Parasite communities of the deep-sea fish Alepocephalus rostratus Risso, 1820 in the Balearic Sea (NW Mediterranean) along the slope and relationships with enzymatic biomarkers and health indicators

This study examines the parasite communities of Alepocephalus rostratus and its influence on some fish biochemical markers and histological alterations. A. rostratus constitutes the second most important fish species, in terms of biomass, inhabiting the deep slope of the Catalan Sea (Balearic Sea, NW Mediterranean). The study revealed eight different parasite species in this host: one coccidian, one digenean, one monogenean, one cestode and four nematodes. The parasite fauna of A. rostratus was partially dominated by larval forms (four of the seven metazoan taxa found), which combined with low species richness corresponds to a parasite fauna pattern more typical of bathypelagic fish species rather than demersal ones. The larval tetraphyllideans and cucullanid nematodes were the predominant species. In relation to depth, differences in abundance of the nematodes Cucullaninae gen. sp. and Hysterothylacium aduncum were found, probably due to the dietary shift in the fish host at greater depth. Thus, Cucullaninae gen. sp. and H. aduncum could be regarded as indicators for discriminating populations of A. rostratus in relation to depth in NW Mediterranean waters. Of the biochemical markers examined, acetylcholinesterase (AChE) and lactate dehydrogenase (LDH) activities and lipid peroxidation (LP) levels, only LP showed significant differences between depths. A positive relationship was found between AChE activity and Tetraphyllidea fam. gen. sp., Anisakis physeteris and H. aduncum abundance and a negative one with the abundance of Cucullaninae gen. sp. LDH showed a positive relationship with the abundance of the parasites Paracyclocotyla cherbonnieri and Tetraphyllidea fam. gen. sp. At cyto-histological level, coccidians were detected in the pyloric caeca with a prevalence of 90% in Barcelona, but in the rest of organs almost no alterations were detected. The restricted macro-planktonic diet of A. rostratus, that maintains it distant from the sea-floor for longer periods than other demersal species, probably makes this species less susceptible to sediment-associated impacts including parasitism. (C) 2015 Elsevier Ltd. All rights reserved.