Economic analysis of monosex culture of giant freshwater prawn (Macrobrachium rosenbergii De Man): a case study

All‐male monosex culture of Macrobrachium rosenbergii (De Man) has emerged as a popular practice in India, especially in the state of Andhra Pradesh. A study was conducted to compare the economics of all‐male, mixed and all‐female culture in 15 adjacent, rectangular ponds of 4000 m² each by stocking juveniles previously reared in a nursery for 60 days. The experiment was conducted using a completely randomized design with three treatments; T₁ (all male), T₂ (mixed) and T₃ (all female), and five replicates for a period of 5 months after the nursery phase. Statistical analysis showed highly significant (P<0.01) differences among the three types of culture. The cost of production was estimated and the economic feasibility of the culture methods was evaluated by cost‐return and partial budgeting analysis. The average weight, productivity and specific growth rate were the highest for all male culture, being 80.92±2.41 g, 1532 kg ha^?1 and 1.97±0.02 respectively. All‐female culture registered significantly higher survival (89.16±0.77%) and the best apparent feed conversion ratio of 1.26±0.02. The economic analysis revealed that all‐male monosex culture of M. rosenbergii was 63.13% and 60.20% more profitable than mixed and all‐female cultures respectively.     

Extra small virus-like particles (XSV) and nodavirus associated with whitish muscle disease in the giant freshwater prawn, Macrobrachium rosenbergii

A disease of Macrobrachium rosenbergii, the giant freshwater prawn, farmed in China was recently recorded in Zhejiang, Jiangsu, Shanghai, Guangxi and Guangdong provinces. The clinical sign of the disease, which develops in post-larvae (PL), is a whitish appearance of the muscles, particularly noticeable in the abdomen. Mortalities may reach 100% in some hatcheries. Investigations by transmission electron microscopy after negative staining of diseased PL homogenates showed the presence of two types of viral particles: one, unenveloped, icosahedral in shape, 26-27 nm in diameter, the second, much smaller, about 14-16 nm in diameter, designated extra small virus particle (XSV). The large virus has a genome with two pieces of ssRNA (RNA-1 and RNA-2), of 3 and 1.2 kb, respectively. Hybridization tests confirmed that this large virus is closely related to M. rosenbergii nodavirus (MrNV) which was isolated from diseased prawns in a hatchery in the French West Indies. Its very small size and hypothesized biochemical and biological characteristics suggest XSV is a new type of crustacean virus. As XSV has always been found associated with the larger virus (nodavirus) and is located in muscle and connective cells of diseased animals, it could be an autonomous virus, a helper-type virus or a satellite-like virus.     

Experimental susceptibility of different life-stages of the giant freshwater prawn, Macrobrachium rosenbergii (de Man), to white spot syndrome virus (WSSV)

Studies were conducted by injecting/feeding white spot syndrome virus (WSSV) derived from infected shrimp, Penaeus monodon (Fabricius), to different life-stages, namely post-larvae, juveniles, sub-adults and adults of Macrobrachium rosenbergii (de Man). The disease was also induced in brood stock, and the eggs and larvae derived from these animals were subsequently tested for WSSV infection. All the stages except egg used for the experiment were found WSSV positive in histopathology, cross infection bioassay and polymerase chain reaction (PCR) analysis. Experimentally infected post-larvae and juveniles showed a high percentage of mortality and an increased rate of cannibalism. The cumulative mortality in post-larvae was up to 28%; with 28–40% cannibalism resulting in a maximum loss of up to 68%. In juveniles, observed mortality and cannibalism were 10–20% and 6.7–30.0%, respectively, and the maximum loss recorded was 50%. In sub-adults, mortality ranged from 2.8 to 6.7%, cannibalism was up to 20% and the total loss was up to 26.7%. Sub-adults and adults were found to be more tolerant to the infection as evidenced by the mortality pattern. A nested (two-step) PCR resulted in a 570-bp product specific to WSSV in all stages, except the eggs.     

Low-cost diet for monoculture of giant freshwater prawn (Macrobrachium rosenbergii de Man) in Bangladesh

An experiment was conducted for 3 months in 12 experimental ponds, each of 30 m², with a view to develop a low‐cost diet for monoculture of Macrobrachium rosenbergii in ponds. Three experimental diets (30% protein) were formulated using fish meal, meat and bone meal, mustard oilcake, sesame meal and rice bran in different combinations partially replacing fish meal by meat and bone meal and sesame meal and assigned to treatments T₁, T₂ and T₃ respectively. A commercial golda feed (Starter‐III) was assigned to T₄ (reference diet). Each treatment had three replicates. Juveniles of M. rosenbergii (2.90±0.21 g) were stocked at the rate of 40 000 ha⁻¹. Prawns were fed three times daily at the rate of 10% and 5% of their body weight at the beginning and for the last 2 months respectively. The ponds were provided with aeration during the night using air pumps. The ranges of water quality parameters recorded in different ponds were: temperature 28.9–32.5°C, dissolved oxygen 5.1–8.1 mg L⁻¹ and pH 6.4–7.7. The results showed that the weight gain of prawns fed diet 1 was significantly higher (P<0.05) than those fed diets 2 and 3, but was not significantly different from those fed diet 4 (reference diet). The feed conversion ratio (FCR) values of diets ranged between 2.21 and 2.96 with diets 1 and 4 showing significantly lower (P<0.05) FCR values. The survivals (%) ranged between 68% and 78% with prawns fed diets 1 and 4 showing significantly higher survival. The production of prawn ranged between 921 and 1428 kg ha⁻¹ and diet 1 resulted in a significantly high (P<0.05) production. A simple economic analysis showed that diet 1 generated the maximum net profit of Tk 159 178 ha⁻¹. The results of the study showed that a diet containing 20% fish meal, 10% meat and bone meal, 15% mustard oilcake, 15% sesame meal, 35% rice bran, 4% molasses and 1% vitamin–mineral premixes may be recommended to the farmers for monoculture of M. rosenbergii in ponds.     

Long-term cryopreservation of spermatophore of the giant freshwater prawn, Macrobrachium rosenbergii (de Man)

Long‐term cryopreservation of the giant freshwater prawn, Macrobrachium rosenbergii, spermatophores using glycerol (Gly) and ethylene glycol (EG) as cryoprotective agents (CPAs) was studied. The tolerance of sperm to cryopreservation was evaluated on the basis of sperm survival and fertilizing ability. The survival of the sperm was determined by trypan blue staining, while the fertilizing ability was assessed from artificial insemination of the cryopreserved spermatophores. The rates of embryo survival on day 5 after spawning and of spermatophores capable of producing embryos survived to hatching were determined. Storage of spermatophores at ?20°C without CPA for a short period of up of 1–5 days decreased the sperm survival significantly and did not preserve fertilizing ability. Preservation at ?20°C in the presence of 10% or 20% Gly or of 10% or 20% EG offered a simple and efficient short‐term storage up to 10 days. For a long‐term storage, cryopreservation in the presence of 20% EG at ?196°C was more efficient than at ?20°C. High sperm survival rates and high fertilizing ability were recorded from those cryopreserved at ?196°C for up to 150 days. High sperm survival rates with moderate levels of fertilizing ability were obtained from those cryopreserved at ?20°C for not more than 30 days. The results indicate that preservation at ?196°C with 20% EG is a suitable procedure for long‐term storage of the giant freshwater prawn spermatophores.     

Rapid detection of Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV), the pathogenic agents of white tail disease of Macrobrachium rosenbergii (De Man), by loop-mediated isothermal amplification

A loop-mediated isothermal amplification (LAMP) procedure is described for rapid diagnosis of white tail disease, a viral disease caused by Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV), in the giant freshwater prawn, Macrobrachium rosenbergii. This method was more sensitive than conventional RT-PCR for detecting the two viruses. A set of four primers, two outer and two inner, were designed for MrNV detection. An additional pair of loop primers was also used in an accelerated LAMP reaction for detection of XSV. Time and temperature conditions were optimized for detection of the two viruses. The LAMP reaction is highly suited for disease diagnosis in developing countries as amplification of DNA can be detected without the use of agarose gel electrophoresis, by the production of whitish precipitate of magnesium pyrophosphate as a by-product.     

Effects of different dosages of astaxanthin on giant freshwater prawn Macrobrachium rosenbergii (De Man) challenged with Lactococcus garvieae

The effects of astaxanthin (AX) injected at 0.67 and 1.34 nmol g^?1 BW^?1 on the survival, antioxidant capacity, total haemocyte count (THC) and hepatopancreas astaxanthin content of giant freshwater prawn, Macrobrachium rosenbergii, challenged with Lactococcus garvieae were evaluated. AX‐injected M. rosenbergii at 1.34 nmol g^?1 BW^?1 had significantly (P≤0.05) higher survival rates. However, AX showed no significant effects on the capacity of certain antioxidant indicators (superoxide dismutase, glutathione peroxidase and glutathione reductase). This implies that L. garvieae infection suppressed the activity of the haemolymph antioxidant system of infected M. rosenbergii. This result suggests that the two different dosages used in this study could not exert significant effects on the tested antioxidant capacity of L. garvieae‐infected M. rosenbergii. On the other hand, AX‐injected M. rosenbergii at either dose showed a significant increase in the THC and hepatopancreas AX content when compared with the challenged control group. Overall, the results of this study indicate that the injected AX led to an improvement in M. rosenbergii's resistance against L. garvieae infection.     

Use of Cyclop-eeze as a substitute for Artemia nauplii in larval rearing of giant freshwater prawn Macrobrachium rosenbergii (De Man 1879)

Four feeding experiments, replacing 25% (T₁), 50% (T₂), 75% (T₃) and 100% (T₄), by dry weight, of the live feed Artemia nauplii for Cyclop‐eeze, a new larval feed that was claimed to contain the highest known levels of astaxanthin and omega‐3 polyunsaturated fatty acids, were compared against a control that was fed with Artemia and egg custard alone, to the larvae of giant freshwater prawn Macrobrachium rosenbergii (De Man 1879). Analysis of different production characteristics of the larvae revealed that the highest survival up to postlarvae (PL) stage was obtained for T₂ in which 50% of the Artemia nauplii were replaced by Cyclop‐eeze [freeze‐dried (FD) deep frozen (DF)], and the highest astaxanthin content of the larval tissue obtained in T₄ in which the larvae were fed 100% Cyclop‐eeze, although the survival rate was the lowest in this treatment. The costs of different treatments were also compared. The Artemia consumption million⁻¹ larvae was the highest in control (11490 g), followed by T₁ (8240 g), T₂ (4990 g), T₃ (3730 g) and T₄, which completely replaced Artemia from stage 5 onwards (1830 g). The highest consumption of Cyclop‐eeze million⁻¹ larvae was in T₄ (1670 and 10 880 g), followed by T₃ (850 and 5560 g), T₂ (410 and 2690 g) and T₁ (230 and 1490 g) of FD and DF, respectively. The astaxanthin contents of the late‐stage larvae fed under the four treatments were 24.90, 27.40, 28.60 and 35.60 μg g⁻¹ tissue for T₁, T₂, T₃ and T₄, respectively, while that of the control was 23.70 μg g⁻¹. The lowest cost of live feeds million⁻¹ PL was obtained for T₂ (US$ 428.60), followed by T₁ (US$ 490.46), control (US$ 529.07) and T₃ (US$ 583.26), while it was the highest for T₄ (US$ 890.93). The results indicated that Cyclop‐eeze could economically replace Artemia nauplii at 50% level that could significantly improve the survival and carotenoid composition of the larvae of M. rosenbergii.     

A sandwich enzyme linked immunosorbent assay (S-ELISA) for detection of MrNV in the giant freshwater prawn,Macrobrachium rosenbergii (de Man)

A sandwich enzyme-linked immunosorbent assay (S-ELISA) was developed to improve diagnosis of white tail disease of the giant freshwater prawn, Macrobrachium rosenbergii, caused by the nodavirus, MrNV. Polyclonal antibodies were produced by immunization of Balb/C mice using a purified suspension of the virus and IgG anti-MrNV were purified from ascitic fluid. A sandwich method was successfully developed, coating first with unlabelled antibody and detecting trapped antigens with a second biotinylated antibody. Reaction was demonstrated using an avidin-peroxidase conjugate. Tissue extracts from M. rosenbergii infected with MrNV or purified viral extracts (control) were successfully identified in an individual ELISA, thus confirming the validity of the method. This S-ELISA should be the technique of choice for epidemiological studies of this disease and is a rapid and inexpensive assay with high specificity and sensitivity.     

Immunomodulatory effect of Cynodon dactylon against white tail disease of giant freshwater prawn,Macrobrachium rosenbergii (de Man, 1879)

The giant freshwater prawn, Macrobrachium rosenbergii, is an economically important and extensively cultured crustacean worldwide. The viral pathogens, Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV) are responsible for causing severe mortalities in the hatchery and nursery phases. This study investigates the protection of postlarvae of freshwater against white tail disease (WTD) using plant extract derived from Cyanodon dactylon and the modulation of the prawn non‐specific immunity. To determine the immunomodulatory effect of C. dactylon extract, the prawn was injected with plant extract and various immunological parameters were estimated. The immunological parameters such as proPO, SOD, THC and clotting time were found to be significantly higher in the plant extract‐injected prawn when compared with control groups. The results of real time PCR analysis revealed up regulation on the expression proPO, SOD and lysozyme genes in MrNV and XSV challenged prawn postlarvae treated with C. dactylon extract. Infectivity experiment showed high relative per cent survival in MrNV and XSV‐challenged prawn postlarvae treated with C. dactylon extract. These results strongly indicate that the administration of C. dactylon plant extract enhances immunity of the prawn. Based on the results, this study recommends that the immersion of postlarvae in C. dactylon plant extract is a potential prophylactic agent against WTD.     

Growth and carcass composition of giant freshwater prawn, Macrobrachium rosenbergii (De Man), fed different isonitrogenous and isocaloric diets

A feeding experiment was conducted for 135 days to observe the effect of different isonitrogenous (35% crude protein) and isocaloric (385 kcal) diets on the growth and carcass composition of giant freshwater prawn, Macrobrachium rosenbergii ( De Man 1879 ). Three experimental diets (ED1, ED2 and ED3) were prepared using locally available ingredients. These diets differed mainly in terms of percent contribution of major protein sources such as fish meal, soybean meal, groundnut oil cake and mustard oil cake. Experimental diets were evaluated against a commercial diet, which served as the control (CD). Juveniles 1.87–2.44 g in size were stocked at a population density of 40 000 ha⁻¹ and fed thrice daily at 10% in the beginning and reducing gradually to 7% and 5% of the body weight during the experimental period. No significant differences (P>0.05) in the growth performance were observed; however, a significantly (P<0.05) higher yield (721.9 kg ha⁻¹ 135 days⁻¹) was recorded for prawn fed with control diet, followed by experimental diet 2 (676.5 kg ha⁻¹ 135 days⁻¹, having soybean meal as a major protein source). The survival ranged between 63.8% and 77.7%, with different diets showing significantly higher survival. The apparent feed conversion ratio values of diets ranged between 3.15 and 3.49, with experimental and control diets showing non‐significantly lower AFCR values. At the end of the experiment, representative specimens from each treatment were collected and their carcass composition was measured. Analysis of variance showed that carcass protein and total carbohydrate contents were significantly (P<0.05) higher in prawns fed on a fish–soybean meal‐based diet (ED3) and a control diet. The total lipid contents of prawns, however, did not differ significantly among the various dietary treatments. The results of our study suggest that the experimental diets could be used effectively for M. rosenbergii without compromising growth and flesh quality.     

Bacterial microflora associated with farmed freshwater prawn Macrobrachium rosenbergii (de Man) and the aquaculture environment

The initial counts of bacteria associated with farmed giant freshwater prawn (Macrobrachium rosenbergii de Man) as well as with the water and sediment from two farms located at Kottayam district in Kerala (India) were determined. A total of 367 randomly selected isolates were characterized and identified. Prawn samples yielded mean microbiological counts of 4.92 log CFU g^?1 of shell with muscle and 7.78 log CFU g^?1 of intestine at 30°C. Bacterial numbers in the intestine of prawn were much higher than those in the pond water. Motile and non‐motile aerobic Gram‐negative bacteria together with Enterobacteriaceae accounted for 60–70% of the mesophiles isolated from water and prawn. However, the microorganisms isolated in significant numbers from shell with muscle and intestine of prawn were not recovered from the growing waters. Among Gram‐positive bacteria, Micrococcus, Bacillus, coryneforms, and Arthrobacter were found. Faecal coliforms and enterococci were found in significant numbers in M. rosenbergii. The rearing practices such as feeding and pond fertilization could have influenced the microflora in prawn. The commensal microflora of freshwater prawn included opportunistic pathogens such as Aeromonas spp. and Streptococcus spp. Storage of prawn at elevated temperatures can permit their survival and growth leading to quality loss. Care should be exercised during handling and processing to prevent contamination of edible meat.     

The androgenic gland and monosex culture of freshwater prawn Macrobrachium rosenbergii (De Man): a biotechnological perspective

Males of the freshwater prawn Macrobrachium rosenbergii (De Man) grow faster and reach a larger size at harvest than females of the species. It is thus obvious that culture of monosex all‐male populations would be economically advantageous. Sexual differentiation in crustaceans is regulated by the androgenic gland (AG), which plays a pivotal role in the regulation of male differentiation and in the inhibition of female differentiation. In M. rosenbergii, AG removal from immature males resulted in sex reversal, with complete female differentiation. Similarly, AG implantations into immature females lead to the development of the male reproductive system. Sex‐reversed M. rosenbergii animals were capable of mating with normal specimens to produce offspring. Early attempts in Israel and more recently, attempts in other countries to establish all‐male populations through manual segregation showed that for the production of monosex prawn populations to be economically feasible, intervention via the AG is probably required. However, a suitable biotechnology is still to be developed, and an androgenic hormone has yet to be identified in decapods. Three lines of aquacultural and biotechnological research and development are proposed for the future: (1) Establishment of monosex cultures through manual segregation, together with the application of selective harvesting and claw ablation, as well as examination of different monosex culture strategies under a variety of economic conditions. (2) Microsurgical intervention in the AG, leading to the development of functional neo‐females, which would subsequently be mated with normal males to produce all‐male progeny. (3) Elucidation of AG bioactive products to enable biochemical or molecular manipulation of sex differentiation.     

Growth and immune response of giant freshwater prawn Macrobrachium rosenbergii (De Man) postlarvae fed diets containing Chlorella vulgaris (Beijerinck)

A 50‐day growth trial was conducted to evaluate the efficacy of Chlorella vulgaris (Beijerinck) as an ingredient in the diets of giant freshwater prawn Macrobrachium rosenbergii (De Man) postlarvae (PL30). Immune response (total haemocyte count and prophenoloxidase activity) was also assessed by subjecting postlarvae to a challenge test against Aeromonas hydrophila (Chester) for 14 days. Iso‐nitrogenous and iso‐lipidic test diets were prepared using a fishmeal‐based‐positive control diet (D0) and four basal diets with inclusion levels of 2% (D2), 4% (D4), 6% (D6) and 8% (D8) C. vulgaris. Postlarvae of M. rosenbergii were randomly stocked (mean initial body weight of 0.19 ± 0.02 g) in 30‐L tanks in three replicates per dietary treatment for evaluation of growth performance. Another set of postlarvae (mean initial body weight of 1.25 ± 0.02 g) was randomly distributed in 95‐L tanks in three replicates per dietary treatment for the assessment of immune response. Results showed that specific growth rate was significantly higher (P < 0.05) in postlarvae fed D4 and D6. Variations in values for carcass protein, lipid, moisture and ash were also evident. Postlarvae fed diets with Chlorella showed increased prophenol oxidase activity and total haemocyte counts. Moreover, survival rate after challenge with A. hydrophila was significantly increased (P < 0.05). Inclusion of C. vulgaris in diets enhanced immune response and resistance of M. rosenbergii postlarvae against A. hydrophila infection.     

Osmoregulation,growth and moulting cycles of the giant freshwater prawn (Macrobrachium rosenbergii) at different salinities

The giant freshwater prawn, Macrobrachium rosenbergii, is a species with a high commercial value in aquaculture. Two experiments were performed to determine the effects of salinities on the osmoregulation, growth and molting cycles of M. rosenbergii during growout. The first experiment was designed to determine whether these animals are capable of adapting to the changes in salinity seen in salinity intrusions in tropical deltas, with an incremental increase in salinity of 3‰ per day from 0‰ to 30‰ Haemolymph osmolality was rapidly regulated up to salinities of 15‰ , whereas animals conformed at higher salinities. The second experiment determined the growth, moulting cycle, osmolality, muscle water content and mortality during a 4‐month experiment at 0‰, 15‰ or 25‰ salinity. The weight gains in 0‰ and 15‰ were not significantly different and were comparable to the growth rates achieved in production farms with body mass increases of 2.6 and 2.3‐fold their initial body mass, respectively, after 4 months. The 25‰ group suffered from low growth, high mortality and a significantly lower moulting frequency. These data show that this species can be reared in brackish water up to 15‰, allowing for farming in the large areas impacted by salt water intrusions in tropical deltas.