Screening factors affecting chitosan extraction from mud crab (Scylla sp.) shell using microwave irradiation for the Response Surface Approach

Extracting chitosan from crab shell using conventional method requires processing in strong acid and alkali conditions under high temperature with long reaction time. Microwave-based extraction proposes shorter processing time, and hence energy and cost efficient. This study intended to screen factors affecting the extraction of chitosan from mud crab shell using microwave irradiation. The factors would be used in Response Surface Methodology (RSM) approach to obtain the optimum conditions for chitosan extraction. Microwave irradiation was employed in all of the three steps of chitosan extraction, the demineralization, deproteination, and deacetylation processes. A fractional factorial design was used to screen eight independent factors to determine the most significant ones to be optimized to determine the maximum value of four responses, which were yield, mineral removal, degree of deacetylation and moisture content. The results show that all of the main independent variables were significant in affecting minimal one of the 4 responses (P < 0.05). Mud crab chitosan had the degree of deacetylation of 87.72 – 95.13 %. Results of the screening analysis concluded, the main independent factors that are going to be applied in the optimization study are NaOH concentration, microwave oven power, and reaction time in deacetylation process.

A Novel Antimicrobial Peptide Sparanegtin Identified in Scylla paramamosain Showing Antimicrobial Activity and Immunoprotective Role In Vitro and Vivo

The abuse of antibiotics in aquaculture and livestock no doubt has exacerbated the increase in antibiotic-resistant bacteria, which imposes serious threats to animal and human health. The exploration of substitutes for antibiotics from marine animals has become a promising area of research, and antimicrobial peptides (AMPs) are worth investigating and considering as potential alternatives to antibiotics. In the study, we identified a novel AMP gene from the mud crab Scylla paramamosain and named it Sparanegtin. Sparanegtin transcripts were most abundant in the testis of male crabs and significantly expressed with the challenge of lipopolysaccharide (LPS) or Vibrio alginolyticus. The recombinant Sparanegtin (rSparanegtin) was expressed in Escherichia coli and purified. rSparanegtin exhibited activity against Gram-positive and Gram-negative bacteria and had potent binding affinity with several polysaccharides. In addition, rSparanegtin exerted damaging activity on the cell walls and surfaces of P. aeruginosa with rougher and fragmented appearance. Interestingly, although rSparanegtin did not show activity against V. alginolyticus in vitro, it played an immunoprotective role in S. paramamosain and exerted an immunomodulatory effect by modulating several immune-related genes against V. alginolyticus infection through significantly reducing the bacterial load in the gills and hepatopancreas and increasing the survival rate of crabs.

Effects of different temperatures on the growth and survival of mud crab (Scylla paramamosain) larvae

This study aimed to evaluate the effects of temperature on the growth and survival of mud crab (Scylla paramamosain) larvae in two stages including zoea-1 to megalopa (the first experiment) and megalopa to crablet-1 (the second experiment). Each experiment was conducted in a completely randomized design with four temperature levels (27, 30, 33, and 36℃) in triplicate. Stocking density of 200 ind./L for the first experiment and 4 ind./L for the second experiment. Fiberglass tanks of 500-L (containing 300-L and 250-L of 25‰ water for the first and second experiment, respectively) were used in the experiments. The results showed that S. paramamosain larvae at zoea-3 and zoea-4 died at 33℃ or above, while the highest survival rate of this stage was found at 27℃ (11.5%). The growth and larval stage index during the zoea to megalopa stage were significantly higher in 30℃ (p<0.05) compared to those in the 27℃ treatment. In the second experiment, the survival rates of crablet-1 were highest (72.9%) at 27℃ and lowest (34,7%) at 36℃. The growth rate of crablets at this stage increased with increased temperature. The highest carapace width and weight (3.41 mm and 0.030 g, respectively) were recorded at 36℃. The findings of this study suggested that mud crab larvae should be reared at the temperature range of 27-30℃ to maximize their production.