Incidence of Nematopsis sp. (Protoctista: Apicomplexa) in Penaeus vannamei and its relationship with physicochemical parameters of water

This study evaluated the incidence of parasitosis caused by Nematopsis sp. (Protoctista: Apicomplexa) in farmed shrimp (Penaeus vannamei) at a farm in the Falcón State, Venezuela, over four months (June–September). A total of 1000 specimens were sampled using a cast net, and microscopic counts of gregarines in the intestines were performed to estimate parasitic load. Concurrently, water physical parameters (pH, salinity, temperature, and transparency) were measured to analyze their relationship with parasitosis incidence. Results showed a significant progressive increase in incidence, from 39.52% in June to 143.52% in September, indicating a considerable rise in parasitosis levels. Monthly variations in physical parameters were observed, with decreases in pH, salinity, and transparency correlating with increased incidence. Correlation analyses revealed a strong negative association between pH and transparency with incidence (r ≈ -0.82, R² ≈ 0.67), and a moderate negative correlation with salinity (r ≈ -0.64). Temperature had a lesser and non-significant influence (r ≈ - 0.28). These findings suggest that environmental factors, especially pH and transparency, play a crucial role in the parasitic dynamics of Nematopsis sp., affecting the health and productivity of P. vannamei. The study emphasizes the importance of continuous monitoring of physicochemical water parameters for sanitary control in aquaculture and recommends integrated strategies considering environmental conditions to prevent parasitic outbreaks.