Riboflavin Requirement of Fingerling Red Hybrid Tilapia Grown in Seawater

Red hybrid tilapia Oreochromis mossambicus × O. niloticus fingerlings were fed diets containing 0, 2.5, 5.0, 10.0, 20.0 and 40.0 mg/kg, and 0, 2.5, 5.0, 7.5, 10.0 and 20.0 mg/kg of riboflavin in separate 8 and 12 wk feeding studies, respectively. The dietary riboflavin level required to provide maximum growth and survival, and prevent deficiency symptoms in red hybrid tilapia fingerlings was found to be approximately 5 mg/kg of diet. In both trials, fish fed the diet devoid of supplemental riboflavin exhibited anorexia, reduced growth and nervous symptoms after 4–6 wk. Mortality began to occur after the sixth week. None of these abnormalities were observed during the first 6 wk in fish fed the riboflavin supplemented diets. However, by the seventh week, fish fed the diet supplemented with 2.5 mg/kg of riboflavin showed reduced appetite and growth rate. In both experiments, short body dwarfism was observed during week 8 for fish fed the diet without riboflavin supplementation. In experiment 1, fish fed the riboflavin-deficient diet had lens cataracts at week 8. This deficiency sign was not observed in experiment 2. Histological studies of liver, kidney, spleen, lateral muscle, gill and gastrointestinal tract revealed no major histopathological changes.     

Responses of pregnant ewes and young lambs to cold exposure

The effects of cold stress were studied in pregnant ewes during the last three weeks of gestation and in their progeny during the first three days of life. In general, ewes were unaffected by treatment whereas changes were observed in the cold-stressed lambs. Cold-induced changes in lambs included physical weakness, depression, and poor nursing response. Serum concentrations of glucose and insulin were lowered whereas concentrations of blood urea nitrogen, alkaline phosphatase, aspartate aminotransferase, lactate dehydrogenase, triglycerides, and cortisol tended to be higher in cold exposed lambs. The mortality rate was higher (40%) in cold-stressed lambs than in lambs kept at warmer temperatures (10%). At necropsy, cold-exposed lambs had reduced amounts of adipose tissue in perirenal areas, and extensive subcutaneous hemorrhages and edema in the distal portions of the thoracic and pelvic limbs.