Studies on the nutrition of marine flatfish. The thiamin requirement of turbot (Scophthalmus maximus).

1. Seven groups of young turbot (Scophthalmus maximus) were given diets containing graded levels of thiamin (0-19--50 mg/kg) for 16 weeks and their growth rate was measured during this period. 2. Good growth was obtained on all these treatments except in the group given the lowest dietary thiamin level (0-19 mg/kg). These fish grew normally until the 12th week but thereafter their weight did not increase. 3. Measurements of erythrocyte transketolase (sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate glycolaldehydetransferase; EC 2.2.1.1) activity at the end of the experiment and of percentage stimulation of erythrocyte transketolase by thiamin pyrophosphate indicated that the apoenzyme was saturated with coenzyme at a dietary thiamin level of 2-6 mg/kg, but not at 1-1 mg/kg. 4. An 8th group of turbot given the thiamin antagonist pyrithiamin (40 mg/kg diet) grew normally for 6 weeks. Thereafter mortalities began to occur and all fish died by the 10th week. No clear-cut signs of thiamin deficiency were observed. 5. The dietary thiamin requirement of turbot is much lower than published requirements of freshwater fish other than carp (Cyprinus carpio) and appears to be between 0-6 and 2-6 mg/kg diet.