Dietary folic acid ( FA ) requirement of a genetically improved Nile tilapia Oreochromis niloticus (Linnaeus, 1758)

Summary The present study was conducted to determine the dietary folic acid ( FA ) requirement of genetically improved Nile tilapia, Oreochromis niloticus . Experimental diets were supplemented with 0.04, 0.22, 0.48, 0.96, 2.25, or 4.07 mg/kg FA , respectively, and fed to three replicate groups of 15 tilapia (mean initial weight = 60.23 ± 2.60 g; mean ±  SD ) for 12 weeks. Results showed that the weight gain rate increased linearly with increasing dietary FA from 0.04 to 0.40 mg/kg, then remained stable with higher supplementation. Similarly, hepatic FA concentration, red blood cell count ( RBC ), hemoglobin concentration ( HB ) and hematocrit ( HCT ) all markedly increased in fish fed with 4.07 mg/kg FA compared to those fed a control diet ( p  < .05). Serum aspartate aminotransferase ( AST ) and alanine aminotransferase ( ALT ) activities decreased with increasing dietary FA ( p  < .05). The FA requirement was estimated to be 0.4 mg/kg based on weight gain rate, and 0.7 mg/kg based on liver FA accumulation.