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— 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.

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.

Color is important factor ornamental fish, especially sword platy fish, because can affect selling value. One factor influences color brightness is carotenoids. Carotenoids cannot synthesized by fish's body so must be supplied through feed provided. Red spinach is a natural ingredient that contains carotenoids. Aim of research was to determine effect of adding red spinach leaf extract to artificial feed to increase color brightness, growth and survival of Xiphophorus helleri . Research method used a completely randomized design with 4 treatments and 4 repetitions. Concentrations of red spinach leaf extract are 0%, 3%, 6% and 9%. Parameters observed were color brightness, absolute weight, absolute length, survival rate and water quality. Results showed that addition of red spinach leaf extract had a significant effect (P<0.05) on brightness of fish color but had no significant effect (P>0.05) on growth, weight, length and survival rate. Highest increase in color brightness and absolute weight growth was obtained in 9% treatment with an average color brightness score of 6.66, an absolute weight of 0.36 g. Highest absolute length growth occurred treatments C (6%) and D (9%) at 0.41 cm and highest survival rate was obtained treatments A, B and C with a survival percentage of 88%.

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.

Aggression occurs when individuals compete over limiting resources. While theoretical studies have long placed a strong emphasis on context-specificity of aggression, there is increasing recognition that consistent behavioural differences exist among individuals, and that aggressiveness may be an important component of individual personality. Though empirical studies tend to focus on one aspect or the other, we suggest there is merit in modelling both within- and among-individual variation in agonistic behaviour simultaneously. Here, we demonstrate how this can be achieved using multivariate linear mixed effect models. Using data from repeated mirror trials and dyadic interactions of male green swordtails, Xiphophorus helleri, we show repeatable components of (co)variation in a suite of agonistic behaviour that is broadly consistent with a major axis of variation in aggressiveness. We also show that observed focal behaviour is dependent on opponent effects, which can themselves be repeatable but were more generally found to be context specific. In particular, our models show that within-individual variation in agonistic behaviour is explained, at least in part, by the relative size of a live opponent as predicted by contest theory. Finally, we suggest several additional applications of the multivariate models demonstrated here. These include testing the recently queried functional equivalence of alternative experimental approaches, (e.g., mirror trials, dyadic interaction tests) for assaying individual aggressiveness.

Changes in water quality and environmental factors have been reported to play key roles on the health and disease susceptibility of the ornamental fish Xiphophorus hellerii (sword tail). This can further be decided by the natural distribution of pathogens with enhanced virulence properties in the aquatic system. As Aeromonas spp. are the major fish pathogens, a detailed analysis on its association with the disease of X.hellerii was conducted in the study. Here, bacterial isolation has been carried out from the surface, gill and intestine of diseased fish, and also from water samples. The twelve bacterial isolates obtained were identified biochemically and also by 16S rDNA sequence analysis as Aeromonas spp.. Among the various virulence properties screened by in vitro and PCR-based methods, most of the Aeromonas spp. were found to be positive for multiple virulence properties. Further disease challenge using the highly virulent Aeromonas veronii XhG1.2 in X. hellerii showed remarkable histopathological changes of the gill, liver, and intestine in the treated fish. This confirmed the hyper -pathogenic potential of XhG1.2 as the disease occurred within a short period of 24 h. The identification of broad range of virulence factors among the fish pathogenic bacterial isolates of aquatic environment indicates the need for periodic screening to predict the threat to aquatic life especially fish.

Mate choice is context dependent, but the importance of current context to interspecific mating and hybridization is largely unexplored. An important influence on mate choice is predation risk. We investigated how variation in an indirect cue of predation risk, distance to shelter, influences mate choice in the swordtail Xiphophorus birchmanni, a species which sometimes hybridizes with X. malinche in the wild. We conducted mate choice experiments to determine whether females attend to the distance to shelter and whether this cue of predation risk can counteract female preference for conspecifics. Females were sensitive to shelter distance independent of male presence. When conspecific and heterospecific X. malinche males were in equally risky habitats (i.e., equally distant from shelter), females associated primarily with conspecifics, suggesting an innate preference for conspecifics. However, when heterospecific males were in less risky habitat (i.e., closer to shelter) than conspecific males, females no longer exhibited a preference, suggesting that females calibrate their mate choices in response to predation risk. Our findings illustrate the potential for hybridization to arise, not necessarily through reproductive \"mistakes\", but as one of many potential outcomes of a context-dependent mate choice strategy.

Understanding the dynamics of species invasions in aquatic ecosystems is crucial for conservation and management efforts. We investigated the influence of species interactions and habitat complexity on biotic resistance to invasion by small-bodied freshwater fishes in peninsular Florida. Specifically, we focused on the interactions between two native species, Florida bass (Micropterus salmoides) and eastern mosquitofish (Gambusia holbrooki), and a common invader, the green swordtail (Xiphophorus hellerii). Our experiments included tanks with varying levels of structural complexity to mimic different habitat types. The presence of both native species significantly reduced swordtail survival, but the effect varied depending on habitat complexity. In habitats with strong predation refuge, mosquitofish facilitated bass predation on swordtails, whereas in habitats with weak predation refuge, bass suppressed mosquitofish aggression, leading to interference. Mosquitofish predominantly occupied vegetated areas and aggressively interacted with swordtails, significantly reducing invader survival. Our findings highlight the importance of considering species interactions and habitat complexity in predicting biotic resistance to invasions. We conclude that diverse interactions among native species can either enhance or impede invasion resistance, with implications for conservation and management strategies. Further research is needed to understand the broader impacts of multiple predators and competitors on invader dynamics in aquatic ecosystems.

Centrocestus formosanus (Nishigori 1924) is a trematode parasite introduced into many parts of the world through the aquarium fish trade. Its infection causes high fish mortalities and economic losses to fish farmers worldwide. In this study, the efficacy of ethanol (95%) extract of Anacardium occidentale (Linnaeus 1753) apple to control C. formosanus infection in Xiphophorus hellerii (Heckel 1848) was investigated. According to Probit analysis, the estimated 96 h LC50 of plant extract for X. hellerii was 387.28 mgL-1. Infected X. hellerii was treated with concentrations of 300, 320, 340, 360, and 380 mgL-1 plant extract with exposure periods of 24 and 48 h. The behavior and mortality of treated and non-treated fish were observed for two weeks. Mortality and parasitic intensity of treated fish were significantly lower than that of non-treated fish during the experiment and recovery period. The parasitic intensity in treated fish decreased significantly with increasing concentration of plant extraction in 24 h and 48 h exposure. The lowest dose of A. occidentale apple extract needed to reduce more than 70% of metacercariae infected to gills of X. hellerii within 24 h was 340 mgL-1. According to the findings, A. occidentale apple extract can effectively control C. formosanus infections in aquarium fish.

Near-infrared (NIR) light constitutes an integrated part of solar radiation. The principal ability to sense NIR under laboratory conditions has previously been demonstrated in fish. The availability of NIR in aquatic habitats, and thus its potential use as a cue for distinct behaviors such as orientation and detection of prey, however, depends on physical and environmental parameters. In clear water, blue and green light represents the dominating part of the illumination. In turbid waters, in contrast, the relative content of red and NIR radiation is enhanced, due to increased scattering and absorption of short and middle range wavelengths by suspended particles and dissolved colored materials. We have studied NIR detection thresholds using a phototactic swimming assay in five fish species, which are exposed to different NIR conditions in their natural habitats. Nile and Mozambique tilapia, which inhabit waters with increased turbidity, displayed the highest spectral sensitivity, with thresholds at wavelengths above 930 nm. Zebrafish, guppy and green swordtail, which prefer clearer waters, revealed significantly lower thresholds of spectral sensitivity with 825-845 nm for green swordtail and 845-910 nm for zebrafish and guppy. The present study revealed a clear correlation between NIR sensation thresholds and availability of NIR in the natural habitats, suggesting that NIR vision, as an integral part of the whole spectrum of visual abilities, can serve as an evolutionarily adaptable trait in fish.