Complete Genome Sequence of Macrobrachium rosenbergii Golda Virus (MrGV) from China

In a meta-transcriptome study of the giant freshwater prawn Macrobrachium rosenbergii sampled in 2018 from a hatchery, we identified a variant of Macrobrachium rosenbergii golda virus (MrGV) in postlarvae without clinical signs. The virus belongs to the family Roniviridae, and the genome of this MrGV variant, Mr-18, consisted of 28,957 nucleotides, including 4 open reading frames (ORFs): (1) ORF1a, encoding a 3C-like protein (3CLP) (4933 aa); (2) ORF1b, encoding a replicase polyprotein (2877 aa); (3) ORF2, encoding a hypothetical nucleocapsid protein (125 aa); and (4) ORF3, encoding a glycoprotein (1503 aa). ORF1a overlaps with ORF1b with 40 nucleotides, where a −1 ribosomal frameshift with slippage sequence 5′-G14925GGUUUU14931-3′ produces the pp1ab polyprotein. The genomic sequence of Mr-18 shared 97.80% identity with MrGV LH1-2018 discovered in Bangladesh. The amino acid sequence identities between them were 99.30% (ORF1a), 99.60% (ORF1b), 100.00% (ORF2), and 99.80% (ORF3), respectively. Phylogenetic analysis of the RNA-dependent RNA polymerase (RdRp) proteins revealed that they clustered together and formed a separate cluster from the genus Okavirus. The finding of MrGV in China warrants further studies to determine its pathogenicity and prevalence within the region.

Assessment of Tilapia–Freshwater Prawn Co-Culture Schemes in Tanks and Lake-Based Cages for Increased Farm Production

The technical viability of tilapia (I-ExCEL strain Nile or red) and giant freshwater prawn (GFP) co-culture in cages-within-tanks was evaluated while appropriate feeding protocols for tilapia-GFP co-culture in cages in a eutrophic lake were determined. Specifically, production parameters in all test species grown for five months in tank co-culture (where only tilapias were fed) were compared, while the best feeding protocol from among the following treatments: (a) Tfed—fed tilapias; (b) GFPfed—fed prawns and (c) T-GFPfed—both species fed, were defined. I-ExCEL Nile tilapias grew faster in tank co-culture whether reared singly or otherwise. However, red tilapia-GFP tank co-culture gave the best results considering key production traits in all test species (red tilapia —2.52%/day specific growth rate or SGR, 83.3% survival; GFP—1.17%/day SGR, 72.85% survival). Lake-based co-culture was technically feasible at stocking densities of 12.5/m2 for tilapia and 2.4 to 4/m2 for prawns even when only tilapias were fed; prawns grew to desired marketable sizes by thriving mainly on detritus and natural food organisms in the lake. However, further refinements can still be made to optimise the co-culture schemes to make them more sustainable and provide artisanal fish farmers options in increasing farm yields through multi-species aquaculture.

Features of arthropod cultivation in the closed water supply installations on the example of a giant freshwater prawn

The cultivation of arthropods in closed water supply installations is a promising area for the development of commercial aquaculture in Russia. The giant freshwater prawn Macrobrachium rosenbergii is gradually becoming an aquaculture species of great commercial value, since it is the largest representative of its genus. In experiment for the prawn containing 3 tanks of the same size were used. The shrimps in the first tank were fed mainly plant food, but with a small proportion of animal food. In the second tank, animal feed was used. In the third tank, the shrimp diet consisted of 80% balanced artificial feed. The percentage of losses was 30, 20 and 7%, respectively. From the experiment, it became clear that main problems characteristic of all decapods, including the giant freshwater prawn, are the lack of high-quality and balanced artificial feeds, as well as problems associated with a decrease in the genetic diversity of artificial populations, which makes it more difficult and expensive to obtain seeding material. Cultivation of giant freshwater prawn in Russia can be quite cost-effective when using closed water supply installations, however, in order to achieve maximum benefits, it is necessary to develop artificial, optimized feeds designed specifically for crustaceans.