Nyctotherus

Fig. A: A ciliate protozoan from the intestine of a Discus. Upper left is a Protoopalina of the same sample which has been stained with Methylene Blue and killed by heat. Fig.B: Side view (?) of the organism.

Nyctotherus sp.
This organism was found in the intestine of a 10cm Discus (Symphysodon) imported from Southeast Asia. The appearance (contractile vacuole, macronucleus and possible micronucleus, close-set longitudinal rows of cilia) is similar to that of Nyctotherus species which are found in the colon of amphibians and in some invertebrates such as cockroaches.
Several of this organism were observable in the sample. It differs from the Opalanids in having an apparent macronucleus and a more rigid cell structure and movement. Numerous Protoopalina were found in the same sample. I have not heard of Nyctotherus being found in fish and this is the first time I have encountered this organism in Discus or any other fish species. It is likely to be a commensal and of dubious pathogenicity.

Fig. C: Live rotating organism showing macronucleus with a roughly triangular shape. Fig.D: Another specimen. Both of these photos show a contractile vacuole at the posterior end.

More photos of Nyctotherus
Go to Protoopalina page