Kawal Waters is one of the waters in Bintan which has good fishery resources, one of that is the blue swimming crab. The Blue Swimming Crab (Portunus pelagicus) is one of the important economic fisheries resources belonging to the Portunidae family. The blue swimming crab is one of the most common organisms used by the community. The purpose of the study was to determine food composition of blue swimming crab (Portunus pelagicus) in Kawal waters of Bintan Island, Riau Island on June 2021. The sampling used random sampling method. There were 34 individuals used for food composition analysis. The  food  composition  in  the  stomach  of blue  swimming  crab  consisted  of three groups of microalgae, crustacea, and detritus. The food composition in the adult size was found microalgae groups with the percentage composition 78%. It was followed by crustacea of 18,06%, and detritus of 5,12%. The highest of indeks of stomatch contens is in morning caught of 1,15 for males and 1,28 for female.

Business Crab (Portunus pelagicus) Kawal Village waters are waters located in the Gunung Kijang area, Bintan Regency, Riau Islands Province. High market demand for crab fishery commodities that triggers excessive exploitation so that it can have an impact on the sustainability of crab resources. This study aims to determine the condition of the sex ratio and the pattern of crab growth in the waters of Kawal Village, Bintan Regency. The method used in this study is a survey method. The sampling technique was carried out using a random census, in which the researcher immediately went down to the field to take a sample of 176 crabs. The results showed a good sex ratio for female crabs at 52% and male crabs at 48%, which has calculated the Chi-square test which between females and males has a balanced ratio, which results in: X² count of 33, 2 while X table is 74,975 which if X² count < X table: male and female sex ratio is balanced. The growth pattern of both female and male crabs in the waters of Kawal Village, Bintan Regency has a negative allometric character where the growth pattern of carapace width is greater than weight growth.

This research aims to determine differences in calcium levels in small crabs (Portunus pelagicus) in three parts, namely carapace/shell, claw feet and abdomen. This research was conducted from May to June 2023 at UD. Bumi Nusantara Pattiro Sompe, Sibulue, Bone Regency, South Sulawesi. The research method used is an experimental method. with three types of samples (abdomen, claw feet and carapace/shell), calcium level parameters with two repetitions. Data were analyzed using T-test. Based on the research results, it shows that the highest calcium levels are in the carapace/shell (46.77%), followed by the claws (41.91%), while the lowest are in the abdomen (40.76%). The conclusion of this study is that there is a significant difference in levels calcium between the carapace/shell and the abdomen and claw legs but did not differ significantly between the abdomen and claw legs.

Swimming crab shell waste is a fishery byproduct that has the potential to pollute the environment if not utilized properly. One alternative utilization is to process it into chitosan, which is then formulated into liquid fertilizer. This study aimed to determine the effect of chitosan concentration based on swimming crab shells on the chemical properties of liquid fertilizer. The study was conducted from February to March 2025. Chitosan and liquid fertilizer production was conducted at the Fishery Products Biochemistry Laboratory, Pangkep State Agricultural Polytechnic. The method used was an experimental laboratory with a Completely Randomized Design (CRD), with three treatments and three replications, with chitosan concentrations of 2%, 4%, and 6%. Data were analyzed using One-Way ANOVA and the W-Tukey HSD test. If the assumption of homogeneity of variance was not met, Welch ANOVA with the Games-Howell test was used to determine differences in effects between treatments. The results showed that the treatment had a significant effect (P<0.05) on most of the chemical properties of liquid fertilizer. The chemical properties of pH were (2.90 3.00 3.23), C-organic were (1.08% 2.72% 4.21%), macronutrients N + P₂O₅ + K₂O were (0.76% 0.64% 1.19%). In conclusion, increasing the concentration of chitosan improves the chemical properties of liquid fertilizer, so that crab shell chitosan has the potential as a material for liquid organic fertilizer formulation.