Pathological study of jundia fingerlings experimentally infected by ich and submitted to conventional treatments

Abstract

The white spot disease is caused by Ichthyophthirius multifiliis (ich), a ciliated parasite characterized by its relatively large size, compared to other protozoans. Ich, one of the most devastating parasites affecting jundia culture, may destroy entire populations within a few hours. This study evaluated the histological effect of ich infection under some conventional treatments on jundia fingerlings. Fifteen fish (3-6 cm) were placed in 21 aquaria (10 L) for 5 days. The following treatments were used: C1: non infected control; C2: infected control; F: formalin (0.2 ml/L); M: malachite green (0.1ml/L); and S: NaCl 1% (10g/L). The treatments were used as 3 baths of 1 h between intervals of 48 h. Total mortality of F fish occurred within 48 h, showing that formalin was toxic to jundia under concentration recommended for parasite treatment of most tropical fish species. The lowest mortality rate (33%) was observed for S fish. The histological evaluation showed that ich caused hyperemia and hyperplasia of gill cells surrounding the parasite. At 96 h, trophozoites were observed with the help of microscope (40x) under the skin of C1 fish. Ich was not visible to the naked eye on C1 fish at the beginning of the experimental period. Tomites, a young stage of ich, burrowed into the skin of jundia, penetrated the subepithelial layer and caused damage. Upper layers of skin were sloughed off within 96 h from fish of all treatments, except S fish. Ich irritates fish tissues, mainly the gill cells, and causes high mortality rate within a very short period of time. Additionally, the employed therapeutic treatments cause adverse changes to different levels of severity, mainly on the gill tissue.