Ectoparasite management in gilthead seabream and European seabass may have deeper implications for farm performance than traditionally assumed. A recent study published in Aquaculture suggests that parasitic infections do not merely cause visible lesions but can alter key physiological parameters linked to growth, feed conversion and resilience in this two cornerstone species.
The research is particularly relevant because it was conducted under commercial co-culture conditions involving both species. Despite sharing the same production environment, parasite prevalence was significantly higher in seabream than in seabass. Overall prevalence reached 46% in seabream compared with 27.6% in seabass, pointing to meaningful interspecific differences in susceptibility.
However, the most significant finding lies not in the epidemiological gap itself, but in the systemic physiological consequences associated with infection.
Among the parasites identified were monogeneans such as Dactylogyrus and Gyrodactylus, the dinoflagellate Amyloodinium, and branchial isopod crustaceans. Although biologically distinct, these groups share a common feature: their capacity to damage gills and body surface, potentially impairing respiratory efficiency and increasing the fish’s physiological maintenance costs.
Infected fish showed significant reductions in red blood cell counts, haemoglobin and haematocrit levels, consistent with anaemic conditions. These changes were accompanied with chronic stress activation, and increased antioxidant responses indicating oxidative stress.
At the immune level, infection was linked to reduced lymphocyte and neutrophil counts and increased eosinophils and basophils, suggesting complex immune modulation that may weaken the fish’s ability to respond to additional health challenges.
From a production standpoint, these findings imply that parasite impact should not be assessed solely through mortality rates or infestation intensity. Subclinical physiological stress may translate into reduced metabolic efficiency, poorer feed utilisation and increased vulnerability to environmental stressors, particularly in intensive systems or during high-temperature periods.
The study also identified distinct seasonal patterns, with some parasites peaking in summer and others in winter. This dynamic reinforces the importance of integrating parasite management into annual producing planning, aligning monitoring and intervention strategies with high-risk periods rather than relying on reactive measures.
In addition, the research incorporated molecular confirmation through PCR techniques, strengthening diagnostic reliability and suggesting that certain infections may be underestimated when relying solely on conventional field diagnostic. Gill damage associated with some parasites is particularly relevant from a production perspective, as it may compromise gas exchange and increase baseline energy expenditure, potentially generating cumulative effects over the production cycle.
In a context of tight margins and growing health pressure, the findings suggest that proactive ectoparasite management could become a critical lever to safeguard production efficiency and reduce hidden losses that do not immediately appear in standard mortality indicators.
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