Identification of a putative cellulase gene in the giant freshwater prawn, Macrobrachium rosenbergii (De Man, 1879)

Nutrition plays an important role in the development of all organisms and in particular that of farmed aquatic species where costs associated with feed can often exceed 60% of total production costs. Crustacean species in addition, have the added metabolic requirement for regular moulting to allow normal growth and this requires large amounts of energy in the form of sugars (glucose). The current study explored the capacity of the giant freshwater prawn to produce endogenous cellulose-degrading enzymes capable of extracting nutrients (simple sugars) from plant sources in formulated feeds used in the prawn aquaculture industry. We identified a putative cellulase cDNA fragment in the target organism of 1576 base pairs in length of non-microbial origin that after protein modelling exhibited a TM-score of 0.916 with a described cellulase reported from another crustacean species. The functional role of cellulase enzymes is to hydrolyse cellulose to glucose and the fragment identified in GFP was highly expressed in the hepatopancreas, the site of primary food digestion and absorption in crustaceans. Hepatopancreatic tissue from Macrobrachium rosenbergii also showed active digestion of cellulose to glucose following an endoglucanase assay. Cellulase gene(s) are present in the genomes of many invertebrate taxa and play an active role in the conversion of cellulose to available energy. Identification and characterization of endogenous cellulase gene(s) in giant freshwater prawn can assist development of the culture industry because the findings confirm that potentially greater levels of low-cost plant-material could be included in artificial formulated diets in the future without necessarily compromising individual growth performance. Ultimately, this development may contribute to more efficient, cost-effective production systems for freshwater prawn culture stocks that meet the animal's basic nutritional requirements and that also support good individual growth rates.

A candidate gene association study for growth performance in an improved Giant Freshwater Prawn (Macrobrachium rosenbergii) culture line

A candidate gene approach using type I single nucleotide polymorphism (SNP) markers can provide an effective method for detecting genes and gene regions that underlie phenotypic variation in adaptively significant traits. In the absence of available genomic data resources, transcriptomes were recently generated in Macrobrachium rosenbergii to identify candidate genes and markers potentially associated with growth. The characterisation of 47 candidate loci by ABI re-sequencing of four cultured and eight wild samples revealed 342 putative SNPs. Among these, 28 SNPs were selected in 23 growth-related candidate genes to genotype in 200 animals selected for improved growth performance in an experimental GFP culture line in Vietnam. The associations between SNP markers and individual growth performance were then examined. For additive and dominant effects, a total of three exonic SNPs in glycogen phosphorylase (additive), heat shock protein 90 (additive and dominant) and peroxidasin (additive), and a total of six intronic SNPs in ankyrin repeats-like protein (additive and dominant), rolling pebbles (dominant), transforming growth factor-β induced precursor (dominant), and UTP-glucose-1-phosphate uridylyltransferase 2 (dominant) genes showed significant associations with the estimated breeding values in the experimental animals (P =0.001−0.031). Individually, they explained 2.6−4.8 % of the genetic variance (R2=0.026−0.048). This is the first large set of SNP markers reported for M. rosenbergii and will be useful for confirmation of associations in other samples or culture lines as well as having applications in marker-assisted selection in future breeding programs.

Modeling meat yield based on measurements of body traits in genetically improved giant freshwater prawn (GFP) Macrobrachium rosenbergii

A single-generation dataset consisting of 1,730 records from a selection program for high growth rate in giant freshwater prawn (GFP, Macrobrachium rosenbergii) was used to derive prediction equations for meat weight and meat yield. Models were based on body traits [body weight, total length and abdominal width (AW)] and carcass measurements (tail weight and exoskeleton-off weight). Lengths and width were adjusted for the systematic effects of selection line, male morphotypes and female reproductive status, and for the covariables of age at slaughter within sex and body weight. Body and meat weights adjusted for the same effects (except body weight) were used to calculate meat yield (expressed as percentage of tail weight/body weight and exoskeleton-off weight/body weight). The edible meat weight and yield in this GFP population ranged from 12 to 15 g and 37 to 45 %, respectively. The simple (Pearson) correlation coefficients between body traits (body weight, total length and AW) and meat weight were moderate to very high and positive (0.75–0.94), but the correlations between body traits and meat yield were negative (−0.47 to −0.74). There were strong linear positive relationships between measurements of body traits and meat weight, whereas relationships of body traits with meat yield were moderate and negative. Step-wise multiple regression analysis showed that the best model to predict meat weight included all body traits, with a coefficient of determination (R 2) of 0.99 and a correlation between observed and predicted values of meat weight of 0.99. The corresponding figures for meat yield were 0.91 and 0.95, respectively. Body weight or length was the best predictor of meat weight, explaining 91–94 % of observed variance when it was fitted alone in the model. By contrast, tail width explained a lower proportion (69–82 %) of total variance in the single trait models. It is concluded that in practical breeding programs, improvement of meat weight can be easily made through indirect selection for body trait combinations. The improvement of meat yield, albeit being more difficult, is possible by genetic means, with 91 % of the variation in the trait explained by the body and carcass traits examined in this study.

Determination of optimum stocking density of Macrobrachium rosenbergii larvae using multiple feed in a commercial hatchery at Cox’s Bazar, Bangladesh

Experimental stocking density of Macrobrachium rosenbergii in larval rearing was conducted in A.G. Aqua Hatchery, Chakaria, Bangladesh to study the effect of different stocking densities on growth, survival rate and diseases stress under hatchery condition. The research work was conducted using six cemented rectangular tanks having 3m3 capacity (1.5mX2mX1m) each. Stocking density were maintained in three experimental setup as 200, 150 and 100ind/L of the T1, T2 and T3 respectively with one replicate each. The larvae were fed with Artemia nauplii, Custard, Maxima and brine shrimp flakes. Water quality was maintained by exchanging 20-30% (12ppt saline water) daily. During the study period, temperature, pH, DO, salinity, nitrite-nitrogen, ammonia and alkalinity were maintained from 28.5-31.5ºC, 7.5-7.8, 5.8-5.9mg/L, 12-13ppt, 0.14-0.2 mg/L, 0.22-0.3mg/L, and 140-160mg/L respectively. The growth rates of larvae at 11th stage were recorded in terms of body length 0.115, 0.136, and 0.169 mm/day whereas body weight were observed 0.000115, 0.000180, and 0.000240g/day. The survival rate of larvae were found 21.8%, 30.4% and 51.3% in treatments T1, T2 and T3 respectively. PL was obtained as 43, 45, and 51PL/L and days required of 41, 38 and 34 days in stocking density of 200, 150, and 100ind/L respectively. It was found that the minimum of 34 days was required to attain the PL (12th stage) using the stocking density of 100 individuals/L. Cannibalism, Zoothamnium, Exuvia Entrapment Disease (EED), and Bacterial Necrosis (BN) were found to be the threat to the commercial hatchery operation that might responsible for potential larval damages which can be reduced by lowering the stocking densities in larval rearing tank that also increased the survival and growth rate.

Estimation of the growth curve parameters in Macrobrachium rosenbergii

Growth is one of the most important characteristics of cultured species. The objective of this study was to determine the fitness of linear, log linear, polynomial, exponential and Logistic functions to the growth curves of Macrobrachium rosenbergii obtained by using weekly records of live weight, total length, head length, claw length, and last segment length from 20 to 192 days of age. The models were evaluated according to the coefficient of determination (R2), and error sum off square (ESS) and helps in formulating breeders in selective breeding programs. Twenty full-sib families consisting 400 PLs each were stocked in 20 different hapas and reared till 8 weeks after which a total of 1200 animals were transferred to earthen ponds and reared up to 192 days. The R2 values of the models ranged from 56 – 96 in case of overall body weight with logistic model being the highest. The R2 value for total length ranged from 62 to 90 with logistic model being the highest. In case of head length, the R2 value ranged between 55 and 95 with logistic model being the highest. The R2 value for claw length ranged from 44 to 94 with logistic model being the highest. For last segment length, R2 value ranged from 55 – 80 with polynomial model being the highest. However, the log linear model registered low ESS value followed by linear model for overall body weight while exponential model showed low ESS value followed by log linear model in case of head length. For total length the low ESS value was given by log linear model followed by logistic model and for claw length exponential model showed low ESS value followed by log linear model. In case of last segment length, linear model showed lowest ESS value followed by log linear model. Since, the model that shows highest R2 value with low ESS value is generally considered as the best fit model. Among the five models tested, logistic model, log linear model and linear models were found to be the best models for overall body weight, total length and head length respectively. For claw length and last segment length, log linear model was found to be the best model. These models can be used to predict growth rates in M. rosenbergii. However, further studies need to be conducted with more growth traits taken into consideration

Reviving the Macrobrachium rosenbergii (de Man) fishery in Vembanad Lake, India

In Vembanad Lake and its confluent rivers (Kerala, India), the catches of Macrobrachium rosenbergii (de Man) were reported to have dwindled to a mere 39 t in the 1980s from average landings of 300 t during the 1960s. This decline is due to the impact of a number of human interventions affecting the ecosystem and, hence, the stocks of M. rosenbergii. Monitoring of landings in 1994-1995 and 1995-1996 indicates an improvement in catches. This paper discusses the reasons for the decline and revival in stocks and suggestions for their replenishment.

Genetic diversity in wild stocks of the giant freshwater prawn (Macrobrachium rosenbergii): implications for aquaculture and conservation

The giant freshwater prawn (Macrobrachium rosenbergii) is cultured widely around the world but little is known about the levels and patterns of genetic diversity in either wild or cultured stocks. Studies have suggested that genetic diversity may be relatively low in some cultured stocks due to the history of how they were founded and subsequent exposure to repeated population bottlenecks in hatcheries. In contrast, wild stocks have an extensive distribution that extends from Southern Asia across Southeast (SE) Asia to the Pacific region. Therefore, wild stocks could be an important resource for genetic improvement of culture stocks in the future. Understanding the extent and patterns of genetic diversity in wild giant freshwater prawn stocks will assist decisions about the direction future breeding programs may take. Wild stock genetic diversity was examined using a 472 base-pair segment of the 16S rRNA gene in 18 wild populations collected from across the natural range of the species. Two major clades ("eastern" and "western") were identifi ed either side of Huxley’s line, with a minimum divergence of 6.2 per cent, which implies separation since the Miocene period (5-10 MYA). While divergence estimates within major clades was small (maximum 0.9 per cent), evidence was also found for population structuring at a lower spatial scale. This will be examined more intensively with a faster evolving mtDNA gene in the future.

Rice-freshwater prawn (Macrobrachium rosenbergii) farms in the Mekong Delta, Vietnam

Aquaculture in riceland has been practiced in Mekong Delta, Vietnam for a long time and integrated rice-freshwater prawn (Macrobrachium rosenbergii) farming has become more and more popular. The integrated farming systems developed and practiced by farmers in the area to produce more food and more cash crops are presented and discussed.

Heterogeneous individual growth of Macrobrachium rosenbergii male morphotypes

In a single cohort of small freshwater prawn, Macrobrachium rosenbergii, the size range of females in the population is rather small. However, among the males, three major morphotypes are found and each has a distinct size category. The differential growth pattern in males, termed "heterogeneous individual growth" (HIG), is a major bottleneck confronting the profitability of farming this species. An attempt is made to understand the cause and impact of HIG on the culture system and methods by which HIG could be minimized in growout in order to maximize the market yield structure of the harvested population.

Genetic improvement of freshwater prawn, Macrobrachium rosenbergii (de Man) in India. Phase two: annual report for period January to December 2012

Macrobrachiurn rosenbergii is one of the widely cultured freshwater prawn species globally. India was the third largest producer of this species in 2007 and its aquaculture production rose to 43,000 metric tons (t) in 2005 froin less than 500 t in 1995. However, since then production has been declining and in 2008-09 it was 12,856 t, a reduction of more than 70% compared to 2005. There are several contributing factors to this decline, such as slow growth rate, poor survival, disease outbreaks, increase in cost of production, and availability of low risk alternative fish species. However, there is a consensus that poor seed quality leading to unsatisfactory growth and survival rates in ponds is one of the major reasons. Hence, the development of a systematic selective breeding program aimed at improving growth rate and ensuring high survival rate of this species was deemed a high priority. The Central Institute of Freshwater Aquaculture (CIFA), Bhubaneswar, India in collaboration with the WorldFish Center, Malaysia initiated a selective breeding program for this species in 2007.