The effects of two levels of vegetable oils on structure of pyloric caeca were studied in Caspian Sea salmon juveniles (Salmo trutta caspius). The levels of dietary vegetable oils comprised of 10% and 20% of total diet and in each level 85% canola and 15% soybean was used. In these experiments, 270 juveniles each weighing 10g were selected, 90 were allocated to the two treatments and 30 for replications and also a control group was considered and fed with commercial food. The juvenile fish were cultured for 8 weeks, fed two times daily and then 6 samples from each treated group were fixed for histological studies. Histological examination under light microscope and using Hematoxylin-Eosin staining was conducted. Results showed that 20% dietary vegetable oil as compared with 10% significantly increased the area and number of pyloric caeca entrocytes. The effect of 20% dietary vegetable oil on the area and number of pyloric caeca entrocytes as compared to the commercial food was not significant. Gap in lumen ceacum was not significant between the two treatments as the lumen diameter increased with increase in dietary oil. We conclude that dietary vegetable oil content at 20% level can increase the area and number of pyloric caeca entrocytes which leads to increase in absorption of nutrients and of higher osmoregulation ability.
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