70 MARCH 2025 • WORLD AQUACULTURE • WWW.WAS.ORG Impacts of Myxobolus and Copepod Infections on Mullet The effects of Myxobolus and copepod infections are evident across all life stages of mullet. Fingerlings and juvenile fish often experience slower growth due to disrupted nutrient absorption caused by Myxobolus infections in the intestines (Figure 2). This stunted growth increases their vulnerability to predation, reducing the number of fish that survive to adulthood. In adults, parasites primarily target the gills and intestines, where Myxobolus cysts cause erosion of cartilage and copepods physically damage gill filaments (Figure 3). This structural breakdown impairs oxygen absorption, causing chronic respiratory stress. Environmental factors like water pollution and rising temperatures worsen the physiological effects of these infections. Polluted waters provide a favorable environment for parasites, further compromising the immune systems of infected fish. Additionally, warmer waters contain less dissolved oxygen, exacerbating the respiratory challenges caused by gill damage. This dual impact increases the likelihood of mortality among infected fish, highlighting the need for comprehensive water quality management to mitigate parasite prevalence. Parasitic infections divert energy from reproductive processes, leading to fewer viable offspring. Female mullet facing chronic infections often experience delayed or incomplete spawning cycles, producing fewer and less viable eggs. Male mullet may also suffer from physical weakness caused by copepod infestations. The overall reduction in reproductive success contributes to declining mullet populations, impacting the long-term sustainability of fisheries and aquaculture activities reliant on these species. These challenges underscore the importance of implementing preventive measures to protect fish health and ensure steady reproductive output. Stunted growth is a common outcome for mullet infected with Myxobolus and copepods. Because of nutrient deficiencies and respiratory impairment, infected fish rarely reach marketable size, resulting in economic losses. Given the centrality of mullet to West African fisheries, addressing the growth impacts of parasitic infections is essential for economic resilience and food security. Histopathology and Advanced Diagnostic Methods In this study, histopathology revealed Myxobolus clusters in gill cartilage, eroding respiratory structures. Copepod infestations showed erosion of gill filaments and mucosal linings, compromising both respiratory and digestive functions. These insights emphasize the need for early detection and intervention, as untreated infections can have severe consequences for fish health. Histopathology is often complemented by molecular diagnostics, such as Polymerase Chain Reaction (PCR) and environmental DNA (eDNA) analysis. PCR allows for the detection of parasite DNA in tissue samples, confirming infections at an early stage. eDNA sampling can identify the presence of parasites in water bodies, enabling proactive management. Immunohistochemistry is another technique that stains specific parasite proteins, helping researchers track parasite distribution within host tissues. Combined with histopathology, these methods provide a comprehensive view of parasite-host interactions, enhancing diagnostic accuracy and supporting targeted treatments. The integration of these techniques enables aquaculture managers to detect infections early and implement effective management practices. By using multiple diagnostic methods, researchers can monitor the spread of parasites more effectively, reducing infection risks in densely populated fish farms. Future Perspectives: Preventive Measures, Treatment Approaches, and Collaborative Research Preventive measures are essential for managing parasitic infections in aquaculture. Regular water quality monitoring is crucial for maintaining conditions that discourage parasite growth. Biosecurity protocols, such as equipment disinfection and stock quarantining, also reduce the likelihood of introducing parasites into cultured fish populations. Integrated Pest Management (IPM) strategies, including habitat modification and biological controls, offer eco-friendly solutions that complement traditional approaches. Genetic research into parasite resistance offers additional preventive options. Selective breeding programs are exploring genetic markers linked to resistance, aiming to produce mullet strains that can naturally withstand infections. These programs have shown success in other aquaculture species and could significantly reduce reliance on chemical treatments. For established infections, traditional treatments like antiparasitic drugs remain common but carry environmental risks. Researchers are increasingly exploring alternatives like probiotics that strengthen fish immune systems and inhibit parasite growth within the host. Certain probiotics create unfavorable conditions for parasites, reducing their impact on fish health. Natural remedies, such as garlic and neem extracts, are also gaining attention due to their anti-parasitic properties, offering a more environmentally friendly approach compared to chemical treatments. Vaccine research is another promising field. Experimental vaccines targeting specific proteins in Myxobolus and copepods may help fish develop immunity to these parasites. DNA-based vaccines, in particular, show potential for providing long-term protection. While challenges remain in effectively delivering vaccines in aquatic FIGURE 3. Histopathology of gills infected by Copepoda, a: normal gill filaments; b and c: gill filaments damaged by copepods.
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