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Mô hình aquaponic được biết đến là mô hình 2 trong 1 kết hợp giữa nuôi thủy sản và trồng rau thủy canh. Đa số các đối tượng thủy sản trong aquaponic đều là các loại các họ rô phi hay da trơn. Nghiên cứu này đưa ra một hướng mới đó là đưa cá chép Nhật bản hay còn gọi là cá Koi kết hợp với aquaponic. Cá Koi một loại cá cảnh giá trị cao đã phát triển rất tốt trong mô hình này. Đề tài bằng tiếng anh, và rất cần thiết cho những ai đang hoạt động trong lĩnh vực nông nghiệp.
Aquacult Int DOI 10.1007/s10499-014-9821-3 Effect of water flow rates on growth of Cyprinus carpio var koi (Cyprinus carpio L., 1758) and spinach plant in aquaponic system Tanveer Hussain • A K Verma • V K Tiwari • Chandra Prakash G Rathore • A P Shete • Neelam Saharan • Received: 22 January 2014 / Accepted: 11 August 2014 Ó Springer International Publishing Switzerland 2014 Abstract The experiment was aimed at standardization of water flow rate in aquaponic system in order to correlate nutrient removal and water quality with growth of Cyprinus carpio var koi (koi carp fingerlings) and Beta vulgaris var bengalensis (spinach) Different flow rates, i.e., 3.2, 1.5, and 1.0 l min-1, were assigned as treatments T1, T2, and T3, respectively, with spinach plants (28 plant m-2), whereas S1 and S2 were the treatments having flow rates of 1.5 and 1.0 l min-1, respectively, without plants Control (C) was set at flow rates of 3.2 l min-1 without plants Treatment T2 (1.5 l min-1) showed highest weight gain of koi carp fingerlings and also height gain of spinach plants as compared to other treatments There was no significant difference in length gain, percentage weight gain, specific growth rate, feed conversion ratio, feed efficiency ratio, and protein efficiency ratio as compared to other treatments and control All the treatments, T1, T2, and T3, effectively remove nitrate (77–78 %), phosphate (47.04–55.06 %), and potassium (22.85–29.16 %) from fish effluent tanks These results suggest that flow rates 3.2, 1.5, and 1.0 l min-1 were effective under aquaponic system Of which, 1.5 l min-1 can be suggested as optimum water flow rate for the growth of spinach and koi carp in aquaponic system as percentage weight gain in fish, percentage height gain, and yield of plants were higher compared to flow rates 3.2 and 1.0 l min-1 Keywords Aquaponic system Á Koi carp Á Spinach Á Flow rate Á Nutrient dynamics Á Nutrient removal Introduction Aquaculture has emerged as a major food producing sector, and it is now a major global industry with total annual production exceeding 63.6 million tons (FAO 2012) Nowadays, scarcity of water has become a major problem in many of the countries because of the T Hussain Á A K Verma (&) Á V K Tiwari Á C Prakash Á G Rathore Á A P Shete Á N Saharan Central Institute of Fisheries Education, Panch Marg, Yari Road, Versova, Andheri (W), Mumbai 400 061, India e-mail: akverma45@yahoo.com 123 Aquacult Int increased human population Water is a prerequisite for successful aquaculture operations Aquaculture practices also generate lots of wastewater, which is one of the major causes of environmental pollution Aquaponics is one of the solutions to both these problems Wastewater from the aquaculture system, which is nutrient-rich water, can be used for growing of plants without addition of any additional chemical nutrients to be added to the system Aquaponics is an integration of recirculating aquaculture systems with soil-less production of plants (Rakocy et al 2006) Recirculating systems are designed in such a manner so as to raise large quantities of fish in relatively small volumes of water and then reusing the wastewater after treating the water for the removal of toxic waste products Aquaponic systems require substantially less water quality monitoring than separate hydroponic or recirculating aquaculture systems Although the practices of fish farming and hydroponics have been traced to ancient times, the combination of these two is quite new Research in aquaponics has began in the 1970s, and the integration of aquaculture and the hydroponic cultivation of plants has been examined repeatedly over the past three decades with a wide variety of system designs, protocols, plant, and aquatic animal species (Rakocy and Hargreaves 1993) Integrated hydroponics and aquaculture was not much successful until the 1980s; however, innovations since the 1980s have transformed aquaponics technology into a feasible system of food production (Diver 2006) McMurtry et al (1993, 1997b) created the first known closed-loop aquaponic system (called an aquavegeculture system) in 1986 that used tilapia culture effluent into sand-planted tomato beds Integration of these techniques can possibly reduce wastes and associated environmental impacts, with additional crop at the same time (Naegel 1977; Quillere et al 1995; Rakocy et al 2006) Recirculating hydroponic systems integrate fish production and plant production, and have been proposed for the control of waste nutrients accumulation from fish culture in a way that consumes less water and produces additional saleable crops (Ghaly et al 2005) Hydroponic plants have been widely used in wastewater treatment systems because they efficiently absorb dissolved compounds in wastewater as nutrients for plant growth (Rakocy et al 1989; Dushenkov et al 1995) Vegetables are good candidate plants for use in recirculating hydroponic systems as they grow rapidly in response to the high levels of nutrients in aquaculture water Different species of vegetables such as ice-lettuce, tomatoes, leaf lettuce, and basil have been successfully grown in aquaculture wastewater (Naegel 1977; Quillere et al 1995; McMurtry et al 1997b; Rakocy et al 2006) However, the goal was to culture a vegetable that will generate the highest level of income per unit area per unit time With this criterion, culinary herbs are the excellent choice as they grow rapidly and fetch high market prices The income from herbs such as basil, cilantro, chives, portulaca, parsley, and mint is higher than that from fruiting crops such as tomatoes, cucumbers, egg plant, and okra (Rakocy et al 2006) Spinach, Beta vulgaris var bengalensis (Chenopodiaceae), is an annual herb with deep taproot and shallow secondary root (Nonnecke 1989) Commonly called spinach, the crop is mainly a winter vegetable crop that survives low temperatures (Nonnecke 1989) The crop can, however, be successfully grown under partial shade in summer provided there is sufficient moisture at the root zone (Klein 2007) Spinach is considered to be a popular salad ingredient rich in iron content and a good source of folic acid Spinach can be grown hydroponically in greenhouse production (Rosik-Dulewska and Grabda 2002) Aquarium fishes are rapidly gaining importance not only because of their aesthetic value but also due to their immense commercial value in the export trade all over the world The ornamental fish production is slowly gaining momentum in India, and efforts have been made to increase the country’s share in global market The world trade of ornamental fish is 123 Aquacult Int estimated to tune of US $ 4.5 billion and striding further, with annual growth rate of about 10 % (Ayyappan et al 2011) Among ornamental fishes, Koi carp, Cyprinus carpio var koi of the cyprinidae family, is a popular fish Koi carp are hardy, so they make an excellent aquarium species as well as laboratory species They are easy to culture and are also available in several varieties Koi carp of Asian origin is an important ornamental species and cultured throughout the world (Hickling et al 2007) It is a fast-growing fish species best suited to farming in ponds and lakes (Hashem et al 1997) Due to ever growing demand of koi carp, there is an urgent need to intensify its culture Like most carps, koi carp excretes large amount of waste because it does not have a stomach and only has an intestinal tract, and thus cannot digest excess of proteins unlike most tropical fishes According to Al-Hafedh (1999), growth rate of fish increases with increase in the level of dietary protein till the optimum level is reached Fish mortality occurs due to excessive accumulation of wastes to toxic levels Thus, high stocking density of koi carp culture necessitates high water exchange, discharge of effluent water leads to pollution of the water bodies Moreover, koi culture system requires a continuous supply of freshwater source that is generally not available in most of the water scarce areas so aquaponic systems are well suited to these conditions In this study, hydroponic barrels planted with spinach B vulgaris var bengalensis were integrated with a recirculating aquaculture tank of koi carp The main objectives of the study were to investigate the effect of flow rate on the growth performance of the koi carp fingerlings and spinach and to analyze the effect of flow rate on water quality and nutrient removal in the aquaponic system Materials and methods Design of experimental aquaponic system The aquaponic recirculating system was designed and set up at the wet laboratory of aquaculture division, CIFE, Mumbai The system consisted of 18 individual, identical aquaponic units, allowing replication of experimental treatments Each aquaponic recirculating system consisted of a fish tank, hydroponics tanks filled with gravel, a submersible pump with pipe arrangement, and ball valves to regulate the water flow rate (Fig 1) Pipelines (15 mm) made of polyvinyl chloride with ball valve (15 mm) were installed to recirculate water between the fish culture tank and hydroponic tanks Rectangular tanks of 180 l (81.2 57 38.8 cm) capacity were selected for fishes Water circulation in the aquaponic system was done by using submersible water pump (Sobo WP1650 1,500 l h-1 at 1.5 m head) Two halves of a HDPE barrel each having size of 0.51 m2 and a depth of 29.4 cm were used for hydroponics tank Hydroponic tanks were filled with the gravel of size ranging from to 15 mm Water from the fish tank to the hydroponics was regulated by 15-mm ball valves provided at both sides of hydroponic tank and water from the hydroponic tank returned by gravity force to the fish tank with help of 15-mm PVC drain pipe For experimental purpose, water was filled up to 120 l The aquaponic system operated constantly with known density of fishes, continuous supply of water (24 h day-1) pumped from the fish tank to the hydroponic barrels via submersible pump, and the flow rate of water is regulated by ball valve Thus, the constant filtration of culture water is maintained 123 Aquacult Int Effluent Clean water Ball valve (water flow regulator) Hydroponic barrel Drainage pipe Aeration Fish tank Submersible Pump Fig Schematic representation of the aquaponic system Fish and spinach plantlets Koi carp fingerlings were procured from commercial breeders of Kurla, Mumbai, and acclimatized for 30 days in a 1,000-l capacity tank Fingerlings of koi carp were stocked in each tank at 1.4 kg m-3 stocking density The size of the fingerlings was measured before stocking The average size and weight of koi carp fingerling at the time of stocking were 6.08 ± 0.04 cm and 5.96 ± 0.05 g, respectively The fingerlings were provided with artificial pelleted feed with 32 % protein, 7.07 % moisture, 8.31 % ether extract, and fed at the rate % of body weight twice in a day Seed of spinach (B vulgaris var bengalensis) was sown in nursery tray with coconut husk medium, adjacent to the experimental setup, and allowed to grow for 15 days before transplanting into the experimental aquaponic systems Spinach plants were transplanted from the trays to hydroponics tanks at a stocking density of 28 no m-2 The size of the plants at the time of stocking was 6.83 ± 0.09 cm Experiment methodology Optimization of flow rate was studied by conducting experiments with different flow rates in an aquaponic system for the period of 45 days Before starting of the experiment, all tanks were properly cleaned and disinfected with KMnO4 solution The groundwater used for the experiment was stored in the reservoir and provided with aeration for days prior to start of the experiment Chemical composition of groundwater used for the experiment was presented in the (Table 1) The experimental design consisted of treatments, each having replicates Different flow rates, i.e., 3.2, 1.5, and 1.0 l min-1, were assigned for T1, T2, and T3 treatments, respectively S1 and S2 were the treatments with water flow 123 Aquacult Int rates 1.5 l min-1 and 1.0 l min-1, respectively, without spinach plants to compare nutrient accumulation (nitrate, potassium, and phosphate) Control (C) was set with water flow rate 3.2 l min-1 without plants in hydroponic tanks with replicates Initially, the system was operated for weeks with few fishes to enhance ammonia level for the growth of nitrifying bacteria After that, spinach plantlets were transplanted in the hydroponic component of the system Sampling Sampling of fishes was carried out at 15 days interval for the assessment of growth (length and weight) Plant growth was monitored once in 15 days by measuring the plant height Water sample analysis Water quality parameters were analyzed during the experimental period with an interval of 10 days using the standard methods outlined in APHA (2005) Sampling was carried out between 8.30 am and 9.30 am on each sampling date Samples were refrigerated at °C in labeled polythene bottles for chemical analysis The water temperature was measured by the thermometer, and pH was measured by using universal pH indicator for all the experimental tanks Dissolved oxygen, free CO2, hardness, alkalinity, ammonia, nitrite, and nitrate were analyzed by standard methods outlined in APHA (2005) Sodium, potassium, and calcium in the water samples were estimated by flame atomic emission spectrometry (FAES) using a flame photometer (Elico CL 378, India) Magnesium, iron, and zinc in the water samples were analyzed by digesting water samples using Supra Pure concentrated acids (Merck) in a microwave-based digestion system (Microwave 3000, Anton Parr, USA) Digested samples were diluted subjected to the analysis of the three elements (Mg, Fe, and Zn) by atomic absorption spectrophotometer (Analyst 800, PerkinElmer, USA) using flame atomization Statistical analysis The obtained data were analyzed using SPSS version 16 in which one-way ANOVA and Duncan’s multiple range test were performed at a significance level of (P \ 0.05) at 95 % confidence limit to know the significant difference between the treatments and control means for different parameters Results and discussion Fish growth parameters This study was set up to compare three different flow rates suitable for the growth of spinach and koi carp under aquaponic system Fish growth, spinach growth, nutrient removal, and water quality parameters were used as indicators of suitability The mean weight of koi carp did not vary significantly (P [ 0.05) on 15 and 30th days (Table 2) The body weight of koi carp at the time of harvest varied significantly (P \ 0.05) among the treatments and control with slightly higher value observed in T2 (8.65 ± 0.01) followed by S1 (8.63 ± 0.02), T3 (8.61 ± 0.02), C (8.60 ± 0.02), S2 (8.59 ± 0.01), and T1 123 Aquacult Int Table Chemical composition of groundwater used for the experiment Water quality parameters Salinity (ppt) 1.61 ± 0.00 pH 7.38 ± 0.01 DO (mg l-1) 6.36 ± 0.09 Free CO2 (mg l-1) 5.23 ± 0.15 Hardness (mg l-1) 418.33 ± 2.88 Alkalinity (mg l-1) 239 ± 0.58 Ammonia (mg l-1) – Nitrite–N (mg l-1) – Nitrate–N (mg l-1) – Phosphate (mg l-1) – Potassium (mg l-1) 18.63 ± 0.07 Calcium (mg l-1) 127.83 ± 0.44 Magnesium (mg l-1) 52.0 ± 0.58 Sodium (mg l-1) 323.17 ± 1.69 Iron (mg l-1) 0.08 ± 0.01 Zinc (mg l-1) 0.12 ± 0.00 (8.58 ± 0.01) (Table 2) The different flow rates did not induce any significant effect on the survival of koi carp among the treatments All the treatments and control showed 100 % survival (Table 2) The percentage of weight gain at the end of 45-day experiment was not significantly different (P [ 0.05) among all treatments and control The highest percentage of weight gain was observed in T2 (45.24 ± 0.46 %) followed by S1 (44.94 ± 0.42 %), T3 (44.47 ± 0.45 %), C (44.12 ± 0.88 %) and S2 (43.85 ± 0.41 %), and T1 (43.89 ± 0.89 %) (Table 2) Specific growth rate (SGR) (% per day) did not show any significant difference (P [ 0.05) among all the treatments and control and followed same trend as that of weight gain showing highest value in T2 (0.83 ± 0.01) and lowest in T1 (0.79 ± 0.01) (Table 2) Treatments and control did not show any significant difference in length gain at the end of 45-day experiment (P [ 0.05) (Table 1) The feed conversion ratio (FCR) did not show any significant difference (P [ 0.05) among all the treatments and control The FCR values varied between 2.28 and 2.34 (Table 1) The feed efficiency ratio (FER) did not show any significant difference (P [ 0.05) among all the treatments and varied between very narrow range from 0.43 to 0.42 (Table 2) The protein efficiency ratio (PER) values varied within narrow range of 1.33–1.36, which was not significantly different in all the treatments and control (Table 2) Total amount of feed delivered was (153.74 ± 0.12 g) in all treatments and control, and the FCR values obtained in this study support the findings of Korkmaz and Cakirogullari (2011); reported FCR value for koi carp was 2.21 fed with 34 % crude protein Plant growth parameters Plant growth is another important aspect in the aquaponic system In our study, spinach was grown in gravel medium in an aquaponic system and supplied with fish wastewater in three different flow rates As Lennard and Leonard (2006) reported 90.9 % removal of nitrate using gravel bed as media for lettuce production, so the gravel media were used for experiment In the present study, height of plant showed significant difference between 123 ± 0.02 100 a 1.33 ± 0.01 a 0.42 ± 0.01 a 2.34 ± 0.04 a 0.81 ± 0.01 a 100 a 1.34 ± 0.01 a 0.42 ± 0.01 a 2.32 ± 0.05 a 0.80 ± 0.01 a 43.89 ± 0.89 a 44.12 ± 0.88 7.76 ± 0.09 a 8.58 ± 0.01 a ± 0.02 e 7.20 ± 0.12 a 7.64 ± 0.03 a 6.56 ± 0.12 a 6.83 ± 0.09 a 6.13 ± 0.12 a 5.95a ± 0.01 3.2 (with plant) T1 7.70 ± 0.06 a 8.60 ab 7.30 ± 0.15 a 7.73 ab 6.70 ± 0.20 a 6.85 ± 0.02 a 6.03 ± 0.13 a 5.97a ± 0.02 3.2 (without plant) C Treatments ± 0.03 100 a 1.36 ± 0.01 a 0.43 ± 0.00 a 2.28 ± 0.02 a 0.83 ± 0.01 a 45.25 ± 0.46 a 7.83 ± 0.03 a 8.65 ± 0.13 b 7.23 ± 0.09 a 7.72 ab 6.66 ± 0.09 a 6.84 ± 0.03 a 6.10 ± 0.12 a 5.96a ± 0.02 1.5 (with plant) T2 Mean values with same superscript did not show any significant difference (P [ 0.05) Survival rate (%) PER FER FCR SGR Percentage weight gain Final Length (g) Final Weight (g) 30-day length (cm) 30-day weight (g) 15-day length (cm) 15-day weight (g) Initial length (cm) Initial weight (g) Fish growth parameters Flow rate (l min-1) Parameter Table Growth performance of koi carp under different flow rates in treatments and control ± 0.03 ± 0.02 100 a 1.34 ± 0.01 a 0.43 ± 0.00 a 2.31 ± 0.02 a 0.82 ± 0.01 a 44.47 ± 0.45 a 7.73 ± 0.09 a 8.61 ab 7.33 ± 0.12 a 7.66 ab 6.50 ± 0.06 a 6.82 ± 0.05 a 6.06 ± 0.12 a 5.97a ± 0.06 1.0 (with plant) T3 ± 0.01 ± 0.02 100 a 1.36 ± 0.01 a 0.43 ± 0.00 a 2.28 ± 0.02 a 0.82 ± 0.01 a 44.95 ± 0.42 a 7.80 ± 0.06 a 8.63 ab 7.26 ± 0.09 a 7.68 abc 6.66 ± 0.03 a 6.80 ± 0.02 a 6.13 ± 0.09 a 5.96a ± 0.02 1.5 (without plant) S1 100a 1.33a ± 0.01 0.42a ± 0.01 2.34a ± 0.02 0.81a ± 0.01 43.85a ± 0.41 7.76a ± 0.12 8.59a ± 0.01 7.20a ± 0.12 7.65a ± 0.02 6.73a ± 0.09 6.78a ± 0.02 6.03a ± 0.09 5.96a ± 0.02 1.0 (without plant) S2 Aquacult Int 123 Aquacult Int treatments On 15th and 30th day of sampling, average height of spinach plant showed significant difference (P \ 0.05); T2 (1.5 l min-1) shows highest plant height of 10.86 ± 0.06 cm and 18.30 ± 0.12 cm on 15th and 30th day, respectively Similarly, at the end experiment, better height was obtained in the flow rate of 1.5 l min-1 as compared to other treatments, whereas no significant difference between treatments was obtained in terms of yield (Table 3) Spinach plants grown in aquaponic tanks were healthy, indicating that there were no major mineral deficiencies or toxicities caused by the wastewater The results of the present study were comparable with the findings of Endut et al (2009) and reported that 1.6 l min-1 showed best plant growth as well as fish growth under an aquaponic system using water spinach and African cat fish Correlation between water volume, fish production, and plant production The mean initial biomass of fish at the start of the experiment did not vary significantly (P [ 0.05), and at the end of 45 days, there was no significant (P [ 0.05) difference found among the treatments (Table 4) in terms of fish biomass, spinach yield, and this clearly indicate that aquaponic treatments with flow rates 3.2, 1.5, and 1.0 l min-1 were found effective producing 1.2 kg of spinach with stocking density 142 g of koi carps, and the observation from the present study states that 142 g of koi carp biomass with water volume of 120 l fulfills the nutrient requirement of spinach plant, at constant water flow rates (3.2, 1.5, and 1.0 l min-1) Thus, plants assimilated the available nutrients from the culture water and maintained the water quality parameters congenial for the growth of koi carp Water quality parameters and nutrient dynamics The water temperature during the study period varied within a range of 25–27.6 °C, with no marked variation between the treatments and control at any given time of sampling The mean value of salinity of water did not show any significant difference (P [ 0.05) among the treatments and control (Table 5) In general, pH varied within a narrow range of 7.38–7.29, and no marked variation was observed among the treatments and control (Table 5) In the present study, water renovation per day was approximately % due to the loss of water through evaporation and transpiration by plant Similarly, Lewis et al (1978) reported that average daily water renovation in a gravel/sand bed system is around 6.6 %, and also, McMurtry et al (1997a) suggested daily water exchange rates were between 1.2 and 4.7 % Table Growth performance of spinach in different treatments Parameters Treatments T1 Initial height (cm) 15-day height 30-day height Final height (cm) Percentage height gain Yield (kg) T2 6.80 ± 0.06a a 10.30 ± 0.10 a 17.60 ± 0.12 a 23.86 ± 0.03 a 251.04 ± 3.41 a 1.25 ± 14.10 T3 6.86 ± 0.03a 10.70b ± 0.11 b 18.10b ± 0.17 b 24.00a ± 0.10 a 251.24a ± 2.47 10.86 ± 0.06 18.30 ± 0.12 24.26 ± 0.09 253.40 ± 0.65 a 1.28 ± 8.21 Mean values with same superscript did not show any significant difference (P [ 0.05) 123 6.83 ± 0.03a b 1.26a ± 15.31 Aquacult Int Table Mean weight of biomass of koi carp, C carpio var koi, and spinach at the end of 45-day rearing Parameters Aquaponic treatments T1 T2 T3 Flow rate (l min-1) 3.2 1.5 1.0 Initial biomass of koi carp (0 day) 142.72a ± 0.35 142.48a ± 0.35 142.14a ± 0.64 Final biomass of koi carp (45 day) 206.32a ± 0.21 206.80a ± 0.42 206.40a ± 0.14 Yield of spinach (kg) a 1.25 ± 14.10 a 1.28 ± 8.21 1.26a ± 15.31 Mean values with same superscript did not show any significant difference (P [ 0.05) The mean dissolved oxygen content in all treatments and control varied significantly (P \ 0.05) The level of dissolved oxygen was highest in C (6.47 ± 0.07 mg l-1), followed by T1 (6.46 ± 0.08 mg l-1), whereas lowest dissolved oxygen concentration was observed in T3 (6.12 ± 0.14 mg l-1) (Table 5) Maintenance of dissolved oxygen is important for fish health and aerobes of biofilter Dissolved oxygen levels should be maintained above mg l-1 for optimum growth of warm water fish (Masser et al 1999) Similarly, activity of nitrifying bacteria to convert harmful ammonia to less harmful nitrate is also dependent on dissolved oxygen Nitrifying bacteria are known to become inefficient at DO levels below mg l-1 (Masser et al 1999) In the present experiment, DO levels in all treatments and control were found to be in favorable ranges (Fig 2) The mean free CO2 was significantly different (P \ 0.05) in all the treatments and control The highest value of CO2 was observed in T3 (5.04 ± 1.07 mg l-1) and S2 (5.00 ± 0.22 mg l-1), whereas lowest was observed in T1 (4.27 ± 0.19 mg l-1) The total alkalinity values did not show any significant difference (P [ 0.05) among the treatments and control (Table 5) Similarly, hardness of water among all treatments and control did not show any significant difference (P [ 0.05) (Table 5) The suggested value of ammonia in a recirculating system should be \1.00 mg l-1 (Van Rijn and Rivera 1990; Nijhof and Bovendeur 1990) A main waste product of the protein catabolism in fish is ammonia (Wood 1993) Ammonia toxicity depends on the water parameters including pH and temperature (Randall and Tsui 2002) Chronic exposure to ammonia reduces growth and survival of the fish at early development stages (Brinkman 2009) Gomułka et al (2011) suggested critical level of the unionized ammonia nitrogen for Leuciscus idus larvae (cyprinidae) was 0.21 mg l-1 (Wood 2004) reported low concentration of ammonia in the water stimulates the growth of fish Nowosad et al (2013) reported that the biomass of the reared fish is the only factor that can influence the ammonia concentration in water, under intensive rearing of Tench tench in controlled condition In the present study, the observed values of ammonia were in the range of 0.03–0.15 mg l-1 NH4–N concentration was highest in control as well as treatment without plants S1 and S2 as compared to treatments T1, T2, and T3 (Fig 3), which indicates the uptake efficiency of the spinach plants Vaillant et al (2004) reported that ammonium (NH4?) is one of the major sources of inorganic nitrogen taken up by the roots of higher plants During the experiment, nitrite–N showed significant difference between treatments and control The mean nitrate–nitrogen concentration varied significantly (P \ 0.05) between treatments and control The highest nitrate–nitrogen level was detected in control (C) (14.65 ± 1.79) followed by treatments S2 (12.38 ± 1.89), S1 (12.22 ± 1.89), T1 (3.48 ± 0.39), T2 (2.78 ± 0.30), and T3 (2.57 ± 0.26) (Table 6) This shows greater assimilation of nitrates by spinach plants Nitrate–N is relatively harmless 123 123 -1 239 ± 0.58 a 418.33 ± 2.88 5.23 ± 0.15 6.36 ± 0.09 236.20 ± 3.49 a 344.02 ± 1.49 a 4.23 ± 0.18 a 6.47 ± 0.07 237.01 ± 3.02 a 348.93 ± 2.59 a a ± 0.08 4.27 ± 0.19 a 6.46 ab Mean values with same superscript did not show any significant difference (P [ 0.05) Alkalinity (mg l ) -1 Hardness (mg l ) -1 Free CO2 (mg l ) DO (mg l ) b 7.34 ± 0.01 7.33 ± 0.01 7.38 ± 0.01 pH -1 1.60a ± 0.08 1.61 ± 0.00 Salinity (ppt) a 1.61a ± 0.08 26.30a ± 0.22 a 3.2 26.31a ± 0.24 3.2 T1 25 C Temperature (°C) Chemical composition of raw water at the beginning of the experiment Flow rate (l min-1) Parameters 237.67 ± 2.93 a a ± 0.94 ± 0.11 349.27 ± 2.58 4.78 ab 6.22 ab a 7.33 ± 0.01 a 1.61a ± 0.08 26.25a ± 0.23 1.5 T2 238.20 ± 2.98 a 349.93 ± 2.43 a 5.04 ± 1.07 b 6.12 ± 0.14 a 7.34 ± 0.01 a 1.61a ± 0.08 26.30a ± 0.21 1.0 T3 238.20 ± 3.00 a a ± 0.26 ± 0.12 349.87 ± 2.67 4.87 ab 6.24 ab 7.34 ± 0.01 a 1.60a ± 0.08 26.23a ± 0.22 1.5 S1 Table Mean of physicochemical parameters and nutrients in fish tank after the experimental period of 45 days for different treatments 238.10a ± 2.90 350.53a ± 2.52 5.00b ± 0.22 6.18ab ± 0.11 7.34a ± 0.01 1.60a ± 0.08 26.26a ± 0.25 1.0 S2 Aquacult Int Aquacult Int Fig Variation in dissolved oxygen concentration throughout the experimental period in treatments Fig Variation in NH4? concentration throughout the experimental period in treatments and is also the preferred form of nitrogen for growing higher plants (Rakocy et al 2006) NO3–N concentrations were detected in the favorable ranges in all treatments and control for koi carp culture (Fig 4) Nitrate–N is not generally of great concern to cultivable organisms, and it has also been proved that aquatic species can tolerate extremely high concentrations ([25 mg l-1) of nitrate–N (Ebeling et al 1993) Poxton and Allouse (1982) recommended that NO3–N concentrations should not exceed 50 mg l-1 in waters used for the culture of fish and shellfish In the present study, mean phosphate levels were lower in the treatments T1, T2, and T3, because of the phosphate utilization by spinach plant as compared to control and S1, S2 (Table 6; Fig 5) Food residues and fecal matter are the major sources of phosphorus in aquaculture effluent The mean value of potassium concentration varied significantly (P \ 0.05) between treatments The potassium level was higher in treatments without plant groups as compared 123 123 -1 0.12 ± 0.00 0.08 ± 0.01 323.17 ± 1.69 52.0 ± 0.58 127.83 ± 0.44 18.63 ± 0.07 – 0.13 ± 0.00 c 0.06 ± 0.00 b 328.41 ± 3.91 b 51.75 ± 1.08 b 129.70 ± 1.24 b 19.36 ± 0.22 c 2.08b ± 1.08 14.65b ± 1.79 0.07 ± 0.05 a 0.03 ± 0.00 a 321.45 ± 3.63 a 46.40 ± 0.93 a 127.30 ± 1.51 a 15.62 ± 0.43 b 0.53 ± 0.07 a 3.48 ± 0.39 a 0.04a ± 0.01 0.06a ± 0.01 3.2 T1 Mean values with same superscript did not show any significant difference (P [ 0.05) Zinc (mg l ) -1 Iron (mg l ) -1 Sodium (mg l ) -1 Magnesium (mg l ) Calcium (mg l ) -1 Potassium (mg l ) -1 Phosphate (mg l ) -1 Nitrate-–N (mg l ) – – Nitrite-–N (mg l-1) 0.09b ± 0.00 0.12b ± 0.01 -1 3.2 – C Ammonia (mg l-1) Chemical composition of raw water at the beginning of the experiment Flow rate (l min-1) Parameters 0.07 ± 0.01 a 0.03 ± 0.00 a 321.01 ± 4.72 a 45.59 ± 1.17 a 127.32 ± 1.30 a 14.25 ± 0.70 a 0.46 ± 0.07 a 2.57 ± 0.26 a 0.05a ± 0.01 0.04a ± 0.01 1.5 T2 0.07 ± 0.00 a 0.03 ± 0.00 a 319.13 ± 5.47 a 45.89 ± 1.28 a 127.2 ± 1.47 a 15.59 ± 0.43 b 0.49 ± 0.08 a 2.78 ± 0.30 a 0.05a ± 0.09 0.04a ± 0.11 1.0 T3 ± 0.15 0.10 ± 0.01 b 0.06 ± 0.00 b 329.30 ± 3.74 b 52.01 ± 1.41 b b 130.32 ± 1.03 c 19.38 ± 0.86 0.98 ab 12.22 ± 1.89 b 0.08b ± 0.00 0.14bc ± 0.01 1.5 S1 Table Mean of physicochemical parameters and nutrients in fish tank after the experimental period of 45 days for different treatments 0.12c ± 0.01 0.05b ± 0.00 334.63c ± 2.72 52.61b ± 1.37 130.63b ± 1.05 19.68c ± 0.28 1.04ab ± 0.16 12.38b ± 1.89 0.08b ± 0.01 0.15c ± 0.01 1.0 S2 Aquacult Int Aquacult Int Fig Variation in NO3 concentration throughout the experimental period in treatments Fig Variation in phosphorus concentration throughout the experimental period in treatments to treatments with plants The highest level of potassium was observed in S2 (19.68 ± 0.28), whereas lowest level was observed in T2 (14.25 ± 0.70) (Table 6) Potassium levels were higher in the treatments without plants Uptake of potassium in plants was affected by the presence of higher Na? levels, which will interfere with the uptake of K? and Ca?2 (Rakocy et al 2006) It was observed that mean value of calcium showed significant difference (P \ 0.05) between treatments and control The mean value of magnesium showed significant difference (P \ 0.05) between treatments and control The higher concentration of calcium and magnesium, due to water used for experiment, was hard The mean value of sodium varied significantly (P \ 0.05) between treatments and control (Table 6), and the 123 Aquacult Int Fig Percentage of nutrient removal after experimental period of 45 days in different treatments concentration of sodium was high because the source of groundwater borewell was located near the Versova coast; this was the possible reason for higher sodium levels in water The mean value of iron in treatments and control showed very negligible variation, and it was ranged between 0.02 and 0.06 mg l-1 It was observed that the mean value of zinc on whole showed significant difference (P \ 0.05) among treatments and control (Table 6) In the present study, iron and zinc were not supplemented so this was the possible reason for negligible concentration of Fe and Zn Percentage of nutrient removal at different flow rates All the treatments T1 (3.2 l min-1), T2 (1.5 l min-1), and T3 (1 l min-1) effectively removed nitrate in the range of 77.2–78.65 % (Fig 6); this indicates that all the treatments efficiently remove nitrate from the polluted aquaculture wastewater Similarly, Ghaly et al (2005) examined the use of hydroponically grown barley for the removal of NO3–N from aquaculture wastewater and reported that NO3–N reductions range from 54.7 to 91.0 % Lennard and Leonard (2006) reported 90.9 % removal of nitrate using gravel bed as media for lettuce production Phosphate removal also showed no significant difference among the treatments, and phosphate removed was in the range of 47.04–55.06 % (Fig 6) Similarly, Lin et al (2002) reported that construction of wetlands system receiving aquaculture effluent effectively removed 32–71 % phosphate Ghaly et al (2005) examined the use of hydroponically grown barley for the removal of PO4–P from aquaculture wastewater and reported 91.8–93.6 % PO4–P removal Clarkson and Lane (1991) evaluated the use of the nutrient film technique for PO4–P removal from aquarium wastewater and observed the reduction of PO34–P from 4.4 to 0.3 mg l-1 using barley in a period of weeks Potassium concentration showed significant difference between the treatments (Fig 6) The percentage removal of potassium was studied at the end of the experiment, which showed 22.85–29.16 %, whereas Ghaly et al (2005) examined the use of hydroponically grown barley for the removal of potassium from aquaculture wastewater and reported potassium reductions ranging from 99.6 to 99.8 % Dontje and Clanton (1999) reported 25–71 % potassium removal in recirculating aquaculture systems using cattails, reed canary grass, and tomatoes grown in sand beds Mant et al (2003) achieved 24.9 % potassium removal using Salix viminalis grown in gravel hydroponic system to treat primary settled sewage In the present study, potassium was not supplemented from outside 123 Aquacult Int source to the aquaponic system Groundwater used for the study contained 18.6 mg l-1 of potassium Conclusion From the study, it was concluded that all the flow rates were found to be effective in terms of fish growth, plant growth, and nutrient removal, but flow rate of 1.5 l min-1 was observed as more effective for better growth of spinach (height gain and yield) and koi carp (percentage weight gain) 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