Diet supplemented with a novel Clostridium autoethanogenum protein have a positive effect on the growth performance, antioxidant status and immunity in juvenile Jian carp (Cyprinus carpio var. Jian)

A ten-week feeding trial was conducted to investigate the effects of the supplementation of Clostridium autoethanogenum protein (CAP) in practical diets on the growth performance, serum chemical parameters, antioxidant status and histopathological examination of the liver and midgut in juvenile Jian carp. Five isnitrogenous and isenergetic diets were formulated with graded levels of CAP (0, 50, 100, 150 and 200 g/kg) to replace plant proteins. The results showed that, final body weight, percent weight gain, specific growth rate, protein retention value, protein efficiency ratio and condition factor were significantly improved in fish fed with CAP, while feed conversion ratio was the opposite(P < 0.05). Visceral somatic index was significantly decreased in the fish fed with CAP (P < 0.05). Serum total cholesterol and total triglyceride contents were significantly increased with increasing dietary CAP levels, and serum lactate dehydrogenase showed an opposite trend (P < 0.05). Meanwhile, aspartate aminotransferase activities were significantly decreased with increasing dietary CAP levels (P < 0.05). The serum activities of the catalase were significantly increased with an increase in CAP levels (P < 0.05); however, malondialdehyde contents showed the opposite trend (P < 0.05). The mRNA expression levels of growth-related genes (PepT-1, PepT-2 and IGF-1), Nrf2 signaling pathway-related genes (Nrf2, Cu/Zn-SOD, HO-1, GPx, Mn-SOD and CAT) and TOR signaling pathway-related genes (TOR, 4E-BP2 and S6K1) were improved by the addition of dietary CAP (P < 0.05). Furthermore, from histological examination, CAP had no obvious effect on the liver and midgut. The present results indicated that CAP supplementation in practical diets has a beneficial effect on growth performance and antioxidant capacity and does not have an obvious effect on the liver and midgut in juvenile Jian carp. This study has shown the potential of converting industrial waste into a high protein feed ingredient for aquafeeds.