This study aimed to investigate the effect of pomegranate (Punica granatum) peel extract (PPE) on growth indices, intestinal bacteria, and total fungi count of Carassius auratus intestine. Ninety C. auratus fries (11.04 ± 0.22 g) were distributed among 15 aquariums (100‐L) in a completely randomized design (triplicated), and were fed diets containing 0.1, 1, 2, and 4% PPE for 60 days at a feeding rate of 2% body weight during the experiment. A spectrophotometry assessment indicated that the total phenol and flavonoid content of PPE was 5.44 ± 0.03 and 49.80 ± 1.00 mg/g, respectively. According to the results, the extract significantly reduced the growth indices (final weight, weight gain, specific growth rate (SGR), and feed conversion ratio (FCR)) at 4% compared to the control (p < .05). PPE did not affect the total aerobic bacteria or total lactic acid bacteria count, but the enteric gram‐negative bacteria count was significantly reduced in the experimental treatments (p < .05). The total fungi count showed a significant increase in all treated fish (p < .05). According to the results, because of the negative effect of the high dose of PPE on growth, there is a recommendation for it to be used at 2% of the diet to reduce intestinal gram‐negative bacteria and increase the total fungi count.

Biochemical changes in barberries during adventitious root formation: the role of indole-3-butyric acid and hydrogen peroxide