Physiological, biochemical and histometric responses of Nile tilapia (Oreochromis niloticus L.) by dietary organic chromium (chromium picolinate) supplementation

Chromium has been recognized as a new and important micro-nutrient, essential for both human and animal nutrition. This study was conducted to evaluate the appropriateness and/or the use of safety level of dietary chromium picolinate (Cr-Pic), and its effects on the physiological responses, the histometric characteristics, and the chemical analysis of dorsal muscles of mono-sex Nile tilapia, Oreochromis niloticus. A total of 420 fingerlings (28.00 ± 0.96 g) were randomly distributed into 21 fiberglass tanks representing seven treatments at a rate of 20 fish m(−3). The control fish group (T(1)) was fed a Cr-Pic free basal diet. Other fish groups were fed the basal diet supplemented with 200 (T(2)), 400 (T(3)), 600 (T(4)), 800 (T(5)), 1000 (T(6)) and 1200 μg Cr-Pic kg(−1) diet (T(7)). Diets were offered to fish at a feeding rate of 3% of life body weight for 12 weeks. Results revealed that blood hematological parameters (hemoglobin, red blood cells, packed cell volume, mean corpuscular hemoglobin concentration, blood platelets, and white blood cells lymphocytes); serum biochemical measurements (total testosterone, high density lipoprotein, total protein, albumin, and globulin); and the dry matter and crude protein of the fish dorsal muscles all have significantly increased (P ⩽ 0.05) in the T(3) treatment compared with the other treatments. Meanwhile, no significant differences were found among all treatments with regard to the histometric characteristics. It can be concluded that Cr-Pic at 400 μg kg(−1) diet (T(3)) seems to be the most appropriate level for O. niloticus fingerlings.