Effect of Alkalinity on Fecundity of Caligus Minimus Parasitizing on Seabass (Lates calcarifer) in Laboratory Condition

Abstract

Caligid copepod is one of the most common parasites in marine fish culture, causing negative effects on growth and survival of its host. This study aims to assess the fecundity of Caligus minimus parasitizing on seabass (Lates calcarifer) and evaluate the parasite’s abundance dynamics under various alkalinity levels. Wild C. minimus were recorded with 60.9 ± 14.3 eggs in its egg string, which varies in length (3.38 ± 0.27 mm), and egg sizes ranging from 0.34 mm (width) to 0.08 mm (length). Wild C. minimus were observed to attach and survive on its host for 50 to 71 days, producing one to three egg strings in its life. Under 60 ppm and 70 ppm of alkalinity condition, the abundance and hatching index of Caligus reached a peak of 734 ± 14.5% and 919 ± 25.5% of the initial infection. There were no records of hatching at 10, 20, 110 and 120 ppm of alkalinity. Within 21 days, no significant difference in the number of egg and egg size under various alkalinity levels were observed. These results demonstrated that alkalinity strongly affects the population of caligid parasites.