Chemotherapy of the ciliate Trichodina sp on juvenile turbot (Colistium nudipinnis) with notes on the susceptibility of fish with abnormal pigmentation

Turbot (Colistium nudipinnis (Waite, 1910)) fingerlings reared from a single batch of eggs during the 1998 breeding season were examined by histopathology during a routine health assessment. Fish exhibiting pigment abnormalities such as brown coloration, extensive ambicoloration, or hypo-melanisation of the ocular surface were significantly smaller, and had a significantly higher prevalence of kidney lesions and the ciliate Trichodina sp. on the gills than did normally pigmented fish. This suggests that abnormally pigmented fish grew more slowly and were more susceptible to disease. Additional fish were exposed to 12 different chemotherapeutic bath treatments to determine the most effective methods of removing Trichodina sp. Treatments which removed 100% of Trichodina sp. while providing 100% survival of fish included 200 ppm formalin for 30 min, 200 ppm formalin for 1 h, fresh water for 30 min, and 25 ppm formalin + 0.08 mg/litre malachite green for 24 h. The recommended treatment against Trichodina sp. for use in a commercial situation is 200 ppm formalin for 30 min. The significance of these findings to culture of turbot in New Zealand are discussed.