Parasite-induced aggression and impaired contest ability in a fish host

Abstract Background Success of trophically transmitted parasites depends to a great extent on their ability to manipulate their intermediate hosts in a way that makes them easier prey for target hosts. Parasite-induced behavioural changes are the most spectacular and diverse examples of manipulation. Most of the studies have been focused on individual behaviour of hosts including fish. We suggest that agonistic interactions and territoriality in fish hosts may affect their vulnerability to predators and thus the transmission efficiency of trophically transmitted parasites. The parasite Diplostomum spathaceum (Trematoda) and juvenile rainbow trout, Oncorhynchus mykiss, were used to study whether infection can alter aggression rates and territorial behaviour of intermediate fish hosts. Results The changes in behaviour of rainbow trout, Oncorhynchus mykiss, infected with an eye fluke Diplostomum spathaceum (Trematoda), was monitored over the course of an experimental infection for 1.5 months. At the beginning of their development, not yet infective D. spathaceum metacercariae decreased the aggressiveness of rainbow trout. By the time that metacercariae were fully infective to their definitive hosts, the aggressiveness increased and exceeded that of control fish. Despite the increased aggressiveness, the experimentally infected fish lost contests for a territory (dark parts of the bottom) against the control fish. Conclusions The results obtained indicate that the parasitized fish pay the cost of aggressiveness without the benefit of acquiring a territory that would provide them with better protection against predators. This behaviour should increase transmission of the parasite as expected by the parasite manipulation hypothesis

Selective Removal of Fish from Reservoirs and Lakes: Interaction of Hydraulic and Ecological Factors

Downstream migration (DSM) of fish through the different types of water intakes is not a random process, but rather a selective removal from the limnetic to the lotic parts of river–lake systems. Selectivity means that the assemblage of migrants does not exactly reflect the composition of the fish community in an upstream reservoir. Some fish are more prone to migrate compared to others, but this is not the only factor affecting DSM. We hypothesize that the interaction of a 3-D “hydraulic funnel” at the water intake with adjacent ecological zones results in the selective removal of fish. We tested our predictions by analyzing the data on DSM and spatial distribution in 13 reservoirs and lakes in Europe and Asia. Water intakes were surrounded by different habitats and located at different depths, from the surface layer to the depth of more than 50 m. Most vulnerable for entrainment by the outflow were the inhabitants of the pelagic zone. The share of fish emigrating from the littoral habitats was much lower compared to pelagic inhabitants. This suggests that littoral habitats saturated with landmarks and shelters hamper DSM more than the vertical physical gradients in the pelagic do. In conjunction with the factors operating on the scale of the whole reservoir, hydro-ecological barriers of different types associated with water intakes play an important role in the selective removal of fish from reservoirs and lakes

Increased ventilation by fish leads to a higher risk of parasitism

Background: Fish are common intermediate hosts of trematode cercariae and their gills can potentially serve as important sites of penetration by these larval stages. We experimentally tested the hypothesis that volume of ventilation flow across the gills contributes to acquisition of these parasites by fish. We manipulated the intensity of ventilation by using different oxygen concentrations. Methods: Juvenile Oncorhynchus mykiss were individually exposed for 10 minutes to a standard dose of Diplostomum pseudospathaceum cercariae at three levels of oxygen concentration, 30, 60 and 90%. Ventilation amplitude (measured as a distance between left and right operculum), operculum beat rate, and the number of cercariae established in the eyes of fish were recorded. Results: Fish reacted to low oxygen concentration with wider expansion of opercula (but not with increasing beat rate), leading to an increase in ventilation volume. As expected, the intensity of infection increased with decreasing oxygen saturation — probably due to a higher exposure to cercariae caused by increased ventilation under low oxygen concentrations. The number of cercariae acquired by an individual fish was positively correlated with ventilation amplitude and with ventilation volume, but not with operculum beat rate. However, even though the infection rate increased under these circumstances, the proportion of larval trematodes successfully establishing in fish eyes decreased with increasing ventilation volume, suggesting that the high flow velocity, although increasing host exposure to cercarial parasites, may interfere with the ability of these parasit es to penetrate their hosts. There was no difference in the behaviour of trematode cercariae exposed to low and high oxygen concentrations. Conclusion: A reduction in oxygen saturation resulted in an increase in ventilation volume across the gills and in doing so an increase in the exposure of fish to cercariae. A significant correlation between ventilation volume and parasitism represents the first experimental evidence that this physiological mechanism generates variation in transmission of parasites to fish hosts. Other factors that modify ventilation flow, e.g. physiological or social stressors, are expected to produce similar effects on the t ransmission success of the parasites penetrating fish hosts using the gills.peerReviewe

Development of an engineering model of fuel pellet sintering in multi-zone furnaces

An engineering model for sintering of fuel pellets is presented. The model is based on a previous, fully developed, mathematical model, which was implemented by the method of finite volumes, for the process of heat-and-mass transfer of a fuel pellet with arbitrary arrangement in the sintering drawing boat. The main task of the engineering model was to accurately simulate the sintering process for fuel pellets in industrial furnaces with different numbers and types of heating zones. The program implementing the numerical calculations had to be undemanding in terms of computing resources and work stably on average (in terms of parameters) personal computers

Are Reactive Oxygen Species Generated in Electrospray at Low Currents?

It was demonstrated that electrospraying (ES) of solvents from a glass capillary proceeds without emission of light provided that the current is kept below a certain critical level (<100 nA at positive potential and <25 nA at negative potential for 96% ethanol; < 40 nA at positive potential for water). Though the onset of corona, as detected by the appearance of light, was always accompanied by a break in the current–voltage slope, such breaks also happened before the onset of corona, so they cannot be used as an adequate indicator of corona ignition. Of four ROS studied (hydrogen peroxide, ozone, hydroxyl radicals, and superoxide anions), only H₂O₂ and ozone were found to be generated at a current of 150–200 nA in detectable quantities: with a yield of 0.5–1 H₂O₂ molecules per electron at positive potential and 1.5–3 at negative potential. Despite the low yield of the ROS, jack bean urease was shown to be inactivated when the enzyme solution with a concentration below 20 μg/mL was electrosprayed at a current of 200 nA. Addition of 0.1 mM EDTA totally protected the activity of the electrosprayed urease

Grouping facilitates avoidance of parasites by fish

Background. Parasite distribution is often highly heterogeneous, and intensity of infection depends, among other things, on how well hosts can avoid areas with a high concentration of parasites. We studied the role of fish behaviour in avoiding microhabitats with a high infection risk using Oncorhynchus mykiss and cercariae of Diplostomum pseudospathaceum as a model. Spatial distribution of parasites in experimental tanks was highly heterogeneous. We hypothesized that fish in groups are better at recognizing a parasitized area and avoiding it than solitary fish. Methods. Number of fish, either solitary or in groups of 5, was recorded in different compartments of a shuttle tank where fish could make a choice between areas with different risk of being infected. Intensity of infection was assessed and compared with the number of fish recorded in the compartment with parasites and level of fish motility. Results. Both solitary fish and fish in groups avoided parasitized areas, but fish in groups avoided it more strongly and thus acquired significantly fewer parasites than solitary fish. Prevalence of infection among grouped and solitary fish was 66 and 92 %, respectively, with the mean abundance two times higher in the solitary fish. Between-individual variation in the number of parasites per fish was higher in the “groups” treatment (across all individuals) than in the “solitary” treatment. Avoidance behaviour was more efficient when fish were allowed to explore the experimental arena prior to parasite exposure. High motility of fish was shown to increase the acquisition of D. pseudospathaceum. Conclusion. Fish in groups better avoided parasitized habitat, and acquired significantly fewer parasites than solitary fish. We suggest that fish in groups benefit from information about parasites gained from other members of a group. Grouping behaviour may be an efficient mechanism of parasite avoidance, together with individual behaviour and immune responses of fishes. Avoidance of habitats with a high parasite risk can be an important factor contributing to the evolution and maintenance of grouping behaviour in fish.peerReviewe