Effect of salinity on survival and growth of giant freshwater prawn Macrobrachium rosenbergii (de Man)

Aquaculture Reports 2 (2015) 26–33

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Effect of salinity on survival and growth of giant freshwater prawn Macrobrachium rosenbergii (de Man) B.K. Chand a , R.K. Trivedi b , S.K. Dubey b,∗ , S.K. Rout b , M.M. Beg a , U.K. Das b a

Directorate of Research, Extension and Farms, West Bengal University of Animal and Fishery Sciences, Kolkata 700037, India Department of Aquatic Environment Management, Faculty of Fishery Sciences, West Bengal University of Animal and Fishery Sciences, Kolkata 700094, India b

a r t i c l e

i n f o

Article history: Received 28 January 2015 Received in revised form 6 May 2015 Accepted 13 May 2015 Keywords: Macrobrachium rosenbergii Salinity tolerance Saline water inundation Median lethal salinity Indian Sundarban

a b s t r a c t Two independent experiments were performed to determine the effects of salinity on survival and growth of juvenile Macrobrachium rosenbergii, first one was to determine the median lethal salinity (MLS-5096 h ) and second one was to assess the survival and growth at different sub-lethal salinities under field condition. In MLS-5096 h study 0, 5, 10, 15, 20, 25 and 30 ppt salinities were used to initially find out the salinity tolerance range. Accordingly, a definitive salinity tolerance test was done in next phase to find out exact median lethal salinity by directly transferring the test species to 21, 22, 23, 24, 25, 26 and 27 ppt salinity for 96 h. The median lethal salinity of M. rosenbergii was estimated at 24.6 ppt. In the second experiment, survival and growth performances of the prawn were recorded at different sub-lethal salinities viz., 5, 10, 15 and 20 ppt along with 0 ppt as control during 60 days culture period. The prawn exhibited lowest final average weight at 20 ppt salinity and significantly highest at 10 ppt salinity. Highest SGR and weight gain were obtained at 10 ppt followed by 5 ppt, 15 ppt and 0 ppt salinity but differences among treatment were not significant (P > 0.05). Survival rate of prawn varied between 91% (at 0 ppt) and 78% (at 20 ppt). The prawn grew and survived satisfactorily at 0–15 ppt salinities, implying that the species can be cultured commercially at wide salinity range. M. rosenbergii can be considered as an ideal species to promote, in view of current and future climate variables as more and more coastal areas of India are going to be vulnerable to saline water inundation. © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction Salinity is one of the important environmental factors affecting survival, growth and distribution of many aquatic organisms (Kumlu and Jones, 1995; Kumlu et al., 1999, 2000). Although many crustaceans exhibit some degree of euryhalinity (Pequeux, 1995), optimal salinity levels for growth, survival and production competence are often species–specific (Parado-Estepa et al., 1987; Rouse and Kartamulia, 1992; Kumlu and Jones, 1995; Kumlu et al., 2001; Romano and Zeng, 2006; Ye et al., 2009). A variety of aquatic crustaceans have been reported to rear in inland saline water around the world (Ferraris et al., 1987; Saoud et al., 2003; Rahman et al., 2005). Thus, it is important to determine the optimum salinity level for each commercial prawn species in culture systems where the salinity can be altered to suit the species.

∗ Corresponding author. Tel.:+91 33 24328749; fax: +91 33 24328749. E-mail address: [email protected] (S.K. Dubey).

In tropics, fluctuations of salinity are very pronounced where the climate is characterized by wet and dry seasons (Suresh and Lin, 1992). But in recent years, climate variability manifested by sea level rise, increased incidence of coastal flood and tropical cyclones, which are responsible for salinity mediated water stress of freshwater fisheries in various parts of the world (Cruz et al., 2007; Badjeck et al., 2010). In West Bengal, India, many areas in Sundarban delta (UNESCO declared World Heritage Site) are vulnerable to saline water inundation and subjected to environmental hazard during extreme weather events like cyclones and storm surges. In 2009, the severe tropical cyclone ‘Aila’ hit the Sundarban, inundating extensive areas with brackish water. It brought huge changes in environmental parameters, especially in water salinity increased from 13.64 ± 6.24 ppt to 17.08 ± 8.03 ppt with an increase of 25.2% (Mitra et al., 2011). Due to salinity intrusion in freshwater aquaculture areas, many freshwater species were subjected to severe salinity stress and some species perished due to their inability to cope up with such extreme conditions. Therefore, it is important to determine the salinity tolerance of freshwater aquaculture species

http://dx.doi.org/10.1016/j.aqrep.2015.05.002 2352-5134/© 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

B.K. Chand et al. / Aquaculture Reports 2 (2015) 26–33

and to ascertain whether some freshwater species can be cultured in brackish water areas. The giant freshwater prawn Macrobrachium rosenbergii has a wide distribution throughout the Indo-Pacific region and most favoured for farming in tropical and subtropical areas of the world (New, 2002, 2005). Salinity plays a critical role on egg, embryo and larval development during life cycle of M. rosenbergii. In its natural setting, gravid females migrate across saline gradients to estuarine downstream to hatch their eggs and larval development takes place in brackish water (Ismael and New, 2000). This freshwater palaemonid prawn is popularly known as ‘scampi’ in Indian trade, farmed chiefly in small to medium-sized earthen ponds in West Bengal, Andhra Pradesh, Tamil Nadu and Kerala in India (Nair and Salin, 2012). Global production of this prawn has increased from 130,689 tons in 2000 to 203,211 tons in 2011 (FAO, 2013). The total scampi production from India in 2010–2011 was about 8778 metric tons and West Bengal was the leading producer. In 2011–12, India exported 2723 metric tons M. rosenbergii with an increase of 31.61% than the previous years (MPEDA, 2011). Freshwater prawn M. rosenbergii has been studied in relation to the effects of different environmental factors (Brown et al., 1991; Chen and Kow, 1996; Manush et al., 2004). The effects of salinity on the growth and survival of several penaeid species have also been extensively studied (Dall et al., 1990). Salinities between 15 ppt and 25 ppt are considered optimal for P. monodon culture (Ferraris et al., 1986a; Chen et al., 1995). It was reported by New (1995) that adult M. rosenbergii can tolerate salinity ranging from 0 ppt to 25 ppt. Huong et al. (2010) studied the effects of salinities (15–25 ppt) on the osmoregulation, growth and moulting cycles of M. rosenbergii at Mekong delta. Yen and Bart (2008) studied negative effect of elevated salinity on the reproduction and growth female M. rosenbergii. But its lethal salinity level, growth and survival rate at different sub-lethal salinities, etc. are still uncertain. To address these issues, the present study was undertaken to determine median lethal salinity (MLS-5096 h ), and to assess the survival and growth rates at different sub-lethal salinities. 2. Material and methods 2.1. Experimental species and acclimation Juveniles of M. rosenbergii were obtained from the spawning of wild broodstock in a commercial hatchery located in Naihati, North 24 Parganas district of West Bengal, India and transported in oxygenated polythene bag (pH 7.5, alkalinity 100 ppm as CaCO3 , hardness 120 ppm as CaCO3 ) to the laboratory. Before experimentation, healthy and active juveniles (transparent body and actively swimming) were segregated into 500 L FRP (fibreglass reinforced plastic) tanks filled with freshwater under constant aeration and acclimatized for three weeks at ambient temperature of 27–29.5 ◦ C. About 30% of water was renewed daily. Prawn were fed ad libitum twice daily (9:00 h and 16:00 h) with commercial pelleted feed (35% crude protein). The leftover food and faecal matters were removed daily by siphoning. 2.2. Salinity tolerance (MLS96 h ) test In the first phase, a non-renewal static toxicity bioassay was done for salinity range finding as described by Peltier and Weber (1985). Juveniles of M. rosenbergii (length: 6.98 ± 0.67 cm; weight: 4.05 ± 0.84 g) were directly transferred to 0, 5, 10, 15, 20, 25 and 30 ppt saline water. Desired salinities were achieved by mixing freshwater with brine water collected from salt pan (>100 ppt salinity). The experimental system consisted of 10 L glass aquaria stocked with ten juveniles/aquarium for 96 h with three replicates.

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The pH and dissolved oxygen of the tanks ranged from 7.2 ppm to 7.6 ppm and 5.8 ppm to 7.6 ppm respectively. As 100% mortality was observed only at 30 ppt, a definitive salinity tolerance test was conducted in the second phase to determine the median lethal salinity concentration. Median lethal salinity (MLS96h ) is defined as the salinity at which survival of test species falls to 50% in 96 h following direct transfer from freshwater to various test salinities (Watanabe et al., 1990). The test species (length: 7.71 ± 0.61 cm; weight: 4.50 ± 0.81 g) were directly subjected to 21, 22, 23, 24, 25, 26 and 27 ppt salinities and observed for 96 h. As per APHA (2012), standard photoperiod of 16 h light: 8 h dark was followed. Each aquarium was covered with a fine meshed nylon net to prevent jumping out the test juveniles. The pH and dissolved oxygen of the aquaria were ranged from 7.0 ppm to 7.8 ppm and 5.5 ppm to 6.75 ppm respectively. Survival was recorded at 24, 48, 72 and 96 h of exposure to each salinity level. Lack of response to mechanical stimuli was the criteria to determine death of juveniles. Dead juveniles were removed during each observation. MLS96 h was calculated by Probit method by pooling the mortality data from replicates within treatments and considered significantly different when the corresponding 95% confidence intervals did not overlap (Finney, 1971). The entire experiment was carried out in Mohanpur campus (Nadia district of West Bengal) of the University in India. 2.3. Field trials on survival and growth at different salinities The field trial was conducted in 5 earthen ponds (0.02 ha each) located at Jharkhali fish farm complex (N 22◦ 01.219 and E 088◦ 41.075 ), a fringe area of Sundarban mangrove eco-region, West Bengal, India. Four different sub lethal salinities, viz., 5, 10, 15 and 20 ppt were chosen to assess the effects of salinity on survival and growth. Simultaneously freshwater (0 ppt salinity) was used as control. The different salinity gradients were created in experimental earthen pond by pumping saline water from the nearby tidal creek connected to river Herobhanga (average salinity 28–30 ppt). Three numbers of fine nylon net happa (12 × 8 × 4 ft) were placed in each earthen pond with support of bamboo frame. Fourty acclimatised M. rosenbergii were randomly sampled, stocked in each happa and allowed to grow for 60 days under ideal farm management. A water depth of 1.2 m was maintained throughout the experiment in each pond. Six numbers of hide outs (PVC pipes of 2 diameter and 1 long) were placed in each happa to act as shelter and avoid cannibalism. Prawn were fed twice a day (9:00 h and 16:00 h) ad libitum with commercial pelleted feed (Charoen Pokphand Group, Samut Sakron, Thailand; 32% crude protein, 4% lipid and 6% fibre). Prawns were blot dried using a tissue paper and the body weight was measured fortnightly; while mortality (if any) was noted daily. The growth performances were calculated in terms of specific growth rate (SGR; %/day), body weight gain (BWG %), average daily growth (ADG; g/day) (Brown, 1957; Hopkins, 1992) by using the following formulae:





SGR %/day =

(LnWf − LnWf ) × 100 t

Where Ln represents the natural log of individual wet weight (g); Wf is the final wet weight, Wi the initial wet weight, t is the duration in day. BWG(%) =

(Wf − Wi) × 100 Wi

Where Wf is the final wet weight and Wi the initial wet weight ADG(g/day) =

(Wf − Wi) t

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Table 1 Salinity tolerance with confidence interval for Macrobrachium rosenbergii estimated using probit. Probability

0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 0.95 0.99

Salinity (ppt)

21.76 22.93 23.82 24.60 25.37 26.17 27.09 28.35 29.38 31.31

Confidence interval (95%) Lower bound 95%

Upper bound 95%

0.74 6.82 11.44 15.49 19.32 23.00 25.76 27.17 27.89 29.07

24.11 24.80 25.35 25.88 26.49 27.45 30.05 35.97 41.25 51.27

Where Wf is the final wet weight, Wi the initial wet weight and t is the duration in day. Survival(%) =

has been demonstrated in Figs. 1 and 2, respectively. The mortality rate was positively correlated with the salinity concentration with correlation coefficient (r) of 0.97.

Number of species survived at end of experiment Number of species stocked ×100

2.4. Water quality Salinity of each treatment was controlled daily and other water quality parameters were monitored fortnightly. Temperature, pH, dissolved oxygen and salinity were determined directly by digital water analysis instrument (HANNA, HI 9828, Germany); while ammonia-nitrogen (NH3 -N) and nitrate-nitrogen (NO2 -N) was measured using HACH spectrophotometer (DR 2800, Germany). Alkalinity and hardness were measured titrimetrically as per APHA (2012). 2.5. Data analysis Final survival and growth performance data of M. rosenbergii at each treatment were analysed by one-way analysis of variance (ANOVA) after confirmation of normality and homogeneity of variance. Log or arcsine transformation of data was performed before the analysis whenever variances were not homogeneous. Tukey (HSD) mean separation test were used to determine the differences among the means. Significant differences are stated at P < 0.05 level unless otherwise noted (Zar, 1999). All statistical analyses were performed using statistical software SPSS 10.0 for Windows (SPSS Inc. Chicago, IL USA). Graphs and plots were generated using statistical software Medcalc® version 12.7.0 (MedCalc Software bvba, Ostend, Belgium). 3. Results 3.1. Salinity tolerance (MLS96 h ) test 100% mortalities were recorded within 24 h upon exposure to 27–30 ppt. In 25–26 ppt, survival rates after 96 h were 17–6%, respectively. In contrast, at 21–22 ppt salinity treatments, survival rates after 96 h were 83–79%, respectively. The Median lethal salinity (MLS96 h ) and confidence limits computed using Probit for M. rosenbergii juvenile is presented in Table 1. The 96 h Median Lethal Salinity of M. rosenbergii was 24.6 ppt with confidence intervals (at 95%) of 15.5–25.9 ppt. The statistical confidence of point estimate values other than 50% can be used to characterize toxicity (lethal salinity). The precision of the MLS96 h test results for a typical sigmoid cumulative distribution dose response curve and time (h) dependent survivorship curve for M. rosenbergii in varied salinities

3.2. Survival and growth at different sub-lethal salinities The initial average body mass of the prawn were not significantly different (P > 0.05) at the commencement of the experiment. Significant differences in monthly average body mass were observed in different salinity treatment (Fig. 3). At the end of 60 days culture period, prawn exhibited the lowest average growth (25.63 g) at 20 ppt and the highest average growth (34.97 g) at 10 ppt. The highest weight gain was obtained in prawn cultured in 10 ppt (23.53 g) followed by 5–15 ppt, but did not differ significantly to each other (P > 0.05). The lowest weight gain was obtained in 20 ppt (13.58 g) which differed significantly (P < 0.05) from other treatments. This growth trend was also true for daily weight gains (Table 2). The specific growth rates (SGR) of prawn were also highest when cultured in 10 ppt (1.86%/day) followed by 5 ppt, 15 ppt salinities and in freshwater (0 ppt) but differences among treatments were not significant (P > 0.05). Significantly lower SGR was obtained in 20 ppt salinity treatment (1.26%/day) (P < 0.05). This growth trend was also similar in case of the percentage body weight gain (BWG %). The SGR in first month (30 days) and second month (60 days) differed significantly (P < 0.05). In case of 30 days SGR, highest growth rate were obtained in freshwater (0 ppt) followed by 5, 10, 15 and 20 ppt salinities. In contrast, this trend was just reverse in 60 days SGR. In 60 days SGR, highest growth rate was obtained in 15 ppt followed by 10 ppt but differences among them were not significant (P > 0.05) (Fig. 4). The survival rate of M. rosenbergii after 60 days trial period was significantly high (P < 0.05) in freshwater (0 ppt) and decreased as salinity increased. The differences in survival rate between 0 ppt and 5 ppt as well as between 5 ppt and 10 ppt were not significant (P > 0.05) (Table 2). The physico-chemical parameters of pond water measured during trial period were depicted in Table 3. 4. Discussion Juveniles or sub-adults of M. rosenbergii occur naturally in estuarine areas of West Bengal are thus adapted to an environment in which salinity levels vary constantly. Results of this study also indicated that the median lethal salinity value of M. rosenbergii is very high (24.6 ppt) and it supports that the species exhibits a wide tolerance to abrupt changes in salinity. Ling (1977) discovered that larvae of M. rosenbergii required brackish water for survival, growth etc. The M. rosenbergii is exposed to a wide range of salinities (0–18 ppt) during it course of life cycle (Limpadanai and Tansakul, 1980; Cheng et al., 2003). In an earlier study, Sandifer et al. (1975) showed that tolerance of post-larval M. rosenbergii to gradual and rapid increases in salinity was around 25 ppt and mortality increased rapidly at levels ≥30 ppt in both cases. Goodwin and Hanson (1975) also stated that larvae and adults of M. rosenbergii are euryhaline to a considerable degree and tolerated salinities up to 21 ppt. Water quality parameters like temperature, pH, dissolved oxygen, alkalinity, ammonia-nitrogen, and nitrate-nitrogen during growth trial period were found within acceptable range for freshwater prawn rearing (Correia et al., 2000; New, 2002; Mallasen et al., 2003) Table 3. Though survival of M. rosenbergii was higher in freshwater (0 ppt) in the study, the highest growth was achieved in 10 ppt. Salinity beyond 15 ppt was not suitable for growth of M. rosenbergii which is agrees well with previous study of Huong et al. (2010). New (2002) suggested that M. rosenbergii can be cultured in brackish water (up to a salinity of 10 ppt), although better pro-

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Fig. 1. Sigmoid cumulative distribution dose response curve for Macrobrachium rosenbergii.

duction, individual size and survival of the stock were observed at a salinity of 5 ppt (Nair and Salin, 2005). In contrary to the present investigation, Singh (1980) demonstrated that freshwater prawns were able to grow in salinity up to 17 ppt with highest growth achieved at salinity between 0 ppt and 2 ppt. Yen and Bart (2008) reported maximum growth of M. rosenbergii at 0 ppt and decreased as salinity increased and halted growth was documented

at 18 ppt, however this study was done with high stocking density. Goodwin and Hanson (1975) indicated that juvenile of M. rosenbergii grew more rapidly in slight brackish water (<5 ppt) when compared to more brackish water up to 15 ppt. Specific growth rates showed a steady decline with the relative increase in total biomass as the prawns become larger and older (Fig. 4). Noteworthy observation in this trial is that after 30 days, SGR raised at

Fig. 2. Survival rate (%) of juvenile Macrobrachium rosenbergii in different salinities at 96 h exposure.

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Fig. 3. Monthly average body weight (g) of Macrobrachium rosenbergii cultured in different salinities for 60 days. The results are expressed as mean ± SD of three replicates Table 2 Initial weight (g), final weight (g), weight gain (g), average daily growth (g/day), specific growth rate (%/day), body weight gain (%) and survival (%) of Macrobrachium rosenbergii reared in different salinities for 60 days. Variables

Initial weight Final weight Weight gain Average daily growth Specific growth rate Body weight gain Survival

Salinity (ppt) 0 (control)

5

10

15

20

11.22 ± 1.39 30.86 ± 2.38b 19.64 ± 1.25b 0.32 ± 0.02b 1.70 ± 0.19ac 177.63 ± 31.56ac 90.66 ± 2.08a

11.30 ± 0.75 32.55 ± 1.12ab 21.25 ± 0.38ab 0.35 ± 0.006ab 1.80 ± 0.16a 188.54 ± 9.78a 88.33 ± 1.52ab

11.43 ± 1.25 34.97 ± 1.11a 23.53 ± 1.10a 0.39 ± 0.01a 1.86 ± 0.16a 208.03 ± 30.57a 86.66 ± 1.52b

11.30 ± 0.81 32.47 ± 0.89ab 21.16 ± 0.27b 0.35 ± 0.004b 1.76 ± 0.07ac 187.80 ± 13.66ac 81.00 ± 1.00c

12.05 ± 0.95 25.63 ± 0.84c 13.58 ± 0.88c 0.22 ± 0.01c 1.26 ± 0.11b 113.46 ± 15.23b 78.00 ± 2.64c

Data are presented as Mean ± SD 0f three replicates. Different superscripts in same row were significantly different (P < 0.05).

higher salinity levels (Fig. 4) revealing that prawn were acclimatising and recovering stress in higher salinity as the culture period progressed. The osmoregulatory process is an important adaptation of many crustaceans to overcome changes in salinity, especially in estuarine and coastal environments (Pequeux, 1995). In this study, M. rosenbergii hyperosmoregulated when salinity was above its iso-osmotic point and hypoosmoregulated when salinity was below this point. Previous studies indicated that M. rosenbergii is an osmoregulator in freshwater up to salinities at the iso-osmotic point (14–15 ppt), whereas it is an osmoconformer at higher salinities (15–28 ppt) (Stern et al., 1987; Funge-Smith et al., 1995; Cheng et al., 2003). This

adaptation is just reverse for typical penaeid shrimp and most crustaceans that inhabit estuarine or marine areas (Mantel and Farmer, 1983; Lemaire et al., 2002). Malecha (1983) also explained that although freshwater prawn tolerate higher than their iso-osmotic point (18 ppt), optimum growth conditions are at fresh or slightly brackish water (0–4 ppt). Changes in relative concentrations of various ions in media, up to 15 ppt, seem to have no significant influence on the haemolymph composition in M. rosenbergii that managed to survive and grow in them (Stern et al., 1987; Huong et al., 2010). Although haemolymph composition and osmolality were not measured in the study, it is well established that external osmolality affects crustacean haemolymph osmolality and ionic

Table 3 Water quality parameters analysed in different salinity treatments during 60 days growth trial of Macrobrachium rosenbergii. Values are presented as Mean ± SD. Parameters

Temperature (◦ C) pH Dissolved oxygen (ppm) NH3 -N (ppm) NO2 -N (ppm) Alkalinity (ppm)

Salinity (ppt) 0 ppt (Control)

5 ppt

10 ppt

15 ppt

20 ppt

31.44 ± 2.87 7.86 ± 0.46 6.02 ± 0.89 0.17 ± 0.10 0.08 ± 0.05 30.25 ± 6.54

32.02 ± 3.17 8.47 ± 0.47 6.02 ± 1.16 0.19 ± 0.09 0.09 ± 0.04 79.30 ± 11.05

31.48 ± 3.28 8.13 ± 0.45 6.50 ± 1.45 0.22 ± 0.05 0.10 ± 0.05 89.50 ± 13.50

31.26 ± 3.30 8.24 ± 0.48 6.41 ± 1.10 0.22 ± 0.01 0.11 ± 0.07 97.45 ± 14.0

31.20 ± 3.31 8.24 ± 0.48 6.41 ± 1.10 0.26 ± 0.08 0.15 ± 0.08 118.25 ± 12.50

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Fig. 4. Monthly average specific growth rate (%/day) of Macrobrachium rosenbergii cultured in different salinities for 60 days. The results are expressed as mean ± SD of three replicates. Different superscripts indicate significantly differences (P < 0.05).

composition (Dall and Smith, 1981; Cheng and Liao, 1986; Lin et al., 2000). According to Woo and Kelly (1995), in freshwater condition aquatic species spend a certain amount of energy to compensate the salt lost through passive diffusion, providing mild brackish water (≤10 ppt) reduces energy expenditure and consequently promotes growth. It is well known that hyper-osmoregulation in crustaceans requires energy in the form of protein (Rosas et al., 1999; Setiarto et al., 2004; Silvia et al., 2004) and or lipids (Lemos et al., 2001; Sang and Fotedar, 2004). In addition to the physiological stress, growth of M. rosenbergii can be affected in higher salinities due to increased energy expenditure, protein sparing and depletion of lipid reserves, which in turn affect biomass when compared to those reared in low salinities. The respiratory metabolism in Macrobrachium showed a general tendency towards low oxygen consumption rates at intermediate salinities as discussed by Moreira et al. (1983). Moreover, freshwater prawn reared in higher salinities need more time and energy to complete their moulting process resulting in a reduction of feeding activity. Although the present study did not analyze the moulting period, it may have influenced the lower food consumption leading poorer growth in higher salinity (Staples and Heales, 1991; Chien, 1992; Jayalakshmy and Natarajan, 1996). In prawn, Lemos et al. (2001) and Sang and Fotedar (2004) have demonstrated reduced growth at high salinities to appetite and reduced food assimilation respectively. In fish also, rearing near their iso-osmotic point has an energy saving effect (Boeuf and Payan, 2001). Fish exposed to increased salinity are likely to face a conflict between the mechanisms of salt uptake and nutrient uptake in the gut. Reductions in growth due to decreased food intake in increasing salinity have been reported in several cultured fish species (Ferraris et al., 1986b; Boeck et al., 2000; Imsland et al., 2001). Increasing inland salinity due to human activity (Williams, 2001) and climatic variability has major economic, social and environmental consequences, threatening the viability of numerous rural communities (Beresford et al., 2001). This picture is quite prominent in coastal areas of West Bengal, especially in Sundarban eco-region (Chand et al., 2012a). River embankment failure

due to sea level rise and subsequent erosion coupled with frequent extreme weather events is a serious and emergent problem in Indian Sundarban region over the past two decades. As a results many areas are inundated by brackish water and converting freshwater to oligohaline zone (Chand et al., 2012b). In this changed scenario, M. rosenbergii has wider potentiality for culture in many brackish water areas of Indian Sundarban delta as well as other tropical deltas and can be used as a climate change adaptation strategy for aquaculture. The results of the present experiments indicated that salinity plays a significant role in the culture of M. rosenbergii and the species showed satisfactory growth and survival at wide salinity range (0–15 ppt). In view of the current and future climate variables, more and more coastal areas of India and other tropical deltaic regions are going to be vulnerable to brackish water inundation. Under such scenario, M. rosenbergii can be considered as an ideal species to promote. Noteworthy this conclusion has significant implications for M. rosenbergii aquaculture, as it can be utilized in farm site selection and salinity maintenance to maximize commercial productivity in coastal inundation prone area. Acknowledgements The authors are grateful to Indian Council of Agricultural Research (ICAR), New Delhi for the financial assistance through the NICRA (National Initiatives on Climate Resilient Agriculture) project entitled “Development of Climate Resilient Aquaculture Strategies for Sagar and Basanti Blocks of Indian Sundarban”. We are grateful to the Deputy Project Director, Sundarban Development Board, Govt. of West Bengal, Kolkata for sharing field laboratory facilities. Additional thanks goes to Mr. Sudan Roy for field assistance. References APHA, 2012. Standard Methods for the Examination of Water and Wastewater, twenty two ed. American Public Health Association, American Water Works Association, and Water Environment Federation, Washington, USA.

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