Spatial variation in the parasitic isopod load of the Japanese halfbeak in western Japan

Abstract

Cymothoid isopods (family Cymothoidae) are commonly found parasitizing diverse fishes, including commercial species. However, the effects of these parasites on host body condition are still poorly known. Here we investigated the spatial variation of the effects of parasite infection on host body condition, using the parasitic load of the cymothoid Mothocya parvostis on the Japanese halfbeak Hyporhamphus sajori at 4 sampling sites in western Japan. M. parvostis prevalence at each site (41.6−74.4%) was higher than that known for other fish host−cymothoid systems (usually less than 30%). The number of isopods in infected hosts, the reproductive status of female isopods (i.e. ovigerous/non-ovigerous), and the body size of female and male isopods relative to the size of their hosts were not significantly different among sites. However, at the site where human activity was most intense, M. parvostis infection had a significantly negative effect on host body condition. These results suggest that the effect of cymothoid infection on host body condition might be benign under natural conditions but becomes detrimental in habitats that are unsuitable for the host, such as highly human-impacted areas.

Temporal changes in streamflow regime and host-related factors affect parasitism of freshwater prawn in Southeast Brazil

“…Posteriorly, the ectoparasites were fixed in 70% ethanol and subsequently identified through specific characteristics (e.g., 2nd pereopod showing five spines in the inner margin of the propodus and the 6th pereopod showing four spines in the propodus and one in merus), according to Lemos de Castro (1985) and Andrade et al (2020). The abundance of ectoparasites was considered as the total number of cymothoid isopods in each host individual, which can be categorised in terms of infestation levels as follows: 0 = no infestation; 1=low infestation; 2-3=high infestation (Horton and Okamura, 2001;Kawanishi et al 2016). The prevalence was calculated as the proportion of prawns infected by cymothoid isopods in relation to the total number of hosts analysed, and the mean intensity was calculated as the total number of cymothoids in a sample of infected host species divided by the number of infected individuals of the host species in the sample (Bush et al 1997).…”