Morphological, biochemical and histological analysis of mud crab ovary and hepatopancreas at different stages of development

Morphometrics and Reproductive Characteristics of the Freshwater Crab Sartoriana spinigera from the Habitat of Ratargul Swamp Forest, Bangladesh: An Approach to Conservation

A total of 332 freshwater crab Sartoriana spinigera samples were collected for eight consecutive months from the Ratargul freshwater swamp forest, Bangladesh, to examine their general morphometrics and reproductive traits. The length-weight relationships of carapace weight with carapace length, width, and depth indicated negative allometric growth. The logarithmic relationship between carapace weight and carapace length, carapace weight and carapace width, and carapace weight and carapace depth exhibited a correlation value of 0.86, 0.79, and 0.56, respectively. Fulton's condition factor and allometric condition factor were found to be highest in March and lowest in October. The sex ratio was 1.59 : 1 for the male to female, which did not show a considerable divergence from the expected 1 : 1 ratio in the chi-square test (P < 0.05). In July, a maximum of mature individuals was collected and investigated. The fertilization was 1297 ± 629 ova, the ovary weight was 447.22 ± 359.39 mg, and the egg diameter was 375.15 ± 130.18 µm. Histological analysis showed that the male hepatopancreas was well organized and decomposition was reported in the female during the vitellogenic stages of the ovary. Spermatogonium cells were found in the male gonad, and cells from the female gonad were in the vitellogenic mature stage. In conclusion, the research will serve as a foundation for future research work on freshwater crab species as well as the conservation and maintenance of the ecological balance of this species in the Ratargul freshwater swamp forest.

Moving towards Gel for Fish Feeding: Focus on Functional Properties and Its Acceptance

To resurrect and establish a low-impact aquaculture practice, gel-based feed applications hold promise. Gel feed is viscoelastic, nutrient-dense, hard, flexible, and appealing, and can be moulded into appealing shapes to ensure rapid acceptance by fish. The purpose of this research is to create a suitable gel feed using various gelling agents and to evaluate its properties and acceptance by a model fish, Pethia conchonius (rosy barb). Three gelling agents, viz. starch, calcium lactate and pectin, were included at 2%, 5%, and 8% in a fish-muscle-based diet. The physical properties of gel feed were standardized using texture profile analysis, sinking velocity, water and gel stability, water holding capacity, proximate composition, and colour. The lowest levels of nutrient leaching protein (0.57 ± 0.15%) and lipid (14.3 ± 14.30%) were observed up to 24 h in the underwater column. The highest score for overall physical and acceptance characteristics was noted for the 5% calcium lactate-based gel feed. Furthermore, a 20-day acceptance feeding experiment was conducted using 5% calcium lactate to examine its suitability as fish feed. The results indicate a better acceptability (3.55 ± 0.19%) and water stability (−2.5 ± 2.5%) of the gel feed compared to the control, with an improvement in nutrient losses. Overall, the study provides an insight into the application of gel-based diets for ornamental fish rearing, besides ensuring an efficient nutrient uptake and minimal leaching to establish a clean aquatic environment.

Vital Carbohydrate and Lipid Metabolites in Serum Involved in Energy Metabolism during Pubertal Molt of Mud Crab (Scylla paramamosain)

Pubertal molt is a vital stage in the cultivation of mature female crabs in the aquacultural industry of Scylla paramamosain. Since fasting occurs during molting, which requires a large supply of energy, internal energy reserves are critical. However, the dynamics of energy supply during pubertal molt is not clear. This study focuses on the variations of carbohydrates and lipids in serum during the pubertal molt of S. paramamosain via a metabolomics approach. Eleven lipid or carbohydrate metabolic pathways were significantly influenced postmolt. A remarkable decrease in carbohydrates in serum suggested that free sugars were consumed for energy. A significant decrease in glucose and alpha-d-glucosamine 1-phosphate showed that chitin synthesis exhausted glycogen, resulting in insufficient glucose supply. An increase in l-carnitine and acetylcarnitine, and a significant decrease in 15 fatty acyls and 8 glycerophosphocholines in serum indicated that carnitine shuttle was stimulated, and β-oxidation was upregulated postmolt. In addition, astaxanthin, ponasterone A, and riboflavin in serum were significantly decreased postmolt. Eleven potential metabolite biomarkers were identified for pubertal molt. Taken together, carbohydrates and lipids were possibly major energy reserves in pubertal molt. This study suggests that an increase in carbohydrate and lipid levels in crab feed may alleviate the effects of fasting during molt and improve farm productivity in mature female crabs.

Use of Pelleted Diets in Commercially Farmed Decapods during Juvenile Stages: A Review

The increasing market demand for decapods has led to a considerable interest in cultivating decapod species at a larger scale. Following the development of hatchery technologies, most research has focused on the development of formulated feeds for commercially farmed decapods once they enter the juvenile stages. The use of formulated feed for decapods at a commercial scale is still in the early stages. This is probably because of the unique feeding behavior that decapods possess: being robust, slow feeders and bottom dwellers, their feeding preferences change during the transition from pelagic larvae to benthic juveniles as their digestive systems develop and become more complex. The current practice of decapod aquaculture involves the provision of juveniles with food such as natural diet, live feed, and formulated feed. Knowledge of nutrient requirements enables diets to be better formulated. By manipulating the levels of proteins and lipids, a formulated feed can be expected to lead to optimal growth in decapods. At the same time, the pellet's physical characteristics are important factors to be considered upon formulating commercially farmed decapod feeds, considering the unique feeding behavior of the decapod. However, most published studies on decapod nutrition lack data on the physical characteristics of the feed types. Thus, it is difficult to establish a standard feed formulation that focuses on the physical pellet properties. Moreover, careful consideration must be given to the feeding behavior of species, as decapods are known as bottom feeders and are robust in terms of handling feed. Information on the pellet forms, diet composition, and unique feeding behaviors in commercially farmed decapods is gathered to suggest potential better formulated diets that can optimize growth and reproduction. Thus, the purpose of this review is to summarize the information that has been published to date and to come up with suggestions on ways to improve the feed formulation in decapods that comply with their feeding behavior and nutrient requirements. Further research is needed to explore the potential of the pelleted feed at the adult stage so the decapod can take full advantage of the nutrients present in the pellets.

Fatty Acid Composition of Hepatopancreas and Gonads in Both Sexes of Orange Mud Crab, Scylla olivacea Cultured at Various Water Flow Velocities

Nutritional quality of the hepatopancreas and gonads of orange portunid mud crab, Scylla olivacea was evaluated for each gender under four treatment of different water velocities (0, 20, 40 and 60 cm s⁻¹), in terms of nutrient reserve and nutrient for reproduction. About 56 crabs were used in this study in which fatty acids composition was analysed using gas chromatography mass-spectrometry (GC-MS). For hepatopancreas analysis, monounsaturated fatty acids (MUFAs) were present in the highest fatty acids concentration, followed by polyunsaturated fatty acids (PUFAs) and, saturated fatty acids (SFAs). However, long-chain polyunsaturated fatty acids (LC-PUFAs) were displayed in low concentration in the hepatopancreas. Total fatty acid (TFAs) composition was significantly higher at moderate velocity of 20 cm s⁻¹ compared to other water velocity treatments. For gonad analysis, 20 cm s⁻¹ showed the highest TFA concentration of 93.34 mg g⁻¹ while, the lowest concentration of 3.90 mg g⁻¹ occurred at 0 cm s⁻¹. There were significant differences in male and female crab’s fatty acids contents of gonads at all flow velocities challenged (p < 0.05). PUFAs and MUFAs were dominant while, SFAs were observed at low concentration. This study revealed that, concentration of PUFAs increased as gonad maturation increased. The decreasing concentration of hepatopancreas fatty acids over the culture period indicated that nutrient was shifted from the hepatopancreas, to be used as energy reserved to gonads for further growth of eggs and offspring. The linkages between water flow strength, hepatopancreas, and gonad fatty acids concentrations, is fundamental knowledge useful in establishing efficient habitat velocities selection which will improve aquaculture production of mud crabs with high quality broodstock.

Metabolomics and gene expressions revealed the metabolic changes of lipid and amino acids and the related energetic mechanism in response to ovary development of Chinese sturgeon (Acipenser sinensis)

Captive breeding has been explored in Chinese sturgeon (Acipenser sinensis) for species protection. However, gonad development from stage II to IV of cultured female broodstocks is a handicap. This study aimed to explore the physiological and metabolic changes during the ovary development from stage II to IV of female Chinese sturgeon and the related energy regulatory mechanism, which may be helpful to address the developmental obstacle. The results showed that the oocyte volume increased and the muscle lipid content decreased with the ovary development. Ovarian RNA levels of most genes related to lipid and amino acid metabolism were higher in stage II and III than in stage IV. Serum contents of differential metabolites in arginine, cysteine, methionine, purine, tyrosine, lysine, valine, leucine and isoleucine metabolism pathways peaked at stage III, while the contents of sarcosine, alanine and histidine, as well as most oxylipins derived from fatty acids peaked at stage IV. These results indicated the more active amino acids, lipid metabolism, and energy dynamics of fish body in response to the high energy input of ovary developing from stage II to III, and the importance of alanine, histidine, taurine, folate and oxylipins for fish with ovary at stage IV.

Identification and expression of prostaglandin E synthase (PGES) gene in the central nervous system and ovary during ovarian maturation of the female mud crab, Scylla olivacea

Prostaglandins have important physiological roles in marine invertebrates, including larval development and reproduction. The prostaglandin E concentration fluctuates during the ovarian development of crustaceans. The biosynthetic pathway of prostaglandin, however, has not been well studied in portunid crabs, including in the mud crab, Scylla olivacea. In this study, the aim was to investigate the presence of prostaglandin E synthase (PGES), enzyme that catalyzes the terminal conversion in the prostaglandin E2 (PGE₂) biosynthesis, and its gene expression in the central nervous system (CNS) and ovary during ovarian maturation of S. olivacea. cDNA sequence encoding PGES was cloned from the S. olivacea ovary. The PGES transcript of S. olivacea (Scyol-PGES) consists of 1258 nucleotides, which encodes for 420 amino acid PGES protein precursor. Investigation of gene expression by RT-PCR indicated that Scyol-PGES was detected in all organs studied. Based on in situ hybridization, Scyol-PGES was detected in the I to III stages for oocyte development of Stage 3 of ovarian development, and in the CNS, including the various neuronal clusters of the brain. In the ventral nerve cord, the Scyol-PGES gene was expressed in the neurons within the subesophageal, thoracic and abdominal ganglia. The Scyol-PGES gene expression as indicated by relative abundance of mRNA in the Stage 4 of ovarian development was greater than that at Stages 1 to 3 of ovarian development. This is the first report on PGES in the mud crab, S. olivacea, and its gene expression suggested the involvement of PGES in the ovarian development of this species.