Effects of sample size on fish parasite prevalence, mean abundance and mean intensity estimates

Abstract

This study considers the effects of sample size on estimates of three parasitological indices (prevalence, mean abundance and mean intensity) in four different host-parasite systems, each showing a different pattern of infection. Monte Carlo simulation procedures were used in order to obtain an estimation of the parasitological indices, as well as their variance and bias, based on samples of different size. Although results showed that mean values of all indices were similar irrespective of sample size, estimates of prevalence were not significantly affected by sample size whereas mean abundance and mean intensity were affected in at least one sample. Underestimation of values was more perceptible in small ( <40) sample sizes. Distribution of the estimated values revealed a different arrangement according to the host-parasite system and to the parasitological parameter. Monte Carlo simulation procedures are, therefore, suggested to be included in studies concerning estimation of parasitological parameters.

Distribution pattern of crustacean ectoparasites of freshwater fish from Brazil

“…method, design and number of samples obtained). Marques & Cabral (2007) demonstrated recently that only the prevalence of parasitic metazoans in fish, including crustacean species, was not affected by the sample size used, while the intensity and abundance are strongly influenced by sampling size. Here, we found a strong positive correlation between the number of fish examined and the number of fish parasitized.…”

“…Many parasite species commonly show overdispersion in different host fish (RÓZSA et al, 2000;MARQUES & CABRAL 2007;POULIN, 2013). This phenomenon occurs mainly due to processes that produce variability in host exposure, host acceptability by the parasite and host immune response.…”

“…For ectoparasitic crustaceans in fish populations, infestation levels are determined by factors operating during and after transmission, particularly those relating to the characteristics of the host, parasite and environment (FRYER, 1968;DOUELLOU & ERLWANGER, 1994;THATCHER, 1998;CARVALHO et al, 2004;MARQUES & CABRAL, 2007;ANEESH et al, 2013). A significant positive correlation between the mean intensity and the mean abundance was found in the dataset analyzed here, whereas prevalence only showed weak positive correlations with the mean intensity and mean abundance of infestation.…”

Spathebothriidea: survey of species, scolex and egg morphology, and interrelationships of a non-segmented, relictual tapeworm group (Platyhelminthes: Cestoda)^*

“…sequenced), Diplocotyle olrikii (n = 8) and Spathebothrium sim- Kuchta et al: Review of Spathebothriidea (Cestoda) plex (n = 2) (see Table 1). Following Marques et al (2007), the D2 region of the 28S rDNA gene (~660 bps) was characterised for all specimens (n = 12) and the ITS-2 region (~600 bps) for each of the specimens, except for replicates of D. olrikii that proved identical based on comparison of 28S sequences (n = 8) (Table 1). These data were combined with published 28S and ITS2 sequences of these three taxa as well as Didymobothrium rudolphii from the work of Marques et al (2007).…”

“…Following Marques et al (2007), the D2 region of the 28S rDNA gene (~660 bps) was characterised for all specimens (n = 12) and the ITS-2 region (~600 bps) for each of the specimens, except for replicates of D. olrikii that proved identical based on comparison of 28S sequences (n = 8) (Table 1). These data were combined with published 28S and ITS2 sequences of these three taxa as well as Didymobothrium rudolphii from the work of Marques et al (2007). Attempts were also made to characterise the cytochrome c oxidase subunit I gene, used for 'species barcoding' in many groups (especially arthropods and vertebrates), using a variety of primer combinations from Littlewood et al (2008) and Moszczynska et al (2009), but without success.…”