Mortality of Juvenile So-iuy Mullet, Liza haematocheilus (Teleostei, Mugilidae), in the Sea of Azov Associated with Metacercariae (Digenea). Sarabeev, V. - Age-dependent patterns, including yearly variations of digenean metacercariae infestations of the introduced species, Liza haematocheilus (Temminck & Schlegel, 1845), were studied. We evaluated the impacts of three metacercaria species, Timoniella imbutiforme (Molin, 1859) Brooks, 1980, Diplostomum spp. and Ascocotyle (Phagicola) longa Ransom, 1920, on juvenile fish in age from one month to 2+ years old from the Molochny Estuary and neighboring waters of the Sea of Azov by applying Croft on’s negative binomial truncation technique, epidemiologic and aggregation indices. Parasite surveys executed in 1997-2014 revealed significant yearly differences in the infection dynamics of studied metacercariae in juvenile fish of L. haematocheilus. Metacercariae were absent or fish harboured several times less parasites in 2005-2013 than in 1997-1999. T. imbutiforme infection exhibits a convex that was observed in a decline of the parasite load aft er an initial increase. The infection load of Diplostomum spp. increased asymptotically with the fish age reaching maximum value in two years old juveniles. Both the abundance and the prevalence of A. (P.) longa were low in juveniles of two month and two years old but relatively high and more or less constant during the rest of the juvenile period. Results of the present study suggest that metacercariae, especially, T. imbutiforme, are associated with mortality of juvenile Liza haematocheilus.
The wide variability in morphological features, geographical and host ranges of mullet acanthocephalan parasite Neoechinorhynchus agilis (Rudolphi, 1819), raises the question of taxonomic status of this species. Rudolphi’s type and Yamaguti`s voucher specimens, as well as our own material from the WW Pacific and NE Atlantic region were used herein to provide comparative morphological analysis. Th e study revealed three different species of Neoechinorhynchus, N. (N.) agilis and N. (H.) personatus Tkach, Sarabeev et Shvetsova, sp. n. in the Atlantic and N. (H.) yamagutii Tkach, Sarabeev et Shvetsova, sp. n. in the Pacific. Strong morphological and morphometric differences were found between three described herein species from different hosts and regions. Th e dividing of N. agilis into three species, two of them are new, provides a basis for the further revision of host-geographical records of mullet acanthocephalan parasites.
To reach ethically and scientifically valid mean abundance values in parasitological and epidemiological studies this paper considers analytic and simulation approaches for sample size determination. The sample size estimation was carried out by applying mathematical formula with predetermined precision level and parameter of the negative binomial distribution estimated from the empirical data. A simulation approach to optimum sample size determination aimed at the estimation of true value of the mean abundance and its confidence interval (CI) was based on the Bag of Little Bootstraps (BLB). The abundance of two species of monogenean parasites Ligophorus cephali and L. mediterraneus from Mugil cephalus across the Azov-Black Seas localities were subjected to the analysis. The dispersion pattern of both helminth species could be characterized as a highly aggregated distribution with the variance being substantially larger than the mean abundance. The holistic approach applied here offers a wide range of appropriate methods in searching for the optimum sample size and the understanding about the expected precision level of the mean. Given the superior performance of the BLB relative to formulae with its few assumptions, the bootstrap procedure is the preferred method. Two important assessments were performed in the present study: i) based on CIs width a reasonable precision level for the mean abundance in parasitological surveys of Ligophorus spp. could be chosen between 0.8 and 0.5 with 1.6 and 1x mean of the CIs width, and ii) the sample size equal 80 or more host individuals allows accurate and precise estimation of mean abundance. Meanwhile for the host sample size in range between 25 and 40 individuals, the median estimates showed minimal bias but the sampling distribution skewed to the low values; a sample size of 10 host individuals yielded to unreliable estimates.