Microalgal Preference and Feeding Density of Selected Microalgae Diets by Blue Swimming Crab Portunus pelagicus (Linnaeus, 1758).

<b>Background and Objectives:</b> Blue swimming crab, <i>Portunus pelagicus</i> (Linnaeus, 1758) are economically important sources of soft-shell products for export demand. However, increasing over-exploitation and pollution towards the sea resources affected the production of the <i>P. pelagicus</i>. The study aimed to determine the microalgal preference and feeding density of the monospecific (<i>Nannochloropsis oculata</i>, <i>Chlorella vulgaris</i>, <i>Isochrysis galbana</i> and <i>Chaetoceros wighamii </i>) by individual <i>P. pelagicus </i>larvae. <b>Materials and Methods:</b> In the microalgal preference study, one polystyrene tray with 100 holes was set up in the experimental tank (200 L) to place the 50 mL centrifuges tube. For feeding density study, the survival rate, Specific Growth Rate (SGR), Body Weight (BW) and Larvae Stage Index (LSI) of each larvae stage were collected from Zoea 1 (Z₁) till megalopa. <b>Results:</b> Results for mean microalgal preference of individual larvae preferred most <i>Chlorella vulgaris</i> during Zoea 1 and 2, the larvae consumed the highest of <i>Nannochloropsis</i> <i>oculata</i>. For Zoea 3 and 4, the highest preference is <i>Isochrysis galbana</i>. For feeding regime, Zoea 1, larvae fed rotifer, <i>Artemia</i> and <i>Chlorella vulgaris</i> (T₃), was the highest survival rate, Zoea 2 was larvae fed rotifer, <i>Artemia</i> and <i>Nannochloropsis oculata</i> (T₅) and both Zoea 3 and Zoea 4, larvae fed rotifer, <i>Artemia</i> and <i>Isochrysis galbana</i> (T₄) was the highest survival rate. The highest SGR and LSI were obtained in T₄ cultured in 14 days. <b>Conclusion:</b> In conclusion, the microalgal preference and feeding density of the selected microalgae are different depending on each larvae stage.

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.

Experimental data on glucose and energy levels of orange mud crab, Scylla olivacea at different water velocities.

The present datasets were conducted to investigate glucose concentration in hemolymph, energy levels at selected body parts (hepatopancreas, muscle, gonad), and feces among different sexes of crabs cultured at four different water velocities (0, 20, 40, and 60 cm/s) during a 60-day culture period. A total of 102 immature crabs (51 males, and 51 females) were sampled from Kuala Muda, Kedah coastal water, Peninsular Malaysia (5°39'N 100°19'E) from April to November of 2018. Results indicated that glucose concentration was the highest at water velocity of 60 cm/s for both male and female crabs (♂: 3.76 ± 0.08 mmol/L; ♀: 3.63 ± 0.06 mmol/L), whereas at 0 cm/s, the lowest levels of glucose concentration (♂: 0.13 ± 0.08 mmol/L; ♀: 0.19 ± 0.06 mmol/L) were recorded. As for energy analysis in hepatopancreas, results showed that both male and female crabs recorded the highest levels at 0 cm/s (no flow) with 37.919 ± 0.07 KJ/g and 34.636 ± 0.50 KJ/g, respectively. Energy for locomotion (muscle) of male crabs recorded the highest at 0 cm/s (♂: 26.823 ± 0.06 KJ/g), meanwhile for females, the highest was recorded at 20 cm/s (26.607 ± 0.34 KJ/g). Energy for reproduction of males could not be compared due to an insufficient available amount of testes/vas deferens, whereas female crabs recorded the highest energy usage at 20 cm/s water velocity (♀: 37.895 ± 0.08 KJ/g). For feces, both male and female crabs recorded the lowest energy at 60 cm/s (♂: 5.841 ± 0.03 KJ/g; ♀: 5.393 ± 0.01 KJ/g). Glucose assessment showed a direct relationship between increased velocity and glucose secretion in hemolymph at high velocity of 60 cm/s (stress condition) compared to other treatments. Regarding energy analysis, this research improved the mechanism of hepatopancreas, gonad, muscle and feces functions in development and reproduction, while it shed light on the influence of velocity on energy metabolism of S. olivacea.