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Fish parasite communities can be directly influenced by characteristics of host species. However, little is known about the host-parasite relationships in commercially important fish of the southeastern Atlantic. To address this knowledge gap, a comparative analysis of the parasite communities of three sympatric Clupeiformes was conducted. Cetengraulis edentulus (Engraulidae), Opisthonema oglinum (Clupeidae) and Sardinella brasiliensis (Clupeidae) were collected from an estuarine lagoon near Rio de Janeiro, Brazil. Prevalence, abundance and aggregation were estimated for infrapopulations; richness, diversity, evenness and dominance for infracommunities. The three component communities were compared using both quantitative and qualitative components. Canonical discriminant analysis was used to determine if a host population could be characterised by the component community of its parasites. Multivariate models revealed that host species, a proxy for diet and phylogenetic relationships, was the main factor influencing the composition of parasite infracommunities. Diet was found to be the main factor shaping the communities of endoparasites, in which digeneans were dominant and best indicator of host population. Ectoparasites (copepods, isopods and monogeneans) displayed strong host-specificity with some species restricted to a single host population. The similarity of the component communities of the two clupeid populations demonstrated the influence of host phylogeny. Parasite infracommunities exhibited low diversity and high dominance, with many taxa restricted to a single host species (specialists) and few occurring in more than one (generalists). Host phylogeny and by extension, diet, morphology and coevolution with parasites appear to be important factors in determining the host-parasite relationships of clupeiform fish in the southeastern Atlantic. [ABSTRACT FROM AUTHOR]

The Brazilian sardine (Sardinella brasiliensis) sustains the most important pelagic fishery off Brazilian waters. The present study evaluated the existence of distinct population-units inferred from body geometric morphometrics and otolith shape analyses using two and three-year-old individuals collected in Rio de Janeiro and Santa Catarina, the two main Brazilian fishery grounds. Univariate and multivariate statistics were performed for the entire dataset and separated by age groups. Re-classification success for combined ages achieved an overall re-classification rate of 84% and 89% for body and otolith signatures, respectively. Moreover, the combination of both techniques improved the overall re-classification success to 93%. However, when both techniques were conducted by age group, it allowed to unravel a more detailed population structure scenario, and a complete group separation (100% re-classification success) was obtained using otolith shape analyses for two-year-old individuals. Both techniques indicated the existence of two different population-units considering the Brazilian geographical extremes of the species' fishing area. Such regional differences are probably related to distinct oceanographic conditions affecting the feeding regime and fish growth. This study clearly shows that S. brasiliensis caught off southeast-south Brazil corresponds to two distinct population-units, and recommends a finer regional fishery management for the species. [ABSTRACT FROM AUTHOR]

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