Variation in the intraspecific relationship between fish length and intensity of parasitic infection: biological and statistical causes

Abstract

In a meta-analysis, the overall mean correlation between fish length and the intensity of parasitic infections derived from 76 different host-parasite species was positive but weak and non-significant, following corrections for sample size. Whether the parasites were acquired by ingestion or by skin contact had no influence on the strength of the relationship. For cestodes, larval digeneans, and gnathiid isopods, however, the mean correlation between fish length and intensity of infection was significant. Some statistical parameters influenced the strength of the raw correlations computed within samples and thus led to over-or under-estimation of the true relationship. Sample size correlated negatively with the value of the correlation coefficients, whereas range in both fish lengths and intensities of infection correlated positively with the value of the correlation coefficients. Distinguishing between statistical noise and the biological processes shaping the size v. intensity relationship will be important if this relationship is to be incorporated into fish population models. 2000 The Fisheries Society of the British Isles

Parasite community of Pagrus pagrus(Sparidae) from Rio de Janeiro, Brazil: evidence of temporal stability

“…older) fish offer larger target areas for parasites transmitted by cercariae, ingest larger quantities of food, and have had more time to accumulate parasites than have smaller (i.e. younger) fish (ZANDER; KESTING, 1998;FIORILLO;FONT, 1999;POULIN, 2000;BUSH et al, 2003;FELLIS;ESCH, 2004;ZANDER, 2004). According to Saad-Fares and Combes (1992), in the case of the digeneans, this correlation might be influenced by changes to the fish diet.…”

Helminth parasite communities of spotted rose snapper Lutjanus guttatus from the Mexican Pacific

“…It could be a biased analysis since our sampling effort just comprised a portion of the entire range of fi sh length. Nonetheless, a meta-analysis performed by Poulin (2000) indicated that the overall, mean correlation between fi sh length and intensity of infection, weighted for sample size, was not signifi cantly different from zero, independent of mode of infection. In the overall samples, metrics of most component species and infracommunities were higher in BB than in MB.…”

“…Given the importance of L. guttatus for fi sheries and aquaculture, it is necessary to improve our knowledge about its parasite diversity and infection levels on wild fi sh populations. In fi sh parasite ecology, there has been some evidence for an increase in parasite diversity with host size (Lo et al, 1998); however, in many cases the correlation between those factors may be weak and non-signifi cant (Poulin, 2000). Other ecological processes may occur at spatial scale.…”

Parasitism by Monogenoidea in Piaractus mesopotamicus (Characiformes, Characidae) cultivated in Paraná River (Brazil)

“…As pointed by Poulin (2000), this pattern cannot be generalized, because in many host-parasite systems the correlation is positive, but weak and non-significant. In the present study, no correlation was observed between the abundance and prevalence of the parasites and the total length of the hosts.…”