Organisms living in aquatic environments are subject to a number of stressors from natural (temperature, predation, food availability) and anthropogenic origins (pesticides, metals, etc). Natural stressors may amplify the effects of contaminants and increase an organism’s sensitivity to them. Understanding the impact of these combined factors is therefore essential for the practical management of contaminants. This study sought to examine how predatory cues affect copper tolerance in the mosquitofish, Gambusia affinis. The influence of predatory cues on fish metabolic rate was also evaluated to gain insight on any interactive effects between the natural stressor and copper. Alarm cues, chemicals released into the water when prey are injured were obtained from humanely sacrificed G. affinis, and kairomones, passive cues released by predators, were obtained from adult bluegill (Lepomis macrochirus). Paired 96-h toxicity tests with copper and predatory cue and with copper alone were conducted to determine the influence of predatory cues on G. affinis sensitivity to the metal. In the presence of alarm cue neither G. affinis copper tolerance or metabolic rate was altered. At copper concentrations ranging from 0.25mg Cu/L - 0.50mg Cu/L kairomone presence had no influence on survival, while between 0.50mg Cu/L and 1.0mg Cu/L, kairomone presence increased survival. Kairomone had no significant effect on metabolic rate. The apparent antagonistic effect between kairomone and copper may have resulted from the presence of organic material from predator-derived cues or from potential changes in fish behavior. This study adds to the growing body of literature which illustrates the complexity of stressor interactions in aquatic systems.

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

Predator cues can influence how aquatic organisms respond to anthropogenic contaminants. This study examined the effects of predator cues on behavior, metabolic rate, and sulfate (as Na2SO4) toxicity in amphipods (Gammarus minus). Predator cues included alarm cue (macerated conspecifics) and kairomone from mosquitofish (Gambusia affinis). Amphipods decreased activity and increased time in refuge when exposed to alarm cue, and increased time in refuge when exposed to kairomone. While median lethal concentrations (96-h LC50) were not influenced by predator cues, analysis of dose response curves indicated that kairomone exposure increased amphipod sensitivity to mid-range concentrations of sulfate (500-1,000 mg/L). Amphipods increased oxygen consumption in response to kairomone but not alarm cue. The influence of predator cues on contaminant lethality can be dependent on the type of cue, and physiological endpoints such as metabolic rate may help explain the basis of observed interactions.

Although it is well documented how introduced species can negatively affect native species, we only poorly understand how they may alter ecosystem functions. We investigated how an invasive fish affected the flux of aquatic insects to terrestrial food webs using mesocosms in a desert spring ecosystem. We compared aquatic insect emergence between alternative community states with monocultures and polycultures of two native species of fish, least chub (Iotichthys phlegethontis) and Utah chub (Gila atraria) plus, introduced western mosquitofish (Gambusia affinis). We tested three hypotheses: (1) aquatic insect biomass will be greater than terrestrial insect biomass and thus, constitute a vital source of energy for terrestrial consumers (2) invasive mosquitofish will negatively impact the biomass of emerging aquatic insects, and (3) terrestrial consumers will negatively respond to decreased emerging aquatic insect biomass. Aquatic insects represented 79% of the flying insect community, and treatments with mosquitofish significantly reduced emergent aquatic insect biomass by 60% relative to the control without mosquitofish. Behavioral traits of invasive species are important, because mosquitofish most heavily affected insects that emerged during the day. Also, spiders that build horizontal webs were negatively correlated with decreasing aquatic insect biomass. Invasive mosquitofish can achieve very dense populations because of their high intrinsic rate of population increase, which can significantly disrupt the flow of energy between aquatic and terrestrial ecosystems, thereby reducing the energy available for terrestrial consumers.

Actualment una de les principals amenaces a la biodiversitat és la introducció d'espècies. Revisant 26 variables de les 69 espècies de peixos continental de la Península Ibèrica concloem que la filogènia, variabilitat i els usos de l'home són necessaris per entendre millor les diferències entres les espècies natives i invasores.Entre les especies més afectades per la introducció de peixos es troben els ciprinodontiformes endèmics del Mediterrani. Aportem les primers dades sobre l'ús d'hàbitats ocasionalment inundats i la selecció de preses del fartet (Aphanius iberus), observant un canvi ontogenètic, clarament relacionat amb el microhàbitat.També demostrem que la salinitat influeix en l'èxit invasor de la gamúsia, afectant la seva densitat i biologia reproductiva. Per altra banda, demostrem experimentalment que amb l'increment de salinitat la gambúsia disminueix la seva agressivitat i captura menys preses, reduint la seva eficàcia competitiva respecte dels ciprinodonts natius. / One of the main current threats to biodiversity is the introduction of invasive species. By reviewing 26 life-history and ecological variables of the 69 inland fish species of the Iberian Peninsula we conclude that phylogeny, variability and human use are needed to a better understanding of the differences between native and invasive species.Among the most threatened species by invasive fish are the Mediterranean endemic cyprinodontiform fish. We report the first data on the use of occasionally-inundated habitats ad prey electivity by the Spanish toothcarp (Aphanius iberus). We observed an ontogenetic diet shift clearly linked to a microhabitat change.We also demonstrate that salinity limits the invasive success of mosquitofish (Gambusia holbrooki), affecting density and life history traits. ON the ohter hand, we experimentally demonstrate that mosquitofish decreases its aggresive behavior and capture less prey, reducing its competitive efficiency with salinity increases regarding to native ciprinodonts.