Ectoparasites of Atlantic mackerels (Scomber colias and S. scombrus): biological tags and macro and microhabitats dynamics

Atlantic chub mackerel, Scomber colias Gmelin, 1789, and Atlantic mackerel, Scomber scombrus L. , 1758, (Teleostei: Scombridae) are two fish species inhabiting the Atlantic Ocean coastal waters, very important to the Portuguese and EU fisheries. The species identification and differentiation when entering the commercial circuit present some difficulties due to their similar morphology and partial habitat overlap. Despite not being present in the identification keys for mackerels, the empirical knowledge of fishermen refers the eye size of S. colias and S. scombrus as a good characteristic to differentiate both species, as the former presents a larger eye than the later. Furthermore, parasites of these species can be used as biological tags to differentiate both hosts. This study aims to verify the usefulness of these two solutions to easily solve the said misidentification problem. For this, fish obtained from commercial catches from northern Portuguese waters were analyzed. It was verified that the eyes of S. colias were significantly larger (≈ 1.66×) than those from S. scombrus of the same size. Additionally, four ectoparasitic species were selected as good biological tags to distinguish between these two mackerels: Pseudokuhnia minor was recorded only for S. colias (97.5% prevalence and mean abundance of 23.95 worms/fish); Caligus pelamydis was recorded only for S. scombrus (69.0% prevalence and mean abundance of 3.12 copepods/fish); and Grubea cochlear and Kuhnia scombri were recorded for both fish, but presented significantly higher prevalence and abundance for S. scombrus (28.6% and 66.7% prevalence and mean abundance of 0.4 and 2.0 worms/fish, respectively), than for S. colias (2.5% and 17.5% prevalence and mean abundance of 0.03 and 0.5 worms/fish, respectively). Taking into account these results, the eye size and the macro-ectoparasites of S. colias and S. scombrus can be useful to successfully identify and differentiate both Atlantic mackerel species. Parasites, especially ectoparasites, are affected by the environment that their hosts occupy. Also, they show a specific distribution among their hosts, living in a welldefined and restricted microhabitat. Apart from the above mentioned goals, this study also aims to describe the S. scombrus’ ectoparasite fauna dynamics at the macro and microhabitat levels. Fish from Matosinhos and Figueira da Foz (two different Portuguese coastal regions) were examined for macro-ectoparasites. Differences in parasites’ infection levels from fish of both regions were found, indicating different preferences in macrohabitat conditions. Regarding the microhabitat of the ectoparasites reported, it could be seen that every species have a very specific distribution within the host. No interspecific interactions were found among the FCUP [Ectoparasites of Atlantic mackerels (Scomber colias and S. scombrus): biological tags and macro and microhabitats dynamics] ii component species, which supports the idea that the driving forces of community structure of parasites are not the interspecific competitions, but the reinforcement of reproductive barriers and thus, enhancement of the chance to mate.