Evaluating the effect of dietary nitrate supplementation on growth, oxygen consumption and reproductive performance of zebrafish (Danio rerio)

Nitrate and nitrite have been long considered hazardous substances for human and animal health. However, recent research has shown multiple benefits of dietary nitrate, mostly attributed to the reduction of ingested nitrate into nitric oxide, a substance known for the control of several physiologic functions. Nonetheless, even though the recently suggested beneficial effects of ingested nitrate have been widely studied in mammals, little is known about this subject on fish. The present study was conducted in order to assess the effect of dietary nitrate supplementation on zebrafish (Danio rerio) growth, reproductive performance and oxygen consumption. Three trials took place successively to analyze each one of those parameters by the mentioned order, using the same set of fish throughout the whole study. Four levels of sodium nitrate (1, 2, 4 and 8%) were tested as a nitrate supplementation source on the diets used in this assessment, against a control diet with no supplementation. Dietary nitrate supplementation showed no improvement in zebrafish growth, but at higher supplementation levels (4 and 8% of sodium nitrate) led to a decreased growth performance, which indicates a toxic effect of nitrate at these levels. Regarding the reproductive performance, nitrate affected spawning frequency positively at a low level (1% sodium nitrate) but showed toxic effects at a high level (8% sodium nitrate). Oxygen consumption was lower in fish fed diets with intermediate nitrate levels (2 and 4% sodium nitrate). Results corroborate previous findings that dietary nitrate promotes an oxygen sparing effect, and broaden this effect to fish, which, to our knowledge, has not been reported yet.