Mosquitofish Gambusia Affinis Research Articles

Effect of Insecticide Dichlorvos on Ovaries of Mosquito Fish Gambusia affinis (Baird and Girard)

The toxicity of insecticide dichlorvos (90%) was tested in ovaries of mosquito fish using three sublethal concentrations (0.3, 0.6, 0.8 µg/L) and studied their effects on the means of body and ovary weights, gonadosomatic index, ovum size and ova number. Results showed that there was a significant (P

Influence of environmental stress on age- and size-at-maturity: genetic and plastic responses of coastal marsh fishes to changing salinities

As sea levels rise, salt water will intrude into freshwater coastal habitats with greater frequency and stress resident organisms inducing physiological trade-offs that influence life history tactics. Western mosquitofish ( Gambusia affinis ) and least killifish ( Heterandria formosa ), collected along a salinity gradient and maintained in a common freshwater environment for two years (≥4 generations), were used to examine historical (genetic effects) and contemporary environmental effects of salinity on age- and size-at-maturity. There was phenotypic plasticity for sexual maturation and genetic variance among source populations for size-at-maturity, but no genetic variance for plasticity itself as indicated by the lack of genetic-by-environment interactions. Gambusia affinis males and H. formosa females exhibited stress by maturing at smaller sizes and older ages in response to being reared in 0 and 12 ppt, respectively. Our results suggest that habitats in which these fishes are most abundant do not correspond to the salinities at which they can rapidly mature at larger sizes, indicating that other environmental factors are also influential to their distribution and abundance along salinity gradients.

Assessment of Two Nonnative Poeciliid Fishes for Monitoring Selenium Exposure in the Endangered Desert Pupfish

We assessed the suitability of two nonnative poeciliid fishes—western mosquitofish (Gambusia affinis) and sailfin mollies (Poecilia latipinna)—for monitoring selenium exposure in desert pupfish (Cyprinodon macularius). Our investigation was prompted by a need to avoid lethal take of an endangered species (pupfish) when sampling fish for chemical analysis. Total selenium (SeTot) concentrations in both poeciliids were highly correlated with SeTot concentrations in pupfish. However, mean SeTot concentrations varied among fish species, with higher concentrations measured in mosquitofish than in mollies and pupfish from one of three sampled agricultural drains. Moreover, regression equations describing the relationship of selenomethionine to SeTot differed between mosquitofish and pupfish, but not between mollies and pupfish. Because selenium accumulates in animals primarily through dietary exposure, we examined fish trophic relationships by measuring stable isotopes (δ 13C and δ 15N) and gut contents. According to δ 13C measurements, the trophic pathway leading to mosquitofish was more carbon-depleted than trophic pathways leading to mollies and pupfish, suggesting that energy flow to mosquitofish originated from allochthonous sources (terrestrial vegetation, emergent macrophytes, or both), whereas energy flow to mollies and pupfish originated from autochthonous sources (filamentous algae, submerged macrophytes, or both). The δ 15N measurements indicated that mosquitofish and mollies occupied similar trophic levels, whereas pupfish occupied a slightly higher trophic level. Analysis of gut contents showed that mosquitofish consumed mostly winged insects (an indication of terrestrial taxa), whereas mollies and pupfish consumed mostly organic detritus. Judging from our results, only mollies (not mosquitofish) are suitable for monitoring selenium exposure in pupfish.

Selenium in aquatic biota inhabiting agricultural drains in the Salton Sea Basin, California

Resource managers are concerned that water conservation practices in irrigated farmlands along the southern border of the Salton Sea, Imperial County, California, could increase selenium concentrations in agricultural drainwater and harm the desert pupfish (Cyprinodon macularius), a federally protected endangered species. As part of a broader attempt to address this concern, we conducted a 3-year investigation to collect baseline information on selenium concentrations in seven agricultural drains inhabited by pupfish. We collected water, sediment, selected aquatic food-chain taxa (particulate organic detritus, filamentous algae, net plankton, and midge [Chironomidae] larvae), and two poeciliid fishes (western mosquitofish Gambusia affinis and sailfin molly Poecilia latipinna) for selenium determinations. The two fish species served as ecological surrogates for pupfish, which we were not permitted to sacrifice. Dissolved selenium ranged from 0.70 to 32.8 μg/L, with selenate as the major constituent. Total selenium concentrations in other environmental matrices varied widely among drains, with one drain (Trifolium 18) exhibiting especially high concentrations in detritus, 5.98-58.0 μg Se/g; midge larvae, 12.7-50.6 μg Se/g; mosquitofish, 13.2-20.2 μg Se/g; and mollies, 12.8-30.4 μg Se/g (all tissue concentrations are based on dry weights). Although toxic thresholds for selenium in fishes from the Salton Sea are still poorly understood, available evidence suggests that ambient concentrations of this element may not be sufficiently elevated to adversely affect reproductive success and survival in selenium-tolerant poeciliids and pupfish.

BINARY FISH PASSAGE MODELS FOR UNIFORM AND NONUNIFORM FLOWS

ABSTRACTBinary fish passage models are considered by many fisheries' managers to be the best available practice for culvert inventory assessments and for fishway design. Misunderstandings between different passage‐modelling approaches often arise, however, because of the absence of a formal comparison between the different approaches that include detailed derivations with consistent terminology and example applications. In this paper, one‐dimensional binary fish passage models were reviewed, and derivations from basic principles were provided for clarification. For uniform flow, a simple exhaustion‐threshold (ET) model equation was derived that predicts the flow velocity threshold in a fishway that causes exhaustion at a given maximum distance of ascent if a fish swims at the optimal ground speed. Velocities at or above the threshold predict failure to pass (exclusion). Velocities below the threshold predict passage. The ET model was therefore intuitive and easily applied to predict passage or exclusion. It was also shown to be consistent with the ascent‐distance (AD) model that shows that fish must adopt an optimal ground speed to maximize AD. The limitation of passage models to uniform flow was addressed by deriving a general model framework for passage that accounts for nonuniform flow conditions more commonly found in the field, including backwater and drawdown water‐surface profiles. Comparison of these models with experimental observations of volitional passage for top‐performing western mosquitofish Gambusia affinis indicates reasonable prediction of binary outcomes (passage or exclusion) if the flow velocity is not near the threshold flow velocity. More research is needed on fish behaviour, passage strategies under nonuniform flow regimes and stochastic methods that account for individual differences in swimming performance. Future experiments should track and measure ground speeds of ascending fish to test passage strategies and to improve model predictions. Stochastic models, such as Monte‐Carlo techniques, that account for different passage performance among individuals and allow prediction of the percentage of fish passing are needed to improve fish passage prediction. Published in 2011 by John Wiley & Sons, Ltd.

Parasitic Nematodes Decrease Fecundity in the Western Mosquitofish, Gambusia affinis

Abstract I tested effects of infection by the parasitic larval nematode Eustrongylides ignotus on reproduction in the livebearing western mosquitofish Gambusia affinis. Generally, parasitized females had fewer developing broods than nonparasitized females. Parasitic nematodes significantly reduced fecundity in the western mosquitofish.

Induction of micronuclei and nuclear abnormalities in erythrocytes of mosquito fish (Gambusia affinis) following exposure to the pyrethroid insecticide lambda-cyhalothrin

In the present study the induction of micronuclei (MN) and nuclear abnormalities (NA) in erythrocytes of mosquitofish (Gambusia affinis) (Baird & Girard 1853) was studied. Fish were exposed to three different concentrations of lambda-cyhalothrin (LCT) (1×10−4μg/l, 2×10−4μg/l, 4×10−4μg/l) for periods of 6, 12, 24, and 48h. NA (notched, lobed, blebbed nuclei), MN, bi-nucleated cells, and the ratio of polychromatic erythrocytes (PCEs) to normochromatic erythrocytes (NCEs) were evaluated to assess genotoxicity and cytotoxicity. LCT significantly induced MN and NA in erythrocytes of G. affinis. The PCE/NCE ratio was also decreased after 24- and 48-h treatments of 4×10−4μg/l LCT. The results show that LCT has genotoxic and cytotoxic potential on G. affinis.

Bioconcentration and depuration of endosulfan sulfate in mosquito fish ( Gambusia affinis)

Endosulfan is an insecticide which has been widely used in agriculture. The technical grade material consists of two isomers (alpha and beta). Under natural environmental conditions, endosulfan is metabolized through oxidation and the main metabolite in the environment is endosulfan sulfate. Most ecotoxicology research has been conducted with technical grade endosulfan to determine effects on non-target aquatic organisms. Little data on the effects of endosulfan sulfate on aquatic organisms are available in the literature. This study characterizes endosulfan sulfate bioconcentration and depuration in mosquito fish ( Gambusia affinis). During the study, G. affinis was exposed to an environmentally relevant endosulfan sulfate concentration of 0.25 μg L −1 for 5 weeks (uptake phase) followed by a 3-week period (depuration phase) in clean water. This study found that G. affinis bioconcentrated endosulfan sulfate. During the exposure phase, fish tissue concentrations of endosulfan sulfate increased with time up to 730 μg kg −1 dw or 215 μg kg −1 ww. The bioconcentration data followed Michaelis–Menten kinetics better than the one-compartment first order kinetics (1-CFOK). Using these models, the bioconcentration factors for endosulfan sulfate-exposed G. affinis were from 687 to 888 L kg −1 in wet weight or 2263 to 2936 L kg −1 in dry weight. During the depuration phase, endosulfan sulfate concentrations in tissue significantly decreased and the data followed first order kinetics. The half-life of endosulfan sulfate in G. affinis was about 9 d. There was no significant difference in standard length or weight between control and exposed fish. The growth data followed the von Bertalanffy growth model. However, the condition factor of exposed fish increased with time during the exposure phase.

Effects of Ammonium Nitrate, Urea, and Sodium Nitrate on Mosquitofish (Gambusia affinis) Survivorship

Abstract. Nitrogenous pollutants are commonly found in freshwater ecosystems due to fertilizer and chemical runoff from farm land and industrial waste. Nitrogenous compounds can result in toxic effects on aquatic vertebrates and invertebrates. The aim of this study was to determine the effects of ammonium nitrate, urea, and sodium nitrate on mosquitofish (Gambusia affinis) survivorship. Ammonium nitrate had a significant negative effect on survivorship, but urea and sodium nitrate had no effect on survivorship. This suggests that mosquitofish may be susceptible to ammonia pollution, but probably can tolerate most environmentally relevant exposures to urea and nitrate.

Effects of mosquitofish and ammonium nitrate on activity of green frog (Lithobates clamitans) tadpoles: a mesocosm experiment

We conducted a mesocosm experiment that allowed us to examine the effects of mosquitofish (Gambusia affinis) and ammonium nitrate on the activity of green frog (Lithobates clamitans) tadpoles under the more natural conditions of a mesocosm as opposed to a laboratory experiment. The proportion of active tadpoles was lower in the presence of mosquitofish than when mosquitofish were not present. There was no effect of ammonium nitrate or interaction between mosquitofish and ammonium nitrate on tadpole activity. These results suggest that green frog tadpoles reduce their activity levels in the presence of mosquitofish, but the ability of ammonium nitrate to mediate the outcome of potential predator–prey interactions between green frog tadpoles and mosquitofish appears to be limited, at least at the ecologically relevant concentration we studied.

Bioaccumulation and toxicity of copper in outdoor freshwater microcosms

This study characterizes the effects of copper (Cu) on Florida apple snails ( Pomacea paludosa) and mosquito fish ( Gambusia affinis) using a replicated outdoor microcosm design. Soils used in this study were collected from two Cu-enriched citrus agricultural sites in South Florida (Agler property (AGLR) in St. Lucie County and Sunrise Boys property (SRB) in Palm Beach County) and a reference site (Equus property) in St. Lucie County. The study included a 5-week aging phase, an 11 month exposure phase, and a 3 month post-treatment (exposure) phase. The aging phase was initiated by flooding agricultural soils with rainwater in 4 m 3 fiberglass microcosm tanks. Introducing juvenile apple snails (≤7 d old) and mosquito fish (2–3 cm) into the microcosm tanks initiated the exposure phase. Survival, growth, and reproduction of apple snails and fish, and Cu uptake in apple snails, fish, and periphyton were determined in this study. Water chemistry (e.g., dissolved Cu concentration, dissolved organic carbon and dissolved oxygen concentrations, pH, hardness, alkalinity, etc.) was measured daily or weekly during the study. Initial soil Cu concentrations in Equus, SRB, and AGLR microcosms were 7, 55, and 99 mg/kg dw, respectively. Dissolved Cu concentrations in Equus, SRB and AGLR microcosms at the beginning of the study were 3, 82, and 43 μg/L, respectively and decreased to low saturation levels of about ≤9 μg/L Cu after the first 3 months of the study. The decrease of dissolved Cu concentrations was likely due to the dilution of rainwater. Snail and fish mortality appeared to be higher in SRB microcosms than in Equus and AGLR microcosms. There was no significant difference in growth of the snails between treatments. Snail growth data followed the von Bertalanffy Model. The maximum shell length, shell height, and shell width of the snails calculated by the von Bertalanffy Model ( L ∞) were 2.76, 2.05, and 2.18 cm, respectively. The maximum wet weight was 9.38 g. Growth rate ( k) of the snails increased in order of shell height (0.459), shell length (0.550), and shell weight (0.598). There was no reproduction in the snails in any treatments including the reference during the exposure phase. However, Cu did not affect reproduction of fish during this period. Copper concentrations in periphyton from Equus, SRB, and AGLR microcosms ranged from 2 to 62, 31 to 371, and 13 to 478 mg/kg, respectively. Copper concentrations in fish at the beginning, days 30 and 150 of the study ranged from 3.19 to 7.53 mg/kg and were not significantly different from the different treatments. Average Cu concentrations in the soft tissue of dead snails from SRB and AGLR microcosms were 4602 mg/kg dw (ranged from 2913 to 8370 mg/kg dw) and 2824 mg/kg dw (ranged from 2118 to 3600 mg/kg dw), respectively. The Cu concentrations in the soft tissue of dead snails found in this study were higher than the tissue Cu concentrations in live aquatic organisms reported in the literature. These high Cu concentrations in edible apple snail soft tissue might pose a risk to Florida apple snail predators, including the snail kite. The post-exposure phase, with snails exposed to only water (i.e., no soils) showed depuration of copper from apple snails and reproduction in all treatments.

Ten novel microsatellite markers for the western mosquitofish Gambusia affinis

We isolated and characterized 10 microsatellite loci from the western mosquitofish, Gambusia affinis. Loci were screened in 30 individuals from a single location from their native range in coastal Texas. The number of alleles per locus ranged from 4 to 25, observed heterozygosity ranged from 0.40 to 0.93, and the probability of identity values from 6.0 × 10−3 to 2.7 × 10−1, with an overall PI for all loci of 1.3 × 10−13. These new loci provide tools for examining the genetic diversity, structure, and pedigree G. affinis populations.

Adaptation to sea level rise: does local adaptation influence the demography of coastal fish populations?

This study compared the growth of two western mosquitofish Gambusia affinis populations that were previously demonstrated to have genetic adaptations that increased survival under lethal salinity exposures. The objective was to evaluate how genetic adaptations to lethal salinity stress affect population demography when exposed to sublethal salinity stress. Results indicate that chronic salinity exposure had a generally negative impact on population size, but fish originating from one of the two populations established with fish from a brackish site exhibited an increase in population size. Saltwater intrusion seems to result in reduced population size for most populations. Some populations inhabiting more saline sites, however, may develop localized adaptations, mitigating the consequences of increased salinity on population productivity.

Spatial and Temporal Distribution of the Asian Fish Tapeworm Bothriocephalus acheilognathi (Cestoda: Bothriocephalidea) in the Rio Grande (Río Bravo del Norte)

Recent collections of the Asian fish tapeworm Bothriocephalus acheilognathi in the Rio Grande have raised concern about the potential impacts on Rio Grande endemic and imperiled fishes. The objectives of this study were to determine distribution and definitive hosts of the Asian fish tapeworm within the Rio Grande drainage and to quantify occurrences and abundances. In total, 1,992 fish spanning 11 families were collected and examined for Asian fish tapeworms in the Rio Grande and the Pecos and Devils rivers. The parasite was collected from red shiners Cyprinella lutrensis, Tamaulipas shiners Notropis braytoni, sand shiners N. stramineus, river carpsuckers Carpiodes carpio, plains killifish Fundulus zebrinus, western mosquitofish Gambusia affinis, blue suckers Cycleptus elongatus, blacktail shiners Cyprinella venusta, proserpine shiners Cyprinella proserpina, and Manantial roundnose minnow Dionda argentosa, with the latter four species being new host records. Monthly collections of red shiners from Big Bend National Park exhibited prevalence levels above 15% in January-March and December and below 10% during April-June and October. With over 50% of the Rio Grande icthyofauna in Texas considered imperiled, the occurrence and pathological effects of the Asian fish tapeworm in combination with reduced water quantity and quality and increased habitat fragmentation are of concern for these taxa.

Relative Size of Males and Competition for Females Induces Homosexual Behavior in the Western Mosquitofish (Gambusia affinis) Under Laboratory Conditions

In an ongoing experiment, we investigated how mating behaviors of male western mosquitofish Gambusia affinis change across a range of temperatures. During behavioral trials, we observed high levels of homosexual behavior between males when in a competitive situation. We observed that when two males are in competition for matings with females, the smaller male performed significantly more homosexual acts than the larger. These results suggest that a dominance relationship develops with males in competition, where large males may dominate small males by not allowing them to copulate with the female, thereby causing an increase in same-sex mating by smaller males. Although preliminary data also indicate a possible relationship between density of males and number of homosexual copulations, we were not able to statistically analyze the relationship because these observations occurred during an ongoing experiment. In a future study, we will seek to understand underlying causes of homosexual behavior in the western mosquitofish.

Life history variation along a salinity gradient in coastal marshes

Coastal habitats are susceptible to changes in the environment associated with alter- ations in salinity. A field study was conducted on natural populations of the sailfin molly Poecilia latipinna, the western mosquitofish Gambusia affinis and the least killifish Heterandria formosa col- lected from coastal marsh sites along a salinity gradient, to investigate the influence of salinity on body condition and reproductive life history traits. In brackish marsh sites male P. latipinna had the best body conditions, while females had similar body conditions across all 3 marsh types. Female P. latipinna had greater reproductive allotment and fecundity in brackish marshes, where this fish was most abundant. Specimens of G. affinis collected from fresh marsh sites had less favorable body condition, and females had lower reproductive allotment and fecundity than those collected from higher salinities. While G. affinis was more abundant in freshwater marshes than in higher salinity marshes, this higher abundance did not correspond with a better body condition or higher reproduc- tive effort, suggesting that G. affinis may be stressed in freshwater. There was no difference in the conditions between (both male and female) H. formosa from fresh and intermediate marshes. Female H. formosa from fresh marshes had a similar reproductive allotment and lower fecundity than those from intermediate marshes. The 3 species exhibited different life history patterns along the salinity gradient, and some of these patterns conflicted with expectations based on species abundances. When assessing habitat quality along an environmental gradient, measures of abundance should be accompanied by more sensitive indicators of environmental stress.

Behavioral Responses of the Endemic Shrimp Halocaridina rubra (Malacostraca: Atyidae) to an Introduced Fish, Gambusia affinis (Actinopterygii: Poeciliidae) and Implications for the Trophic Structure of Hawaiian Anchialine Ponds

In the Hawaiian Islands, intentionally introduced exotic fishes have been linked to changes in native biodiversity and community composition. In 1905, the mosquito fish Gambusia affinis was introduced to control mosquitoes. Subsequently, G. affinis spread throughout the Islands and into coastal anchialine ponds. Previous studies suggest that presence of invasive fishes in anchialine ponds may eliminate native species, including the endemic shrimp Halocaridina rubra. We examined effects of G. affinis on H. rubra populations in anchialine ponds on the Kona-Kohala coast of the island of Hawai‘i. In the presence of G. affinis, H. rubra exhibited a diel activity pattern that was not seen in fishless ponds. Shrimp in ponds with fish were active only at night. This pattern was evident in anchialine ponds and in laboratory experiments. In laboratory predation experiments, G. affinis preferentially consumed smaller H. rubra, and in the field the H. rubra collected from invaded sites were larger than those from fishless ponds. Analysis of trophic position using stable isotope analyses showed that feeding of H. rubra was not significantly distinct from that of snails, assumed to feed at trophic level 2.0 on epilithic algae, but G. affinis was slightly omnivorous, feeding at tropic level 2.2. The mosquito fish diet was apparently composed primarily of algae when the defensive behavior of H. rubra made them substantially unavailable as prey. The effect of successful establishment of G. affinis on shrimp behavior has the potential to alter abundance of benthic algae and processing and recycling of nutrients in anchialine pond ecosystems.

Effects of potential predator and competitor cues and sibship on wood frog (Rana sylvatica) embryos

Abstract Chemical cues emitted from predators or competitors are often important for animals living in aquatic ecosystems as they allow potential prey to assess predation risk and make appropriate risk-sensitive responses. In our experiment, we examined if wood frog (Rana sylvatica) embryos exposed to potential predator and competitor cues would alter their time to hatching, size at hatching, or survivorship. Eggs from four different sibships were subjected to a variety of cues including dragonfly larvae (potential tadpole predator), mosquitofish (Gambusia affinis; a non-native potential egg and tadpole predator), and overwintered tadpoles of Rana sp. (potential competitors). We found no significant effects of any of the cues. However, we did find significant variation in mean time to hatching and mean hatchling size among sibships. Our results suggest that wood frog embryos may have limited ability to respond to some cues at the embryonic stage, at least for the concentrations and conditions used in this experiment. Our results do indicate genetic or parental effects can affect embryonic wood frog development rate and hatchling size.

Western Mosquitofish Predation on Native Amphibian Eggs and Larvae

ABSTRACT The western mosquitofish (Gambusia affinis) is commonly stocked for mosquito control, but this species has the potential to negatively impact native amphibians through predation on early life stages. We examined predation by western mosquitofish on eggs and larvae of wood frog (Rana sylvatica), American toad (Bufo americanus), eastern tiger salamander (Ambystoma tigrinum tigrinum), and western chorus fiog (Pseudacris triseriata triseriata) using a series of laboratory microcosm experiments. There were no eggs of any amphibian species consumed by western mosquitofish, and only one predation attempt was observed on a western chorus frog egg. No predation was observed on larvae of wood frog or American toad, and there was no significant difference in the percentage of larvae of these two species missing at the end of the experimental trials (11% and 6%, respectively). However, eastern tiger salamander and western chorus fiog larvae experienced significantly higher predation rates than the other two amphibian species, with approximately 59% of tiger salamander and 92% of chorus frog larvae missing at the end of the experiments. Based on these results, we do not recommend stocking western mosquitofish into waterways that contain early life stages of native amphibian species.

Time course evaluation of N-nitrosodialkylamines-induced DNA alkylation and oxidation in liver of mosquito fish

Here we simultaneously measured N7-alkylguanines and 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) in liver of small fish, respectively, to assess the time course of the formation and removal of alkylation and oxidative damage to DNA caused by N-nitrosodialkylamines. Mosquito fish ( Gambusia affinis) were killed at various times during (4 days) and post-exposure (16 days) to N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) alone or their combination with concentrations of 10 and 50 mg/l. The modified guanine adducts were sensitively and selectively quantitated by isotope-dilution LC–MS/MS methods. During exposure, N7-methylguanine (N7-MeG) and N7-ethylguanine (N7-EtG) in liver DNA increased with the duration and dose of N-nitrosodialkylamine exposure, while 8-oxodG was dose-dependently induced within 1 day. It was found that NDMA formed substantially more N7-alkylated guanines and 8-oxodG than NDEA on the basis of adducts formed per micromolar concentration, suggesting that NDMA can be more easily bioactivated than NDEA to form reactive alkylating agents with the concomitant formation of oxygen radicals. After cessation of exposure, N7-alkylguanines remained elevated for 1 day and then gradually decreased over time but still higher than the background levels, even at day 16 (half-lives of 7–8 days). However, 8-oxodG was excised quickly from liver DNA and returned to the background level within 4 days post-exposure (half-lives less than 2 days). Taken together, this study firstly demonstrated that in addition to alkylation, N-nitrosodialkylamines can concurrently cause oxidative damage to DNA in vivo.