The evaluation of bacterial single cell protein on performance, digestive enzymes activity, gut histology and gut microbiota of rainbow trout (Oncorhynchus mykiss) fry

The aim of this study was to evaluate fish meal replacement by a bacterial single cell protein (IPL68) on growth performance, digestive enzymes activity (protease, lipase and α-amylase), gut histology and gut microbiota in rainbow trout fry (initial weight = 2.51 ± 0.55 g) for 6 weeks. Five diets were formulated with different bacterial SCP level (0:D1, 25:D2, 50: D3, 75:D4 and 100: D5 %) to replace fishmeal protein. At the end of the trial, body weight gain, specific growth rate, condition factor and hepatosomatic index showed the higher values than other diets with a significant differences (P<0.05). The food conversion ratio had the lowest and highest values in D3 and D5 diets, respectively, with a significant difference (P<0.05). The survival rate in all experimental diets was 100%. The highest activity of protease, lipase and α-amylase enzymes was observed in the intestines of fish fed with D3 diet, which showed a significant difference compared to D4 and D5 diets (P<0.05). The highest number of total bacteria and lactic acid bacteria was observed in diet D3, which was significantly different from other diets (P<0.05). The highest villus height (µm) and the ratio of villus height to crypt depth was observed in fish fed with D3 diet, which was not significantly different from D1, D2 and D4 diets, but showed a significant difference with D5 diet (P<0.05). Based on the obtained results, D3 diet can be suitable for the growth of rainbow trout fry compared to other diets.