Environmental factors can affect the relationship between Nile tilapia and its parasites in cage systems culture

Abstract

Parasites represent a serious obstacle in Brazilian intensive fish farming, and then, monitoring parasitic infestations in aquaculture is a duty of every tilapia producer. The objective of this study was to identify the branchial ectoparasites of Nile tilapia, evaluate the correlation between parasitic intensity, host biometrics, and limnological variables, as well as to identify gill histological changes in fish. Thus, fish representing the three phases (I, II, and III) of production were collected in two commercial fish farms - 1 and 2, necropsied, and their parasites quantified and identified. The gill alterations were processed for histological analysis. Cichlidogyrus sclerosus and Scutogyrus longicornis (Monogenoidea), and Lamproglena monodi (Lernaeidae) have been identified in the tilapia gills. The highest intensities of Monogenoidea infestation were in summer and autumn in both fish farms, with a positive correlation between parasites and water temperature. Infestation by L. monodi occurred only in Fish farm 2, with greater infestations in winter and spring, with a negative correlation between water temperature and parasitism. There was also an increase in parasitism according to the weight and length of the fish in the two fish farms. Histological changes such as hyperplasia, lamellar hypertrophy, and the presence of basophilic cysts on the secondary lamellae were detected in tilapia. Thus, water quality parameters and season of the year, which are closely related, can affect communities of parasites that infest Nile tilapia grown in cages. These findings are important to assist in planning disease control and prevention strategies for Nile tilapia fish farming, to reduce economic losses resulting from fish diseases and death.