Introduction
The african Lake Malawi/Nyasa represents one of the major underexploited fishery resources, since it contains more endemic fish species than any other lake in the world (Rico and Turner, 2002). African cichlids are highly appreciated “colourful rock dwelling fishes” by aquarists worldwide. This peculiarity induced fishery program which is operating since the early 1970s (Msukwa et al., 2021). The ornamental fish export trade is mostly based on fish from the Lake Malawi, with an average of 28,000 live fish being exported annually and valued at US$218,000 at 2020 prices (Msukwa et al., 2021). Despite their huge economic importance, management of ornamental fisheries is challenged by a paucity of information on the status of the exploited fish stocks (Dee et al., 2014). Fish can dysplay aspecific signs of disease as emaciation, exophthalmia, keratitis and skin lesions, as nodules and black spots. Mycobacterial infection is probably the most common chronic disease affecting aquarium fish species (Noga, 2010). Cichlids are known for a territorial behaviour and sexual aggression, making these animals prone to skin damage, which might become the site of bacterial penetration and transformation of dermal mycobacteriosis into systemic granulomatous infection (Novotny et al., 2010). Regarding viral diseases, those associated with viruses in the familyIridoviridae are reported in ornamental fish. Among viruses of this family, Megalocytivirus and Ranavirus are considered highly pathogenic iridoviruses and are frequently associated with highly mortality outbreaks, whereas Lymphocystivirus is mainly associated with a self-limiting cutaneous nodular disease (Whittington et al., 2010; Johan and Zainathan, 2020). Thanks to high species diversity and a broad range of speciation mechanisms, cichlid fish represent a textbook model in parasite evolutionary biology. Despite their importance, among the biological agents of disease, cichlid parasites remain understudied (Vanhove et al., 2016).
The huge relevance of these fish species is not counterbalanced by literature references regarding pathologic conditions with only a limited amount of papers being available (Paperna et al., 2001; Birkbeck et al., 2011; Lewisch et al., 2016).
This study aims to focus on debilitated ornamental cichlids that were sampled during routine fish management activities. Our goal is to add knowledge of their health status to the scientific community and exotic fish trade industry. To achieve this, a multidisciplinary approach was performed, to investigate pathological patterns and search for the most probable microbiological agents responsible for subtle disease.