Patrick Silan

Enlargement of the host range of Polylabris tubicirrus (Monogenea, Polyopisthocotylea) under fish-farming conditions

In the Mediterranean Sea, Polylabris tubicirrus (Monogenea, Polyopisthocotylea) is found only on breams of the genus Diplodus : D. sargus, D. annularis, D. vulgaris. The discovery of this parasite on farmed gilt head sea breams (Sparus aurata) raises the problem of the enlargement of the host range of a parasite under artificial conditions of confinement, and of the potential danger this type of transfer can involve.

Theoretical and mathematical approach of some regulation mechanisms in a marine Host-Parasite system

Host-parasite systems offer such a complex behaviour that few quantitative analysis of their coupled dynamics have been performed. Many intertwinned factors play a role, such as intensity-dependent (intra or interspecific competition, pathogeny, immunological reactions) and/or intensity-independent (abiotic factors, host ethology). Most biomathematical approaches to host-parasite systems are concerned with infectious processes. Corresponding epidemiological models are not well-adapted to macroparasites whose demographical behaviour is quite specific: host mortality, parasite fertility and sometimes recruitment mechanisms depend on the amount of already fixed parasites on a given host and not on the mere existence of parasites. Overdispersion processes are fundamental and determine for a large part the regulation of both populations. A central issue is therefore a reliable description of these processes and their interactions with the global dynamics of the system. Our goal is to develop a mixed deterministic and stochastic model describing the dynamics of a host-parasite system (fish-helminth parasite) having a direct cycle within a marine environment. A dynamical analysis combining a deterministic approach and a stochastic one adapted to macroparasites allows the introduction of spatial and temporal heterogeneities. A particular effort is made towards the recruitment process.

Biology of Serranicotyle labracis, ectoparasite of Dicentrarchus labrax (Teleostei): contribution to the study of its populations

Serranicotyle labracis (Van Beneden and Hesse, 1863) Maillard, Euzet and Silan, 1988 (synonym: Microcotyle labracis Van Beneden and Hesse, 1863) is a monogenean Polyopisthocotylea and a gill parasite of the bass Dicentrarchus labrax (Linné, 1758). Analysis of a western Mediterranean population of this parasite (Gulf of Lions, Languedoc, France) clarified several aspects of its biology. Its location in the gill biotope (Silan et al. 1987) was not fundamentally different from that found by Oliver (1977) and Winch (1983), but its distribution in host populations differed from that reported in the earlier studies; it displayed a negative binomial distribution in the study zone. At a finer level of observation, the behaviour of the hosts, as a function of degree of maturity and sex, appeared to determine more than any other factor the extent of infestation by the parasite. Previous suggestions in the literature to account for these differences in population dynamics are discussed.

Stochastic Simulation of a Marine Host-Parasite System Using a Hybrid MPI/OpenMP Programming

We are interested in a host-parasite system occuring in fish farms, i.e. the sea bass - Diplectanum aequans system. A discrete mathematical model is used to describe the dynamics of both populations. A deterministic numerical simulator and, lately, a stochastic simulator were developed to study this biological system. Parallelization is required because execution times are too long. The Monte Carlo algorithm of the stochastic simulator and its three levels of parallelism are described. Analysis and performances, up to 256 processors, of a hybrid MPI/OpenMP code are then presented for a cluster of SMP nodes. Qualitative results are given for the host-parasite system.