This is a protozoan parasite. Body dorsoventrally flattened. Dorsal surface convex and ventral surface flat. Several paralle, arching rows of cilia on ventral surface. Oral basket protrusible, conspicuous, opening on anterior part of ventral surface. Length 21.3 – 41.7 µm and width 13.3 — 38.6 µm. The disease caused by Chilodonella sp. called Chilodoneliasis.
Ichthyophthirius sp. is a Protozoan parasite. Body is oval shaped but it can change its shape to considerable extent if necessary. Diameter was 37.2— 68.9 p.m. The body bears a large number of cilia over the whole surface area. It has a tubules mouth. Both micro and macro nucleus are present. The nucleus is horse shaped and rotating in nature. The disease caused by Ichthyophthirius sp. called ich or white spot or ichthyophthiriasis disease
Pallisentis sp. is a “spiny-headed” worms isolated from skin and fin of different fishes. Body shows externally three recognizable regions: i) the proboscis ii) neck and iii) the trunk. Proboscis is a hollow, subglobular to cylindrical structure, always armed with a set of posteriorly pointing hooks. It is a retractable. The neck is short and behind the proboscis, it is never armed. The trunk is a sack like structure, straight or curving. Body length 8.0—30.5 mm and width 0.3—0.5 mm. The disease caused by Pallisentis sp. called pallisentiosis.
Argulus sp. is well known as “Fish louse”. Argulus sp. is an ectoparasite mostly found on body surface and fins of fish. Body of Argulus spp. is divided into three regions: cephalothorax, thorax and abdomen. Length 3.00 — 5.12 mm. Body dorso-ventrally flattened. Two sucker to attach with fish. One pair of compound eye present that can be moved. Both reproductive and breathing organs are situated in the tail. Mouth is situated behind the probosis. Female is larger than male. The disease caused by Argulus sp. called argulosis.
Lernaea sp. is most harmful, parasite of cultured freshwater fish commonly name anchor worm. It is a copepod parasite. Elongated form with two anchoring device at the head to attach. Two greenish egg sacs at the posterior end. There are some small swimming legs which are very minute is numbers. Females are parasitic and males are free living, length 1.15- 1.52 mm (Without Uropod) and width 0.124-0.133 mm. The disease caused by Lernaea sp. called Lemaeosis.