Feasibility assessment of replacing fishmeal with<i> Clostridium</i><i> autoethanogenum</i> protein in commercial whiteleg shrimp diets: Impacts on growth, muscle characteristics, and health

Abstract

Single -cell protein (SCP) is a promising feed ingredient often referred to as bioprotein, microbial protein, or biomass. In this study, we explored the effects of replacing fishmeal with a novel single -cell protein, Clostridium autoethanogenum protein (CAP), on the growth performance, immunological responses, muscle characteristics, intestinal and hepatopancreas histology, survival rate and bacterial resistance in whiteleg shrimp (Litopenaeus vannamei). The shrimp postlarvae (PL), sourced from Thailand and confirmed free of various pathogens, were acclimated and reared in a controlled water recirculation system. Four replicated aquariums, each containing twenty shrimps with an average weight of approximately 3.25 g, were assigned to each experimental group (N = 4). Experimental diets, designed based on a commercially relevant feed formula, were provided four times per day over an 8 -week period. The experimental diets included a control diet and three diets with different levels of fishmeal replaced by CAP at 30% (4.5SCP group), 66.7% (9SCP group), and 100% (20SCP group). The results revealed a significant reduction in the growth performance of shrimp in the 20SCP group, with a lower final weight (16.77 +/- 0.76 g), weight gain (415.9 +/- 24.7%), specific growth rate (2.93 +/- 0.08%), and average daily growth (0.24 +/- 0.02 g/day) compared to the control group (18.96 +/- 0.27 g, 484.8 +/- 13.3%, 3.15 +/- 0.04%, 0.28 +/- 0.01 g/day, respectively). In contrast, shrimp in the 4.5SCP and 9SCP groups, however, did not exhibit such adverse effects and had growth parameters comparable to the control group. Replacing fishmeal with SCP at 100% (20SCP group) significantly increased the muscle hardness but decreased the muscle springiness, chewiness and cohesiveness of whiteleg shrimp. Histological analysis of the midgut revealed that the 20SCP group exhibited a thinner wall thickness (51.9 +/- 17.4 mu m), wider villi width (80.86 +/- 15.87 mu m), and longer villi height (85.24 +/- 17.41 mu m) compared to the control group (66.9 +/- 19.1 mu m, 50.35 +/- 11.47 mu m, 52.92 +/- 23.58 mu m, respectively). Compared to the control group, immune parameters such as phagocytic rate, respiratory burst activity, and total hemocyte count, but not phenoloxidase activity, were often lower in shrimps that ingested higher levels of SCP. The transcript level of most immune and physiologically related genes analyzed was not significantly modulated in the hemocyte, hepatopancreas, foregut and midgut on days 28 and 56. The findings suggest that replacing fishmeal with up to 60% CAP in shrimp diets could be a feasible option, providing a novel protein source for sustainable aquaculture practices. Further research is necessary to elucidate the precise mechanisms underlying these effects and optimize CAP inclusion levels for enhanced shrimp performance and health.