Abstract
The major parasitic crustaceans infecting cultured fish species comprise Branchiurans, Leaneids, Ergasilids and Isopods causing wounds that serve as portal entry for bacterial, fungi and viral infections eventually result to morbidity, mortality and economic loss thereby necessitating investigation on prevalence and effects on predilection site of Clarias gariepinus in this study. Four hundred and eighty four fish samples of Clarias gariepinus at various developmental stages were randomly selected from fish farms across the three agro – ecological zones in Lagos Stata, Nigeria. The samples collection lasted eighteen months covering both wet and dry season while parasitology and histology examinations were carried out in a laboratory using standard methods.. The wet mounts were prepared for skin and gills. Water quality parameters monitored were pH, water temperature, dissolved oxygen, ammonia, nitrite, iron concentration, alkalinity, hardness and turbidity according to respective manual guidelines. Descriptive statistics such as frequency count, percentages, standard deviation were used to determine the level of prevalence, occurrence and distribution of the parasites. Argulus species (Branchiuran) was the only parasitic crustacean observed in this study with low prevalence and intensity of infection of 1.05% and 2 respectively found on the gills of fingerlings during the rainy season. The histological examination on infected gill revealed no alteration. The water parameters were within the acceptable limit for fish survival. The low prevalence and loads of Argulus sp indicated good management practices which possibly suppress the propagation of the parasites despite the expected influence of optimum temperature and low dissolved oxygen in favour of the parasites. Therefore, good management practices should be encouraged to reduce rate of parasitic infection that often being a primary pathway to secondary infections.

Key words: Key Words: Argulus sp, prevalence, parasitic loads, management practices, culture systems