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    Health assessment of grey mullet Mugil cephalus based on interrelationship between parasite co-infections and relative condition factor
    (Wiley-Blackwell, 2016) Ozer, A.; Cankaya, E.; Kirca, D. Yilmaz
    This study aimed to assess the health status of grey mullet Mugil cephalus by means of relative condition factor under the coexisting parasite groups within seasons. Fish were captured monthly in the Lower Kzlrmak Delta in Samsun, Turkey, from December 2011 to November 2012. A total of five taxonomic groups containing 13 parasite species were constituted: Trichodina (Trichodina puytoraci, T.lepsii), Monogenea (Ligophorus cephali, L.mediterraneus, Gyrodactylus sp., Microcotyle mugilis), Digenea (Ascocotyle (Phagicola) longa, Diplostomum spathaceum, Tylodelphys clavata, Posthodiplostomum sp., Haplosplanchnus pachysomus), Acanthocephala (Neoechinorhynchus agilis) and Copepoda (Ergasilus lizae). Only one mullet was not parasitized and 13.8%, 36.3%, 29.2%, 16.2% and 4.5% were infected by one, two, three, four and five parasite groups respectively. Health assessment of mullets was performed by means of relative condition factor based on weight-length relationship estimated by robust regression methods. General linear modelling was employed to investigate any effect of season and infection load on this condition measure. Potential impacts of multiple parasitism on the community, which have been largely overlooked in the literature, were first visually revealed by relating the levels of co-infections (in terms of prevalence and intensity) to the seasons. Then, a correlation analysis was carried out between condition estimates and the log-ratios of relative abundances of parasite groups. The results showed that mullets suffering from Monogenea-Digenea-Acanthocephala (M-D-A) and also along with Copepoda (M-D-A-C) co-infection had weights less than expected (K-n<1) under winter conditions. However, Trichodina involved co-infections appeared to prefer large sized hosts (K-n>1) particularly in autumn.
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    Quantal models: a review with additional methodological development
    (Routledge Journals, Taylor & Francis Ltd, 2009) Cankaya, E.; Fieller, N. R. J.
    Analysis of quantal models is a particular aspect of the general problem of investigating multimodality. The distinction is that the spacings between modes are integral multiples of some unspecified fundamental unit and that the number of modes is not defined. Such semi-structured models arise in a wide variety of contexts such as biology, cosmology, archaeology and molecular physics. This paper presents a brief review of their historical development in such areas as an aid to their recognition in other contexts as well as giving guidance to their analysis from the statistical viewpoint. The available methodology for their analysis is collated into a coherent and self-contained account, establishing various optimality properties under particular parametric distributional assumptions. An illustrative power study shows how dependence on sample size and failure of assumptions such as underlying distribution, origin of measurements and independence affect the power of various analyses. These aspects are illustrated by an example from developmental biology.