Assessing the role of host traits as drivers of the abundance of long‐lived parasites in fish‐stock assessment studies

Abstract

In order to identify the best tools for stock assessment studies using fish parasites as biological indicators, different host traits (size, mass and age and their interaction with sex) were evaluated as descriptors of cumulative patterns of both parasite abundance and infracommunity species richness. The effect of such variables was analysed for a sample of 265 specimens of Percophis brasiliensis caught in the Argentine Sea. The abundances and species richness were modelled using generalized linear mixed models (GLMMs) with negative binomial and Poisson distribution respectively. Due to collinearity, separate models were fitted for each of the three main explanatory variables (length, mass and age) to identify the optimal set of factors determining the parasite burdens. Optimal GLMMs were selected on the basis of the lowest Akaike information criteria, residual information and simulation studies based on 10 000 iterations. Results indicated that the covariates length and sex consistently appeared in the most parsimonious models suggesting that fish length seems to be a slightly better predictor than age or mass. The biological causes of these patterns are discussed. It is recommended to use fish length as a measure of growth and to restrict comparisons with fish of similar length or to incorporate length as covariate when comparing parasite burdens. Host sex should be also taken into account for those species sexually dimorphic in terms of morphology, behaviour or growth rates.

Cestode and nematode larvae of hygienic-sanitary importance parasitizing Percophis brasiliensis (Actinopterygii) collected from fish markets of the municipality of Niterói, RJ, Brazil

“…This finding corroborates Spalding et al (2007), who demonstrated that the marine ecoregions have relatively homogeneous species compositions that are clearly distinct from adjacent systems. Therefore, features observed among and within ecoregions can influence fish parasite communities and explain the differences in species assemblages of parasites of P. brasilensis from waters off Argentine and Uruguay (Braicovich & Timi 2008Braicovich et al, 2016Braicovich et al, , 2017, and from off the state of Rio de Janeiro, Brazil, observed in previous studies and reinforced by the present study. Braicovich & Timi (2008) reported that trypanorhynch metacestodes and third-stage nematode larvae found in P. brasiliensis were collected from the abdominal cavity, viscera and mesentery, which are the same infection sites found in the present study.…”

“…Both these species had high prevalences in the present study, although the number of parasites collected for each species was much higher for P. brasiliensis collected in Argentina, which suggests a difference between these two distinct marine ecoregions, i.e., Southeastern Brazil and Uruguay-Buenos Aires Shelf. Braicovich et al (2016) evaluated different fish traits as descriptors of patterns of cumulative parasite abundance and infra-community species richness, and identified the best tools for comparative studies of stock assessment using P. brasiliensis collected from Mar del Plata, Argentina, and three of its more common long-lived parasites -the nematode H. deardorffoverstreetorum, the cestode G. carvajalregorum, and the acanthocephalan Corynossoma australe -considered in others studies as suitable biological tags for stock assessment in the Southwestern Atlantic province (Braicovich & Timi, 2008. Braicovich et al (2017) subsequently studied the parasite composition of P. brasiliensis from nine localities, including the previous sampled localities from the Uruguay-Buenos Aires Shelf zoogeographic ecoregion (Braicovich & Timi, 2008, and added the sampled localities of Cabo Frio (Southeastern Brazil), Rio Grande do Sul (Rio Grande), Villa Gessel, and Neocochea (Uruguay-Buenos Aires Shelf) of the Warm Temperate Southwestern Atlantic province.…”

“…Trypanorhynch cestodes and anisakid and raphidascaridid nematodes parasitizing P. brasiliensis have been reported in studies about the composition and structure of parasite assemblages in Brazil, Uruguay and Argentina. These helminth larvae were recognized as biological markers as host stock descriptors and as biogeographic indicators (Braicovich & Timi, 2008Braicovich et al, 2016Braicovich et al, , 2017.…”

Influence of confluent marine currents in an ecotonal region of the South-West Atlantic on the distribution of larval anisakids (Nematoda: Anisakidae)

“…To analyze the relative contribution of host/abiotic variables on parasite distribution, Euclidean distance matrices of both prevalence and mean abundance were analyzed by distance-based multiple linear regressions (DistLM) [ 49 ] with significance testing based on 9999 permutations. As host-related predictor variables, the host species and their trophic level and mean total length were included in the models due to their known influence on parasite burdens [ 45 , 50 , 51 ]. Abiotic predictor variables were latitude, longitude and year of capture.…”

Experimental evidence that host choice by parasites is age-dependent in a fish-monogenean system

“…For example, potential hosts assigned to an adult class that are collected in the field can belong to different cohorts of both males and females, i.e. a mixture of age classes and sex, which can obscure the effect of age in susceptibility to infections (Braicovich et al 2016;Timi and Poulin 2020). Thus, to properly address the effect of the host age-structure, one needs to experimentally isolate the potential confounding effects of cohort and sex (Izhar and Ben-Ami 2015).…”