Water quality parameters
Table 2 summarizes the water quality parameters observed in the study. The water quality parameters in the BFT treatments were similar, and analysis of variance revealed that there were significant differences between treatment groups for dissolved oxygen (DO), NO2-N, NO3-N, and alkalinity (P < 0.05). All the observed parameters remained similar to those found in conventional hatchery systems with high levels of water exchange. The BFT hatchery systems showed similar results with the addition of carbon sources to P. vannamei, as reported by de Lorenzo et al. (2016a).
In shrimp hatchery systems, it is crucial to manage water quality parameters carefully to ensure the optimal survival and viability of the shrimp. Any variations in these parameters beyond a certain range can have a severe impact on production and result in significant economic losses (Mohanty et al., 2018). Temperature is one of the most important factors influencing physiological responses in organisms, such as respiration, metabolism, growth, and reproduction (Zweig et al., 1999). Cultured shrimp grow best at temperatures ranging from 24 to 32°C (González et al., 2010). During the study, the average temperature ranged from 27°C to 29°C, which was the optimal temperature for all the treatments. Well-maintained aeration for a sufficient supply of DO is necessary for shrimp and for the formation of biofloc (Verdegem et al., 2023). The lethal DO concentration for P. vannamei has been reported to be 1.0 ppm (Hopkins et al., 1991). The DO levels ranged from 5.30 to 6.24 mg L-1 in all the tanks. The lower pH values were possibly a result of high respiration rates by a large number of microorganisms, which may have increased carbon dioxide concentrations. The permissible pH limit for P. vannamei is 7.5 to 8.5 (Wang et al., 2004). The pH was significantly lower in the BFT, ranging from 7.54 to 7.83, than in the control (8.05). Similarly, the TAN levels were significantly lower (0.69 to 0.78 mg L-1) than those in the control (1.07 mg L-1). These lower levels may be caused by the inclusion of carbon sources. However, the mean values of pH and TAN in the BFT treatments remained at optimum levels throughout the experiment (Panigrahi et al., 2019).
Ammonia (NH3-N) and nitrite (NO2-N) are highly toxic to cultured shrimp. High nitrite concentrations have been shown to significantly impact the circulatory and immune systems of aquatic organisms (Schuler, 2008). The concentration of NH3-N ranged from 0.12 to 0.36 mg L-1. The NH3-N was significantly lower in the BFT (0.12 mg L-1) than in the control (0.36 mg L-1). The levels of NO2-N ranged from 0.06 to 1.53 mg L-1. The lowest concentrations were observed in the BFT (0.06 mg L-1), while the highest were found in the control treatment (1.53 mg L-1), which is unfavorable for optimal culture conditions (Kavitha et al., 2017). For a successful P. vannamei culture, the optimal NO2-N concentration is <1.0 mg L-1 (Kirchman, 1994). Nitrate (NO3-N) is an inorganic nitrogen compound formed at the end of the nitrification process. The concentration of nitrate is usually greater than that of ammonia and nitrite (Robles‐Porchas et al., 2020). High levels of nitrate have been shown to affect the osmoregulation and oxygen transport of cultured aquatic species (Valencia-Castañeda et al., 2020). In the BFT treatments, the observed nitrate values ranged from 1.94 to 2.05 mg L-1, lower than those in the control groups, which had a value of 2.77 mg L-1. These results for nitrate are similar to those reported by Furtado et al. (2015). The relatively stable concentrations of NH3-N, NO2-N, and NO3-N in the BFT treatments may be attributed to effective nitrification processes. Alkalinity, which is the buffering capacity of water, can significantly impact primary productivity (Boyd et al., 2016). In the present investigation, the alkalinity of the BFT ranged from 127.08–128.17 mg L-1, which was significantly greater than that of the control (91.38 mg L-1).
Table 2. Water quality parameters of P. vannamei between the M1 and PL10 phases
|
Parameter
|
Biofloc treatments
|
Control
|
P value
|
|
Fructose
|
Lactose
|
Dextrose
|
|
Temperature (°C)
|
28.34 ± 0.46a
|
29.16 ± 0.33ab
|
28.80 ± 0.33ab
|
29.63 ± 0.13b
|
0.114
|
|
DO (mg L-1)
|
5.81 ± 0.09ab
|
5.96 ± 0.09c
|
6.24 ± 0.32c
|
5.30 ± 0.10a
|
0.032
|
|
Salinity (g L-1)
|
32.05 ± 0.03a
|
32.27 ± 0.18a
|
32.11 ± 0.06a
|
32.29 ± 0.10a
|
0.375
|
|
pH
|
7.54 ± 0.20a
|
7.83 ± 0.14a
|
7.70 ± 0.15a
|
8.05 ± 0.29a
|
0.401
|
|
TAN (mg L-1)
|
0.78 ± 0.04a
|
0.69 ± 0.02a
|
0.72 ± 0.02a
|
1.07 ± 0.34a
|
0.434
|
|
NH3-N (mg L-1)
|
0.18 ± 0.13a
|
0.12 ± 0.02a
|
0.23 ± 0.17a
|
0.36 ± 0.03a
|
0.511
|
|
NO2-N (mg L-1)
|
0.13 ± 0.06a
|
0.16 ± 0.10a
|
0.06 ± 0.04b
|
1.53 ± 0.17a
|
<0.001
|
|
NO3-N (mg L-1)
|
1.94 ± 0.11b
|
2.05 ± 0.04b
|
2.00 ± 0.07b
|
2.77 ± 0.14a
|
<0.001
|
|
Alkalinity (mg L-1)
|
127.92 ± 1.00b
|
128.17 ± 0.27b
|
127.08 ± 0.58b
|
91.38 ± 0.57a
|
<0.001
|
All the values are the means ± SEs (standard errors) of three replicate analyses.
Data with different superscript letters in the same row are significantly different (P < 0.05).
Biofloc volume
The volume of biofloc increased gradually in all treatments over time (Figure 1); however, the greatest floc volume was observed for dextrose (1.62 ml L-1), followed by fructose (1.12 ml L-1) and lactose (0.84 ml L-1). Similar levels of floc volume were reported by Panigrahi et al. (2019). However, the lowest floc volume could be because lactose, being a disaccharide, is harder to break down than monosaccharides such as dextrose and fructose, resulting in less floc. Compared to fructose, dextrose is derived from simple starch, which makes it easier to break down and thus forms flocs more easily.
The percentages of the survival rates for different treatments are presented in Table 3. The highest survival rate for PL1 was observed for dextrose (93%), followed by fructose (88.67%) and lactose (86.33%), while the lowest survival rate was in the control group (79.33%) (P > 0.05). For PL5 and PL10, the trends were similar; the survival rates were 90.67%, 85.67%, 78.33%, and 66.67% for the dextrose, fructose, lactose, and control treatments, respectively. One-way ANOVA revealed that the mean percentages of PL5 and PL10 were not significantly different (P < 0.05) among the treatments.
In biofloc technology, maintaining a suitable carbon-nitrogen ratio is crucial. The choice of carbohydrate source is one of the main factors since different carbon sources have different effects on cultured species (Crab et al., 2010; Wei et al., 2016; Tinh et al., 2021). In this study, M1 to PL10 were reared under three treatments with different carbon sources—fructose, lactose, and dextrose—at a ratio of 15:1, and the control treatment without the addition of a carbohydrate source. The average survival rate was significantly greater in the BFT treatment group (71% to 86%) than in the control group (53%). Similar studies have shown that the survival of shrimp in BFTs ranges from 80% to 100% of that of control shrimp (Panjaitan, 2011; Anand et al., 2013; Xu et al., 2016). The current results showed higher survival levels than those of de Lorenzo et al. (2016) under the carbon source dextrose, which may be due to the lower stocking density of larvae adapted to the present study. The overall survival in all biofloc-treated groups surpassed the rate appropriate for the species (70%, FAO, 2003) and that appropriate for the experimental hatcheries (Aranguren et al., 2006; Louis et al., 2006; de Lorenzo et al., 2016a, 2016b). Based on these results, among all the carbon sources used, fertilization with dextrose can be efficiently maintained in the hatchery system.
Table 3. Survival performance of P. vannamei between the M1 and PL10 stages
|
P. vannamei larval stage
|
Treatments (%)
|
P value
|
|
Fructose
|
Lactose
|
Dextrose
|
Control
|
|
M1 Stocked
|
100 nos L-1
|
100 nos L-1
|
100 nos L-1
|
100 nos L-1
|
|
PL1
|
88.67 ± 2.33ab
|
86.33 ± 5.81ab
|
93.00 ± 3.61b
|
79.33 ± 2.33a
|
0.158
|
|
PL5
|
85.67 ± 2.96b
|
78.33 ± 4.33ab
|
90.67 ± 4.37b
|
66.67 ± 4.41a
|
0.015
|
|
PL10
|
80.33 ± 4.70bc
|
71.33 ± 2.40b
|
86.33 ± 3.84c
|
53.71 ± 3.39a
|
0.001
|
All the values are the means ± SEs (standard errors) of three replicate analyses.
Data with different superscript letters in the same row are significantly different (P < 0.05).