Abstract
The efficacy of a single cell protein (SCP) methanotroph (Methylococcus capsulatus, Bath) bacteria meal (FeedKind®, Calysta, Menlo Park, CA, United States), in Pacific white shrimp (Penaeus vannamei) diets was studied to determine growth performance, survival rate and disease resistance against Vibrio parahaemolyticus causing Acute Hepatopancreatic Necrosis Disease (AHPND). The growth trial was assigned in a completely randomized design (CRD) with four treatments and 5 replicates of each, T1: a fishmeal-based control containing 15% fish meal and 3 diets with graded levels of methanotroph bacteria meal, namely T2: 5% methanotroph bacteria meal, T3: 10% methanotroph bacteria meal, and T4: 15% methanotroph bacteria meal. Shrimp were fed ad libitum for 6 weeks on trial diets to assess growth. Subsequent to the growth trial, three replicates of the same groups were exposed to V. parahaemolyticus by a single bath challenge and held for a further 15 days on the same diets as the growth study to assess survival and resistance. No significant differences (p > 0.05) in survival or in growth performance, including final weight, weight gain, specific growth rate, feed consumption or feed conversion ratio of white shrimp fed feeds containing methanotroph bacteria meal or control diets for 6 weeks. Immune markers such as hemocyte counts, phenoloxidase, superoxide dismutase and lysozyme activity were similar across all groups after the 6-week feeding trial. In a V. parahaemolyticus challenge, methanotroph bacteria meal in the diet significantly promoted the survival rate, and the reduction of Vibrio sp. in the hepatopancreas of white shrimp. Hemocyte count and phenoloxidase activity showed no significant differences (p > 0.05) between diet treatment groups, but hemolymph protein was significantly higher (p < 0.05) in shrimp fed diets containing 15% methanotroph bacteria meal after challenge. The Vibrio colony counts from hepatopancreas in the treatment groups were all significantly lower than the control (p < 0.05). The findings show that methanotroph bacteria meal can entirely replace fishmeal in white shrimp diets and the 15% inclusion of methanotroph bacteria meal in shrimp diet shows no adverse effects on growth performance, feed utilization and survival rate. In addition, shrimp fed methanotroph bacteria meal diets exhibited improved survival rates to an AHPND challenge.
Highlights
The increase in aquaculture in recent years has led to a concomitant increase in demand for fishmeal with approximately 75% of the global production of fishmeal in 2018 utilized in aquaculture (FAO, 2018)
The growth performance of white shrimp fed different levels of methanotroph bacteria meal for 6 weeks showed no significant differences (p > 0.05) in terms of final weight, weight gain, specific growth rate, feed consumption, and feed conversion ratio when compared to the control diet
This study has successfully shown that Pacific white shrimp fed diets where fishmeal is replaced with the single cell protein methanotroph bacteria meal, FeedKind, for 6 weeks shows comparable levels of growth and survival to shrimp fed standard feeds containing 15% fishmeal (T1)
Summary
The increase in aquaculture in recent years has led to a concomitant increase in demand for fishmeal with approximately 75% of the global production of fishmeal in 2018 utilized in aquaculture (FAO, 2018). Swine meat meal has been used to replace 35% of the protein contribution of fishmeal but, at higher levels, caused nutritional imbalances in Penaeus vannamei (Hernández et al, 2008). Alternative proteins such as yeast, fungi, microalgae, and bacteria can serve as single cell protein sources for animals and several studies have investigated the utility of these proteins in a variety of animal feeds (Qui and Davis, 2017a,b; Qui et al, 2017; Linder, 2019; Glencross et al, 2020; Jones et al, 2020); their use in aquaculture species have been recently reviewed by Glencross et al (2020)
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