatures would reduce the effect of western mosquitofish on the habitat use, activity, and feeding of least chub, 3) western mosquitofish would not be able to overwinter without warm refuges, and 4) western mosquitofish reproduction would be delayed or absent at colder temperatures, whereas colder temperatures would not inhibit least chub recruitment. At the individual scale cold temperatures reduced the aggression and predation of western mosquitofish on least chub. However at the population scale there was little recruitment in the cold treatment and juvenile least chub did not survive the winter in the cold treatment. Adult least chub successfully overwintered at freezing temperatures whereas western mosquitofish had no recruitment in the cold treatment during the summer and no western mosquitofish survived the winter. There is adequate niche separation among the adults to promote coexistence but the juveniles of both species require warm habitat in the spring and summer to survive freezing winter temperatures. Habitat manipulation may reduce the availability of warm winter refuges for western mosquitofish while leaving warm habitats during the spring for least chub spawning and recruitment. Transplanting least chub to former cold habitats could eliminate western mosquitofish because of niche separation between the species along a temperature gradient. We suggest that the niche separation hypothesis has general application for the restoration of a variety of threatened native species.

Studies in Europe, Japan, and North America have reported that wild fish exposed to treated sewage effluents can exhibit significant physiological and reproductive abnormalities consistent with exposure to hormonally active chemicals. The main objective of this research project was to examine the estrogenic and androgenic activity in treated sewage to determine the risk associated with treated sewage discharges in Australia and New Zealand. Several bioassays, including a sheep estrogen receptor and a rainbow trout androgen receptor binding assay, were set up and validated with model compounds. The assays were then used to measure the estrogenic and androgenic activity in sewage samples from 15 municipal sewage treatment plants (STP) utilizing a variety of treatment technologies. Raw sewage samples contained high levels of both estrogenic and androgenic activity, up to 185 ng/L estradiol equivalents (EEq) and up to 9330 ng/L testosterone equivalents (TEq), respectively. Secondary treatment processes such as activated sludge had the greatest impact on removal of biological activity from the wastewater. The estrogenic and androgenic activity in final treated effluents were <1 to 4.2 ng/L EEq and <6.5 to 736 ng/L TEq, respectively. Based on lowest observable effective concentrations reported in the literature, these levels are unlikely to induce biological effects in exposed fish in the short term. To examine potential long-term effects, resident mosquitofish chronically exposed to undiluted treated sewage were sampled. Several morphological biomarkers indicative of endocrine disruption were measured and compared with mosquitofish captured at a reference site. Mosquitofish captured in a constructed wetland for tertiary treatment of secondary treated sewage exhibited morphological differences such as elongated anal fins consistent with exposure to androgenic chemicals, although this effect was not measurable in fish collected at sites further downstream or at any of the other sites. Based on these results, it is unlikely that mosquitofish populations would be significantly affected by exposure to final treated sewage. A reverse transcription real-time polymerase chain reaction (RT-PCR) method to measure the production of a female-specific protein (vitellogenin) mRNA in adult male mosquitofish was developed, and this could be used as a rapid test to detect early changes in individuals exposed to estrogenic activity.

Freshwater fish species have been introduced into freshwater systems around the world, primarily for aquaculture, ornamental fish trade and sport fishing. Their introduction into estuarine systems is uncommon however, instances do occur and their establishment success and impacts on these estuarine systems is not well documented. The extent of invasion by four freshwater fishes in a RAMSAR listed estuarine system, the Wilderness Lakes, Western Cape was investigated. This thesis determined the relative abundance and distribution of alien fishes in relation to the native fish biota, their establishment success in the system, what factors inhibited their establishment and whether the introduction of alien fishes negatively impacted the native fish biota. The distribution and abundance of fishes were assessed primarily using fyke nets, seine nets and gill nets in each of the lakes, interconnecting channels and the Touw Estuary. The fish fauna was made up of euryhaline marine species comprising 46%, native estuarine species comprising 18%, catadromous species comprising 7% and freshwater alien species comprising 29% of the total biomass sampled. A total of 26 species were sampled in the system, three of which were considered alien; Oreochromis mossambicus, Gambusia affinis and Cyprinus carpio, and Micropterus salmoides were not sampled but confirmed in the system. Establishment success was determined by evidence of: a sustainable breeding population, a wide distribution, abundant in the sampling area, and all size classes of fish sampled. Gambusia affinis and Oreochromis mossambicus have been recorded in the system for a minimum of 13 and 26 years respectively. They were widely distributed and highly abundant and are established in the system. Micropterus salmoides was first recorded in the system in 1985 but abundances have remained low with fish appearing to be limited to Island Lake and Langvlei. Reproduction appeared to be limited by higher salinity and these factors indicated that this was a casual species which relies on repeated introductions for population maintenance. Cyprinus carpio spawned successfully in 2010 and was widely distributed but abundances were still low with a total of 15 fish being sampled throughout the system, and was thus in the establishing phase. As these are considered freshwater alien species, the physico-chemical parameters in the estuarine environment inhibiting the establishment success of the alien fishes were investigated. Gambusia affinis and O. mossambicus were not limited by the physical environment, and while O. mossambicus cannot tolerate temperatures below 11⁰C, temperatures only dropped below its tolerance for a total of two days between February 2010 and February 2011. Cyprinus carpio and M. salmoides were restricted by salinity in Rondevlei and Langvlei but could tolerate salinity in Island Lake and the Touw Estuary during closed mouth phases. While adults appeared to tolerate the salinity in the system, egg and larval development could be affected thus reducing the viability of the population. The abundance of alien fishes did not negatively impact the abundance of native fish species. The interactions between the native and alien fish biota tended towards biotic acceptance where, as alien abundance increased so did native fish abundance. The impacts of the alien fishes on the native fish biota were assessed by comparing the fish community from a study completed in 1985 to the findings of this study. From these two studies there were no apparent negative impacts on the native fish biota and the fish community composition would most likely be structured by estuarine mouth opening events.