Specific growth rate and proximate carcass composition of fresh-water prawn cultured in different salinity conditions in fresh water ponds of Haryana

K L Jain, R K Gupta and Balraj Singh*

Department of Zoology and Aquaculture, CCS Haryana Agricultural University, Hisar
*Fisheries officer State Department of Fisheries, Hisar, Haryana
gupta_raj123@yahoo.com

Abstract

Differences in physico-chemical conditions of the pond waters contribute to specific growth rate, which along with carcass composition provide a direct indication of qualitative growth of an animal.  In the present study, these parameters with reference to fresh-water prawn cultured in different salinity conditions are reported.

Growth performance of the grow-outs of Macrobrachium rosenbergii at four different salinities observed for 150 days, indicated 268 percent gain in body length from 5.60 cm to 20.27 cm and weight increased from 2.63 to 70.50 g at 2 ppt of water salinity, with  an average estimated production of 1102.77 kg ha-1, whereas at 6 ppt production was at the lowest (117.42 kg ha-1). The mean Macrobrachium rosenbergii weight gain  in grow out at 2ppt was 73.13±0.06g. Low values in growth parameters were recorded at 4 and 6 ppt ponds (39.0±0.03g and 30.0± 0.06). SGR (2.21 g d-1) being highest at 2 ppt salinity also followed a similar trend along with highest survival percentage (54.31), suggesting  low salinity pond water as the favorable medium for optimum pond productivity for scampi production. The analysis of prawn grow-outs for proximate carcass composition at different salinity however showed insignificant changes in composition at different salinities, except for the total ash contents and gross energy contents.

Key words: carcass composition, freshwater scampi, Macrobrachium rosenbergii, salinity lavels in grow-out ponds

Introduction

The rapidly emerging problems of rising water table and soil salinization in arid and semi-arid canal irrigated areas of north India having brackish groundwater is causing great concern to the scientists and planners. These waters are neither fit for agriculture or industries nor for human consumption, because of high salinity. Some euryhaline fish species like mullets, milkfish and seabass are already cultured in this university (Garg et al 2004).The freshwater prawn (Macrobrachium rosenbergii) commonly known as scampi has been the focus of research in India on account of the success achieved in its commercial farming in southern states. Work on freshwater prawn, however, has been underway in different parts of the world since 1879 to augment sustainable production in farms and hatcheries as well as to ensure fast growing varieties through genetic and stock manipulation. Macrobrachium rosenbergii is commercially important because of protein rich nutritional qualities. These are found in most inland freshwater areas including lakes, rivers, swamps, irrigation ditches, canals and ponds, as well as in estuarine areas. Most species require brackish water in the initial stages of their life cycle. Macrobrachium rosenbergii fulfill many of the criteria required for culture in fresh and saline water (Pillay 1990). Cultural practices of prawns in freshwater ponds are already described (Jhingran 1991). Jain et al (2006)   described the use of low saline ground water for the  rearing of post larvae of Macrobrachium rosenbergii  and the grow-out in the sub-tropical climate of this state.  Considerable disparity in growth rates has been reported in ponds with different salinities. Differences in other physico-chemical conditions of the pond waters also contribute to specific growth rate, which along with carcass composition provide a direct indication of qualitative growth of an animal.  Therefore, in the present study, these parameters with reference to fresh-water prawn cultured in different salinity conditions  are reported.
 

Material and methods               

A 150-day monoculture of giant freshwater prawn was carried out in semi-arid region (Lat. 29o, 10/N; Long. 75o46/E) of Haryana (India), using inland saline groundwater. The 20 days old prawn larvae (PL20), mean body wt. 0.010 g were obtained from BQMR hatchery, Nellere (AP), and were acclimated, cultured and fed first in nursery ponds (0.1 ha each), as mentioned in Jain et al (2006). These were harvested and  transferred in different grow-out ponds (0.4ha each ) located in villages and maintained at 2, 4 and 6 ppt of salinity in water. The salinity lavels were maintained as were dilution of the high salinity ( >6ppt) naturally available tube-well water with canal water The control ponds contained fresh canal water (0 ppt salinity). For each salinity treatment two ponds of similar dimensions were used at the same location. The prawns were fed daily according to the known  feeding schedule (Table 1) and the feeding rates were adjusted, based on the weight gain by the sampled prawn after every 10 days.

Plankton (Phytoplankton and Zooplankton) were analyzed quantitatively according to the standard methods (Wetzel and Likens 1979). Water temperature (oC) and pond productivity of the treatment ponds were also monitored regularly following APHA 1998.The prawns were subjected for the analysis of their carcass composition, such as the dry matter, crude protein, crude lipids, crude fiber, ash etc.  using standard methods (AOAC 1995). Weight gain in terms of differences between final weight (W₂) and initial weight (W₁) and Specific growth rate (SGR % g d-1) were calculated using their initial/final weights following standard formulae (Steffens 1989 ).

Results and discussion           

Growth performance of the grow-outs of Macrobrachium rosenbergii at four different salinities (Table 2 and 3 ) indicated 268 percentage gain in body length at 2 ppt of water salinity, with  an average estimated production of 1103kg ha.

There was an increase in average length from 5.60 cm to 20.27 cm and weight increased from 2.63 to 70.50 g, showing an average estimated production of 1103 kg ha-1. Whereas, at 6 ppt it was the lowest (117 kg ha-1). SGR and SGRL values at 2 ppt were highest i.e. 2.21 per cent g d-1 and 0.86 per cent cm per day, with highest weight to length ratio (CF)  of 0.87 due to more gain in weight  per unit change in length. Feed conversion ratio, appear to be a better estimate for grow-outs. It was also minimum (1.60) at 2 ppt and maximum (2.51) at 6 ppt showing higher weight gain for the unit food consumed at 2 ppt.  The prawn mortality was also highest (79.00%) at 6 ppt.

The analysis of prawn grow-outs for proximate carcass composition (Table 3) at different salinity showed insignificant changes in composition at different salinities, except for the total ash contents and gross energy contents.

The ash content of grow-out were highest at 6 ppt (0.53%) and lowest at 2 ppt (0.37%). On the contrary, the gross energy contents were highest at 2 ppt (5.14 kJ g-1). The crude protein values were  significantly low  (19.15%) at 6 ppt salinity treatment. Low  condition factor  values in fish maintained in  low salinities  because of  high mean shell fish weight at these salinities can be attributed to relatively high fat deposition (Carcass fat : 0.24%,).

The physico-chemical and biological characteristics of these ponds (Table 4) clearly revealed salinity dependant increase in  conductivity, from 593.60 ds cm-1 at 0 ppt to 1749.60 ds cm-1 at 6 ppt, affecting grossly the primary pond productivity in the form of phytoplankton density i.e. it was maximum at 2 ppt (416.07) and minimum at 6 ppt (255.87).

Similarly, the zooplankton number also varied in the same proportions i.e. 238.53 at 2 ppt and 148.87 at 6 ppt. Bicarbonate ions decreased from 123.73 to 76.67 mg l-1 at 2 and 6 ppt salinity, respectively. The BOD value also showed a significant increase from 2.88  at 2 ppt, 3.53 mg l-1 at 6 ppt, salinity.

These studies provide a good indication of the optimum response of scampi, Macrobrachium rosenbergii at 0-2 ppt salinity of water for high growth and survival of the grow-outs. Any further increase (>2 ppt) in water salinity represses shellfish growth. Shellfish production appeared restricted by low primary productivity in higher salinity ponds and the low DO availability. While, NH4-N levels increased significantly (P<0.05) with increase in the salinity of water, resulting in low shellfish growth at higher salinities. The water condition in these ponds was almost free of carbon-dioxide. It may be attributed to its continuous utilization by the phytoplankton’s. Alkalinity, net primary productivity and phytoplankton population in general were high in ponds with 0 or 2 ppt saline water coinciding with high growth. Further, alkalinity and net primary productivity (NPP ) showed a significant and positive correlation with shellfish weight gain indicating that increase in shell fish biomass can also be attributed to the increased pond productivity. NPP showed a direct correlation with alkalinity, phytoplanktons and zooplanktons indicating high productivity in ponds with 0 or 2 ppt saline water. Some earlier workers like Liang et al (1981), Olah et al (1986), Garg and Bhatnagar ( 2000) and  Jain (2004) have also evidenced a positive correlation of primary productivity with fish growth/yield. NH4-N increased significantly with increase in the salinity of the water. Since high concentrations of ammonia causes osmoregulatory imbalances, and also interferes with the oxygen and carbon-di-oxide exchange in the blood (Garg 1996), ammonia stress thus might be  contributing  to low growth of prawn at higher salinities. Garg (1996)  reported high accumulations 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) studied the effect of different salinity levels (0 to 16 ppt) and also showed better growth performance of Macrobrachium rosenbergii at salinity level of 2 ppt, with the highest percent food conversion efficiency of prawn, which decreased with increase in the salinity level. They further revealed that 6 ppt salinity is more detrimental for the growth of Macrobrachium rosenbergii. The growth rates in terms of total body length and 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 under field conditions.

Lower growth at higher salinities may also be attributed to the difference in water chemistry. The inland saline groundwater has high levels of calcium, magnesium and high hardness which are low in freshwater. The high saline water in this study also revealed high chlorides and hardness.  High hardness at high salinities of the inland saline groundwater might have repressed growth in scampi.  On the contrary high alkalinity at 2 ppt (129.93 mg l-1) favored high pond productivity, thus increased prawn productivity.

The zooplankton population was also low at high salinities, resulting in low weight gain  in shell fish. As far as nutrients are concerned, total kjeldahl nitrogen. NO3-N and o-PO4 in general decreased with increase in salinity which may be attributed to slower rate of decomposition/mineralization in saline water.

Livestock wastes, following microbial degradation  in a aquatic ecosystem, alter the physico-chemical characteristics of the medium by releasing carbon-di-oxide, bounded  minerals and nutrients which were present earlier relatively in insoluble form (Cappenberg et al 1982). According to Chattopadhyay and Mandal (1980) decomposition of manures decrease with increasing salinity , thus reducing the  release of nutrients from organic fertilizers.

High length gain up to 20.27 cm in the present studies was observed in ponds with 0 to 2 ppt. Theodore et al (1980) reported that Macrobrachium rosenbergii grew from 5.60 cm to 20.27 cm in a period of 5 months (salinity 0 to 12%) showing a better increase in length and weight of prawn in low saline water. Comparatively low growth at the higher salinities was also attributed to the high hardness and poor water quality. The data show survival of 54.31 per cent grow out at 2 ppt., revealing that 0-2 ppt inland saline groundwater as more conducive for the growth of scampi, due to the favorable physico-chemical conditions in the ponds and not due to the dietary supplementation because all ponds have received equal quality and quantity of feed and fertilizers.

From the present studies it is thus evident that growth in scampi is not only affected by the salinity level but also by the physico chemical characteristics of pond water. 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).                         

Conclusions            

• Primary productivity at low salinity was high  in these ponds and caused higher prawn production with 268 percentage gain in body length and  an average estimated production of 1102.77 kg ha-1 at 2 ppt of water salinity.

  
  

• The proximate carcass composition of grow-out however did not differ significantly at all salinity levels

Reference 

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Received 20 November 2007; Accepted 29 April 2008; Published 3 July 2008

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