Heterotrophic versus mixed BFT system: Impacts on water use,suspended solids production and growth performance of Litopenaeus vannamei

The Biofloc Technology System (BFT) is characterized by stimulating the development of a microbial community that acts mainly in the maintenance of water quality but also promotes other benefits such as increased productivity, biosafety and serves as a supplementary source of food for reared animals. Two main groups of bacteria are involved in nitrogen removal in this system: heterotrophic bacteria and autotrophic nitrifying bacteria, present in the aggregates. Different fertilization techniques can be used for the formation and maintenance of bioflocs, depending on which group of bacteria the predominance is preferred. This study aimed to analyze the effect of different organic fertilization techniques on the bioflocs establishment, amount of water used, the production of suspended solids and the growth performance of Litopenaeus vannamei reared in the BFT System. Shrimp juveniles were stocked in 150-liter tanks at a stocking density of 300 shrimps/m³. Three treatments (in triplicate) were tested using different fertilization techniques: 1) without supplementary organic fertilization; 2) organic fertilization according to nominal ammonia reading (heterotrophic/chemoautotrophic = “mixed” system) and 3) organic fertilization according to estimated ammonia production (heterotrophic). The temperature, salinity, dissolved oxygen, pH, ammonia, nitrite, nitrate, alkalinity and total suspended solids (TSS) of the water were monitored. The water quality parameters were influenced by the treatments with differences found in the concentrations of ammonia, nitrite, nitrate, pH, alkalinity and TSS. Ammonia levels were higher in control treatment since no organic fertilization was performed. Nitrite levels were lower in heterotrophic system since the nitrifying pathway was suppressed due to daily fertilization, also resulting in lower nitrate levels. There were significant differences in the growth performance parameters, with the highest final weight and yield, as well as the lowest FCR, found in the mixed treatment. There were no significant differences among survival. The mixed system treatment used less water during production cycle compared to other treatments while the volume of solids removed was almost four times greater in the heterotrophic treatment compared to the others. These results show that adopting a mixed heterotrophic/chemoautotrophic biofloc system improves shrimp growth performance, optimize water use and decrease solids production.     

The effect of different alkalinity levels on <Emphasis Type="Italic">Litopenaeus vannamei</Emphasis> reared with biofloc technology (BFT)

The initial stages of rearing marine shrimp using biofloc technology (BFT) involve the biofloc formation process. At the same time, there is an increase in the levels of total suspended solids and a decrease in alkalinity and pH. This reduction of alkalinity and pH occurs due to the consumption of inorganic carbon by the autotrophic bacteria present in the bioflocs and biofilms. The aim of this study was to evaluate the effects of different alkalinities on water quality and the zootechnical performance of the marine shrimp Litopenaeus vannamei in a BFT system. The experiment consisted of four treatments, with three replicates each: 75, 150, 225 and 300 mg CaCO₃/L. To maintain the alkalinity at the established level, sodium bicarbonate was applied. For the experiments, twelve experimental units (area = 0.20 m²) with an effective volume of 50 L were stocked with 30 juvenile L. vannamei (0.20 ± 0.07 g), to achieve a stocking density of 150 shrimps/m² and were maintained for an experimental period of 49 days. The 75 treatment presented the highest levels of ammonia and nitrite throughout the study, compared to the 150 and 300 treatments. The results showed that higher alkalinity favors biofloc formation and the establishment of nitrifying bacteria.     

Nursery performance of Pacific white shrimp (Litopenaeus vannamei Boone, 1931) cultivated in a biofloc system: the effect of adding different carbon sources

Effect of different carbon sources on nursery performance of Pacific white shrimp (Litopenaeus vannamei) cultivated in biofloc system was investigated. Shrimp postlarvae (98.47 ± 8.6 mg) were fed for 32 days in tanks with water volume of 130 L and density of 1 individual L^?1. One control treatment and four biofloc treatments (BFT1, BFT2, BFT3 and BFT4) with adding different carbon sources including molasses, starch, wheat flour and mixture of them, respectively, were considered at equal weight ratios. According to the results, salinity, dissolved oxygen and pH were not significantly different among the biofloc treatments (P > 0.05). Maximum pH (8.27) and maximum dissolved oxygen (6.35 mg L^?1) were recorded in the control. Maximum (0.43 mg L^?1) and minimum (0.09 mg L^?1) ammonia were recorded in the control and BFT2, respectively (P < 0.05). Using simple carbohydrates (molasses and starch) lowered the ammonia concentration significantly. The highest increase in body weight (1640.43 ± 231.28 mg), growth rate, specific growth rate (8.97 ± 0.42% per day) and biomass (190.29 ± 26.83 mg) were found in BFT1 and the highest survival (90 ± 0.77%) was found in BFT4. The highest feed conversion (1.52 ± 0.23) and the lowest feed efficiency (66.81 ± 7.95) were observed in the control (P < 0.05). The proximate composition analysis revealed an increase in lipid and ash in biofloc treatments. Results indicated that using biofloc technology with zero‐water exchange system and adding carbon sources could help to recycle waste and improve the water quality. Moreover, the type of carbonaceous organic matter as a substrate for heterotrophic bacteria would be effective in degradation and metabolization of ammonia and nitrite.     

Effect of different biofloc system on water quality,biofloc composition and growth performance in Litopenaeus vannamei (Boone, 1931)

The experiment was conducted with three biofloc treatments and one control in triplicate in 500 L capacity indoor tanks. Biofloc tanks, filled with 350 L of water, were fed with sugarcane molasses (BFT_S), tapioca flour (BFT_T), wheat flour (BFT_W) and clean water as control without biofloc and allowed to stand for 30 days. The postlarvae of Litopenaeus vannamei (Boone, 1931) with an Average body weight of 0.15 ± 0.02 g were stocked at the rate of 130 PL m^?2 and cultured for a period of 60 days fed with pelleted feed at the rate of 1.5% of biomass. The total suspended solids (TSS) level was maintained at around 500 mg L^?1 in BFT tanks. The addition of carbohydrate significantly reduced the total ammonia‐N (TAN), nitrite‐N and nitrate‐N in water and it significantly increased the total heterotrophic bacteria (THB) population in the biofloc treatments. There was a significant difference in the final average body weight (8.49 ± 0.09 g) in the wheat flour treatment (BFT_W) than those treatment and control group of the shrimp. Survival of the shrimps was not affected by the treatments and ranged between 82.02% and 90.3%. The proximate and chemical composition of biofloc and proximate composition of the shrimp was significantly different between the biofloc treatments and control. Tintinids, ciliates, copepods, cyanobacteria and nematodes were identified in all the biofloc treatments, nematodes being the most dominant group of organisms in the biofloc. It could be concluded that the use of wheat flour (BFT_W) effectively enhanced the biofloc production and contributed towards better water quality which resulted in higher production of shrimp.     

Biofloc technology with addition molasses as carbon sources applied to Litopenaeus vannamei juvenile production under the effects of different C/N ratios

The current study was conducted to evaluate the effects of increasing carbon to nitrogen (C/N) ratios on water quality, growth performance, and body composition of Litopenaeus vannamei juveniles. Shrimp with initial average weight of 2.50?±?0.3 g were cultivated for 35 days in 300-L tanks (160 L of water volume) with a density of 1 g per liter. The experiment was performed in five treatments with three replicates. One control group and four biofloc treatments with different C/N ratio were considered: C/N of 10 (CN10), 14 (CN14), 18 (CN18), and 22 (CN22). Shrimp were fed three times a day, and molasses just was added as a carbon sources to the biofloc treatments after each feeding. According to the results, the lowest amount of dissolved oxygen (5.33 mg L^?1) and pH (7.83) was observed in CN22 treatment, which showed a significant difference with other treatments (P?<?0.05). The highest level of total ammonia nitrogen (1.05 mg L^?1) and nitrite (mg L^?1) were recorded in control group, while the highest total density of heterotrophic bacteria was obtained in CN22 treatment. Growth performance parameters were at the highest level in the CN14 treatment, so the highest amount of final weight (6.88 g), biomass, and survival rate (94.79%) were observed in this treatment. The biochemical composition (protein, lipid, and ash) of the shrimp body and produced biofloc were affected by different C/N ratios, so these parameters were increased by rising of C/N ratio. In general, this study showed that the growth performance and body composition of Pacific white shrimp juveniles and water quality were suitable for rearing in biofloc system with C/N ratio of 14 than other treatments.

     

Biofloc technology application as a food source in a limited water exchange nursery system for pink shrimp Farfantepenaeus brasiliensis (Latreille, 1817)

In a 30‐day experiment, Farfantepenaeus brasiliensis PL₂₅ (25 ± 10 mg; 17.9 ± 1.6 mm) were raised in nine circular floating cages with a stocking density of 1000 shrimp m^?3. Three treatments were evaluated: (1) culture in BFT system plus a commercial feed supply (BFT+CF); (2) culture in BFT system without feed supply (BFT) and (3) culture in clear water with feed supply (control). Post‐larvae (PL) final weight (218.9, 236.5 and 176.0 mg, for BFT+CF, BFT and control respectively), final biomass (17.9, 15.7 and 8.2 g) and weight gain (193.9, 211.5 and 151.0 mg) were similar in the BFT regardless of whether they were fed a commercial diet (P>0.05), but were both significantly higher than the control (P<0.05). Survival (81.5%, 67.0% and 84.8% respectively) and final length did not differ between treatments (P>0.05). The biofloc analysis identified five main microorganism groups: protozoa (ciliate and flagellate), rotifers, cyanobacteria (filamentous and unicellular) and pennate diatoms. Free living bacteria and attached bacteria in bulk were 25.73 ± 8.63 and 0.86 ± 3.17 × 10⁶ mL^?1 respectively. Proximate analysis in the biofloc indicated high levels of crude protein (30.4%). Results confirmed favourable nutritional quality of biofloc, and enhanced growth and production of F. brasiliensis PL in biofloc systems.     

Soybean molasses as an organic carbon source in the farming of Litopenaeus vannamei (Boone, 1931) in a biofloc system

Soybean molasses was evaluated as a partial replacement for sugarcane molasses as a carbon source for biofloc development in the superintensive culture of Pacific white shrimp (Litopenaeus vannamei). A 50‐day study was conducted with juvenile (3.2 g) shrimp stocked in 16 800 L tanks at a stocking density of 250 shrimp m^?3. Control of total ammonia concentration was performed by the addition of combined mixtures of soybean and sugarcane molasses to the culture water. Three different molasses treatments were evaluated using different soybean‐to‐sugarcane molasses ratios: 15–85%, 38–62% and 60–40% respectively. The control group was treated only with sugarcane molasses. Water quality, chlorophyll a concentration, heterotrophic bacterial load, Vibrio spp. concentration and zootechnical indexes were all evaluated. Total ammonia concentration was controlled by heterotrophic and chemotrophic pathways. Biofloc formation, as quantified by measuring the total suspended solids, was not altered. The Vibrio spp. concentration showed a significant reduction in treatments with soybean‐to‐sugarcane molasses ratios of 38–62% and 60–40%. All combined mixtures of soybean and sugarcane molasses could maintain water quality and productivity in the superintensive culture of L. vannamei using the biofloc system. Thus, the potential use of a residue from agroindustry as a carbon source in a biofloc culture is demonstrated.     

Effect of using sodium bicarbonate to adjust the pH to different levels on water quality,the growth and the immune response of shrimp Litopenaeus vannamei reared in zero‐water exchange biofloc‐based culture tanks

The bioflocs technology proved to be a sustainable technique used in zero‐water exchange shrimp culture systems. However, the pH and alkalinity may decrease due to the biofloc formation process and Nitrification. A 48‐day experiment was performed to investigate the effects of different pH (7.1–7.6; 7.6–8.1) conditions on water quality, the growth and the health status of shrimp in biofloc technology (BFT) through using sodium bicarbonate to adjust pH respectively. Two pH treatments and one control were compared: T0 — control, T1 — pH 7.6 — NaHCO₃, T2 — pH 8.1 — NaHCO₃, each treatment consisted of three replicate tanks (90 L water volume) and each replicate stocked with 30 shrimp (equivalent to 333 shrimp m^?3). Significant physical, chemical and biological differences (P < 0.05) were detected among treatments. At the end of the experiment, water quality, the growth and the immune response of shrimp in control were significantly lower (P < 0.05) than the other treatments. Moreover, the T2 treatment had a better performance in these three aspects. The results indicated that it was necessary to adjust the pH and alkalinity in the BFT, and a higher pH as well as alkalinity for shrimp growth and the stability of the BFT were more favourable.     

Short‐term effect of the inoculation of probiotics in mature bioflocs: Water quality parameters and abundance of heterotrophic and ammonia‐oxidizing bacteria

The aim of this study was to evaluate the short‐term effect of probiotic inoculation on the abundance of heterotrophic and ammonia‐oxidizing bacteria in mature biofloc, as well as on total suspended solids (TSS), chlorophyll‐a and nitrogenous compounds in water. A completely randomized design consisting of five treatments (three commercial probiotics, one native consortia and one control) was performed. At the beginning of the experiment (day 1), each treatment was inoculated with the respective probiotic: PondPlus^® (PP), Efinol^® PT (EF) and Epicin^® ponds (EP), native consortia UE, whereas the control was not inoculated. Water parameters and bacterial abundance were evaluated at 0, 2, 4, 6 and 8 days. The addition of probiotics, either native or commercial, did not show any significant effect on the TSS, Chl‐a and colony‐forming unit (CFU) of heterotrophic bacteria when they were added to the systems containing mature biofloc. A significant increase in ammonium oxidizing bacteria was registered with the probiotics PP and EP, although the levels of total ammonia nitrogen, NO₃‐N and NO₂‐N were statistically similar among all treatments. Modifications on most of the parameters measured were associated with the factor of time, rather than the inclusion of probiotics. Results suggest that the bacterial conglomerates in mature stage contain well‐established bacterial communities that are difficult to be affected by the addition of probiotics.     

Moderate salinities enhance growth performance of Nile tilapia (Oreochromis niloticus) fingerlings in the biofloc system

The biofloc technology (BFT) has recently gained attention as an economic and environmentally sustainable system for aquaculture. The use of BFT with salinized water could be used to minimize the negative effects of nitrogenous waste and improve the growth performance of Nile tilapia. This work evaluated the growth performance, survival, gill lesions, and fillet composition of tilapia fingerlings (Oreochromis niloticus) reared during 70 days with different salinities (0, 4, 8, 12, and 16 g/L) in a biofloc previously developed. The results indicated that the use of mature bioflocs alone was sufficient to avoid fingerling mortality due to nitrite peaks. Moreover, the salinized water, especially between 4 and 8 g/L (maximum points around 6 g/L), can be recommended in BFT to improve the growth performance of tilapia in the initial culture phase. The salinity level that was evaluated did not affect fillet composition nor the occurrence of gill lesions. The total ammonia nitrogen concentration was lower in freshwater than in salinized water (p < 0.05). Nitrite peaks in salinities of 12 and 16 g/L appeared later and were higher in comparison to other treatments. Considering minimal water exchange in BFT, the use of salinized water in this system may be environmentally viable.     

The quantity of artificial substrates influences the nitrogen cycle in the biofloc culture system of Litopenaeus vannamei

This study evaluated the influence of different quantities of artificial substrate on water quality and the performance of Litopenaeus vannamei in an integrated biofilm-biofloc culture system. Thus, three treatments were performed: the control, the treatment without the addition of artificial substrate; T200, the treatment with a 200 % increase in the lateral area of the tanks using artificial substrates; and T400, the treatment with a 400 % increase in the lateral area of the tanks using artificial substrates. The study was conducted in nine 800 L tanks over 60 days. The animals were stocked at an initial density of 300 shrimp.m⁻² (equivalent to 500 shrimp m^-3), with an initial weight of 1.27 g (± 0.48). Ammonia concentrations did not differ significantly between treatments (p > 0.05). Increasing the amount of substrate from 200 % to 400 % did not cause significant differences in the nitrite concentrations between these treatments. However, in the control treatment, nitrite remained high (above 20 mg.L^-1) for a long period, negatively affecting shrimp performance. Nitrate was lower in T400, indicating a more dynamic process in the nitrogen cycle when the quantity of artificial substrate increased. Weekly growth rates, final weight, survival, and productivity were higher in the treatments integrating biofilm and biofloc substrates and did not show significant differences between T200 and T400. The results demonstrate the importance of artificial substrates in enhancing the water quality in biofloc culture systems over the long term, mostly in terms of maintaining nitrite concentrations below levels toxic to L. vannamei. The performance of the shrimp and the improved water quality at the end of the study reflected the advantages provided by incorporating artificial substrates in shrimp biofloc culture.     

Zootechnical and physiological responses of whiteleg shrimp (Litopenaeus vannamei) postlarvae reared in bioflocs and subjected to stress conditions during nursery phase

The objective of this study was to assess zootechnical and physiological performance of Litopenaeus vannamei postlarvae (PL) reared in three environments (CW, clear water; B, biofloc; BS, biofloc with artificial substrates) at three stocking densities (300, 600, 900 PL/m³) for 8 weeks. At the end of experimentation, shrimp were subjected to hypoxia, and physiological response was again assessed. During rearing, low levels of total ammonia nitrogen, nitrite (NO₂^?) and nitrate (NO₃^?) were observed in B and BS for 600 and 900 PL/m³. For 300 PL/m³, a slight accumulation of NO₂^? and NO₃^? was detected. For the same stocking density, shrimp reared in B and BS showed significantly higher weights than those grown in CW, except for final weight. No significant differences were observed in survival. The use of biofloc and artificial substrates permitted doubling density from 300 to 600 PL/m³ without affecting growth, survival, feed conversion rate and obtaining twice the biomass. Shrimp grown in B and BS stored a surplus of glycogen and carbohydrates in their hepatopancreas, which probably gave them a better physiological capacity to counteract high‐stocking densities and hypoxia. A tendency of a higher adenylate energetic charge was observed in shrimp maintained in B and BS.     

The effects of artificial substrate and stocking density on Pacific white shrimp (Litopenaeus vannamei) performance and water quality dynamics in high tunnel-based biofloc systems

The use of artificial substrates in shrimp aquaculture may allow for production of shrimp at increased densities while providing a growth medium for microbes that assist with water quality processes and provide supplemental nutrition for shrimp. Greenhouse-based shrimp production systems can extend the shrimp production season in temperate climates while conserving water and energy. For this study, we evaluated the effects of providing extra substrate and shrimp density on water quality and shrimp production in greenhouse-based biofloc systems. Four 11-m³, wood framed, and rubber-lined tanks were constructed in each of four high tunnel greenhouses (for a total of 16 tanks). Four treatments were evaluated: high-density stocking with substrate (HDS), high-density stocking with no substrate (HDNS), low-density stocking with substrate (LDS), and low-density stocking with no substrate (LDNS). Each treatment was randomly assigned to one tank in each tunnel to block for location. No artificial heat was used, and shrimp were grown for 120 days. High-density systems were stocked at 200 shrimp/m³ while low-density tanks had 100 shrimp/m³. Adding substrate increased total in-tank surface area by 13.4%. The addition of substrate had no significant effect on any shrimp production or standard water quality parameters. Shrimp had significantly greater final weight, faster growth rate, and lower feed conversion rate in low-density treatments (P ≤ 0.02 for all). Total shrimp biomass production was significantly higher in high-density treatments (HD: 4.0 kg/m³; LD: 2.3 kg/m³; P < 0.05). There were no significant differences in survival between densities (HD: 91.3%; LD: 94.5%; P = 0.43). Peak and overall mean nitrite levels were significantly higher in high-density treatments compared to low-density treatments. Dissolved oxygen levels and pH over the course of the study were significantly lower in high-density treatments, likely due to increased respiration rates in the water column. This project shows the feasibility of shrimp production in temperate climates with no artificial heat using high tunnel greenhouses, few impacts of added substrate on shrimp production, and increased shrimp density can result in much larger harvests with few negative impacts on production metrics.     

Nursery of young Litopenaeus vannamei post-larvae reared in biofloc- and microalgae-based systems

A 13-day nursery trial was conducted to evaluate the performance of young Litopenaeus vannamei post-larvae (from PL₆ to PL₁₈) reared in both biofloc and microalgae-based systems at a stocking density of 67 PLs L⁻¹. The effects of different concentrations of total suspended solids (TSS) on PL performance were also evaluated. One experimental group was reared in a conventional microalgae-based system with daily water exchange and daily addition of microalgae (herein called microalgae treatment). The other two experimental groups were reared using biofloc technology (BFT) with daily dextrose addition and no water exchange, but in the “Biofloc-500” treatment, TSS were maintained at around 500 mg L⁻¹, while in the “Biofloc-700” treatment, TSS were maintained at around 700 mg L⁻¹. Water quality variables remained within the appropriate range for larval culture. In microalgae treatment, ammonia control was likely associated with its assimilation into microalgae biomass and daily water exchange. In biofloc tanks, however, the addition of dextrose stimulated the production of bacterial biomass from ammonia. This system required only 12.9% of the water used by the microalgae treatment since water was not exchanged during the culture. The nursery of young PLs resulted in similar (P > 0.05) performance in all treatments: survival >94%, PL length ∼ 11.5 mm, and PL dry weight ∼ 1.2 mg. In addition, the salinity stress test (>90.0%) was not significantly different among treatments. Our results indicate that BFT can be as effective as the microalgae-based system for the nursery of young L. vannamei post-larvae. We also found that post-larvae performance was similar (P > 0.05) between biofloc treatments, indicating that organisms can tolerate environments with large quantities of solids.     

Effect of different total suspended solids levels on a Litopenaeus vannamei (Boone, 1931) BFT culture system during biofloc formation

In a Biofloc Technology System (BFT), there is constant biofloc formation and suspended solids accumulation, leading to effects on water quality parameters that may affect the growth performance of cultured shrimp. This study aimed to analyse during biofloc formation the effect of different total suspended solids (TSS) levels on water quality and the growth performance of Litopenaeus vannamei shrimp in a BFT system. A 42‐day trial was conducted with treatments of three ranges of TSS: 100–300 mg L^?1 as low (TL), 300–600 as medium (TM) and 600–1000 as high (TH). The initial concentrations of 100 (TL), 300 (TM) and 600 mg L^?1 (TH) were achieved by fertilization before starting the experiment. Litopenaeus  vannamei juveniles with an average weight of 4.54 ± 1.19 g were stocked at a density of 372 shrimp m^?3. Physical and chemical water parameters and shrimp growth performance were analysed. After 6 weeks, TSS mean concentrations were 306.37, 532.43 and 745.2 mg L^?1 for, respectively, TL, TM and TH treatments. Significant differences (P < 0.05) were observed in TSS, settleable solids, pH, alkalinity and nitrite, especially between the TL and TH treatments. Similarly, differences (P < 0.05) were observed in the growth performance parameters, specifically final weight, survival, feed conversion and productivity. The water quality parameters at lower range of total suspended solids concentration (TL) treatment resulted in a better performance of L. vannamei in the BFT system. The maintenance at range of 100–300 mg L^?1 TSS is thus important to the success of shrimp culture.     

Effects of three carbohydrate sources on water quality,water consumption,bacterial count,growth and muscle quality of Nile tilapia (Oreochromis niloticus) in a biofloc system

This study compared the effect of three sources of carbohydrates: sugar, wheat and malt flours, on water quality, water consumption, bacterial load, growth and flesh quality of Nile tilapia. Adults (120.6 ± 0.64 g) were stocked in 1.2‐m³ fibreglass tanks at a rate of 25 fish/m³. Carbohydrates were added to the biofloc tanks at a C:N ratio of 20:1. Water flow in the non‐biofloc control tanks was adjusted to 0.6 L/day. The 105‐day experiment was conducted in triplicates. Results showed that biofloc treatments (BFT) with zero water exchange had significantly higher mean total ammonia, nitrites, nitrates, alkalinity, total suspended solids and lower pH than the control treatment. The sugar BFT had the highest floc volume. Growth parameters and feed conversion ratio did not differ significantly among treatments. However, tilapia in the malt flour and control treatments had close values. Gross fish yield was higher (p < .05) in the control than the BFT treatments. Water consumption/kg tilapia produced in the control was 42 times higher than the BFT groups. Protozoa dominated the biofloc biota, and wheat flour was the best in harbouring higher bacterial populations in the gut. Protein content and ∑n‐3 fatty acids were highest in the wheat flour biofloc, while malt flour biofloc had the highest lipids. The sugar biofloc had the highest n‐3/n‐6 ratio. Tilapia muscles in the malt flour and control treatments had the highest protein and lipid contents respectively. Tilapia muscles in the wheat flour BFT had the highest ∑n‐3 fatty acids and n‐3/n‐6 ratio. It can be concluded that farming tilapia in BFT using malt or wheat flours as carbon sources is more economical in saving great amount of water with minimal discharge of pollutants without affecting tilapia growth or flesh quality.     

Effect of the addition of Chaetoceros calcitrans,Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and growth of Litopenaeus vannamei (Boone) postlarvae reared in a biofloc system

The aim of this study was to evaluate the effect of the addition of Chaetoceros calcitrans, Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and the growth of Litopenaeus vannamei postlarvae reared in a biofloc system . Four treatments were used: BFT (biofloc system without feed and no addition of diatoms); BFT‐F (biofloc system with feed and no addition of diatoms); BFT‐D (biofloc system with the addition of diatoms and no feed); and BFT‐FD (biofloc system with the addition of feed and diatoms), all in triplicate. The shrimp (16 ± 0.02 mg) were stocked at 2500 postlarvae m^?3 and fed a commercial feed. Diatoms were added on the 1st, 5th, 10th and 15th day at a density of 5 × 10⁴ cells mL^?1 for each species. No significant differences (P > 0.05) between treatments were observed for gross primary production, net ecosystem production and water column respiration rate. However, significant differences (P < 0.05) were observed for nitrite, orthophosphate, alkalinity, final weight, weight gain, yield, feed conversion ratio (FCR), phytoplankton and cyanobacteria composition. The BFT‐FD treatment had better performance parameters for final weight (270 mg), weight gain (254 mg), yield (0.67 Kg m^?3) and FCR (0.61), indicating the benefits of the diatoms C. calcitrans, Navicula sp. and P. tricornutum for decreasing cyanobacteria and improving growth of L. vannamei postlarvae reared in biofloc systems.     

Effect of bioflocs on growth and immune activity of Pacific white shrimp,Litopenaeus vannamei postlarvae

The bioflocs technology (BFT) for shrimp production has been proposed as a sustainable practice capable of reducing environmental impacts and preventing pathogen introduction. The microbial community associated with BFT not only detoxifies nutrients, but also can improve feed utilization and animal growth. Biofloc system contains abundant number of bacteria of which cell wall consists of various components such as bacterial lipopolysaccharide, peptidoglycan and β‐1, 3‐glucans, and is known as stimulating nonspecific immune activity of shrimp. Bioflocs, therefore, are assumed to enhance shrimp immunity because they consume the bioflocs as additional food source. Although there are benefits for having an in situ microbial community in BFT systems, better understanding on these microorganisms, in particular molecular level, is needed. A fourteen‐day culture trial was conducted with postlarvae of Litopenaeus vannamei in the presence and absence of bioflocs. To determine mRNA expression levels of shrimp, we selected six genes (prophenoloxidase1, prophenoloxidase2, prophenoloxidase activation enzyme, serine proteinase1, masquerade‐like proteinase, and ras‐related nuclear protein) which are involved in a series of responses known as the prophenoloxidase (proPO) cascade, one of the major innate immune responses in crustaceans. Significant differences in shrimp survival and final body weights were found between the clear water and in the biofloc treatments. mRNA expression levels were significantly higher in the biofloc treatment than the clear water control. These results suggest that the presence of bioflocs in the culture medium gives positive effect on growth and immune‐related genes expression in L.vannamei postlarvae.     

Effect of biofloc technology on growth of speckled shrimp,Metapenaeus monoceros (Fabricus) in different feeding regimes

The effects of biofloc technology (BFT) were tested on growth performance, water quality, haemolymph parameters and hepatopancreas histology with and without BFT for the speckled shrimp. In this study, eight different experimental groups were formed (four BFT and four control groups) to measure the effects of different feeding rates on compensatory growth of speckled shrimp. BFT treatments were performed with zero water exchange and planned as BFT1: gradually feed decreasing group 4, 2 and 1% bw, BFT2: 4% bw, BFT3: 2‐days feed with 4% bw, 1‐day fasted, and BFT4: 1‐day feed with 4% bw, 1‐day fasted. In control treatment, the same trial groups were constituted for comparing with BFT at a 50% daily water exchange: C1 (gradually feed decreasing group: 4%, 2% and 1% bw), C2 (4% bw), C3 (2‐days feed with 4% bw, 1‐day fasted), C4 (1‐day feed with 4% bw, 1‐day fasted). There were significant differences between BFT and C groups in terms of some water quality (p < 0.05). In general, BFT had an effect on haemocyte profile. At the histological examination, there were no pathological findings in both BFT and control groups. The growth parameters of speckled shrimps in BFT groups, as well as the whole body crude protein ratios and crude ash contents, were higher than the control group (p < 0.05). The results confirmed that biofloc utilization increased with decreasing feeding.