Comparison of growth and survival rates of A. testudineus across different RAS systems
In the comparison of
A.
testudineus across three systems, the advanced RAS showed significantly higher weight (22.34 g) compared to the low-cost RAS (18.63 g) and FRP tanks (9.11 g) (Table 1). Weight in the advanced RAS increased markedly from 1.95 g to 60 g (Fig 3). Similarly, fish length was greater in the advanced RAS (9.38 cm) than in the low-cost RAS (9.12 cm) and FRP tanks (7.25 cm) (Table 1). Studies have shown similar trends, with higher growth rates in larger RAS than in small size RAS for Nile tilapia (330.82 g vs. 138.84 g)
(Martins et al., 2009) and increased length in semi-intensive systems (
Chakraborty, 2016). In a related study, Vietnamese koi had greater final length (14.40 cm) compared to Thai koi (13.50 cm) in Bangladesh
(Nabi et al., 2020).
In the study, the advanced RAS system showed the highest per cent increment in
A.
testudineus weight (78.68%), followed by the low-cost RAS (70.35%), both of which were statistically comparable. The FRP tanks had the lowest weight increase (59.73%). Similarly, the highest per cent increment in length (19.24%) was observed in the advanced RAS, with decreases to 18.14% in the low-cost RAS and 16.51% in the FRP tanks.
Patra (1994) also found that a 40% protein diet led to the highest weight gain in
A.
testudineus, with a negative correlation to FCR and PER. Survival rates for
A.
testudenius varied significantly by tank type: 100% in low-cost RAS, 97.61% in advanced RAS and 86.77% in regular FRP tanks (control).
Kohinoor et al., (2016) reported 89% survival for Vietnamese Koi versus 85% for Thai Koi.
Martins et al., (2009) found 100% survival in
O.
niloticus in middle and high accumulation RAS systems.
Daily weight gain (ADG) and specific growth rate (SGR) in A. testudenius
The highest daily weight gain (0.69 g) in
A.
testudineus was observed in advanced RAS, followed by low-cost RAS (0.56 g) and FRP tanks (0.24 g). The specific growth rate (SGR) was significantly higher in advanced RAS (4.08%) compared to low-cost RAS (3.74%) and FRP tanks (3.17%) (CD=0.38; p=0.05) (Table 1).
Mota et al., (2018) reported increased growth in turbot under high pH.
Ridha and Cruz (2001) found higher weight gain and daily growth in
O.
niloticus with media block biofilters (267.4 g, 1.18 g/day) compared to biofilter chips (264.1 g, 1.16 g/day).
Chakraborty (2016) observed higher average daily growth (1.77 g) and SGR (5.18%) in semi-intensive systems compared to control systems (1.20 g, 4.79%).
Kristan et al., (2018) noted a higher SGR for
Ctenopharyngodon idella in RAS (0.49%) versus ponds (0.12%).
Szczepkowski et al., (2011) found that pikeperch in larger fish groups had the highest body length (34 mm) but the lowest SGR (9.2% /day), while smaller fish groups had the highest SGR (10.1% /day). In a fresh water-based RAS,
Moses et al., (2024) reported a maximum weight gain and SGR in Asian seabass when supplemented with Vitamin C at 0.8% inclusion.
Protein efficiency ratio (PER) in different systems and feed conversion ratio (FCR) by A. testudenius
A study on the effect of different systems on PER found that FRP tanks had a significantly lower PER (1.88) compared to low-cost RAS (2.50) and advanced RAS (2.70), with the latter two being statistically similar (Table 1). Advanced RAS also showed the lowest FCR (1.09), which was statistically similar to low-cost RAS (1.27), while FRP tanks had a significantly higher FCR (2.36) for
A.
testudenius (Table 1).
Watanabe et al., (1993) found that the highest daily weight gain of juvenile
O.
niloticus occurred at 18-32
oC (0.30 g/day) and the lowest FCR (1.27) at 32oC.
Kohinoor et al., (2016) reported that Vietnamese koi exhibited higher weight (138.91 g), specific growth rate (SGR) (4.06%) and lower FCR (1.58) compared to Thai Koi (89 g, 3.70%, 1.60).
Water quality parameters in different systems
Temperature, pH and dissolved oxygen
The study found that water temperature was highest in advanced RAS (29.02
oC), followed by low-cost RAS (28.66
oC) and FRP tanks (28.46
oC), aligning with
Nabi et al., (2020), who reported a suitable temperature range (29.11-30.88
oC) for Vietnamese Koi growth. Optimal temperatures for red tilapia and juvenile yellowtail kingfish in RAS were 27
oC
(Watanabe et al., 1993) and 26.5
oC
(Abbink et al., 2012), respectively. FRP tanks had the highest pH (8.25), followed by low-cost RAS (7.82) and advanced RAS (7.56). Optimal pH for different species in RAS varied, with 7.90 for marine finfish
(Gopalakrishnan et al., 2019), 7.16-7.85 for yellowtail kingfish
(Abbink et al., 2012) and 7.39-7.75 for
A.
testudenius (Nabi et al., 2020). Dissolved oxygen was lowest in FRP tanks (5.10 mg/l) and highest in low-cost RAS (5.92 mg/l), with optimal levels for other species ranging from 6.07-7.74 mg/l for yellowtail kingfish
(Abbink et al., 2012) to 4.72 mg/l for marine fish broodstocks
(Gopalakrishnan et al., 2019).
Total alkalinity and total hardness
The study showed that total alkalinity was lowest in advanced RAS (87.59 mg/l), followed by low-cost RAS (92.36 mg/l) and FRP tanks (179.05 mg/l). Although no specific data on alkalinity’s effect on
A.
testudenius are available, climbing perch showed better growth in systems with water hardness between 117.14 and 127.11 mg/l (
Chakraborty and Haque, 2014).
Martins et al., (2009) reported alkalinity levels of 72.4, 46.15 and 130.75 mg/l for
O.
niloticus in high, middle and low water exchange RAS systems.
Summerfelt et al., (2015) found that varying alkalinity levels (10, 70 and 200 mg/l as CaCO
3) affected Atlantic salmon health in recirculating systems, with low alkalinity (10 mg/l) leading to CO2-related health issues. The optimal alkalinity in a low-cost RAS for marine finfish broodstock development was 108.75 mg/l
(Gopalakrishnan et al., 2019). Water hardness was lowest in FRP tanks (118.31 mg/l) compared to low-cost RAS (121.28 mg/l) and advanced RAS (123.72 mg/l).
Davidson et al., (2017) observed water hardness levels of 289 and 306 mg/l for post-smolt Atlantic salmon under different NO
3-N treatments in freshwater RAS.
Ammonia, nitrite and nitrate content
The study found that ammonia levels were significantly lower in low-cost RAS (0.009 mg/l) compared to advanced RAS (0.042 mg/l) and FRP tanks (0.286 mg/l), with ANOVA revealing lower ranges in low-cost (0 to 0.100 mg/l) and advanced RAS (0 to 0.267 mg/l) than in FRP tanks (0 to 0.9 mg/l). For
O.
niloticus in RAS, ammonia levels varied from 0.07 to 0.36 mg/l
(Martins et al., 2009), 2.93 mg/l
(Soto-Zarazua et al., 2010) and 0.089 to 0.094 mg/l
(Davidson et al., 2017). Gopalakrishnan et al., (2018) found unionized ammonia at 0.001 mg/l in low-cost RAS. Nitrite content was also lowest in low-cost RAS (0.008 mg/l), followed by advanced RAS (0.067 mg/l) and FRP tanks (0.134 mg/l), ranging from 0 to 0.156 mg/l. Reported nitrite levels were 0.59 to 0.72 mg/l in simple recirculating systems with
O.
niloticus (
Ridha and Cruz, 2001) and 0.007 mg/l in low-cost RAS for marine fish broodstock
(Gopalakrishnan et al., 2019). Nitrate levels were lowest in low-cost RAS (1.73 mg/l) compared to advanced RAS (3.40 mg/l) and FRP tanks (7.83 mg/l). Nitrate ranged from 0.11 to 5.8 mg/l
(Soto-Zarazua et al., 2010) to 63.02 mg/l
(Martins et al., 2009), with a maximum of 1.38 mg/l in semi-intensive systems for
A.
testudineus (
Chakraborty, 2016) and 90 to 125.9 mg/l for turbot in RAS
(Mota et al., 2018).
Total suspended solids and total dissolved solids
The study found that low-cost RAS was most efficient in removing total suspended solids (TSS) at 20.00 mg/l, followed by advanced RAS (58.21 mg/l), while FRP tanks were least effective (158.74 mg/l) (Table 2). This trend was consistent across all sampling weeks. In comparison,
Zhang et al., (2011) reported TSS levels of 68.40 mg/l in a primary biological pond, 53.20 mg/l at the inlet and 9.30 mg/l at the outlet of a filtration system in an integrated recirculating aquaculture setup. Total dissolved solids (TDS) were lowest in FRP tanks (132.40 ppm), followed by advanced RAS (192.67 ppm) and highest in low-cost RAS (241.81 ppm), with significant interactions between sampling weeks and systems. During the culture of post-smolt Atlantic salmon,
Davidson et al., (2017) reported a maximum TSS level of 1.23 mg/l in freshwater RAS.
Salinity and conductivity
The study showed that salinity levels were significantly lower in FRP tanks (241.84 ppm) compared to low-cost RAS (552.67 ppm) and advanced RAS (331.40 ppm) (Table 2).
Mota et al., (2018) reported stable salinity levels in recirculating aquaculture systems, while
Mojer et al., (2021) observed salinity ranging from 3.2-8.2 PSU in earthen ponds and 0.60-0.67 PSU in plastic RAS tanks. Conductivity followed a similar trend, with FRP tanks showing the lowest levels (385.87 mS/cm), followed by advanced RAS (499.69 mS/cm) and low-cost RAS (602.74 mS/cm) (Table 2).
Martins et al., (2009) found the highest conductivity in high water exchange RAS (1404.88 mS/cm) and the lowest in low water exchange systems (744.21 ìS/cm).
Davidson et al., (2017) recorded a maximum conductivity of 1322 mS/cm in freshwater RAS during the culture of post-smolt Atlantic salmon.