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.