Molecular approach and techniques used in the diagnosis of fish parasites

Aquaculture is considered an integral part of achieving food security and poverty reduction by providing nutritional, and livelihood security to millions of people around the world. However, poor health management and a lack of proper diagnostic facilities create problems in the early identification of pathogens leading to mass mortality in fish. However, fish, like any animal, are exposed to and susceptible to a wide range of diseases and parasites. Parasitic diseases of fish are usually encountered more often than microbial diseases. From 30%-50% of the cases received at several fish disease, diagnostic laboratories involve parasites. Some of the parasites could not be differentiated by conventional diagnostic methods from other phenotypically similar pathogens of the same genera. Some attempts have been made using biochemical tests, DNA homology, and protease variability. Moreover, most molecular technologies are mostly lab-based and need time to provide information on parasitic infections. Additionally, such technology couldn’t be used in the field, providing direct information on potential parasitic pathogens to adopt immediate management measures and avoid disease outbreaks and production loss. However, in the last fifteen years or so, great advances have taken place in understanding the molecular biology of fish pathogens and their hosts. Among them, vast fields of molecular study like Nucleic acid-based approach, PCR, ITS, RT-PCR, LAMP, Luminex, RAPD, AFLP, RFLP, and microsatellites have been used for parasitic disease diagnosis. Detection of nucleic acid molecules has demonstrated its usefulness for highlighting hardly cultivable, non-cultivable, and even dead microorganisms, generating appropriate novel or replacement technologies. Thus, a better understanding of molecular tools developed for the detection of specific parasites would be helpful to increase diagnostic precision, aid carrier detection, and promote species discoveries in different parasitic groups. Further, studies are still necessary to increase our knowledge about molecular tools in the detection of a diverse group of parasites associated with the disease in fish and also from fish to humans.