Effects of Intermittent Exposure to Therapeutic Levels of Formalin on Growth Characteristics and Body Condition of Juvenile Rainbow Trout

Abstract

The effects of twice weekly exposure to formalin (200 mg/L in a 1-h static bath) on juvenile rainbow trout Oncorhynchus mykiss (57.4 g initial weight) were assessed in a completely random, matched-pairs, 12-week growth trial. Growth rates, appetite, feed conversion, and body condition index of the fish were not significantly affected by formalin treatment after 6 and 12 weeks. There was also no evidence of a cumulative effect of formalin treatments over time, because the similarities between treated and untreated groups of fish persisted over the 12-week trial. Formalin-treated fish had significantly better fin condition and a lower incidence of corneal opacity than did untreated fish. This study showed that formalin, in a 1-h static bath at 200 mg/L repeated twice weekly, can be used as a disease prophylaxis regime with no negative effects on growth.