Macrobrachium Rosenbergii Larvae Research Articles

Kalman Filter-Based Data Stabilization for an Automated Water Quality Monitoring System in Macrobrachium Rosenbergii Larvae Culture

Manual monitoring and management of water quality parameters in Macrobrachium Rosenbergii (freshwater prawn) larval culture are labourintensive, time-consuming, and susceptible to human error. This research aims to develop and evaluate an automated water quality monitoring system for freshwater prawn larval culture, with a specific emphasis on data stabilization. An ESP32 microcontroller is implemented to allow remote communication using an internet connection. The system continuously monitors critical parameters using sensors such as temperature, pH, turbidity, and Total Dissolved Solids (TDS), facilitating remote real-time data acquisition. The Message Queuing Telemetry Transport (MQTT) publish-subscribe protocol is employed for seamless communication between the microcontroller and the monitoring dashboard. A Kalman filter is integrated into the system, enabling real-time sensor noise reduction and dynamic adaptation to changes. The filtered data are displayed remotely using a Node-RED dashboard with graphical representations. The implementation of the ESP32 microcontroller with the MQTT protocol and Node-RED has proven to be a robust platform for seamless data communication and presentation. Integration of the Kalman Filter significantly mitigates fluctuations in sensor readings. This is further proven by comparisons of the filtered data with known-good sensors, which have shown minimal to acceptable error percentages between 1% - 8.5%, where the error can mainly be attributed to environmental factors. Overall, this study has established a framework that can contribute to improving aquaculture practices and promoting environmental sustainability infreshwater prawn culture operations. The validated system provides valuable insights that assist farmers in facilitating a more efficient prawn culture operation.

Light spectrum effects on giant freshwater prawns, Macrobrachium rosenbergii: Larval development, survival and preferences

The objective of this study was to evaluate the influence of different light spectra on growth, development indices, survival and color preferences in Macrobrachium rosenbergii larvae. First (trial 1, 25 days), prawns (100 larvae/L) were randomly allocated to 30 cylindrical plastic containers (1 L). This trial was designed with five treatments (light spectra) and six replications: red light, blue light, green light and white light or absence of light (controls) in the 12:12 light:dark (LD) cycle. Next (trial 2), 30 groups of five larvae in two different development stages (VII and XI) were allocated to a system of compartments with different lights: white, red, blue or green. This system was connected by tubes to enable light spectra choices. Final weight, weight gain, consumption and metamorphosis significantly improved under the white light condition versus the other tested groups (p<0.05). Survival, the Larval Stage Index, the Larval Condition Index and final biomass clearly improved under the white light condition (p<0.05). Conversely, the red light and no light conditions obtained unsatisfactory results. White light was preferred in larvae stage VII (p<0.05), but this behavior changed to blue when prawns reached life stage XI (p<0.05). These findings suggest that white light may be the best choice to optimize larval growth and survival, while color preferences may vary with development stage.

Development of microbound diet and its application on Macrobrachium rosenbergii larvae and postlarvae

The aquaculture sector actively seeks innovative methods to enhance growth and nutrition in aquatic organisms. Microbound diets (MBDs), known for their finely ground pellets often combined with binders to encapsulate nutrients are gaining prominence. This study aimed to develop an MBD and assess its impact on the growth and body composition of giant freshwater prawn, Macrobrachium rosenbergii larvae and postlarvae (PL) through two feeding trials. Various binders (agar, zein, alginate, carrageenan, and carboxymethyl cellulose) were tested during the development of MBD and were compared with live feed (rotifer). The first feeding trial demonstrated improved larval growth with MBD with agar, reaching an average of Stage XII, compared to those fed the control diet, which only reached Stage IX. The second feeding trial investigated the effect of feeding regimes on giant freshwater prawn PL, consisting of (i) one-time feeding in the morning, (ii) one-time feeding at night, (iii) two-time feeding, (iv) three-time feeding, and (v) four-time feeding. Results showed that two-time feeding had comparable survival rates and growth performance to three-time feeding (survival rate= 43–45 % and weight gain= 0.09–0.11 g), with the best feed conversion ratio in two-time feeding (1.70) and the highest level of highly unsaturated fatty acids (25–26 %) in PL fed one-time and three-time. Overall results suggest that MBD with agar holds promise as a binder with two-time and three-time feeding, enhancing the quality of giant freshwater prawn PL. Further research on extending the duration of the experiment is recommended to assess PL moulting patterns and performance, as varied feeding regimes may significantly impact growth and moulting.

Dietary supplements of β-1,3/1,6-glucan derived from baker’s yeast results in enhanced seed production and robustness in larvae of the freshwater prawn Macrobrachium rosenbergii (De Man, 1879)

Dietary supplements of β-1,3/1,6-glucan derived from baker’s yeast results in enhanced seed production and robustness in larvae of the freshwater prawn Macrobrachium rosenbergii (De Man, 1879)

Streptomyces sp. MUM 195J: A Promising Probiotic for Controlling Vibrio parahaemolyticus Infection in Aquaculture

Aquaculture is gaining prominence in meeting the increasing global food demand. However, persistent episodes of pathogenic infections have greatly affected production and incurred substantial financial losses to the industry. Regrettably, there is a lack of effective contemporary therapeutic measures to control infectious diseases in aquaculture. The repercussions of antimicrobial resistance have underscored the drawbacks of the contemporary practice of relying solely on antibiotics in disease control. The aquaculture industry needs a safer, environmentally viable, and economically efficient means for disease management. In this regard, this study aims to investigate the effectiveness of mangrove-derived Streptomyces sp. probiotics in controlling Vibrio parahaemolyticus infections. In vitro screenings were undertaken to evaluate the inhibitory activity of five Streptomyces sp. isolates. Subsequently, a series of in vivo trials was conducted, with the Malaysian giant freshwater prawn, Macrobrachium rosenbergii larvae as the animal model. Following that, molecular analyses were employed to examine the changes in gene expression. In essence, Streptomyces sp. MUM 195J emerges as a promising probiotic strain that demonstrates a strong inhibitory effect against V. parahaemolyticus. Its application as a feed additive elevates the survival rate of M. rosenbergii threefold, thus demonstrating efficacy at par with florfenicol antibiotic when challenged with the V. parahaemolyticus pathogen. Besides, Streptomyces sp. MUM 195J elevated the growth rate of M. rosenbergii by 17%. Real-time quantitative polymerase chain reaction (RT-qPCR) analysis revealed that probiotic supplementation elevated the immune function of the animal. Additionally, Streptomyces sp. MUM 195J demonstrates the potential to ameliorate the quality of the rearing water.

Isolation and characterization of a novel temperate bacteriophage infecting Aeromonas hydrophila isolated from a Macrobrachium rosenbergii larvae pond

Aeromonas hydrophila is an opportunistic pathogen that frequently leads to significant mortality in various commercially cultured aquatic species. Bacteriophages offer an alternative strategy for pathogens elimination. In this study, we isolated, identified, and characterized a novel temperate A. hydrophila phage, designated as P05B. The bacteriophage P05B is a myovirus based on its morphological features, and possesses the capability to lyse A. hydrophila strains isolated from shrimp. The optimal multiplicity of infection (MOI), adsorption rate, latent period, and burst size for phage P05B were determined to be 0.001, 91.7 %, 20 min, and 483 PFU/cell, respectively. Phage P05B displayed stability across a range of temperatures (28–50 °C) and pH values (4.0–10.0). Sequence analysis unveiled that the genome of phage P05B comprises 32,302 base pairs with an average G + C content of 59.4 %. A total of 40 open reading frames (ORF) were encoded within the phage P05B genome. The comparative genomic analyses clearly implied that P05B might represent a novel species of the genus Bielevirus under Peduoviridae family. A phylogenetic tree was reconstructed, demonstrating that P05B shares a close evolutionary relationship with other Aeromonas and Aeromonas phages. In conclusion, this study increased our knowledge about a new temperate phage of A. hydrophila with strong lytic ability.

Assessment of Larval Health and Metamorphosis of the Giant Freshwater Prawn Macrobrachium rosenbergii Larvae during Acute Exposure to Imidacloprid

An acute toxicity study of imidacloprid on the larval health and metamorphosis of the giant freshwater prawn Macrobrachium rosenbergii larvae were carried out during the months of January–August 2021 at the aquatic animal raring and experimenting facility in the Cochin University of Science and Technology, Kerala, India. Imidacloprid is a broad-spectrum neonicotinoid insecticide used against sucking pests infecting agricultural crops as both contact poison and stomach poison. The present study investigated the adverse effects of imidacloprid on the survival rate, feeding behaviour, larval quality and incidence of metamorphosis in Macrobrachium rosenbergii larvae. The 48 h median lethal concentrations (LC50 values) and safe concentration of imidacloprid determined for different larval stages (Zoea I–XI) of M. rosenbergii ranged between 0.000635–0.001388 mg l-1 and 0.000055–0.000191 mg l-1, respectively. Larvae exposed to imidacloprid for 48 h showed decrease in survival rate with increase in concentration of imidacloprid. The results of larval condition index (LCI) that indicates the larval quality showed that imidacloprid reduced the larval health significantly (p&lt;0.05) at high concentrations and is potent to delay the incidence of metamorphosis. The feeding rate of larvae exposed to different concentrations of imidacloprid were found to be significantly (p&lt;0.05) reduced due to paralytic effect of imidacloprid. The present work provides relevant data beneficial for the risk assessment of imidacloprid in M. rosenbergii.

Effects of Thermocyclops decipiens and Artemia Nauplii for Larval Rearing of Macrobrachium rosenbergii (De Man, 1879)

This study examines the effects of the freshwater cyclopoid Thermocyclops decipiens and Artemia nauplii on the growth and survival of Macrobrachium rosenbergii (De Man, 1879) larvae during the rearing phase. M. rosenbergii larvae were divided into three groups and fed exclusively with either Artemia nauplii or T. decipiens, and a mixed diet (50% T. decipiens and 50% Artemia nauplii) in triplicate. The results indicated that M. rosenbergii larvae reached 90% post larvae (PL) on the 23rd day of the mixed diet feeding regime, followed by 88% and 82% PL on the 24th and 26th days when fed with Artemia nauplii and T. decipiens , respectively. The highest length and weight of M. rosenbergii PL were observed in the mixed diet treatment with 14.37±0.51mm and 0.76±0.04mg, respectively. The specific growth rate and percentage weight gain were significantly (p &amp;lt; 0.05) higher in the mixed feeding treatment. However, the survival of larvae was highest (69.89±4.55%) in the Artemia nauplii treatment. The larval stage index (LSI) of M. rosenbergii larvae fed on different feeding regimes was mixed diet &amp;gt; Artemia nauplii &amp;gt; T. decipiens. The biochemical constituents of M. rosenbergii PL showed that protein concentration was higher in the larvae fed with T. decipiens, while carbohydrate and lipid content were also high in mixed feeding regimes. Results indicated that the larval stage index and growth parameters of M. rosenbergii larvae were highest in the mixed diet treatment

Study on microflora structure of Macrobrachium rosenbergii larvae and environmental water at different developmental stages

16S rRNA gene sequencing was used to analyze the changes in the microbial community structure of Macrobrachium rosenbergii (M. rosenbergii) larvae and environmental water at different stages (0, 7, 14 and 21 days). The PICRUSt was used to precalculated the predicted genes and their functions. The Alpha and Beta diversity analysis showed that the abundance and uniformity of the flora of larvae and water samples were significantly different at four stages. At the phylum level, Proteobacteria, Planctomycetes, Firmicutes and Bacteroidetes were the dominant flora of larvae, while Proteobacteria, Bacteroidetes and Actinobacteria were the dominant flora of environmental water. But at the genus level, Raoultella and Blastopirellula were the main changes in larvae, and Dyadobacter, Flavobacterium and Pseudomonas were the main changes in environmental water. The gene function prediction analysis indicated that the amino acid metabolism, immune system, immune system disease, nervous system, sensory system and other pathways enriched in the different stages of larvae and environmental water were closely related to the breeding of M. rosenbergii. This research might provide theoretical basis and guidance for the high-quality breeding of M. rosenbergii.

Low water pH depressed growth and early development of giant freshwater prawn Macrobrachium rosenbergii larvae

Macrobrachium rosenbergii is one of the shellfish species with high aquaculture value due to its increasing market demand. However, the comparatively low production volume compared to demand coupled with the rapid decline of the natural environment, consequently, drives the potential depletion of the wild population. The decrease in water pH related to anthropogenic pollution is one of the most critical factors affecting the early life performances of M. rosenbergii. Therefore, this study was designed to examine the effect of low water pH on feeding, growth and development of M. rosenbergii early life stages. Experimental water pH was set as neutral (7.7 ± 0.4); mild-acidic (6.4 ± 0.5) and acidic (5.4 ± 0.2) with triplication at a stocking density of 2 larvae/L for 30 days. As expected, M. rosenbergii larvae were highly sensitive to acidic pH with no larvae survived beyond 48 h of exposure. Feeding, survival and growth of larvae were adversely affected by mild-acidic pH exposure as compared to neutral pH. Larvae exposed to mild-acidic water pH experienced a prolonged larval period and only metamorphosed to the post-larval stage at day-30. Whilst under neutral water pH, larval that metamorphosed to post-larval was first observed on day-23. The negative impact of decreased pH, even in mild-acidic pH exposure, on the feeding, survival, growth and development of M. rosenbergii larvae highlights the urgency of periodic pH monitoring during M. rosenbergii larviculture.

Transcriptome Analysis Reveals the Molecular Response to Salinity Challenge in Larvae of the Giant Freshwater Prawn Macrobrachium rosenbergii.

Salinity is a crucial factor influencing the growth, development, immunity, and reproduction of aquatic organisms; however, little is known about the molecular mechanism of the response to salinity challenge in larvae of the giant freshwater prawn Macrobrachium rosenbergii. Herein, larvae cultured in three treatment groups with salinities of 10, 13, and 16‰ (S10, S13, and S16) were collected, and then transcriptome analysis was conducted by RNA-seq. A total of 6,473, 3,830 and 3,584 differentially expressed genes (DEGs) were identified in the S10 vs. S13 comparison, S10 vs. S16 comparison and S13 vs. S16 comparison, respectively. These genes are involved in osmoregulation, energy metabolism, molting, and the immune response. qPCR analysis was used to detect the expression patterns of 16 DEGs to verify the accuracy of the transcriptome data. Protein–protein interaction (PPI) analysis for DEGs and microsatellite marker screening were also conducted to reveal the molecular mechanism of salinity regulation. Together, our results will provide insight into the molecular genetic basis of adaptation to salinity challenge for larvae of M. rosenbergii.

The giant freshwater prawnMacrobrachium rosenbergiialters background colour preference after metamorphosis from larvae to postlarvae: In association with nature of phototaxis

The giant freshwater prawn Macrobrachium rosenbergii larvae have apposition eyes and are positively phototactic, whereas the postlarvae (PL) have superposition eyes and are negatively phototactic. M. rosenbergii has colour vision as early as larval stage. We discovered that M. rosenbergii alters background colour preference after metamorphosis from larvae to PL in association with nature of phototaxis. The test circular glass aquaria covered with a pair of two-colour papers contained with a group of 100 larvae or 20 Pl, and the number of individuals in each colour background was recorded five times for each colour pair. The background colours tested were light blue, green, yellow, red, white and black. The numbers of larvae or PL in each colour background of different pairs were analysed by the Thurstone's law of comparative judgment. In the larvae, significant bias towards yellow was evident. In the PL, of the four pairings of black with other colours, all biased to black. The mean z-scores were highest for yellow in the larvae, and for black in the PL. To determine the possible background brightness preference of the larvae and PL, six different colour backgrounds were presented in pairs. The larvae significantly preferred light blue over dark blue, white over yellow and white over black. The PL exhibited reversed preference. The relationship between z-scores and light reflectance levels of five colour papers was significantly positive in the larvae and negative in the PL. The observed background colour preference was probably due to relative brightness rather than chromaticity difference.

Evaluation of different diets to replace Artemia nauplii for larval rearing of giant freshwater prawn (Macrobrachium rosenbergii)

A study was conducted on Macrobrachium rosenbergii larvae to evaluate the efficiency of different diets to replace Artemia nauplii in the feeding scheme. The study included two experiments performed at pilot scale in 12-L tanks using a recirculating system. Larval stocking density was 100 larvae/L. After 7 days of feeding by Artemia nauplii, different diets, included wet and dry diets and decapsulated Artemia cysts, were tested to replace Artemia nauplii. An extra treatment using only decapsulated Artemia cysts throughout the complete larval rearing was also included. The results showed that feeding larvae exclusively decapsulated cysts for the complete rearing cycle was not appropriate. When gradually replacing up to 50% of the Artemia nauplii ration with wet or dry diets, good results in terms of growth, survival and quality of the larvae were obtained, similar to the control treatment receiving only Artemia nauplii. However, abruptly replacing 50% of the Artemia nauplii ration with artificial diets negatively affected larval development. Weaning could start from larval stage V, with about 25% of the Artemia nauplii replaced with artificial diet. Subsequently, the weaning ration could be increased up to 50% from stage IX to postlarva stage. Artificial diets should be provided in different particle size ranges based on the larval stage, gradually increasing from 250 to 1000 μm from stage V to postlarva stage. The results obtained in the present study may aid future research and serve as a baseline for further optimization of feeding strategies in prawn larviculture.

Comparing Na/K-ATPase activity of Macrobrachium rosenbergii (de Man) larvae at specific developmental stages, using different sodium vs potassium and calcium vs magnesium concentrations, and sodium potassium adsorption ratio (SPAR) mediums

The present study analyzed the Na/K-ATPase activity (μmolADP/mgprotein/h) of Macrobrachium rosenbergii larvae at specific developmental stages using different environmental concentrations of sodium vs potassium and calcium vs magnesium, for pairwise comparison. In addition, we also compared the effect of various sodium potassium adsorption ratio (SPAR) mediums to Na/K-ATPase activity. The first experiment compared the effect of sodium concentrations (4000 and 5000ppm) vs potassium concentrations (150 and 200ppm), while the second experiment compared the effect of calcium concentrations (180 and 240ppm) vs magnesium concentrations (300 and 400ppm), as in pairwise combination on the Na/K-ATPase activity. The third experiment compared Na/K-ATPase activity for various SPAR mediums (20, 30, 40 and 50). Larval condition index (LCI), larval dry weight and percent survival were determined at the 1st, 4th, 7th and 11th stages for each experiment. For each experimental treatment, triplicate 80-l closed-loop RAS systems were used. Initial larvae stocking density was 300 larvae l−1. For each container, a 40mg batch of larvae was collected at each of the 4 larval stages to analyze Na/K-ATPase activity and LCI. These results revealed that at the 1st and 4th larval stages both sodium and potassium independently and in combination, affected (P<0.05) Na/K-ATPase activity. However, at the 7th stage, enzyme activity was confirmed only among the treatments, independently. At the 11th stage, enzyme activity was demonstrated among the combined treatments, in addition to potassium, alone. Calcium and magnesium only showed larval Na/K-ATPase activity independently at the 1st and 4th larval stages. Results also showed that at the 1st and 4th larval stages, Na/K-ATPase activity was significantly higher for SPAR 20 but, at the 7th and 11th stages the enzyme activity was significantly higher at both SPAR 20 and 30. Accordingly, our findings have demonstrated that, Na/K-ATPase activity is highly variable during M. rosenbergii larval development and that it is mainly affected by interactions of common environmental macro-elements involved in larval osmoregulation. As such, we recommend M. rosenbergii hatcheries to operate as close as possible to SPAR 30 for early larval development and SPAR 40 for later larval development.

Colour preference and colour vision of the larvae of the giant freshwater prawn Macrobrachium rosenbergii

This paper reports on the innate colour preference and colour vision in the hatchery-reared larvae (10–16days old, stages IV–VIII) of the giant freshwater prawn Macrobrachium rosenbergii (De Man) based on their response to coloured beads in a grey-walled tank under natural illumination. Plastic beads (4.1mm in diameter) of different colours (dark blue, light blue, light green, yellow, red, white, black, and grey) in various combinations were suspended in the water 5cm from the water surface and 12–20cm from the tank walls where the larvae rested in the absence of aeration. The larvae swam head first straight toward the beads and gathered around them. The number of larvae was highest around the dark blue, light blue, and white beads; lowest around the black, red, and light green beads; and moderate around the yellow bead. Tests with different colours in combination with three shades of grey indicated that the larvae of M. rosenbergii discriminated colours by chromaticity. The preference for blue seemed to be an innate rather than a learned ability since the larvae did not prefer the yellow and red beads that were more similar to the colours of the egg custard and the Artemia nauplii on which they had been reared.

Evaluation of Using Decapsulated Artemia Cysts and Artemia Nauplii or Commercial Feed as Starter Feed for Freshwater Prawn Macrobrachium rosenbergii Larvae

The present study was carried out to evaluate the effect of decapsulated Artemia cysts as direct food for Macrobrachium rosenbergii larvae on the growth and survival rate. Macrobrachium rosenbergii larvae (48 hour after hatching) weighted about 0.03 mg were reared (50 larvae/L) in cylindro-conical rearing fiberglass tanks (10 L) under controlled conditions. The larvae were fed on Commercial diet 46% crude protein (T1), DE capsulated Artemia cysts (T2), Artemia naupli (T3) and DE capsulated cysts & Artemia naupli at constant ratio (1:1) (T4). Three replicates for each treatment. Water parameters in all tanks were recorded. After 21-days rearing period, feeding of the larvae with commercial dietresulted in a significantly (P≤0.05) lower average weight (0.18 mg), mean length gain (4.80 mm), weight gain (0.15mg), K factor (0.16) and SGR (8.53%/d) compared to the other groups. Group T2 (fed with DE capsulated Artemia cysts) resulted in good survival (87%) of larvae, which was not significantly different from T4 (fed with 1:1 ,86.4%) and T3 (fed with Artemia nauplii ,86%). These results indicated that the use of decapsulated Artemia cysts (low price) appear to be a suitable feed for exogenous feeding in M. rosenbergii larvae. However, Artemia nauplii are more expensive than some commercial feeds.

Growth performance and survival rate of Macrobrachium rosenbergii (De Man, 1979) larvae using different doses of probiotics.

The efficiency of probiotics (Ecomarine) in rearing of Macrobrachium rosenbergii larvae was evaluated in a commercial prawn hatchery for five weeks. Stage-1 (zero age) larvae (of length: 2 mm; weight: 0.12 mg) were stocked at the rate of 100 L(-1). The experiment determined the growth rate, survival rate of the larvae for the both treatment and control groups. Final average weight were found 8.39 ± 3.28E-04 and 8.18 ± 2.86E-04 mg and length were found 9.08 ± 0.649 and 9.02 ± 0.081 mm for treatment and control group respectively. Comparatively higher growth performance was observed in treatment than control. Post Larvae (PL) was first observed 20th days of culture in treatment tanks whereas PL in control tanks was found 24th days of culture. Survival rate was found 58 and 46% in treatment and control group respectively. There was significant (p < 0.05) survival rate between two experiment groups. This study revealed that probiotics could be better in quality seed production of M. rosenbergii while significant changes were not noticed in the physic-chemical parameters i.e., water temperature, salinity, DO, pH, nitrate-NO2, hardness and alkalinity observed in both the treatments.

Measuring changes in locomotor activity of freshwater prawn larvae in response to exposure to water contaminants using the ViewPoint software and video tracking system (728.25)

As the population grows, so does the drive for urbanization. Urbanization and the resulting anthropogenic activities have an impact on the quality of nearby water resources. Puerto Rico’s population density is one of the highest in the world. We seek to develop a protocol to measure how Puerto Rico´s high level of urban development has impacted the behavior and nervous system function of river fauna. We have started by recording movement trajectory and velocity of freshwater prawn larvae during five consecutive periods of 10‐minutes light/dark cycles, using ViewPoint´s Zebrabox. Larvae of Macrobrachium rosenbergii, a species raised through aquaculture in Puerto Rico, were more active during dark cycles, whereas those of M. carcinus, the prawn species found most commonly in Puerto Rico´s rivers, were more active during the light cycles. Recordings were then made before and after exposure to two contaminants found in Puerto Rico´s urban rivers, chromium (Cr3+) and dibutyl phthalate (DBP), in levels allowed by the EPA for drinking water. Exposure of M. rosenbergii larvae to Cr3+ did not produce any significant changes in locomotion, whereas exposure of M. carcinus larvae to DBP did, affecting parameters such as total distance travelled at slow and fast speeds. This protocol will continue to be used to test effects of other river contaminants on locomotion at various developmental stages of prawns.Grant Funding Source: Supported by: NSF HRD‐1137725; NIH NIGMS 5SC3GM084763

Nitrate and Phosphate Toxicity on Post Larvae of the Giant Fresh Water Prawn (Macrobrachium rosenbergii) Individual and Synergistic Effects

The indiscriminate use of fertilizers has resulted in nutrient enrichment giving rise toeutrophic conditions in many freshwater bodies in Sri Lanka. Few studies have investigatedeffects of field levels of nitrate and phosphate on commercial freshwater species. The presentstudy therefore attempted to assess the individual and synergistic effects of nitrate andphosphate on post larvae of the Giant fresh Water Prawn Macrobrachium rosenbergii, whichare released in large quantities into reservoir systems of the dry zone of Sri Lanka.The post larvae were collected from a culture facility in Pambala, Chilaw, and wereacclimatized. After the measurement of the initial body lengths the larvae were introducedinto 500 ml glass beakers (n=10 per beaker) containing five field based concentrations ofeither nitrate (0.01 – 100 mg l-1) or phosphate (0.001 – 10 mg l-1). Controls and treatmentswere maintained in triplicate. Synergistic effects were also tested for 0.1 mg l-1 of phosphatewith three concentrations of nitrate (0.1, 1, 10 mg l-1). Survival, growth and the feedingbehaviour of the post larvae were monitored as end points of the empirical acute toxicity (96hr) trials. Results revealed that both nitrate and phosphate enhances mortality levels in prawnlarvae when acting alone at concentrations of 0.01 mg l-1and above for nitrate and 0.001mgl-1and above for phosphate. For instance, mortality in controls was 13.3 %, and for the twonutrients at the lowest test levels i.e. 0.01 mg l-1 of nitrate and 0.001 mg l-1 of phosphate, were23% and 20%, respectively. The synergistic effects with both nitrate and phosphate werelower than the additive effects of each, at all tested levels, but were greater than the recordedindividual effects. The synergistic mortality with 10 mg l-1 of nitrate and 0.1 mg l-1 ofphosphate was greater than mortality induced by each nutrient acting alone. In contrast tomortality, effects on growth were not apparent with either nitrate or phosphate acting alonenor synergistically, while the phosphate alone and both nutrients acting synergistically,appeared to cause reduced feeding. These findings highlight the need for investigating effectsof nutrient enrichment, and specifically their synergistic effects, on commercially exploitedspecies in order to predict levels of sustainability of the inland fishery resources of Sri Lanka.

Study on growth and survival of giant freshwater prawn Macrobrachium rosenbergii (de man) larvae under different culture systems

The present study was made to determine the effects of different larvi culture techniques. These techniques are operated for the survival of prawn larvae (from eggs to post larvae) on the water quality; the effect of stocking density on survival of the post larvae; and economical aspects of the three culture techniques. The three larvi culture techniques studied were: (1) the Clear water system with partial changes of water, (2) the green water system with a separate sub sand filter out side of the tank and (3) the green water system with a closed recirculation water system with a sub sand filter inside rearing tank. The results showed that the mean productions of metamorphosed post larvae prawn per liter of water in the three systems were compared. Fluctuations in the production of post larvae were greater in the clear water system than in the other two types of closed system. During the course of trails in the clear system, the ammonia level was intermittently high and might have caused high larval mortality.