The role of pelagic swarm fish (Myctophidae: Teleostei) in the oceanic life cycle of Anisakis sibling species at the Mid-Atlantic Ridge, Central Atlantic

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Abstract
First information is provided on the parasitation and feeding ecology of the myctophid fish species Myctophum punctatum and Notoscopelus kroyeri from the Mid-Atlantic Ridge (MAR), Central Atlantic. Four different parasite species were found in both fish with a similar high prevalence and intensity of infestation. The digeneans Gonocerca phycidis and Lethadena sp. were isolated as adults from the stomach, larval tetraphyllidean cestodes (Scolex pleuronectis) from the intestine, and genetically identified larval anisakid nematodes of Anisakis simplex (s.s.) from the body cavity. No further Anisakis sibling species could be identified. Both myctophids had small pelagic crustaceans, mainly copepods and hyperiids, within their stomach contents. Ostracods, euphausiids, decapods, and amphipods were minor food components, demonstrating the pelagic environment for both fish. The recorded parasites including the anisakid A. simplex (s.s.) perform pelagic life cycles within the region, benefiting from extensive diurnal vertical migrations of their fish hosts. Comparison of the host range among the anisakis sibling species suggests that the A. simplex complex has low host specificity, infecting toothed and baleen whales on their extensive oceanic migrations. This contrasts the Anisakis physeteris complex that is restricted to toothed whales of the families Kogiidae and Physeteridae. Specificity in the teleost intermediate hosts for both complexes seems to be low, and sympatric occurrence of different siblings within the same intermediate hosts is likely. Myctophid swarm fish as important copepod feeders at the MAR significantly contribute to the oceanic anisakid nematode life cycle, especially considering the 100% prevalence and high intensity of infestation. Further genetic identification of Anisakis nematodes is needed in order to understand the sibling species distribution, along the MAR and within other oceanic environments.

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