Exposure to microplastics impairs digestive performance, stimulates immune response and induces microbiota dysbiosis in the gut of juvenile guppy (Poecilia reticulata)

Microplastics (MPs) are widely distributing in aquatic environment. They are easily ingested by aquatic organisms and accumulate in digestive tract especially of intestine. To explore the potential effects of MPs on intestine, here we, using juvenile guppy (Poecilia reticulata) as experimental animal, investigated the response characteristics of digestion, immunity and gut microbiota. After exposure to 100 and 1000 μg/L concentrations of MPs (polystyrene; 32-40 μm diameters) for 28 days, we observed that MPs could exist in guppy gut and induce enlargement of goblet cells. Activities of digestive enzymes (trypsin, chymotrypsin, amylase and lipase) in guppy gut generally reduced. MPs stimulated the expression of immune cytokines (TNF-α, IFN-γ, TLR4 and IL-6). Through high throughput sequencing of 16S rRNA gene, decreases in diversity and evenness and changed composition of microbiota were found in guppy gut. PICRUSt analysis revealed that MPs might have effects on intestinal microbiota functions, such as inhibition of metabolism and repair pathway. Our findings suggested that MPs could retain in the gut of juvenile guppy, impair digestive performance, stimulate immune response and induce microbiota dysbiosis in guppy gut. The results obtained here provide new insights into the potential risks of MPs to aquatic animals.

Predation pressure shapes brain anatomy in the wild

There is remarkable diversity in brain anatomy among vertebrates and evidence is accumulating that predatory interactions are crucially important for this diversity. To test this hypothesis, we collected female guppies (Poecilia reticulata) from 16 wild populations and related their brain anatomy to several aspects of predation pressure in this ecosystem, such as the biomass of the four major predators of guppies (one prawn and three fish species), and predator diversity (number of predatory fish species in each site). We found that populations from localities with higher prawn biomass had relatively larger telencephalon size as well as larger brains. Optic tectum size was positively associated with one of the fish predator’s biomass and with overall predator diversity. However, both olfactory bulb and hypothalamus size were negatively associated with the biomass of another of the fish predators. Hence, while fish predator occurrence is associated with variation in brain anatomy, prawn occurrence is associated with variation in brain size. Our results suggest that cognitive challenges posed by local differences in predator communities may lead to changes in prey brain anatomy in the wild.

Toxic effects of the herbicide Roundup in the guppy Poecilia vivipara acclimated to fresh water

Although it is believed that glyphosate-based herbicides are relatively nontoxic to humans, its broad use in agriculture and consequent contamination of aquatic systems is a concern. In the present study, reproductive (sperm quality) and biochemical parameters (acetylcholinesterase and glutathione S-transferase activity, lipoperoxidation, and antioxidant capacity against peroxyl radicals) were evaluated in adult guppies (Poecilia vivipara) acclimated to fresh water and exposed (96 h) to environmentally realistic concentrations of glyphosate (130 and 700 μg L(-1)) as the commercial formulation Roundup. Male guppies exposed to Roundup showed a poorer sperm quality, measured as reduced plasmatic membrane integrity, mitochondrial functionality, DNA integrity, motility, motility period and concentration of spermatic cells, than those kept under control condition (no Roundup addition to the water). Most of the spermatic parameters analyzed showed strong association to each other, which may help to understand the mechanisms underlying the observed reduction in sperm quality. Exposure to Roundup did not alter the biochemical parameters analyzed, though differences between genders were observed and deserve further investigations. Findings from the present study suggest that exposure to environmentally relevant concentrations of Roundup may negatively affect at long-term the reproduction of P. vivipara, with consequent changes in fish populations inhabiting environments contaminated with the herbicide.

Genotoxic and mutagenic assessment of iron oxide (maghemite-γ-Fe2O3) nanoparticle in the guppy Poecilia reticulata

The environmental risk of nanomaterials (NMs) designed and used in nanoremediation process is of emerging concern, but their ecotoxic effects to aquatic organism remains unclear. In this study, the citrate-coated (maghemite) nanoparticles (IONPs) were synthesized and its genotoxic and mutagenic effects were investigated in the female guppy Poecilia reticulata. Fish were exposed to IONPs at environmentally relevant iron concentration (0.3 mg L^-1) during 21 days and the animals were collected at the beginning of the experiment and after 3, 7, 14 and 21 days of exposure. The genotoxicity and mutagenicity were evaluated in terms of DNA damage (comet assay), micronucleus (MN) test and erythrocyte nuclear abnormalities (ENA) frequency. Results showed differential genotoxic and mutagenic effects of IONPs in the P. reticulata according to exposure time. The IONP induced DNA damage in P. reticulata after acute (3 and 7 days) and long-term exposure (14 and 21 days), while the mutagenic effects were observed only after long-term exposure. The DNA damage and the total ENA frequency increase linearly over the exposure time, indicating a higher induction rate of clastogenic and aneugenic effects in P. reticulata erythrocytes after long-term exposure to IONPs. Results indicated that the P. reticulata erythrocytes are target of ecotoxicity of IONPs.

Sex in troubled waters: Widespread agricultural contaminant disrupts reproductive behaviour in fish

Chemical pollution is a pervasive and insidious agent of environmental change. One class of chemical pollutant threatening ecosystems globally is the endocrine disrupting chemicals (EDCs). The capacity of EDCs to disrupt development and reproduction is well established, but their effects on behaviour have received far less attention. Here, we investigate the impact of a widespread androgenic EDC on reproductive behaviour in the guppy, Poecilia reticulata. We found that short-term exposure of male guppies to an environmentally relevant concentration of 17β-trenbolone-a common environmental pollutant associated with livestock production-influenced the amount of male courtship and forced copulatory behaviour (sneaking) performed toward females, as well as the receptivity of females toward exposed males. Exposure to 17β-trenbolone was also associated with greater male mass. However, no effect of female exposure to 17β-trenbolone was detected on female reproductive behaviour, indicating sex-specific vulnerability at this dosage. Our study is the first to show altered male reproductive behaviour following exposure to an environmentally realistic concentration of 17β-trenbolone, demonstrating the possibility of widespread disruption of mating systems of aquatic organisms by common agricultural contaminants.

Acute exposure to environmentally relevant concentrations of benzophenone-3 induced genotoxicity in Poecilia reticulata

The organic UV filter benzophenone-3 (BP-3), widely used in the commercial formulations of sunscreens and personal care products, is considered an emerging pollutant and has been associated with several human and environmental health concerns. However, knowledge about their mode of action and ecotoxicity on aquatic biota is scarce. In this scenario, the objective of this work was to evaluate the genotoxic, mutagenic, and erythrotoxicity effects of BP-3 in the guppy Poecilia reticulata after acute exposure. Adult females of P. reticulata were exposed to three non-lethal and environmentally relevant concentrations of BP-3 (10, 100, and 1000 ng L^-1) during 96 h of exposure, and the somatic parameter [Fulton condition factor (K)], genotoxicity (comet assay), mutagenicity [micronucleus (MN) and erythrocyte nuclear abnormalities (ENA) tests] and erythrotoxicity parameters (such as total cell area and nucleus-cytoplasmic ratio) were analyzed. Results showed that the general physiological condition (K value) of fish was not affected by acute exposure to BP-3. However, BP-3 induced DNA damage at 100 and 1000 ng L^-1 and increased the frequency of total ENA at 1000 ng L^-1, specially lobed nucleus, when compared to control group, indicating its genotoxic and mutagenic effects. Furthermore, the BP-3 did not induce significant changes in the total cell area and nucleus-cytoplasmic ratio. In summary, results showed that the BP-3 at environmentally relevant concentration was genotoxic to freshwater fish P. reticulata, confirming its environmental risk.

The agricultural contaminant 17β-trenbolone disrupts male-male competition in the guppy (Poecilia reticulata)

Despite a growing literature highlighting the potential impact of human-induced environmental change on mechanisms of sexual selection, relatively little is known about the effects of chemical pollutants on male-male competition. One class of environmental pollutant likely to impact male competitive interactions is the endocrine-disrupting chemicals (EDCs), a large and heterogeneous group of chemical contaminants with the potential to influence morphology, physiology and behaviour at minute concentrations. One EDC of increasing concern is the synthetic, androgenic steroid 17β-trenbolone, which is used globally to promote growth in beef cattle. Although 17β-trenbolone has been found to cause severe morphological and behavioural abnormalities in fish, its potential impact on male-male competition has yet to be investigated. To address this, we exposed wild male guppies (Poecilia reticulata) to an environmentally realistic concentration of 17β-trenbolone (average measured concentration: 8 ng/L) for 21 days using a flow-through system. We found that, in the presence of a competitor, 17β-trenbolone-exposed males carried out more frequent aggressive behaviours towards rival males than did unexposed males, as well as performing less courting behaviour and more sneak (i.e., coercive) mating attempts towards females. Considering that, by influencing mating outcomes, male-male competition has important consequences for population dynamics and broader evolutionary processes, this study highlights the need for greater understanding of the potential impact of EDCs on the mechanisms of sexual selection.

Casting a wider fish net on animal models in neuropsychiatric research

Neuropsychiatric disorders, such as schizophrenia, are associated with abnormal brain development. In this review, we discuss how studying dimensional components of these disorders, or endophenotypes, in a wider range of animal models will deepen our understanding of how interactions between biological and environmental factors alter the trajectory of neurodevelopment leading to aberrant behavior. In particular, we discuss some of the advantages of incorporating studies of brain and behavior using a range of teleost fish species into current neuropsychiatric research. From the perspective of comparative neurobiology, teleosts share a fundamental pattern of neurodevelopment and functional brain organization with other vertebrates, including humans. These shared features provide a basis for experimentally probing the mechanisms of disease-associated brain abnormalities. Moreover, incorporating information about how behaviors have been shaped by evolution will allow us to better understand the relevance of behavioral variation to determine their physiological underpinnings. We believe that exploiting the conservation in brain development across vertebrate species, and the rich diversity of fish behavior in lab and natural populations will lead to significant new insights and a holistic understanding of the neurobiological systems implicated in neuropsychiatric disorders.

Comparing Long-Read Assemblers to Explore the Potential of a Sustainable Low-Cost, Low-Infrastructure Approach to Sequence Antimicrobial Resistant Bacteria With Oxford Nanopore Sequencing

Long-read sequencing (LRS) can resolve repetitive regions, a limitation of short read (SR) data. Reduced cost and instrument size has led to a steady increase in LRS across diagnostics and research. Here, we re-basecalled FAST5 data sequenced between 2018 and 2021 and analyzed the data in relation to gDNA across a large dataset (n = 200) spanning a wide GC content (25-67%). We examined whether re-basecalled data would improve the hybrid assembly, and, for a smaller cohort, compared long read (LR) assemblies in the context of antimicrobial resistance (AMR) genes and mobile genetic elements. We included a cost analysis when comparing SR and LR instruments. We compared the R9 and R10 chemistries and reported not only a larger yield but increased read quality with R9 flow cells. There were often discrepancies with ARG presence/absence and/or variant detection in LR assemblies. Flye-based assemblies were generally efficient at detecting the presence of ARG on both the chromosome and plasmids. Raven performed more quickly but inconsistently recovered small plasmids, notably a ∼15-kb Col-like plasmid harboring bla KPC . Canu assemblies were the most fragmented, with genome sizes larger than expected. LR assemblies failed to consistently determine multiple copies of the same ARG as identified by the Unicycler reference. Even with improvements to ONT chemistry and basecalling, long-read assemblies can lead to misinterpretation of data. If LR data are currently being relied upon, it is necessary to perform multiple assemblies, although this is resource (computing) intensive and not yet readily available/useable.

Behavioural responses of feral and domestic guppies (Poecilia reticulata) to predators and their cues

Predation is an important factor during adaptation to novel environments, and the feralisation of introduced domestic species often involves responding appropriately to allopatric predators despite a background of domestication and inbreeding. Twenty years ago, domestic guppies were introduced to a semi-natural environment at Burgers' Zoo in the Netherlands, where they have since been exposed to avian predation. We compared predation-linked behaviours in this feral population and in domestic guppies akin to the original founders. We found that both populations responded to a novel predator and to conspecific alarm cues. However, shoaling, an important anti-predator behaviour, was higher among feral guppies both at baseline and when exposed to the novel predator. We did not observe a linked suite of anti-predator behaviours across shoaling, predator inspection, alarm substance sensitivity and boldness, suggesting that these responses may be decoupled from one another depending on local predation regimes. As we compared two populations, we cannot identify the causal factors determining population differences, however, our results do suggest that shoaling is either a particularly consequential anti-predator adaptation or the most labile of the behaviours we tested. Finally, the behavioural adaptability of domestic guppies may help to explain their success as an invasive species.

Effects of the SSRI citalopram on behaviours connected to stress and reproduction in Endler guppy, Poecilia wingei

Psychoactive drugs, such as selective serotonin reuptake inhibitors (SSRI) have been identified in high levels in effluents from Swedish sewage treatment plants (STP) at concentrations high enough to give pharmacological effects in fish. In humans SSRIs are used in the treatment of depression and they have anxiolytic effects. In the present study we exposed Endler guppy (Poecilia wingei) of both sexes to citalopram that showed the highest concentrations of SSRIs in STP effluents and studied reproductive and non-reproductive behaviour. Male courting behaviours were not affected compared to control fish after 14-28 days exposure to 1 μg L(-1). In two experiments exposing both sexes to 0.2, 2.3 or 15 μg L(-1) for 21 days, fish exposed to the two highest doses showed anxiolytic effects when placed in a novel environment (novel tank diving test, NT). Males were only affected by exposure to 15 μg L(-1). They had significantly longer latency to explore the upper half of the aquarium, more visits and longer time spent in the upper half, and showed less bottom freezing behaviour, all markers of anxiolytic behaviour. In females exposure to 2.3 or 15 μg L(-1) significantly increased freezing behaviour, while no effects on other behaviour variables were observed. No effects on shoaling behaviour could be discerned. These results show that citalopram have anxiolytic effects on guppy fish and thus affect ecologically relevant behaviours of importance to survival of fish.

Life-time exposure to waterborne copper II: Patterns of tissue accumulation and gene expression of the metal-transport proteins ctr1 and atp7b in the killifish Poecilia vivipara

The involvement of transporting proteins on copper (Cu) bioaccumulation was evaluated in the killifish Poecilia vivipara chronically exposed to environmentally relevant concentrations of waterborne Cu. Fish (<24 h-old) were maintained under control condition or exposed to different waterborne Cu concentrations (5, 9 and 20 μg/L) for 28 and 345 days in saltwater. Following exposure periods, Cu accumulation and the expression of genes encoding for the high affinity Cu-transporter (ctr1) and the P-type Cu-ATPase (atp7b) were evaluated. Whole-body metal accumulation and gene expression were evaluated in fish exposed to 28 days. Similarly, in fish exposed to 345 days, liver, gills and gut were also evaluated. No fish survival was observed after exposure to 20 μg/L for 345 days. Whole-body Cu accumulation was significantly higher in fish exposed to 20 μg/L Cu for 28 days and in fish exposed to 9 μg/L for 345 days in comparison to control animals. Similarly, tissue Cu accumulation was significantly higher in fish exposed to 9 μg/L for 345 days in comparison to control animal. However, no significant accumulation was observed in fish muscle. Following exposure for 28 days, whole-body ctr1 expression was slightly induced in fish exposed to 9 μg/L. In turn, no significant change in ctr1 expression was observed following exposure to Cu for 345 days. Differently, whole-body atp7b expression was markedly up-regulated in the whole-body of fish exposed Cu for 28 days and in tissues of fish exposed to Cu for 345 days. These findings indicate the expression of atp7b is more responsive to Cu accumulation in P. vivipara than ctr1 expression and, therefore, more suitable to be used as a biomarker of exposure to this metal. Also, we argue that the expression of atp7b is sustained at elevated levels for as much time as fish are maintained in Cu contaminated water.

Determining the efficacy of guppies and pyriproxyfen (Sumilarv® 2MR) combined with community engagement on dengue vectors in Cambodia: study protocol for a randomized controlled trial

Background

Evidence on the effectiveness of low-cost, sustainable, biological vector-control tools for the Aedes mosquitoes is limited. Therefore, the purpose of this trial is to estimate the impact of guppy fish (guppies), in combination with the use of the larvicide pyriproxyfen (Sumilarv® 2MR), and Communication for Behavioral Impact (COMBI) activities to reduce entomological indices in Cambodia.

Methods/design

In this cluster randomized controlled, superiority trial, 30 clusters comprising one or more villages each (with approximately 170 households) will be allocated, in a 1:1:1 ratio, to receive either (1) three interventions (guppies, Sumilarv® 2MR, and COMBI activities), (2) two interventions (guppies and COMBI activities), or (3) control (standard vector control). Households will be invited to participate, and entomology surveys among 40 randomly selected households per cluster will be carried out quarterly. The primary outcome will be the population density of adult female Aedes mosquitoes (i.e., number per house) trapped using adult resting collections. Secondary outcome measures will include the House Index, Container Index, Breteau Index, Pupae Per House, Pupae Per Person, mosquito infection rate, guppy fish coverage, Sumilarv® 2MR coverage, and percentage of respondents with knowledge about Aedes mosquitoes causing dengue. In the primary analysis, adult female Aedes density and mosquito infection rates will be aggregated over follow-up time points to give a single rate per cluster. This will be analyzed by negative binomial regression, yielding density ratios.

Discussion

This trial is expected to provide robust estimates of the intervention effect. A rigorous evaluation of these vector-control interventions is vital to developing an evidence-based dengue control strategy and to help direct government resources.

Trial registration

Current Controlled Trials, ID: ISRCTN85307778. Registered on 25 October 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2105-2) contains supplementary material, which is available to authorized users.

Habitat fragmentation caused by contaminants: Atrazine as a chemical barrier isolating fish populations

Information on how atrazine can affect the spatial distribution of organisms is non-existent. As this effect has been observed for some other contaminants, we hypothesized that atrazine-containing leachates/discharges could trigger spatial avoidance by the fish Poecilia reticulata and form a chemical barrier isolating upstream and downstream populations. Firstly, guppies were exposed to an atrazine gradient in a non-forced exposure system, in which organisms moved freely among the concentrations, to assess their ability to avoid atrazine. Secondly, a chemical barrier formed by atrazine, separating two clean habitats (extremities of the non-forced system), was simulated to assess whether the presence of the contaminant could prevent guppies from migrating to the other side of the system. Fish were able to avoid atrazine contamination at environmentally relevant concentrations (0.02 μg L^-1), below those described to cause sub-lethal effects. The AC₅₀ (atrazine concentration causing avoidance to 50% of the population) was 0.065 μg L^-1. The chemical barrier formed by atrazine at 150 μg L^-1 (concentration that should produce an avoidance around 82%) caused a reduction in the migratory potential of the fish by 47%; while the chemical barrier at 1058 μg L^-1 (concentration that produces torpidity) caused a reduction in the migratory potential of the fish by 91%. Contamination by atrazine, besides driving the spatial distribution of fish populations, has potential to act as a chemical barrier by isolating fish populations. This study includes a novel approach to be integrated in environmental risk assessment schemes to assess high-tier contamination effects such as habitat fragmentation and population displacement and isolation.

Reprint of "Effects of the SSRI citalopram on behaviours connected to stress and reproduction in Endler guppy, Poecilia wingei"

Psychoactive drugs, such as selective serotonin reuptake inhibitors (SSRI) have been identified in high levels in effluents from Swedish sewage treatment plants (STP) at concentrations high enough to give pharmacological effects in fish. In humans SSRIs are used in the treatment of depression and they have anxiolytic effects. In the present study we exposed Endler guppy (Poecilia wingei) of both sexes to citalopram that showed the highest concentrations of SSRIs in STP effluents and studied reproductive and non-reproductive behaviour. Male courting behaviours were not affected compared to control fish after 14-28 days exposure to 1 μgL(-1). In two experiments exposing both sexes to 0.2, 2.3 or 15 μgL(-1) for 21 days, fish exposed to the two highest doses showed anxiolytic effects when placed in a novel environment (novel tank diving test, NT). Males were only affected by exposure to 15 μgL(-1). They had significantly longer latency to explore the upper half of the aquarium, more visits and longer time spent in the upper half, and showed less bottom freezing behaviour, all markers of anxiolytic behaviour. In females exposure to 2.3 or 15 μgL(-1) significantly increased freezing behaviour, while no effects on other behaviour variables were observed. No effects on shoaling behaviour could be discerned. These results show that citalopram have anxiolytic effects on guppy fish and thus affect ecologically relevant behaviours of importance to survival of fish.

Environmentally relevant concentrations of benzophenone-3 induce differential histopathological responses in gills and liver of freshwater fish

BP-3 is one of the most used organic UV filters. However, its widespread use and release into aquatic environment can induce ecotoxicological impact on aquatic organisms. Thus, the aim of the current study is to evaluate the gills and liver of freshwater fish Poecilia reticulata subjected to acute exposure (96 h) to BP-3 at environmentally relevant concentrations (10-1000 ng L^-1). The study was based on adopting qualitative and semi-quantitative approach to assess histopathological changes and integrated the biomarker response in order to investigate organ-specific responses to BP-3 exposure. BP-3 has induced high histopathological index associated with circulatory disturbances, as well as with regressive and immunological changes in gills, whereas the hepatic histopathological index was associated with circulatory disturbances. Moreover, lower BP-3 concentrations were mostly associated with changes in gills, whereas higher BP-3 concentration was mostly linked to hepatic changes. In conclusion, acute exposure to BP-3 at environmentally relevant concentrations had stronger impact on gills than on the liver of P. reticulata, which confirmed organ-specific responses to UV filters.

Early visual experience influences behavioral lateralization in the guppy

Individual differences in lateralization of cognitive functions characterize both humans and non-human species. Genetic factors can account for only a fraction of the variance observed and the source of individual variation in laterality remains in large part elusive. Various environmental factors have been suggested to modulate the development of lateralization, including asymmetrical stimulation of the sensory system during ontogeny. In this study, we raised newborn guppies in an asymmetric environment to test the hypothesis that early left-right asymmetries in visual input may affect the development of cerebral asymmetries. Each fish was raised in an impoverished environment but could voluntarily observe a complex scene in a nearby compartment containing a group of conspecifics. Using asymmetric structures, we allowed some subjects to observe the complex scene with the right eye, others with the left eye, and control fish with both eyes. Among asymmetrically stimulated fish, the mirror test revealed eye dominance congruent with the direction of asymmetric stimulation, while controls showed no left-right laterality bias. Interestingly, asymmetric exposure to social stimuli also affected another aspect of visual lateralization-eye preference for scrutinizing a potential predator-but did not influence a measure of motor asymmetry. As the natural environment of guppies is fundamentally asymmetrical, we suggest that unequal left-right stimulation is a common occurrence in developing guppies and may represent a primary source of individual variation in lateralization as well as an efficient mechanism for producing laterality phenotypes that are adapted to local environmental conditions.

Analyzing complement activity in the serum and body homogenates of different fish species, using rabbit and sheep red blood cells

Alternative complement activity was determined in whole body homogenates (WBHs) and serum samples of different fish species, by measuring the amount of sample that induces 50% hemolysis of red blood cells using the ACH50 assay (Alternative Complement pathway Hemolytic activity). Values of ACH50 obtained for serum samples were about two-fold higher when using rabbit red blood cells (RRBC), as compared to sheep red blood cells (SRBC). The increase in ACH50 when using RRBCs for WBH samples was 28, 7 and 4 folds for guppy, molly and zebrafish, respectively. Large variability in complement activity was evident between fish species for both serum and WBHs. Evaluating the effect of freeze-thaw cycles on complement revealed significant reduction in complement activity in all tested samples. Loss of activity following three freeze-thaw cycles amounted to 48-59% when serum was tested and over 95% loss in activity for WBH. To our knowledge, this is the first study where fish WBHs were used for assaying complement activity. Our results support the suitability of this method in evaluating complement activity in small fish species or larvae, where blood cannot be obtained, as long as samples can be tested upon first thawing.

Proteomic and histopathological response in the gills of Poecilia reticulata exposed to glyphosate-based herbicide

Glyphosate-based herbicides (GBH) are one of the most used herbicide nowadays, whilst there is growing concern over their impact on aquatic environment. Since data about the early proteomic response and toxic mechanisms of GBH in fish is very limited, the aim of this study was to investigate the early toxicity of GBH in the gills of guppies Poecilia reticulata using a proteomic approach associated with histopathological index. Median lethal concentration (LC50,96 h) was determined and LC50,96h values of guppies exposed to GBH were 3.6 ± 0.4 mg GLIL(-1). Using two-dimensional gel electrophoresis associated with mass spectrometry, 14 proteins regulated by GBH were identified, which are involved in different cell processes, as energy metabolism, regulation and maintenance of cytoskeleton, nucleic acid metabolism and stress response. Guppies exposed to GBH at 1.82 mg GLIL(-1) showed time-dependent histopathological response in different epithelial and muscle cell types. The histopathological indexes indicate that GBH cause regressive, vascular and progressive disorders in the gills of guppies. This study helped to unravel the molecular and tissue mechanisms associated with GBH toxicity, which are potential biomarkers for biomonitoring water pollution by herbicides.

A neglected fish stressor: mechanical disturbance during transportation impacts susceptibility to disease in a globally important ornamental fish

The transport of fish in aquaculture and the ornamental trade exposes fish to multiple stressors that can cause mass mortalities and economic loss. Previous research on fish transport has largely focussed on chemical stress related to deterioration in water quality. However, mechanical disturbance during routine fish transport is unpredictable and is a neglected potential stressor when studying fish welfare. Stress-induced immunosuppression caused by mechanical disturbance can increase the chances of contracting infections and can significantly increase infection burden. Here, using a model host-parasite system (guppy Poecilia reticulata and the monogenean ectoparasite Gyrodactylus turnbulli) and a new method of bagging fish (Breathing Bags™), which reduces mechanical disturbance during fish transport, we investigated how parasite infections contracted after simulated transport impact infection trajectories on a globally important ornamental freshwater species. Guppies exposed to mechanical transport disturbance suffered significantly higher parasite burden compared to fish that did not experience transport disturbance. Unfortunately, there was no significant reduction in parasite burden of fish transported in the Breathing Bags™ compared to standard polythene carrier bags. Thus, transport-induced mechanical disturbance, hitherto neglected as a stressor, can be detrimental to disease resistance and highlights the need for specific management procedures to reduce the impact of infectious diseases following routine fish transport.

Salinity-dependent copper accumulation in the guppy Poecilia vivipara is associated with CTR1 and ATP7B transcriptional regulation

Copper (Cu) accumulation and regulation of key-genes involved in Cu homeostasis were evaluated in freshwater- and saltwater-acclimated guppies Poecilia vivipara. Fish were exposed (96h) to environmentally relevant concentrations of dissolved Cu (0, 5.0, 9.0 and 20.0μg/L). In freshwater guppies, gill and liver Cu accumulation was dependent on Cu concentration in the exposure medium. In saltwater guppies, this dependence was observed only in the gut. These findings indicate that Cu accumulation was salinity- and tissue-dependent. Key genes involved in Cu metabolism were sequenced for the first time in P. vivipara. Transcripts coding for the high-affinity copper transporter (CTR1) and copper-transporting ATPase (ATP7B) were identified using polymerase chain reaction (PCR) and gene sequencing. The full-length CTR1 open reading frame (1560bp) and a partial ATP7B (690bp) were discovered. Predicted amino acid sequences shared high identities with the CTR1 of Fundulus heteroclitus (81%) and the ATP7B of Sparus aurata (87%). Basal transcriptional levels addressed by RT-qPCR in control fish indicate that CTR1 and ATP7B was highly transcribed in liver of freshwater guppies while CTR1 was highly transcribed in gut of saltwater guppies. This could explain the higher Cu accumulation observed in liver of freshwater guppies and in gut of saltwater guppies, because CTR1 is involved in Cu uptake. Reduced gill mRNA expression of CTR1 was observed in freshwater guppies exposed to 20.0μg/L Cu and in saltwater guppies exposed to 5.0μg/L Cu. In turn, reduced mRNA expression of gut ATP7B was observed in freshwater and salt water guppies exposed to 9.0 and 20.0μg/L Cu. Liver CTR1 and ATP7B transcription were not affected by Cu exposure. These findings suggest that gill CTR1 and gut ATP7B are down-regulated to limit Cu absorption after exposure to dissolved Cu, while liver CTR1 and ATP7B levels are maintained to allow Cu storage and detoxification. In conclusion, findings reported here indicate that Cu accumulation in the euryhaline guppy P. vivipara is tissue specific and dependent on water salinity. They also suggest that Cu homeostasis involves a differential transcriptional regulation of the newly identified Cu transporters, CTR1 and ATP7B.

Success of the receptor noise model in predicting colour discrimination in guppies depends upon the colours tested

Accurate knowledge of species colour discrimination is fundamental to explain colour based behaviours and the evolution of colour patterns. We tested how the receptor noise limited model, widely used in behavioural ecology, matched actual colour discrimination thresholds obtained using behavioural tests. Guppies (Poecilia reticulata) were first trained to push a target coloured disk placed among eight grey disks of various luminances on a grey plate. Guppies were then tested to find target disks, which varied in colour contrast from the plate. The target disks followed a gradient going from high contrast to inconspicuous against the grey background. We plotted the percentage of correct choices of each colour in the gradient against the model prediction and determined the discrimination thresholds using the inflection point of the fitted sigmoid curve. We performed the experiment on six colour gradients: red, orange, yellow, green, blue and purple. Four colour gradients: red, orange, green and blue, showed a discrimination threshold that matched the model predictions. However, deviations of the model for the yellow and purple gradients suggest that ecological relevance of some colours could affect decision-making in behavioural tests and that we can no longer assume that the rules for colour discrimination are independent of colours.

Life-time exposure to waterborne copper III: Effects on the energy metabolism of the killifish Poecilia vivipara

Copper ions (Cu) are essential to life maintenance, nonetheless, elevated concentrations can be hazardous. Acute and sub-chronic toxic effects of this metal are well known and are usually related to enzymatic inhibition, elevated ROS production and dysfunction of energy metabolism. Despite that, chronic studies are extremely rare. Therefore, the aim of this study was to assess the effects of chronic exposure to 5, 9 and 20 μg/L Cu (28 ad 345 days) on the energy metabolism and survival of the killifish Poecilia vivipara. To accomplish that, we evaluated the activity of enzymes related to aerobic (pyruvate kinase (PK); citrate synthase (CS)) and anaerobic metabolism (lactate dehydrogenase (LDH)) in whole-body (28 days) or in gills, liver and muscle (345 days) of exposed fish. Additionally, whole-body oxygen consumption was evaluated in fish exposed for 28 days and hepatic and muscular expression of genes involved in mitochondrial metabolism (cox I, II and III and atp5a1) was assessed in animals exposed for 345 days. Finally, final survival was evaluated. Following 28 days, Cu did not affect survival neither enzyme activities. However, increased whole-body oxygen consumption was observed in comparison to control condition. After 345 days, 76.8%, 63.9%, 60.9% and 0% survival were observed for control, 5, 9 and 20 μg/L groups, respectively. Animals exposed to 5 and 9 μg/L had a significant reduction in branchial and muscular LDH activity and in hepatic PK activity. Also, exposure to 9 μg/L significantly increased hepatic CS activity. For gene expression, Cu down-regulated muscular cox II (9 μg/L) and III (5 and 9 μg/L), and up-regulated hepatic atp5a1 (9 μg/L). Findings reported in the present study indicate that chronic exposure to Cu induces tissue-specific responses in key aspects of the energetic metabolism. In gills and muscle, Cu leads to reduced energy production through inhibition of anaerobic pathways and mitochondrial respiratory chain. This effect is paralleled by an increased ATP consumption in the liver, characterized by the augmented CS activity and atp5a1 expression. Finally, reduced PK activity indicate that oxidative stress may be involved with the observed outcomes.

Phylogenetic characteristics, virulence properties and antibiogram profile of motile Aeromonas spp. isolated from ornamental guppy (Poecilia reticulata)

Aeromonas spp. are opportunistic pathogenic bacteria related to an assembly of infectious diseases in ornamental fish. In the present study, virulence properties and antibiotic susceptibility of 52 guppy-borne Aeromonas spp. were investigated. The isolates were identified as A. veronii (n = 34), A. dhakensis (n = 10), A. hydrophila (n = 3), A. caviae (n = 3) and A. enteropelogenes (n = 2) by gyrB gene sequencing. The gyrB sequence deviation within and among the species ranged from 0 to 2.6% and 2.7-9.2%. Each species formed a distinct group in the unrooted neighbor-joining phylogenetic tree. The phenotypic virulence factors such as β-hemolysis, slime, caseinase, DNase, gelatinase and lipase production were observed in 28 (53.9%), 33 (63.5%), 28 (53.9%), 42 (80.8%), 37 (71.2%) and 42 (80.8%) isolates, respectively. The virulence genes were detected by PCR assay in the following proportions- act (84.6%), hly (80.8%), aer (73.1%), lip (73.1%), gcaT (73.1%), ascV (53.8%), ahyB (53.8%) fla (51.9%), alt (48.1%), ast (36.5%) and ser (34.6%), respectively. The amoxicillin, ampicillin, imipenem, nalidixic acid, oxytetracycline and rifampicin were resistant to more than 70.0% of the isolates in antibiotic susceptibility test. Our study suggests that the ornamental guppy can be a potential reservoir of virulent and multi-drug resistant Aeromonas spp.

Brain size does not impact shoaling dynamics in unfamiliar groups of guppies (Poecilia reticulata)

Collective movement is achieved when individuals adopt local rules to interact with their neighbours. How the brain processes information about neighbours' positions and movements may affect how individuals interact in groups. As brain size can determine such information processing it should impact collective animal movement. Here we investigate whether brain size affects the structure and organisation of newly forming fish shoals by quantifying the collective movement of guppies (Poecilia reticulata) from large- and small-brained selection lines, with known differences in learning and memory. We used automated tracking software to determine shoaling behaviour of single-sex groups of eight or two fish and found no evidence that brain size affected the speed, group size, or spatial and directional organisation of fish shoals. Our results suggest that brain size does not play an important role in how fish interact with each other in these types of moving groups of unfamiliar individuals. Based on these results, we propose that shoal dynamics are likely to be governed by relatively basic cognitive processes that do not differ in these brain size selected lines of guppies.