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The presence of antibiotics including norfloxacin in the aquatic environment may cause adverse effects in non-target organisms. But the toxic mechanisms of fluoroquinolone to fish species are still not completely elucidated. Thus, it is essential to investigate the response of fish to the exposure of fluoroquinolone at molecular or cellular level for better and earlier prediction of these environmental pollutants toxicity. The sub-chronic toxic effects of norfloxacin (NOR) on swordtail fish (Xiphophoru s helleri) were investigated by measuring mRNA expression of cytochrome P450 1A (CYP1A), cytochrome P450 3A (CYP3A), glutathione S-transferase (GST) and P-glycoprotein (P-gp) and their corresponding enzyme activities (including ethoxyresorufin O-deethylase, erythromycin N-demethylase and GST. Results showed that NOR significantly affected the expression of CYP1A, CYP3A, GST and P-gp genes in swordtails. The gene expressions were more responsive to NOR exposure than their corresponding enzyme activities. Moreover, sexual differences were found in gene expression and enzyme activities of swordtails exposed to NOR. Females displayed more dramatic changes than males. The study further demonstrated that the combined biochemical and molecular parameters were considered as useful biomarkers to improve our understanding of potential ecotoxicological risks of NOR exposure to aquatic organisms.

Sperm competition is expected to favour the evolution of traits that influence the performance of sperm when they compete to fertilize a female's eggs. While there is considerable evidence that selection favours increases in sperm numbers, much less is known about how sperm quality contributes towards competitive fertilization success. Here, we determine whether variation in sperm quality influences competitive fertilization success in the green swordtail Xiphophorus helleri, a highly promiscuous livebearing fish. We use artificial insemination as a method of controlled sperm delivery and show that sperm swimming velocity is the primary determinant of fertilization success when ejaculates from two males compete to fertilize a female's eggs. By contrast, we found no evidence that sperm length had any effect on siring success. We also found no evidence that pre- and postcopulatory sexual traits were phenotypically integrated in this species, suggesting that the previous observation that reproductive skew favours males with high mating rates is unlikely to be due to any direct association between sperm quality and male sexual ornamentation.

Genetic and morphological variation within species are determined by intrinsic and extrinsic factors, which jointly or separately can promote population divergence. In freshwater systems, the structure of the basins, geographic distance, climatic fluctuations of the Pleistocene as well as extant environmental variation are important drivers of population divergence. Xiphophorus hellerii is a fish widely distributed in basins of the Gulf of Mexico slope. We used mitochondrial DNA sequences, geometric morphometrics and ecological niche modeling to investigate the roles of geographic and environmental factors in population divergence of X. hellerii. We found strong genetic structure conforming to the Stream Hierarchy and isolation by distance models. Demographic tests and ecological niche modeling suggested that the niche and populations of the species underwent contractions and expansions during the Pleistocene. Body shape of X. hellerii varied among basins and hydrological regions. Temperature seems to affect body shape, as individuals with shallow bodies were found in basins with low temperature and high altitudes. We found significant relationships between genetics, morphology, geography and the environment. Our study suggests that X. hellerii from different basins and hydrological regions have followed independent evolutionary routes and that environmental and geographical factors have played an important role in population divergence.

Ornamental fish farming is globally a key sector of aquaculture. The purpose of this study was to report on the parasitic fauna of ornamental fish from seven farms in the East Azerbaijan province in northwestern Iran. Between November 2020 and February 2021, a total of 600 freshwater ornamental fish of six species, including goldfish (Carassius auratus), angel (Pterophyllum scalare), guppy (Poecilia reticulata), dwarf gourami (Colisa lalia), swordtail (Xiphophorus helleri), and cichlid (Cichlasoma sp.) were collected for parasitological analysis. Six ciliate protozoan species (Trichodina mutabilis, Trichodina nobilis, Trichodina spp., Heteropolaria lwoffi, Ichthyophthrius multifiliis, and Chilodonella spp.), three species of monogenean trematodes (Dactylogyrus dulkeiti, Dactylogyrus spp. and Gyrodactylus spp.), two species of crustacean arthropods (Lernaea cyprinacea and Argulus japonicus), and a nematode (Capillaria spp.) were identified among the examined fish. Parasites were detected in the fish from 5 of 7 farms, with an overall parasitic prevalence in 26.33% (158/600) of the fish. Fish infection rates with protozoans, monogenean trematodes, crustacean arthropods, and nematodes were 16.83, 13.17, 4, and 0.33% respectively. The highest prevalence was found in X. helleri infected with Gyrodactylus spp. and P. scalare infested with Trichodina spp. Moreover, 9/100 and 10/100 of goldfish were infected with A. japonicus and L. cyprinacea, compared to 2/500 and 3/500, respectively, for all other species in combination, which is a statistically significant result (p < 0.01). Assessment of farmed fish parasitic fauna is important to inhibit the spread of infections, ensure fish production and improve fish health.

The Tampa Bay region of Florida exhibits the highest concentration of ornamental aquaculture facilities in the USA. Because of the diversity of aquaculture products (~800 species and varieties) and extensive production history (began in the 1930s and 1940s), this region could be a hotspot for escaped ornamental fish. We evaluated the scope of ornamental fish invasions in this region by examining (1) escape vectors and (2) the distribution of escaped fish. We investigated potential pathways of fish escape including theft/vandalism, fish transport, bird carry-off, and through effluent discharge. Fish were sampled at the effluent discharge and continued into the surrounding environment. The dominant escape vector was through farm effluents; there was no evidence that theft/vandalism, fish transport, or bird carry-off contributed to fish escape. Most captured fish were natives, especially the ubiquitous Eastern Mosquitofish ( Gambusia holbrooki ). Ornamental species and varieties were also captured, especially cichlids and poeciliids such as the Green Swordtail ( Xiphophorus hellerii ) and Southern Platyfish ( Xiphophorus maculatus ). Ornamental fish were often found in the immediate vicinity of fish farms but were rarely captured in the surrounding environment. Catch per unit effort and ornamental fish diversity declined when moving away from the aquaculture facility effluent and was reduced at sites with a detention pond. The observed fish distribution might be due to relatively cold water in sub-tropical Florida, predatory fish in the environment, and additional factors related to the physical or biological habitat. Ultimately, few ornamental fishes have established in this region despite a long period of extensive culture.

Sexual selection acting on male traits through female mate choice is commonly inferred from female association preferences in dichotomous mate choice experiments. However, there are surprisingly few empirical demonstrations that such association preferences predict the likelihood of females reproducing with a particular male. This information is essential to confirm association preferences as good predictors of mate choice. We used green swordtails (Xiphophorus helleri) to test whether association preferences predict the likelihood of a female reproducing with a male. Females were tested for a preference for long- or short-sworded males in a standard dichotomous choice experiment and then allowed free access to either their preferred or non-preferred male. If females subsequently failed to produce fry, they were provided a second unfamiliar male with similar sword length to the first male. Females were more likely to reproduce with preferred than non-preferred males, but for those that reproduced, neither the status (preferred/non-preferred) nor the sword length (long/short) of the male had an effect on brood size or relative investment in growth by the female. There was no overall preference based on sword length in this study, but male sword length did affect likelihood of reproduction, with females more likely to reproduce with long- than short-sworded males (independent of preference for such males in earlier choice tests). These results suggest that female association preferences are good indicators of female mate choice but that ornament characteristics of the male are also important.

Hurricanes Irma and Maria were category 5 hurricanes that devastated parts of Central America in September 2017. Hurricane Irma passed northern Puerto Rico on September 6; Maria reached Puerto Rico as a category 4 hurricane on 20 Sep 2017. These hurricanes had devastating effects on the people living in Puerto Rico, but less is known about how the hurricanes impacted Puerto Rico's wildlife. The National Ecological Observatory Network (NEON) provides a large ecological database covering all American states and Puerto Rico. NEON includes comprehensive information about fish species and environmental variables at multiple sites collected at time periods from late 2014 to present. Aquatic sample collection in Puerto Rico has been performed at Rio Guilarte and Rio Cupeyes. Data collection from these two sites occurred around the same time before the hurricanes in February 2017, and also occurred shortly after the hurricanes. Gambusia affinis (western mosquitofish), Xiphophorus hellerii (green swordtail), and Poecilia reticulata (guppy) were collected in Rio Guilarte. Agonostomus monticola (mountain mullet) was collected in Rio Cupeyes. The focus of this study was to determine if the hurricanes had an impact on the mean length of each fish species, which would suggest eco-evolutionary effects of hurricanes on fish populations. The results indicate that while all four species' lengths decreased, on average, only the decreases in green swordtail and mountain mullet were significant. Hurricanes, storms, and floods are happening at increasingly higher severity. This analysis identifies direct biological effects caused by severe short-term ecological disruptions on multiple fish species.

— Palatability of sodium cholate (10 –1 M), sodium taurocholate (10 –1 M), and dehydrocholic acid (0.5 × 10 –3 M) for Mexican cavefish Astyanax fasciatus (blind form), silver dollar Metynnis argenteus , Nile tilapia Oreochromis niloticus , green swordtail Xiphophorus hellerii , and roach Rutilus rutilus was assessed. All substances have a significant taste effect, but the reaction of fishes to their taste is different and the responses to the same substance were different. Taste attractiveness for bile substances (sodium taurocholate, dehydrocholic acid) was found only in Mexican cavefish, which allows it to feed on specific food (bat guano) available in cave reservoirs where other food resources are extremely insignificant. For the rest of the fishes, bile substances had an inert or aversive taste, which can prevent coprophagy and contribute to long-term preservation of feces in the environment, which are an important source of odor signals for fish. It has been proposed to consider bile substances as important chemical regulators of fish relationships in aquatic communities.

This study's objective was to determine effect of two different anaesthetics 2-phenoxyethanol and clove oil on the sedation of some aquarium fish species. The induction and recovery times were determined at five stages of melanistic and not melanistic clownfish (Amphiprion ocellaris) and different sexes of Swordfish (Xiphophorus helleri). Clownfish were tested with 0.4, 0.6 and 0.8 ml/l phenoxyethanol and 0.5, 1 and 1.5 ml/l clove oil. Swordfish were tested with 1, 3 and 5 ml/l phenoxyethanol and 2, 4, 6 ml/l clove oil. For short-term application the safe dose for clownfish was 0.4 ml/l phenoxyethanol and 1 ml/l clove oil. For swordtail fish, the ideal amount of phenoxyethanol was 5 ml/l and 6 ml/l clove oil. These safe doses reduce handling stress and mortality.