Mosquitofish Gambusia Affinis Research Articles

Stakeholder perceptions and strategies for management of non-native freshwater fishes of Andaman and Nicobar Islands, India

Abstract This article examines the non-native fishes in the freshwater bodies of Andaman and Nicobar Islands with a focus on understanding the perception of stakeholders towards providing management solutions. A total of 56 freshwater fish species were reported from Andaman and Nicobar Islands of which 23 species were non-native to the Islands introduced either accidentally or deliberately. Among the 23 fishes introduced, 13 species were found to be transplanted from Indian waters into the Islands and 10 species were non-native to Indian waters. Mosquito Fish (Gambusia affinis), Mozambique Tilapia (Oreochromis mossambicus), Silver Barb (Barbonymus gonionotus), Red Bellied Pacu (Piaractus brachypomus), and Common Carp (Cyprinus carpio) are some of the important invasive species found here. Stakeholder perception studies were undertaken through semi-structured questionnaire and five point likert scale questions. The respondents (N=133) were classified into two groups as a) Fish farmers and b) Research/development personnel. Multinomial logistic regression analysis revealed that the profession of the respondents significantly influenced the awareness about the non-native fishes (p<0.001). Fish farmers (4.04±0.04) and Research/development (4.47±0.21) respondents mutually agreed on the need for awareness and education on the issue of non-native fishes (p<0.01). A management framework is suggested to address the issue of non-native fishes towards effective planning, conservation and management of the fragile Island ecosystems.

Identifying threats from introduced and translocated non-native freshwater fishes in Croatia and Slovenia under current and future climatic conditions

Introduced and translocated non-native species are a major threat to biodiversity, especially in aquatic habitats. Efforts aimed at the mitigation of impacts and the implementation of preventative measures for the conservation of native biota must rely upon an accurate evaluation of the risks posed by non-native invasive species and are expected to be strengthened by international collaboration. In this study, 76 non-native freshwater fish species of which 48 extant (both introduced and translocated) and 28 horizon were screened for their risk of invasiveness in the neighbouring countries of Croatia and Slovenia under current and future climatic conditions. Using the Aquatic Species Invasiveness Screening Kit (AS-ISK), threshold scores for the Basic Risk Assessment (BRA) and for the combined BRA and Climate Change Assessment (BRA + CCA) allowed to distinguish with a high level of accuracy between low-, medium- and high-risk species – the latter representing ≈70% of the screened species. Brown bullhead Ameiurus nebulosus, round goby Neogobius melanostomus, topmouth gudgeon Pseudorasbora parva and Wels catfish Silurus glanis were the highest-scoring species for Croatia, and Ameiurus nebulosus, snakehead Channa argus and Pseudorasbora parva for Slovenia. There were discrepancies in medium- and high-risk rankings between Croatia and Slovenia for 12 species. Upon comparison of the BRA outcomes with those based on the Freshwater Fish Invasiveness Screening Kit (the predecessor of the AS-ISK), the risk changed for six species in Croatia and five in Slovenia. After accounting for predicted climate change conditions, the BRA + CCA risk scores increased for ≈50% of the species, with western mosquitofish Gambusia affinis, channel catfish Ictalurus punctatus and black carp Mylopharyngodon piceus achieving the highest score increment for Croatia, and round goby Neogobius melanostomus and Chinese (Amur) sleeper Perccottus glenii for Slovenia. The present outcomes will assist decision-makers in the implementation of appropriate measures for the management of extant non-native species and the potential introduction of horizon species. This is important for the regulation of pet trade and aquaculture as well as for management strategies aimed at the conservation of native biodiversity, which in the case of neighbouring countries/jurisdictions will benefit from joint efforts relying on a full risk assessment for the species classified at higher risk of invasiveness.

Determination of the lethal concentration 50% (LC50) of lead chloride and its accumulation in different organs of Gambusia affinis fish

In the present research, mosquito fish Gambusia affinis have been exposed to lead chloride during 24, 48, 72 and 96 hours in order to evaluate the lead chloride lethal 50 (LC50) concentration and the Its residue in certain organs of fish. Usage of the EPA computer software based on Finney Probit Analysis method has been statistically tested for the data collected LC50 values of G. affinis if 24, 48, 72 and 96 hours were found to be 59.4, 55.9, 51.1 and 49. 0 mg/L, respectively. LC50 decreased as mean exposure times. 20 fish were placed in each concentration of four sublethal concentrations 20 and 25 mg/L for two acute periods 24 and 96 hours as well as 10 and 5 mg/l for chronic periods 15 and 30 hours. The testes were carried out as three replications, the accumulation of lead in various fish organs was determined by Atomic Absorption Spectrophotometer. The finding revealed that the accumulation of PbCl2 on different organs of G. affinis be time dependent fashion and Pb-content in organs increased significantly time dependent at chronic exposure as compared as acute- exposure.

Environmental temperature during early life affects the personality of mosquitofish in adulthood.

Personality has been observed in a variety of animal taxa with important implications in ecology and evolution. Exploring the influence of environmental temperature during early life on personality could help to understand the ontogeny of this phenotypic trait in animals. In this study, we reared newborn mosquitofish Gambusia affinis at high (30°C) and low (25°C) water temperatures and measured their shyness and exploration upon sexual maturity. We tested the repeatability of each behavioral trait; the correlation between them; and the effects of rearing temperature, sex, and body length on the behaviors. When growing up at low temperatures, female fish exhibited repeatability in shyness and exploration, and males exhibited marginal repeatability in shyness. However, neither of the 2 behaviors were repeatable when the fish were reared at high temperatures. There was a negative correlation between shyness and exploration, indicating that the 2 behaviors comprise a behavioral syndrome in this species. Mosquitofish reared at high temperatures were more explorative than those reared at low temperatures, while there was no difference in shyness between the 2 treatments. Body length and sex had no significant effects on the average values of the 2 behaviors. The results indicate that environmental temperature during early life could shape the personality of mosquitofish and modify the average of the behavioral traits. These findings might provide insights to understand the ontogeny of animal personality and how changes in environmental temperature influence animal dispersal by shaping their personality.

Feeding Ecology of Age‐0 Gar at Texoma Reservoir Inferred from Analysis of Stable Isotopes

AbstractConservation and restoration of gar (Lepisosteidae) populations in North America are increasingly of interest to fisheries managers. Alligator Gar Atractosteus spatula are being stocked as age‐0 fish in efforts to re‐establish extirpated populations. However, gars are known to be highly cannibalistic in hatcheries, suggesting that age‐0 Alligator Gar introduced into natural habitats may face predation pressures from other gar species, limiting the likelihood of released fish recruiting to the population. Furthermore, introduced age‐0 gar may not have the proper prey resources for rapid growth that would facilitate recruitment to adulthood. Texoma Reservoir, located on the Oklahoma–Texas border, hosts four native gar species, including the Alligator Gar, whose population is supported by supplemental stocking of age‐0 fingerlings. We investigated feeding by age‐0 gar to obtain a baseline level of trophic ecology for this group of fishes, including the potential for poststocking cannibalism. Food webs were reconstructed via analysis of carbon (δ13C) and nitrogen (δ15N) isotopes using Bayesian mixing model approaches. Isotopic values for age‐0 fish of all four gar species were similar. Invertebrates represented a large fraction of the diet for all gars, followed by Common Carp Cyprinus carpio and Grass Carp Ctenopharyngodon idella. Competitive interactions among Bluegill Lepomis macrochirus, White Bass Morone chrysops, White Crappie Pomoxis annularis, and young gar may occur for invertebrates, shads Dorosoma spp., and Western Mosquitofish Gambusia affinis but are likely short‐lived due to the rapid growth of age‐0 gar after their transition to piscivory. Trophic position of age‐0 Alligator Gar, Longnose Gar Lepisosteus osseus, and Spotted Gar Lepisosteus oculatus was positively related to TL, but this relationship was not observed for Shortnose Gar Lepisosteus platostomus. In Texoma Reservoir, the four native gar species, including stocked Alligator Gar, appear to have adequate food resources for recruitment, with little indication of within‐family or interspecific predation. This suggests that stocked Alligator Gar quickly acclimated to their new environment.

Transcriptomic changes in western mosquitofish (Gambusia affinis) liver following benzo[a]pyrene exposure.

Widely distributed western mosquitofish (Gambusia affinis) has been used as a new model species for hazard assessment of environmental stressors such as polycyclic aromatic hydrocarbons (PAHs). However, most of the PAH studies using G. affinis rely on targeted biomarker-based analysis, and thus may not adequately address the complexity of the toxic mechanisms of the stressors. In the present study, the whole transcriptional sequencing of G. affinis liver after exposure to a PAH model, benzo[a]pyrene (BaP) (100μg/L), for 20days was performed by using the HiSeq XTen sequencers. In total, 58,156,233 and 51,825,467 clean nucleotide reads were obtained in the control and BaP-exposed libraries, respectively, with average N50 lengths of 1419bp. In addition, after G. affinis was exposed for 20days, 169 genes were upregulated, and 176 genes were downregulated in liver. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were applied to all the genes to determine the genes' biological functions and processes. The results clearly showed that the differentially expressed genes were mainly related to immune pathways and metabolic correlation pathways. Interestingly, almost all the pathways related with the immunity were upregulated, while the metabolism pathways were downregulated. Lastly, quantitative real-time PCR (qRT-PCR) was performed to measure expressional levels of twelve genes confirmed through the DGE analysis. These results demonstrate that BaP damages immunity and enhances the consumption of all available energy storage to activate mechanisms of the detoxification in G. affinis. Up until now, the present study is the first time that a whole transcriptome sequencing analysis in the liver of G. affinis exposed to BaP has been reported.

Mosquitofish avoid thermal stress by moving from open water to the shade of the mangrove Rhizophora mangle

Mangrove trees provide environmental buffering for animals by reducing daytime water thermal maxima. Shade from Rhizophora mangle trees reduces thermal stress for the mosquitofish Gambusia affinis. Data were collected from mangrove forests in Quintana Roo, Mexico, at 2 sites: (1) Soliman Bay, a mangrove forest decoupled from direct ocean water, and (2) La Lunita with semi-direct access to ocean water. During cooler morning hours at Soliman Bay, large numbers of mosquitofish foraged in open channels. At the same time, few mosquitofish utilised shaded areas within the R. mangle prop roots. When channels exceeded water temperatures above 38°C, mosquitofish migrated into the shaded areas provided by R. mangle trees. Channel water reached a daytime maximum temperature of 46°C, while daytime-shaded R. mangle areas remained 6.2°C cooler. Temperature rise and abundance shifts were not found in La Lunita, which has water temperatures of 27 to 28°C throughout the day. Size distributions between both localities showed mosquitofish caught in Soliman Bay to be >10% smaller than the mosquitofish from La Lunita, which had a greater abundance of mature adults. In Soliman Bay, mosquitofish were small, and the thermal stresses may impose serious developmental impacts that would be reduced by occupying water shaded by R. mangle. Refuge from R. mangle provides environmental buffering for fish, and future increasing water temperatures may reveal a greater use of this little-known mechanism. This study provides an example of a mechanism whereby mangroves support intertidal biodiversity through environmental buffering.

Side-effects of a neonicotinoid insecticide (actara®) on a non-target larvivorous fish Gambusia affinis: Growth and biomarker responses

Actara® 25 WG belongs to neonicotinoids, which is the most widely used insecticide class for controlling various insect pests in the world. The present study was aimed to assess the potential hazards of this insecticide on the mosquitofish Gambusia affinis following a chronic exposure. The female adults were collected during the reproduction period and exposed to various concentrations (10, 20 and 40 mg.L−1) during 28 days. The effect of actara was investigated on morphometric and selected biomarker measurements. Results showed that the compound was found to affect significantly the condition factor at days 21 and 28 of exposure with the highest concentration. However, the treatment had no effect on hepato-somatic and gonado-somatic indices. Biochemical analyses revealed an increase in glutathione S-transferase activity and carbonylated protein content, and a decrease in acetylcholinesterase activity for the three tested concentrations while the vitellin level was reduced only for the highest concentration. Thus, this product can pose side-effects on this non-target freshwater fish.

Susceptibility of betanodavirus in a newly established vertebra-derived cell line from Mosquitofish (Gambusia affinis).

In the present study, a new cell line from the vertebra of mosquitofish Gambusia affinis was successfully established and characterized. The cell line is named as bone Gambusia affinis (BGA) and subcultured for more than 55 passages in Leibovitz's/L15 medium supplemented with 15% FBS at 28°C. The cell line has a modal chromosome number of 48. Molecular characterization of the partial sequence of the coi gene confirmed the origin of the BGA cell line from mosquitofish. These cells exhibited epithelial morphology confirmed by the cytokeratin marker. The BGA cells showed mineralization of their extracellular matrix when stained with alizarin red and von Kossa stain. BGA cells were found to be susceptible to RGNNV and SJNNV strains of betanodavirus (NNV) showing cytopathic effect with multiple vacuolations in the cells. The RT-PCR confirmed the betanodavirus infections in BGA cells. The SEM micrograph showed the morphological changes observed in the cell during virus infection. The in vivo challenge experiment also showed the viral replicating efficiency in the Gambusia affinis with increasing viral titre. Thus, our present results show that the BGA cell line is a useful tool for isolating betanodavirus and could be used to investigate bone cell differentiation and extracellular matrix mineralization.

The effect of cadmium exposure on the cytoskeleton and morphology of the gill chloride cells in juvenile mosquito fish (Gambusia affinis)

One of the wide spread aquatic organisms in the rivers of Indonesia is the mosquito fish (Gambusia affinis (Baird and Girard, 1853)). Mosquito fish are invasive species that can adapt to environmental changes, also they act as bioindicator species for polluted environments. The study aims to determine the effects of the exposure to cadmium on the cytoskeleton and morphology of the gill’s Chloride Cells (CCs) in the mosquito fish. In cadmium treated mosquito fish (0.03 mg/L for 28 days), the immuno-fluorescent light microscope showed strong absorption of actin stain and strong primary MT antibody uptake in CC and apical epithelia. Scanning electron microscopy observations showed a change in microfilament organized at the CC's apex, with the appearance of some actin filament aggregates. Higher cadmium concentrations (0.03 and 0.015 mg/L) did not alter such reorganization. Microtubules weren’t significantly affected by similar exposures. SEM analysis showed that cadmium exposure induced a significant increase in CC's surface area. After 28 days, the density of CC also increased. It was observed that there is an increase of CC's surface area, although the CC density didn’t increase significantly. The results of this study confirmed the cytotoxic effects of cadmium on mosquito fish.

Domperidone treatment advances onset of puberty in the viviparous mosquitofish Gambusia affinis

BackgroundAlthough dopamine (DA) exerts modulatory effect on reproduction in the majority of fishes, its role is not clearly understood in viviparous species. The aim of this investigation was to determine the influence of DA antagonist domperidone (DOM) on puberty in the viviparous species Gambusia affinis.ResultsTreatment of 1.5 or 4 mg DOM to 25 days post-hatching (DPH) juveniles for a period of 35 days resulted in dense aggregations of gonadotropin-releasing hormone (GnRH)-immunoreactive fibres in the proximal pars distalis (PPD) region of the pituitary gland in contrast to faintly seen fibres in treatment controls. In the ovary, the follicles belonging to stages I–IV did not differ significantly among different experimental groups. However, stage V (vitellogenic) follicles were completely absent in treatment controls in contrast to their presence in 1.5 or 4 mg DOM-treated fish. Besides, the diameter of stage V follicles was significantly higher in 1.5 mg DOM-treated fish compared with 4 mg DOM-treated fish.ConclusionsThe results suggest that DOM treatment triggers the follicular development and promotes the early onset of puberty, possibly by attenuating the dopaminergic inhibition on GnRH fibres, for the first time in a viviparous species.

Development and characterization of a skin cell line (SGA) from the mosquitofish Gambusia affinis and its susceptibility to fish Betanodavirus

A new continuous cell line designated as SGA has been developed from the skin tissue of the freshwater mosquitofish Gambusia affinis. The cell line grew well in Leibovitz's L-15 medium supplemented with 15% fetal bovine serum at 28 °C. Immunophenotyping of the cell line showed the epithelial nature of the cells. Chromosome number analysis showed that SGA cells have a modal diploid chromosome number of 48. Replication of the two different strains of betanodavirus (RGNNV and SJNNV) in SGA cell line showed the maximum virus titre of 108.82 TCID50 mL−1 for RGNNV and 107.2 TCID50 mL−1 for SJNNV. The cytopathic effect in the cell line was observed at 3 days post-infection (dpi) and multiple vacuolations were observed at 7 dpi. Further, DsRed2 plasmid was efficiently delivered into SGA cell line and was found that these cells were transfectable and can be used for assessing gene promoter activity. In vivo challenge experiments using the RGNNV infected cell culture supernatant showed signs of the disease in healthy mosquitofish with mortality commencing from 15 dpi. The above results suggest that the cell line is permissive for propagating betanodavirus and also could be an essential tool for studying the molecular pathogenesis of betanodavirus infection.

Domperidone treatment attenuates stress-induced suppression of reproduction in viviparous mosquitofish Gambusia affinis.

The aim of this study was to determine the effect of stress on reproduction and the possible involvement of dopaminergic systems in the reproductive stress response in the mosquitofish Gambusia affinis. Exposure of fish to aquaculture stressors (four 10 min episodes of stress, each corresponding to a different stressor such as handling, chasing, frequent netting and low water levels), for a period of 30 days caused reduction in the mean numbers of stage I-IV follicles associated with lower number of pregnant females and embryos in most of the developmental stages compared with experimental controls. Besides, increase in the intensity of labelling and the per cent area of tyrosine hydroxylase (TH; a rate-limiting enzyme in the biosynthetic pathway of catecholamines)- immunoreactive (ir) neurons was observed in the preoptic area (POA) and the nucleus preopticus (NPO) regions of the brain concomitant with reduction in the labelling of gonadotropin releasing hormone-immunoreactive (GnRH-ir) fibres in the proximal pars distalis (PPD) of the pituitary gland in stressed fish compared with experimental controls. Treatment of domperidone (DOM) caused an increase in the number of stage II and V follicles and promoted pregnancy rate concomitant with an increase in the number of embryos at various developmental stages compared with those of experimental controls. Similar treatment to stressed fish caused an increase in the number of stages I-V follicles compared with those in stress alone group. The GnRH fibres showed increased immunolabelling in stress + DOM treated fish compared with stress alone fish. On the other hand, TH-immunoreactivity in the POA and the NPO regions was reduced in stress + DOM treated fish compared with stress-alone group. These results suggest that stress inhibits follicular development and subsequent hatching success through the suppression of GnRH and that the inhibition appears to be mediated through dopamine, for the first time in a viviparous fish.

Molecular Detection of Mosquitofish (Gambusia affinis) in the South-western Region of Bangladesh

Molecular Detection of Mosquitofish (Gambusia affinis) in the South-western Region of Bangladesh

Pathological Study of Experimental Glyphosate Toxicity in Mosquito Fish Gambusia affinis

The present study deals with the effect of herbicide glyphosate on mosquito fish Gambusia affinis. Fish were exposed to different concentrations of the mentioned pesticide, behavioral and histological effects of various concentrations of glyphosate on mosquito fish Gambusia affinis in the acute exposure (96) hours were investigated.There were behavioral changes on the exposed fishes represented by nervous symptoms, loss of equilibrium, increas in respiration rate, opening of mouth and histological changes were determined in gills after acute exposed such as hyperplasia, hemorrhage, aneurysms, separation of epithelial layer, clubbing with sickle lamellae, hypertrophy, destroyed and fusion of secondary lamellae.The liver tissues were showed that hypertrophy of nucleus and necrosis and degeneration and swelling of cells, increasing of size and bleeding and congestion of blood vessels and bilirubin pigment diffusing around bile duct, in kidney tissues there were necrosis and degeneration of epithelial cells of tubules, increasing of size of Bowman᾿ s capsule, congestion and atrophy and disappear of glomerulus, separation of tubules, increasing of size and congestion of blood vessels, bleeding between tubules and bilirubin pigment diffusing around blood vessels.

Impacts of non-native fishes under a seasonal temperature gradient are forecasted using functional responses and abundances

Developing predictive methods to forecast the impacts of existing and emerging invasive species is of critical importance to biodiversity conservation. However, invader impacts are context-dependent, making reliable and robust predictions challenging. In particular, it is unclear how temporal variabilities in relation to temperature regime shifts influence invader ecological impacts. In the present study, we quantify the functional responses of three coexisting freshwater fishes: the native freshwater River Goby Glossogobiuscallidus, and the non-native Mozambique Tilapia Oreochromismossambicus and Western Mosquitofish Gambusiaaffinis, under two temperature treatments using chironomid larvae as prey. This was used along with fish abundance data to determine temporal differences in ecological impacts of each fish species between seasons (i.e. at two corresponding temperatures). All three fish species exhibited potentially population-destabilizing Type II functional responses. Their maximum feeding rates were consistently higher in the warm temperature treatment, whereas attack rates tended to be reduced. Non-native Mozambique Tilapia had the highest maximum feeding rate under both temperature treatments (18 °C and 25 °C), followed by the non-native Western Mosquitofish and lastly the native River Goby, suggesting greater per capita impacts on native prey by non-native fishes. The predatory fish abundances differed significantly according to season, with native River Goby and non-native Mozambique Tilapia generally more abundant than non-native Western Mosquitofish. By multiplying functional response maximum feeding rates with abundances of each fish species across the seasonal gradient, the relative impact potential of non-native Mozambique Tilapia was consistently higher compared to that of native gobies. Western Mosquitofish impacts were less apparent, owing to their low abundances. We demonstrate how seasonal temperature fluctuations affect the relative impact capacities of introduced species and the utility of consumer functional response and the relative impact potential metric in impact forecasting.

Populations Structure of Mosquitofish Gambusia Affinis (Baird and Girard; 1853) in Four Different Lakes in Benghazi, Libya

Populations Structure of Mosquitofish Gambusia Affinis (Baird and Girard; 1853) in Four Different Lakes in Benghazi, Libya

Inter‐specific differences in invader and native fish functional responses illustrate neutral effects on prey but superior invader competitive ability

AbstractInter‐specific interactions are key factors in the structuring and functioning of ecological communities. Therefore, it is necessary to assess species interactions, such as predator–prey dynamics and competitive exclusion, within the context of continuing global species introductions. The aim of the present study was to assess ecological impacts and competitive exclusion dynamics involving co‐occurring introduced and native fish species, using the multiple predator functional response (FR) approach.We use comparative FR analysis (resource uptake as a function of resource density) to assess inter‐specific interactions between the invasive western mosquitofishGambusia affinisand the native freshwater river gobyGlossogobius callidustowards chironomid larvae. The FR was derived for each fish species as individuals and when in heterospecific pairings. Data from single individuals were used to predict the expected FR of individuals when in heterospecific multiple predator combinations. Expected FRs were then compared to the observed FRs of each predator in combination trials, enumerated using prey items in their gut contents.Both fish species displayed TypeIIFRs, however, in single fish trials, invasive mosquitofish had significantly higher FRs (curve asymptotes; i.e. shorter handling times and higher maximum feeding rates) than native river gobies. Heterospecific mosquitofish‐river goby combinations revealed that the FR of the river goby was reduced (i.e. longer handling times and lower maximum feeding rates) by the presence of mosquitofish, whereas this combination greatly enhanced mosquitofish FR magnitudes (i.e. shorter handling times and higher maximum feeding rates). The heterospecific treatments resulted in neutral impacts on prey and there were clear inter‐species interference in favour of the non‐native mosquitofish.This study demonstrates how multiple predators can alter the shape of individualFRs, with neutral effects on prey but superior invader competitive ability. This has implications for predicting the naturalisation success of invasive predators, as predatory and competitive interactions with native predators and prey may facilitate rather than impede establishment.

Immobilization Threshold and Fish Conductivity of Two Small Fishes

AbstractPower transfer theory (PTT), a useful paradigm in electrofishing, asserts that the threshold power density (Dt, μW/cm3) transferred from water to fish for immobilization is dependent on the conductivity (μS/cm) of the water (σw) and of the fish (σf). Larger differences between the two conductivities require higher applied power densities and may make capture more difficult. Over a range of water conductivities, Dt as a function of σw will form a U‐shaped curve, and the minimum provides an estimate of σf and Dm (the lowest value of Dt that occurs when σw and σf are equal). Studies have demonstrated a narrow range of σf (56–160 μS/cm) relative to the conductivity of natural waters (10–5,000 μS/cm). However, these σf values are for larger species. Electrofishing may also be directed at the capture of smaller species or diverse communities. In an experimental tank, we estimated Dm and σf for a small cyprinid, the Red Shiner Cyprinella lutrensis (TL = 35–64 mm) and a smaller poeciliid, the Western Mosquitofish Gambusia affinis (TL = 23–46 mm). We estimated Dm and σf to be 120 μW/cm3 and 23 μS/cm, respectively, for Red Shiners (n = 72) and 143 μW/cm3 and 23 μS/cm, respectively, for Western Mosquitofish (n = 23). These values for σf are less than half the minimum of previously reported values, and our Dm estimates are less than those that have been reported for game species of similar length (200–300 μW/cm3). Our results serve to explain why smaller species require higher applied power densities and are more difficult to capture from an assemblage of various species and sizes.

Kairomone-induced changes in mosquito life history: effects across a food gradient

The aquatic immature stages of species with complex life histories exhibit a range of defense mechanisms in response to predator released kairomones (PRK). Employing these costly mechanisms often results in delayed metamorphosis. Larvae of the house mosquito Culex pipiens (Linnaeus) show a rare exception of accelerated metamorphosis in response to kairomones originated from the mosquitofish Gambusia affinis (Baird and Girard). In a series of lab experiments we examined whether this response is context-dependent with respect to food availability (i.e. applied only when food is abundant and cost is low). We examined life history variables of C. pipiens larvae, reared at different levels of food availability, either with or without PRK. We further examined the effect of PRK on the foraging behavior of the larvae at different instars. We also examined the effect of PRK-induced behavior on larvae survival under actual predation. We showed that the response of C. pipiens larvae to PRK was independent of food availability. Larvae exposed to PRK were less active and survived longer when exposed to direct predation. Exposure to both PRK and small food amounts also resulted in reduced adult size and survival period. The effects of food and PRK were independent of one another. We argue that for organisms with short development time, such as mosquitoes, decreasing time to metamorphosis may be the main feasible refuge from increased predation risk. Hence, Culex larvae exploit their capability for rapid development rate as a main anti-predator mechanism, minimizing the time spent in high-risk environments by accelerating metamorphosis, regardless of available resources, at the expense of other life history traits.