Mixed culture purple phototrophic bacteria is an effective fishmeal replacement in aquaculture

Abstract

Aquaculture is the fastest growing animal food production industry, now producing 50% of all food fish. However, aquaculture feeds remain dependent on fishmeal derived from capture fisheries, which must be reduced for continued sustainable growth. Purple phototrophic bacteria (PPB) efficiently yield biomass from wastewater with high product homogeneity, a relatively high protein fraction, and potential added value as an ingredient for fish feeds. Here we test bulk replacement of fishmeal with PPB microbial biomass in diets for Asian sea bass ( Lates calcarifer ), a high value carnivorous fish with high protein to energy requirement. Mixed culture PPB were grown in a novel 1 m 3 attached photo-biofilm process using synthetic and real wastewater. Four experimental diets were formulated to commercial specifications but with the fishmeal substituted (0%, 33%, 66%, and 100%) with the synthetic grown PPB biomass and fed to a cohort of 540 juvenile fish divided amongst 12 tanks over 47 days. Weight and standard length were taken from individual fish at 18, 28, and 47d. No significant difference in survival was observed due to diet or other factors (94–100%). There was a negative correlation between PPB inclusion level and final weight ( p = 5.94 × 10 −5 ) with diet accounting for 4.1% of the variance over the trial (general linear model, R 2 = 0.96, p = 1 × 10 −6 ). Feed conversion ratio was also significantly influenced by diet ( p = 6 × 10 −7 ) with this factor accounting for 89% of variance. Specifically, feed conversion ratio (FCR) rose to 1.5 for the 100% replacement diet during the last sample period, approximately 1.0 for the partial replacement, and 0.8 for the nil replacement diet. However, this study demonstrates that bulk replacement of fishmeal by PPB is feasible, and commercially viable at 33% and 66% replacement.

The Future of Aquatic Protein: Implications for Protein Sources in Aquaculture Diets

“…The microbial biomass produced from various microorganisms, also known as ''microbial protein'' or ''single-cell protein,'' is a promising substitute for animal-or plant-derived ingredients for aquafeeds 19,[70][71][72][73][74] (Figure 3B). Among the highly diversified group of microorganisms, bacteria, yeasts, and microalgae are generally regarded as having the highest potential for aquafeeds.…”

“…Among the highly diversified group of microorganisms, bacteria, yeasts, and microalgae are generally regarded as having the highest potential for aquafeeds. [70][71][72][73] To achieve this potential there should be a focus on improving the scale of production, which will ensure the process chain is environmentally sustainable and reduce the cost of production. [70][71][72] Bacteria and yeasts have a relatively high protein content (50%-65% and 45%-55%, respectively), with amino acid profiles that are comparable with fish meal 70,72,73 and can potentially be used as either functional feed additives or as alternative raw materials.…”

“…[70][71][72][73] To achieve this potential there should be a focus on improving the scale of production, which will ensure the process chain is environmentally sustainable and reduce the cost of production. [70][71][72] Bacteria and yeasts have a relatively high protein content (50%-65% and 45%-55%, respectively), with amino acid profiles that are comparable with fish meal 70,72,73 and can potentially be used as either functional feed additives or as alternative raw materials. 70,[72][73][74][75][76][77] The nutritional profile of bacteria and yeasts can also be manipulated or enhanced by modifying the culture media, growth conditions, and post-harvest treatments.…”

“…[70][71][72] Bacteria and yeasts have a relatively high protein content (50%-65% and 45%-55%, respectively), with amino acid profiles that are comparable with fish meal 70,72,73 and can potentially be used as either functional feed additives or as alternative raw materials. 70,[72][73][74][75][76][77] The nutritional profile of bacteria and yeasts can also be manipulated or enhanced by modifying the culture media, growth conditions, and post-harvest treatments. 70,72 The resulting microbial biomass produced can provide excellent nutritional characteristics for aquatic animals.…”

Purple bacteria as added-value protein ingredient in shrimp feed:Litopenaeus vannameigrowth performance, and tolerance againstVibrioand ammonia stress

“…All previous studies on PNSB as protein ingredient were performed with pure cultures. Only recently, Delamare-Deboutteville et al (2019) have tested mixed PNSB cultures. They observed a similar performance compared to a commercial feed for the Asian sea bass ( Lates calcarifer ) up to a protein substitution level of 21%.…”