Coral reef fish density and species richness are often higher at sites with more structural complexity. This association may be due to greater availability of shelters, but surprisingly little is known about the size and density of shelters and their use by coral reef fishes. We quantified shelter availability and use by fishes for the first time on a Caribbean coral reef by counting all holes and overhangs with a minimum entrance diameter ≥3 cm in 30 quadrats (25 m2) on two fringing reefs in Barbados. Shelter size was highly variable, ranging from 42 cm3 to over 4,000,000 cm3, with many more small than large shelters. On average, there were 3.8 shelters m−2, with a median volume of 1,200 cm3 and a total volume of 52,000 cm3m−2. The number of fish per occupied shelter ranged from 1 to 35 individual fishes belonging to 66 species, with a median of 1. The proportion of shelters occupied and the number of occupants increased strongly with shelter size. Shelter density and total volume increased with substrate complexity, and this relationship varied among reef zones. The density of shelter-using fish was much more strongly predicted by shelter density and median size than by substrate complexity and increased linearly with shelter density, indicating that shelter availability is a limiting resource for some coral reef fishes. The results demonstrate the importance of large shelters for fish density and support the hypothesis that structural complexity is associated with fish abundance, at least in part, due to its association with shelter availability. This information can help identify critical habitat for coral reef fishes, predict the effects of reductions in structural complexity of natural reefs and improve the design of artificial reefs.

-To clarify the role of the nutria Myocastor coypus in the epidemiology of domestic fasciolosis in Loire-Atlantique (department of western France), 438 nutrias were trapped in 9 humid areas of the department and 304 nutrias were trapped in 3 farms where Fasciola hepatica was present; all animals were necropsied. Liver flukes were found in 160 nutrias: 38 nutrias randomly taken in the department (8.7%) and 122 trapped in fasciolosis areas (40.1%). The average parasitic burden was 5.7 flukes per nutria. Sixty-five percent of the liver flukes measured more than 18 mm (size of sexual maturity). The coproscopic examinations carried out on 144 infected nutrias showed that 90% of the infected nutrias shed fluke eggs. The hatching rate was 39.6%. Two groups of 100 Lymnaea truncatula snails, originating from 2 different populations, were exposed to F. hepatica miracidiae hatched from eggs collected from infected nutrias. The prevalence of the infection was 74% and 58.6% in the 2 groups of snails. The average redial burden was 6.2 rediae per snail. The total number of metacercariae was 72.4 metacercariae per snail producing cercariae. Two groups of 5 sheep were orally infected by 150 metacercariae of nutria or sheep origin, respectively. The installation rates of F. hepatica in sheep were respectively 31.6% and 29.6% for the two groups. Specific antibody kinetics of sheep were similar whether the metacercariae were of nutria or sheep origin. M. coypus allows the complete development of F. hepatica and releases parasitic elements that are infective for domestic ruminants. Because of its eco-ethologic characteristics, the nutria could be a potential wild reservoir of F. hepatica in France.epidemiology / Fasciola hepatica / wild fauna / Myocastor coypus / rodent Résumé -Le ragondin, hôte réservoir de Fasciola hepatica en France. Pour préciser le rôle du ragondin Myocastor coypus dans l'épidémiologie de la fasciolose domestique en Loire-Atlantique (département de l'ouest de la France), 438 ragondins provenant de 9 zones humides du département Vet. Res. 32 (2001) 499-508 499

Summary:With the objective of studying the role of wild fauna in the epidemiology of fasciolosis disease, a definitive wild-host inventory was carried out in a french farm where infected domestic hosts (cows) cohabit with wild potential ones.

We examined the diurnal refuges occupied by the nocturnal squirrelfish, Holocentrus rufus, to describe refuges and the behavior associated with their use and to determine which, if any, refuge characteristics were selected. We tagged 21 H. rufus on two sites on a fringing reef in Barbados, West Indies, identified the refuges they used (n = 57), measured ten characteristics of each refuge and the surrounding microhabitat, and monitored their refuge use for 4 weeks. To evaluate refuge selection, we measured the same characteristics on a comparable number of unused potential refuges (n = 67) on the same reefs and used classification tree models to determine which characteristics separated used from unused refuges. Each fish used 1-9 refuges, which did not overlap among individuals and were defended against intrusion by conspecifics and some heterospecifics. Fish with more than one refuge frequently moved among them. There was strong site fidelity with no immigration of untagged fish or emigration of tagged fish on either reef during the study period and no additional refuges being occupied over the 4-week period. Refuges were primarily holes, open at one or two ends, which varied in size, distance from the reef edge, entrance orientation, and vertical relief at the entrance. Holes used as refuges differed significantly from unused holes mainly in characteristics related to the vertical position of their entrance, but the classification tree models differed for the two sites. This study provides the first detailed information on characteristics of daytime refuges used by a nocturnally active reef fish and the first evidence of selectivity of refuges. It suggests that the abundance and characteristics of holes on reefs could influence the density of H. rufus on natural reefs.

Experimental infections of Galba truncatula with 4 isolates of Fasciola hepatica miracidia differing by their mammalian origin (cattle, nutrias, rabbits, or sheep) were carried out to determine if parasite origin had an effect on the number of free rediae, their growth, and their larval productivity in each redia category. The mammalian origin of miracidia had a significant influence on the numbers of free rediae (they were higher in cattle-group snails) and the lengths of rediae (they were lower in rabbit groups). The redia category had also a significant effect on body and pharyngeal measurements. In all groups, the majority of cercariae (55.8-63.2%) were produced by the daughter rediae (R2a rediae) originating from the first mother redia. Compared with the other groups, the mean number of cercariae at day 49 postexposure was twice as high in cattle groups. In contrast, the mean number of daughter rediae produced by each second-appearing mother redia or each R2a redia was higher in the nutria, rabbit, and sheep groups. The mammalian origin of F. hepatica miracidia had an effect on the number of live rediae, their length, and their redial and cercarial productivity.