Nutritional properties of wild and fattening mud crab (Scylla serrata) in the south-eastern district of Bangladesh

Mud crab (Scylla serrata) is one of the most important crustacean species in Bangladesh due to its high economic value. Crab fattening is widely practiced in the country to meet export demand while the supply for domestic consumption is mainly dependent on wild sources. This work reported for the first time a comparative evaluation of the nutritional properties of wild and fattening mud crabs. For this purpose, the proximate compositions were determined in terms of total contents of protein, moisture, ash, lipid, and minerals. Female fattening mud crabs had the highest levels of protein (17.07 ± 1.52%) and moisture (76.95 ± 1.39%) content, while the highest percentages of ash (4.9 ± 1.03%) were detected in male fattening mud crabs. Male fattening mud crabs also contained high amounts of minerals, especially calcium (1199.71 ± 343.43 mg/100g) and iron (14.21 ± 1.28 mg/100g). Male and female wild crabs showed the highest levels of magnesium and phosphorus, respectively. Additionally, the calculated percentage of recommended nutrient intake (RNI) value revealed that mud crab contributes 4.4-59.99%, 6.6-53.98%, and 7.33-54.53% for infants, adults, pregnant and lactating women, respectively. The present study indicates that mud crab had a balanced nutritional composition that would be nutrient-rich excellent diet for consumers.

Muscle proximate composition of various food fish species and their nutritional significance: A review

Today, there is a growing awareness about the importance of eating nutritious foods and fish is gaining momentum as a result of its unique nutritional benefits. Fish are considered as nutritionally valuable part of the human diet because of the presence of both macronutrients (proteins, lipids and ash) and micronutrients (vitamins and minerals). These nutrients are indispensable in human nutrition and have proven to be involved in several metabolic functions. The nutritional content can be used to rank different fish species based on their nutritional and functional benefits, allowing consumers to make better decisions according to their requirements. Proximate composition of fish includes determination of moisture, protein, fat and ash contents, which constitutes about 96%-98% of the total constituents of the fish body. The study of these components gives us a clear understanding in assessing the energy value of the fishes. In the present study, an attempt has been made to provide a concise review about the proximate composition of various fish species from different parts of the world in order to evaluate the high-protein, low-fat food with excellent nutritional values and to enlighten the different exogenous and endogenous factors that are actually responsible for their variation. The review also provides an insight into the characteristics of the chemical composition of various fish species, which are gaining importance for the sector involving fish and fishery products for domestic and foreign trade and for appreciating as animal feed all over the world.

Nutrition and Functions of Amino Acids in Aquatic Crustaceans

Crustaceans (e.g., shrimp and crabs) are a good source of protein-rich foods for human consumption. They are the second largest aquaculture species worldwide. Understanding the digestion of dietary protein, as well as the absorption, metabolism and functions of amino acids (AAs) and small peptides is essential to produce cost-effective and sustainable aquafeeds. Hepatopancreas (the midgut gland) is the main site for the digestion of dietary protein as well as the absorption of small peptides and AAs into the hemolymph. Besides serving as the building blocks of protein, AAs (particularly aspartate, glutamate, glutamine and alanine) are the primary metabolic fuels for the gut and extra-hepatopancreas tissues (e.g., kidneys and skeletal muscle) of crustaceans. In addition, AAs are precursors for the syntheses of glucose, lipids, H₂S, and low-molecular-weight molecules (e.g., nitric oxide, glutathione, polyamines, histamine, and hormones) with enormous biological importance, such as physical barrier, immunological and antioxidant defenses. Therefore, both nutritionally essential and nonessential AAs are needed in diets to improve the growth, development, molt rate, survival, and reproduction of crustaceans. There are technical difficulties and challenges in the use of crystalline AAs for research and practical production due to the loss of free AAs during feed processing, the leaching of in-feed free AAs to the surrounding water environment, and asynchronous absorption with peptide-bounded AAs. At present, much knowledge about AA metabolism and functions in crustaceans is based on studies of mammals and fish species. Basic research in this area is necessary to lay a solid foundation for improving the balances and bioavailability of AAs in the diets for optimum growth, health and wellbeing of crustaceans, while preventing and treating their metabolic diseases. This review highlights recent advances in AA nutrition and metabolism in aquatic crustacean species at their different life stages. The new knowledge is expected to guide the development of the next generation of their improved diets.

Amino acid compounds released by the giant freshwater prawn Macrobrachium rosenbergii during ecdysis: a factor attracting cannibalistic behaviour?

Ecdysis is a common phenomenon that happens throughout the life phase of the giant freshwater prawn Macrobrachium rosenbergii. It is vital to better understand the correlation between cannibalism and biochemical compound that exists during the moulting process. The objective of the present study was to determine the amino acid profile released by M. rosenbergii during the ecdysis process that promotes cannibalism. To accomplish this, changes in amino acid levels (total amino acid (TAA) and free amino acid (FAA)) of tissue muscle, exoskeleton, and sample water of culture medium from the moulting (E-stage) and non-moulting (C-stage) prawns were analysed using high-performance liquid chromatography (HPLC). Comparison study revealed that among the TAA compounds, proline and sarcosine of tissues from moulting prawn were found at the highest levels. The level of FAA from water that contains moulting prawns (E-stage) was dominated by tryptophan and proline. Significant values obtained in the present study suggested that these amino acid compounds act as a chemical cue to promote cannibalism in M. rosenbergii during ecdysis. The knowledge of compositions and compounds that were released during the moulting process should be helpful for better understanding of the mechanism and chemical cues that play roles on triggering cannibalism, and also for future dietary manipulation to improve feeding efficiencies and feeding management, which indirectly impacts productivity and profitability.

Biomolecular changes that occur in the antennal gland of the giant freshwater prawn (Machrobrachium rosenbergii)

In decapod crustaceans, the antennal gland (AnG) is a major primary source of externally secreted biomolecules, and some may act as pheromones that play a major role in aquatic animal communication. In aquatic crustaceans, sex pheromones regulate reproductive behaviours, yet they remain largely unidentified besides the N-acetylglucosamine-1,5-lactone (NAGL) that stimulates male to female attraction. In this study, we used an AnG transcriptome of the female giant freshwater prawn (Macrobrachium rosenbergii) to predict the secretion of 226 proteins, including the most abundantly expressed transcripts encoding the Spaetzle protein, a serine protease inhibitor, and an arthropodial cuticle protein AMP 8.1. A quantitative proteome analysis of the female AnG at intermolt, premolt and postmolt, identified numerous proteins of different abundances, such as the hemocyanin subunit 1 that is most abundant at intermolt. We also show that hemocyanin subunit 1 is present within water surrounding females. Of those metabolites identified, we demonstrate that the NAGL and N-acetylglucosamine (NAG) can bind with high affinity to hemocyanin subunit 1. In summary, this study has revealed components of the female giant freshwater prawn AnG that are released and contribute to further research towards understanding crustacean conspecific signalling.