Euhaplorchis californiensis Cercariae Exhibit Positive Phototaxis and Negative Geotaxis.

Parasites often use external cues to identify and move toward environments where they are likely to encounter suitable hosts. The trematode parasite Euhaplorchis californiensis produces cercariae that emerge from California horn snails ( Cerithideopsis californica [= Cerithidea californica]) to infect California killifish ( Fundulus parvipinnis) as second intermediate hosts. Based upon work on a congeneric Euhaplorchis species from Florida, and based on the ecology of its killifish host, we hypothesized that E. californiensis cercariae in southern California estuaries are positively phototactic and negatively geotactic, using both sunlight and gravity to guide their movement to the upper water column. To distinguish positive phototaxis from negative geotaxis, we first quantified E. californiensis movement in response to light along a horizontal plane and determined they were positively phototactic. In a second experiment, we quantified E. californiensis movement along a vertical plane in response to an overhead light, a light from below, or no light. We found that E. californiensis exhibit negative geotaxis in the absence of light, but will swim in the direction of gravity to move toward a light source from below. Thus, E. californiensis are both positively phototactic and negatively geotactic, but cercariae prioritize phototactic cues. These results suggest that E. californiensis cercariae aggregate in the open water, indicating that the pelagic zone represents an area of high infection risk for California killifish hosts.

Parasitism, personality and cognition in fish.

It is well established that parasites can have profound effects on the behaviour of host organisms, and that individual differences in behaviour can influence susceptibility to parasite infections. Recently, two major themes of research have developed. First, there has been a growing interest in the proximate, mechanistic processes underpinning parasite-associated behaviour change, and the interactive roles of the neuro-, immune, and other physiological systems in determining relationships between behaviour and infection susceptibility. Secondly, as the study of behaviour has shifted away from one-off measurements of single behaviours and towards a behavioural syndromes/personality framework, research is starting to focus on the consequences of parasite infection for temporal and contextual consistency of behaviour, and on the implications of different personality types for infection susceptibility. In addition, there is increasing interest in the potential for relationships between cognition and personality to also have implications for host-parasite interactions. As models well-suited to both the laboratory study of behaviour and experimental parasitology, teleost fish have been used as hosts in many of these studies. In this review we provide a broad overview of the range of mechanisms that potentially generate links between fish behaviour, personality, and parasitism, and illustrate these using examples drawn from the recent literature. In addition, we examine the potential interactions between cognition, personality and parasitism, and identify questions that may be usefully investigated with fish models.

The relationship between handling time and cortisol release rates changes as a function of brain parasite densities in California killifish Fundulus parvipinnis.

This study validated a technique for non-invasive hormone measurements in California killifish Fundulus parvipinnis, and looked for associations between cortisol (a stress hormone) and 11-ketotestosterone (KT, an androgen) release rates and the density or intensity of the trematode parasites Euhaplorchis californiensis (EUHA) and Renicola buchanani (RENB) in wild-caught, naturally infected F. parvipinnis. In experiment 1, F. parvipinnis were exposed to an acute stressor by lowering water levels to dorsal-fin height and repeatedly handling the fish over the course of an hour. Neither parasite was found to influence cortisol release rates in response to this acute stressor. In experiment 2, different F. parvipinnis were exposed on four consecutive days to the procedure for collecting water-borne hormone levels and release rates of 11-KT and cortisol were quantified. This design examined whether F. parvipinnis perceived the water-borne collection procedure to be a stressor, while also exploring how parasites influenced hormone release rates under conditions less stressful than those in experiment 1. No association was found between RENB and hormone release rates, or between EUHA and 11-KT release rates. The interaction between EUHA density and handling time, however, was an important predictor of cortisol release rates. The relationship between handling time and cortisol release rates was negative for F. parvipinnis harbouring low or intermediate density infections, and became positive for fish harbouring high densities of EUHA.

Changes in reproductive physiology of mangrove rivulus Kryptolebias marmoratus following exposure to environmentally relevant doses of ethinyl oestradiol.

Kryptolebias marmoratus exposed to 4 ng l(-1) of ethinyl oestradiol (EE2) for 30 days experienced significant changes in endogenous 17ß-oestradiol (E2) and 11-ketotestosterone (KT) and qualitative changes in gonad morphology. Both hermaphrodites and males showed a significant decrease in E2, whereas only males exhibited a significant decrease in KT. Exposure to EE2 resulted in a decrease in spermatid and spermatocyte density in males and an increase in the number of early stage oocytes in hermaphrodites.

Behavioural syndromes in fishes: a review with implications for ecology and fisheries management.

This review examines the contribution of research on fishes to the growing field of behavioural syndromes. Current knowledge of behavioural syndromes in fishes is reviewed with respect to five main axes of animal personality: (1) shyness-boldness, (2) exploration-avoidance, (3) activity, (4) aggressiveness and (5) sociability. Compared with other taxa, research on fishes has played a leading role in describing the shy-bold personality axis and has made innovative contributions to the study of the sociability dimension by incorporating social network theory. Fishes are virtually the only major taxon in which behavioural correlations have been compared between populations. This research has guided the field in examining how variation in selection regime may shape personality. Recent research on fishes has also made important strides in understanding genetic and neuroendocrine bases for behavioural syndromes using approaches involving artificial selection, genetic mapping, candidate gene and functional genomics. This work has illustrated consistent individual variation in highly complex neuroendocrine and gene expression pathways. In contrast, relatively little work on fishes has examined the ontogenetic stability of behavioural syndromes or their fitness consequences. Finally, adopting a behavioural syndrome framework in fisheries management issues including artificial propagation, habitat restoration and invasive species, may promote restoration success. Few studies, however, have examined the ecological relevance of behavioural syndromes in the field. Knowledge of how behavioural syndromes play out in the wild will be crucial to incorporating such a framework into management practices.