Histopathology and autoecology of Didymocylindrus simplex (Digenea: Didymozoidae), parasite of Katsuwonus pelamis (Scombridae) in the Southwestern Atlantic Ocean, off South America

Pathological alterations and autoecology of Didymocylindrus simplex in Katsuwonus pelamis (Linnaeus, 1758) in the Southwestern Atlantic Ocean off of South America are presented. This is the first record of the species in the region; the specimens are described. The pathologic changes observed most often were infiltration of lymphocytes and slight fibrosis of the connective tissue surrounding the parasite. The typical aggregated distribution pattern was observed for Didymocylindrus simplex Ishii, 1935. Statistical analysis demonstrated no correlation between the abundance and prevalence of parasites with the total length of the host. The sex of the host does not influence the prevalence and intensity of infection

Responses of Nile tilapia to different levels of water salinity

A 45 day experiment was carried out to evaluate the effect of water salinity on the performance, haematological parameters and histological characteristics of the gills of the Nile tilapia, Oreochromis niloticus. The water salinity levels evaluated were: 0, 7, 14 and 21 g L-1. Nile tilapia specimens (1.62 ± 0.01 g), distributed into 20 fibreglass tanks (100 L) at a density of 15 fish per tank. There were no significant differences of the water salinity levels on daily feed intake; however, there were differences (P < 0.05) on the daily weight gain, feeding conversion rate and survival. The best results were observed for the water salinity levels of 0 and 7 g L-1. There were no differences (P > 0.05) between these levels. Regarding the haematological parameters, it was observed that the percentage of the haematocrits and the erythrocyte count were influenced (P < 0.05) by the water salinity level, which was not observed for the leukocyte count. The observed histopathological alterations were chloride cell hypertrophy, epithelial lifting, structure alteration, telangiectasia, primary lamellae cells aggregation, fusion and occurrence of aneurisms of different sizes in some secondary lamellae. Regarding the frequency of gills infection intensity, there were slight changes between the salinities of 0, 7 and 14 g L-1 and moderate changes at 21 g L-1. It is concluded that Nile tilapia can be reared in water salinities of up to 7 g L-1 without damage to the parameters evaluated in this work