Histological changes in Nile tilapia fed essential oils of clove basil and ginger after challenge with Streptococcus agalactiae

Dietary supplementation with natural products is a promising alternative for increasing immunological capacity and disease resistance in farmed fish. However, information about the effects of these additives on morphology and functionality of fish organs are scarce. The aim of this study was to verify the effects of dietary supplementation with essential oils of clove basil (Ocimum gratissimum L.) and ginger (Zingiber officinale Rosc.) on gut morphology and histological alterations in internal organs of Nile tilapia (Oreochromis niloticus). Juveniles (1.84 ± 0.52 g) were fed for 55 days with supplemented diets (0.5, 1.0% and 1.5%) and challenged via gavage with S. agalactiae. At 55 days of supplementations and ten days after challenge, samples of intestine, liver, spleen, heart and gills were collected. After processing, the tissue sections (3-5 μm) were made and stained with Harris' hematoxylin and eosin for analysis. At 55 days of supplementation, fish fed basil at 1.5% showed reduced pyknosis in hepatocytes and this oil also reduced steatosis in ventricle. In the gills, fish fed basil at 0.5% and 1.0% and ginger at 0.5% showed reduced degree of epithelial detachment in the secondary lamellae while fish fed ginger at 1.0% and 1.5% showed reduced interlamellar hyperplasia. Ten days after infection, the degree of hepatic congestion was reduced in fish fed basil at 1.5%, as well as hepatic steatosis in those supplemented with ginger at 0.5% and basil at 0.5%. Basil supplementation at 1.5% was responsible for reduced degree of hepatic necrosis. Steatosis in heart tissue was reduced in fish fed basil at 0.5% and infected. In the gills, congestion was attenuated in fish fed basil at 1.0% and 1.5%. When added to the diet in moderated doses, the essential oils did not cause harm to the organs, being useful to ameliorate tissue damages, even in situations of infection.