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.