Occurrence of two myxosporean parasites in the gall bladder of white seabream (L.) (Teleostei, Sparidae), with the morphological and molecular description of n. sp.

Myxosporeans are widespread cnidarian parasites that usually parasitize fish as part of their complex life cycle, thus constituting a potential threat for the aquaculture industry. White seabream (L.) is a commercially valuable sparid fish reared in Southern European aquacultures. Nonetheless, knowledge on myxosporean infections potentially harming the sustainable production of this fish is extremely limited. In this study, a myxosporean survey was conducted on specimens reared in two Southern Portuguese fish farms. Two coelozoic myxosporeans were detected infecting the gall bladder, and are herein reported based on microscopic and molecular procedures: n. sp. and Rocha et al., 2013, previously described from reared stocks of gilthead seabream in the same geographic locality. n. sp. is the 12 species of the genus to be reported from Southern European sparids, reinforcing a substantial radiation of within this fish family and geographic region. SSU rRNA-based Bayesian inference and maximum likelihood analyses revealed n. sp. positioned separately from other sparid-infecting spp. reported from Southern European countries, demonstrating that this species does not share a more immediate common ancestor with its closest relatives based on host affinity and geography. The recognition of a novel sparid-infecting lineage within the clade strengthens the contention that this genus entered sparid fish multiple times, namely in the Southern European region. The identification of infections in demonstrates that host shift has occurred among sparids reared in the Southern Portuguese coast. This agrees with the broad host specificity that is usually attributed to this genus, and that may be suggested to be the outcome of the capacity of the morphotype to undergo host shift/switch based on our findings and the limited molecular data available for this genus. Thus, a better understanding of host-associated diversification and dispersal mechanisms requires the increasing availability of molecular data from infections of the same species occurring in multiple hosts and geographical locations.