Growth, survival and production of Macrobrachium rosenbergii (de Man) in nursery ponds

K L Jain, R K Gupta, V P Sabhlok, B Singh* and M Jindal 

Department of Zoology and Aquaculture, CCS Haryana Agricultural University, Hisar 125 004, India

* Fisheries officer State Department of Fisheries, Hisar, Haryana
gupta_raj123@yahoo.com

Abstract 

The freshwater prawn (Macrobrachium rosenbergii) commonly known as scampi have been the focus of research in India in the recent past few years. Because of the consistent increase in ground water salinity throughout south-eastern countries, there has been a need to study to utilize low saline water for the rearing of post larvae of Macrobrachium rosenbergii, which constitute a major step in prawn culture. Therefore, in the present study, efforts were made to compare the growth, survival and production of prawns in nursery ponds both with respect to water salinity as well as changes in hydro-biological conditions. A 40 days monoculture of Macrobrachium rosenbergii (PL20) at different salinities (0, 2, 4 and 6 ‰) was carried out.

Studies revealed highest prawn growth with SGR of 14.41% in ponds, maintained at 2‰ salinity, in comparison with other salinity treatments and control. Condition factor was also at the lowest (1.36) at this salinity, indicating weight gain was faster than skeletal growth. DO, BOD and pH remained at optimal levels at this salinity. Free carbon-dioxide was almost negligible. Nutrient release however decreased with increase in the salinity level of the water, while NH4-N levels increased. There was an inverse relationship between nutrient release and conductivity/salinity, indicating slower rate of decomposition/mineralization in saline water ponds. Phytoplankton population decreased reciprocally with increased salinity (>2 ppt). Zooplankton population was also highest at 2‰ salinity. The effect of various types of shelter/ hide outs such as plastic nets, PVC pipes, earthen pipes, aquatic weeds and plant bushes with roots (Sarkanda) on survival and growth of prawn juveniles under field conditions indicated significantly higher mortality in aquatic weed (40.10%) treatment and 100 per cent mortality after 15 day in ponds having bushes with roots (Sarkanda), due to higher organic matter accumulation.

Key words: freshwater prawn culture, hydrobiological factors, water salinity

Introduction

The freshwater prawn (Macrobrachium rosenbergii) commonly known as scampi, have been the focus of research in India because of the success achieved in its commercial farming in southern states. The species thrive well in fresh water even at higher hardness (Prakash 1992), but the juveniles are more tolerant to low water salinity than the adults as the brooders prefer to breed in brackish water (Pillay 1990). The rapidly emerging problem of water table rise and secondary soil salinization in arid and semi-arid canal irrigation areas of north India having brackish groundwater is causing great concern to the scientists and agriculturists Recent studies (Jain et al 2008) has indicated significant effects of salinity on prawn grow-outs. Most important aspect in prawn culture is growth and survival of the post larval stage (PL₂₀)) in nursery ponds. Therefore, in the present study, efforts were made to compare the growth and survival of prawn post larvae in nursery ponds with respect to both water salinity and the kind of shelters to be used for their protection in a pond as prawn juveniles show cannibalism. Ponds shelters in nursery ponds are thus important for the survival and growth of these juveniles.

Material and methods 

Studies were carried out in the farm nursery ponds located in certain villages in and around Hisar (Lat. 29o10N, Long.75o46/E) India. The experiment was conducted in eight nursery ponds (Each of 0.1 ha).The experimental ponds contained tube well water (8-10 ppt salinity) mixed with canal water and ponds were maintained with 2, 4 and 6 ppt of saline water. Prior to the commencement of treatment, the nursery ponds were dried completely until the soil cracked, cleaned and limed @ 350 kg ha-1 y-1. After liming, ponds were filled with water (up to 15 cm) and  fertilized with cow dung (@ 5000 kg ha-1 y-1), urea (@ 250 kg ha-1 y-1) and SSP (@ 500kg ha-1 y-1), and all nursery ponds were filled with desired salinity water (up to 90 cm depth).

PL20 of Macrobrachium rosenbergii (mean body wt. 0.01 g) obtained from BQMR hatchery, Nellere (AP), were acclimated to desired salinity before stocking. These were stocked @ 30000 per hectare. To maintain the desired level of salinities water was replenished often as required. All these ponds were provided with perforated P.V.C. pipe shelter (covering about 1/4th area of the pond bottom).Feeding schedule i e starting with starter A, was adjusted after every 10 days, and based on the weight gained as per the following food schedule i.e. Starter A up to 20 days of culture, having an average body weight up to 1.5 g and Starter B for 1.5 to 5.0 g larvae.              

 In other experiments various other shelters like earthen pipes, aquatic weeds and sarkanda bushes with roots were also tested. Physico-chemical characters of water were analyzed according to APHA (1998). Planktons were analyzed quantitatively according to the standard methods (Wetzel and Likens 1979). The ponds were completely drained after forty days and the juvenile prawn were harvested, counted, weighed to nearest gram and stocked further in grow-out ponds. Live weight gain, increase in length, growth per cent gain, survival and specific growth rate (% g d-1) were calculated using standard methods (Steffens 1989).

Results  

Effect of water salinity

The present studies on growth performance of Macrobrachium rosenbergii post-larvae (PL20) observed for 40 days at four different salinities (Table 1) indicated maximum growth in terms of both live weight gain and gain in length at salinity of 2 ppt.

Length increased on an average from 1.37 cm to 6.17 cm and live weight from 0.01 g to 3.19g, leading to an average recorded estimated production of 66.4 kg ha-1. It, however, differed marginally from the data recorded for growth performance at 0 ppt, as it showed an estimated production of 63.0 kg ha-1. The growth performance at 6 ppt was the lowest, showing a weight gain of 2.39 g and gain in length up to 5.23 cm, with an estimated production of 20.4 kg ha-1 only. The post larvae mortality also increased with the increased salinity from 30.5 per cent at 0 ppt to 71.3 per cent at 6 ppt. It was also lowest (31.1%) at 2 ppt of salinity.

The data in table 2 represent estimated value for specific growth rate (SGR), specific growth relationship with length (SGRL) and condition factor (CF) of Macrobrachium rosenbergii post-larvae under experimental conditions at four different salinities.

SGR and SGRL values were again highest at 2 ppt salinity i.e. 14.4 per cent g per day and 1.01 per cent cm per day, respectively. Lowest weight to length ratio (1.36) at 2 ppt salinity revealed i.e. lowest gain in weight in PL20 stage for per unit change in length at this salinity. Whereas, at 6 ppt it was estimated to be the highest (1.68) and the SGRL value at this salinity was reciprocally at the lowest (0.80).

The data on pond water quality conditions at different salinity is shown in table 3.

The physico-chemical and biological conditions of this pond clearly revealed increase in conductivity from 565 cm ^-1 at 0 ppt to 1449 S cm ^-1 at 6 ppt, affecting grossly the primary pond productivity. The phytoplankton number was also at maximum at 2 ppt (374) and minimum at 6 ppt (200). Similarly the zooplankton number varied in proportions i.e. 236 at 2 ppt and 141 at 6 ppt. The increase in conductivity at 2 to 6 ppt was result of increased chloride ions, whereas bicarbonate ions decreased from 156 mg l^-1 to 144 mg l^-1 at 2 and 6 ppt salinities, respectively. The BOD level showed a marginal increase from 3.28 at 2 ppt to 3.92 mg l^-1 at 6 ppt salinity.

Effect of shelter types in nursery ponds

Five kinds of substrates like plastic nets, perforated PVC pipes earthen pipes, aquatic weeds and sarkanda bushes with roots (Table 4) were tested in the ponds.

Shelters provided covered one fourth of the total nursery pond surface area. Growth performance and survival of scampi (PL20) with different types of shelters observed for 40 days revealed maximum growth in terms of both live weight gain and gain in length occurred in ponds provided with plastic nets. There was an increase in body length on an average from 1.40 cm to 6.07 cm and live weight increased from 0.013 g to 3.19 g, leading to estimated production of 74.2 kg ha^-1. It, however, differed little from the data recorded for growth performance with PVC pipes and earthen pipes. It showed an estimated production of 71.7 kg ha^-1 and 72.2 kg ha^-1, respectively. The growth performance with aquatic weeds and bushes with roots was the lowest, with an estimated production of 39.7 kg  ha^-1. The post-larvae mortality was found to increase with the use of shelters of organic material. There occurred 100 per cent mortality in pond with bushes along with roots. SGR and SGRL values (Table 5) further showed PVC pipes and plastic nets more useful as shelter, as these values were in the highest range in these treatments. CF values was also lowest for PVC pipes (1.41) and highest (1.83) for aquatic weeds.

The data in table 6, further demonstrated that using organic materials (aquatic weeds and bushes with roots) grossly affect pond productivity by reducing the amount of carbonates, bicarbonate and alkalinity as well as dissolved oxygen to 3.27, 67.5, 70.8 and 2.92 mgl-1, respectively.

The phytoplankton number were, however, maximum in ponds with bushes (760) and minimum with aquatic weeds (122), possibly due to less light penetration into pond water, as the flouting aquatic weeds covered most of the water surface area. Similarly, the zooplankton number also varied in same proportion i.e. 308 with bushes bearing roots and 84.7 with aquatic weeds. The BOD levels showed values significantly higher in water with dead organic material shelters i.e. 5.37, which possibly resulted in high PL20 mortality due to simultaneous low dissolved oxygen levels (2.92 mg l-1)    

Discussion  

These studies provide a good indication of the impact of varying levels of salinity on the growth performance of scampi, Macrobrachium rosenbergii, revealing that 0-2 ppt as the most optimum level of salinity, required for high growth and survival of the PL20. Any further increase (>2 ppt) in water salinity represses shellfish growth. Shellfish productions appeared restricted by low primary productivity, low DO and increased NH4-N levels.         

Same was also evidenced earlier (Jain 2004) who documented a positive correlation of primary productivity with fish growth/yield. Since high concentrations of ammonia causes osmo-regulatory imbalances, and also interferes with the oxygen and carbon-dioxide exchange in the blood (Garg 1996), ammonia stress might have contributed to the low growth of prawn at higher salinities. Garg (1996) reported higher accumulation of NH4-N with increase in salinity resulting in low growth of carps.

These findings are further corroborated by other studies. Theodore et al (1980) showed better growth performance of Macrobrachium rosenbergii at a salinity level of 2 ppt. These authors have reported that percentage conversion efficiency of prawn was at the highest at 2 ppt, which decreased with further increase in the salinity level revealing that 6 ppt is more detrimental for the growth of Macrobrachium rosenbergii. The growth rates in terms of total length and body weight of Macrobrachium rosenbergii in 2 ppt water (SW) were greater than that in 6 ppt. These authors have further indicated that increased salinity appeared to have a growth depressive effect. Studies of Sandifer et al (1975) have also revealed high growth of scampi at 2 ppt when cultured under field conditions. Moreover, maintenance of ionic and osmotic equilibrium in lower salinity levels probably required less energy expenditure than at higher salinity, resulting in better growth at lower salinity (Alavas 1998). The inland saline groundwater has further high levels of calcium, magnesium and high hardness. The high saline water in this study also revealed high chlorides and hardness (Table 3), which repressed growth in scampi, hence retarded prawn productivity. On the contrary high alkalinity at 2 ppt (129.93 mg l-1) favored high pond productivity, thus increased prawn productivity.   

Conclusions 

• Comparison of growth performance of prawn (PL20) at different salinities revealed the maximum growth in terms of length and weight and lowest mortality at 2 ppt because of the optimum physico-chemical parameters including primary productivity.

  
  

• Among the shelter types used, PVC shelters other than organic materials were more condusive for prawn culture, as these amounts to higher DO levels and low organic pollution.            

References

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Received 12 July 2008; Accepted 7 October 2008; Published 5 December 2008

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