Our research, based at the Laboratory of Biodiversity and Environment, Interactions - Genomes (LBEIG), USTHB, aims to significantly increase the number of Digenea species. Digenea are flatworm parasites that live mainly in the digestive tracts of teleost fish. However, our understanding of these parasites along the Algerian coast is limited. A parasitological investigation of diagenetic trematodes in three fish species from Algeria marine fish was conducted from 2022 to 2023. The study identified three trematodes species belonging to the Opecoelidae family, and their identification was based on morphological data with key identification. We have given a very detailed morphological description, illustrating for the first time the male and female genitalia with the whole body. Gaevskajatrema perezi (Mathias, 1926), Gibson & Bray, 1982, was found in the intestines of the Symphodus tinca Linnaeus, 1758 (Labridae); Allopodocotyle israelensis, Fischthal (1980), was recorded from the intestine in the Pomadasys incisus (Bowdich, 1825). Additionally, Bathycreadium elongatum (Maillard, 1970), Bray, 1973, was recorded in the intestine of the Phycis phycis (Brünnich) (Gadiformes: Phycidae); all of these parasites were recorded for the first time in Algeria. This study contributes to the knowledge of Digenean diversity by documenting newly recorded species in Algerian waters, either through new host associations or from previously unreported localities. The morphological data are provided to support this new host and locality record, enriching the parasitological inventory of Mediterranean marine fish.