Zero-water Exchange Research Articles

Nutritional Optimization for Zero Water Exchange Aquaculture: A Study of Dietary Protein Levels for Pangasionodon Hypopthalmus

Nutritional Optimization for Zero Water Exchange Aquaculture: A Study of Dietary Protein Levels for Pangasionodon Hypopthalmus

Responses of Digestive, Antioxidant, Immunological and Metabolic Enzymes in the Intestines and Liver of Largemouth Bass (Micropterus salmoides) under the Biofloc Model.

To investigate the activities of intestinal digestive enzymes, liver antioxidant enzymes, immunological enzymes, and glucometabolic enzymes in largemouth bass (Micropterus salmoides) under the biofloc model, an experiment was conducted in 300-liter glass tanks. The experiment comprised a control group, which was fed a basal diet, and a biofloc group, where glucose was added to maintain a C/N ratio of 15. Each group had three parallel setups, with a stocking density of 20 fish per tank. The experiment ran for 60 days, employing a zero-water exchange aquaculture model. The results showed that at the end of the culture period, there were no significant differences between the initial weight, final weight, WGR, SGR, and SR of the biofloc group and the control group of largemouth bass (p > 0.05), whereas the lower FCR and the higher PER in the biofloc group were significant (p < 0.05); intestinal α-amylase, trypsin, and lipase activities of largemouth bass in the biofloc group were significantly increased by 37.20%, 64.11%, and 51.69%, respectively, compared with the control group (p < 0.05); liver superoxide dismutase and catalase activities, and total antioxidant capacity of largemouth bass in the biofloc group were significantly increased by 49.26%, 46.87%, and 98.94% (p < 0.05), while the malondialdehyde content was significantly reduced by 19.91% (p < 0.05); liver lysozyme, alkaline phosphatase, and acid phosphatase activities of largemouth bass in the biofloc group were significantly increased by 62.66%, 41.22%, and 29.66%, respectively (p < 0.05); liver glucokinase, pyruvate kinase, glucose-6-phosphate kinase, pyruvate kinase, glucose-6-phosphatase, and glycogen synthase activities were significantly increased by 46.29%, 99.33%, 32.54%, and 26.89%, respectively (p < 0.05). The study showed that the biofloc model of culturing largemouth bass can not only enhance digestive enzyme activities, antioxidant capacity, and immune response but can also promote the process of glucose metabolism and reduce feeding costs. This study provides data support for healthy culturing of largemouth bass in future production, provides a theoretical reference for optimizing the biofloc technology culture model, and is crucial for promoting the healthy and green development of aquaculture.

Biofloc technology (BFT) for indoor rearing of Clarias batrachus (Linn)

Increasing human population trends from 1.5 to 6.4 billion, with a projected growth to 9 billion by 2050, necessitates production diversification, which has been estimated at 840 million, in order to prevent malnutrition. The natural resources, particularly the fish reserves in lakes, rivers, and oceans, are negatively impacted by the population's exponential development. In order to encourage sustainable farming, aquaculture production must be increased without significantly utilizing the necessary natural resources. Sustainable fish farming is a method of managing suitable benthic conditions and water quality in a culture system while having a low environmental impact. In order to provide a nutrient-balanced diet, particularly one high in protein, animal husbandry and fishing are the two sources of animal protein. Fish products are the safest group of muscle protein, which contains all needed amino acids, essential fatty acids. Since very few literatures is available in the Biofloc technology (BFT), the present dissertation encompasses the research work from a very grass-root level i.e. from water analysis of BioFloc system to study of different rearing techniques and their effects on the growth of Clarias batrachus. The Biofloc aquaculture system is an eco-friendly one that produces using organic debris and recycled nutrients including phytoplankton, bacteria, dead organic matter by manipulating the C/N ratio to transform harmful nitrogenous wastes into beneficial microbial protein. which aids in water quality improvement in a zero-water exchange system. It may serve as a comprehensive supply of nourishment for aquatic species, as well as some bioactive substances that will improve growth, survival, and defense mechanisms, and it may serve as a unique way to aquaculture health management by boosting animals' innate immune systems.

Sugarcane bagasse improved growth performance, digestive enzyme activity, microbial dynamics, and mRNA transcripts of immune-, growth, and antioxidant -related genes of Litopenaeus vannamei in a zero-water exchange system

Pacific white shrimp (Litopenaeus vannamei) were grown in a biofloc rearing systems with (control treatment) or without sugarcane bagasse (SB treatment), with 3 replicate systems per treatment. SB, is an economic carbohydrate source. Parameters monitored were water-quality, growth indices, digestive enzymes activity, and microbial dynamics. Messenger RNA levels of immune-related, growth-related, and antioxidant genes in hepatopancreas and muscle and gene's single nucleotide polymorphism (SNP) were also considered. The outdoor ponds (44.5 m3), were each stocked with 600 L. vannamei larvae with an initial weight of 0.024 g) to start a three-month experiment. The biofloc development was in two aerated active suspension tanks to which SB (about 700 g/day, adjusted every two weeks) was added to maintain the of the C/N at 16. The water quality parameters, digestive enzyme activity, growth, and survival (P ≤ 0.05) in the SB group was improved compared to the control. SB also increased the total heterotrophic microbiota compared to the control. The mRNA levels of immune- related genes (lipopolysaccharides/b-glucan- binding protein, β-glucan-binding protein, lysozyme, prophenoloxidase, crustin, transglutaminase, and hemocyanin) and antioxidant genes (superoxide dismutase and glutathione peroxidase) significantly increased in SB group (P ≤ 0.05) compared to the control treatment. The SB group was the highest in all growth- related genes such as insulin- like growth factors (I and II), growth hormone, myosin, and paramyosin. Eight SNPs were detected in the hemocyanin gene, and an adenine insertion (ins A-554) was recorded at a high body weight. Our findings implied that using SB, as a carbon source in biofloc system without artificial feeding, could improve water quality, growth indices, digestive enzymes, microbial dynamics and the mRNA levels of all immune-, growth- related and antioxidant genes in L. vannamei.

Rearing European Eel (Anguilla anguilla) Elvers in a Biofloc System.

European eel (Anguilla anguilla) elvers (initial body weight (BW) = 3 g) were raised in triplicate for 60 days in a biofloc system (BFT) at 21 °C. Data from the current first study evaluating this farming technology indicated that European eel elvers adapted well to BFT systems as data on growth performance (specific growth rate = 1.48% ± 0.13 BW/day and FCR = 1.05 ± 0.09) indicated, with production costs using BFT being lower than conventional RAS units. The most critical issues associated with this aquaculture system were the maintenance of the biofloc in tanks by the regular addition of refined sugar (46% C) to keep a relationship for C:N of 20:1, and the prevention of emergence of opportunistic pathogens like the monogenean Pseudodactylogyrus sp. The overall results of this study in terms of elvers' performance and quality and the composition of the biofloc material and its microbial composition indicated that BFT, which is considered to be one of the most cost-effective, sustainable, and environmentally friendly farming systems due to its zero water exchange and improvement of feed conversion ratio by the dietary contribution of bioflocs, may be satisfactorily used for farming European eels elvers at a density of 2 kg/m3. However, further studies are needed to test this technology with older eel stages.

Performance of hatchery-produced and feed-weaned fingerlings of striped murrel Channa striata (Bloch, 1793) in biofloc system in the subtropical climate

The performance of hatchery-produced and pellet-feed-weaned fingerlings of striped murrel, Channa striata (Bloch, 1793) was assessed in the biofloc tanks for growth and survival, in a subtropical climate. The rearing was undertaken in two phases with an increase in fish size. In the first phase, fingerlings (weight 1.94±0.71 g, length 6.29±0.81 cm) were stocked @ 200 m-3 in the biofloc tanks, which were reduced to 15 m-3 in the second phase using the same stock. The fish attained a length of 25.44±1.81 cm and weight of 149.60±28.58 g in 10 months with overall survival of 93% at the end of the second phase. The total fish biomass recorded was 9.7 kg m-3 at the final harvest. The growth parameters were found temperature-dependent, which recorded 15±1.0 to 28±1.5ºC and 'W' values were found to follow Fulton's cube law during the entire culture period. The exponent (b) of 3.278 was recorded as the highest in July 2020 and lowest at 2.210 in December 2020. The lowest R2 was 0.768 and highest 0.943 during December and April respectively whereas, the recorded ‘K’ of 0.611 was the lowest in winter and highest being 0.908 in August. The study demonstrated a higher culture potential of striped murrel with hatchery-produced and feed-weaned seed in the biofloc system with zero-water exchange. Keywords: Condition factor, Fulton's cube law, Growth, Production, Survival, Zero-water exchange

Nitrification and denitrification processes in a zero-water exchange aquaculture system: characteristics of the microbial community and potential rates

​The zero-water exchange aquaculture has been identified as a promising method of farming to decrease the environment pressure of aquaculture and to increase profits. However, the ecological functions (e.g., nitrogen removal) and microbial biodiversity of the zero-water exchange pond aquaculture system are relatively understudied. In the present study, the zero-water exchange pond aquaculture system were constructed to investigated the microbial communities, sediment potential nitrification and denitrification production rates. And five functional genes (AOA amoA, AOB amoA, nirS, nosZ, and hzsB) were used to quantify the abundance of nitrifying and denitrifying microorganisms. The results showed that the sediment of the system had excellent potential nitrification-denitrification performance, with potential nitrification and denitrification rate were 149.77-1024.44 ng N g−1 h−1 and 48.32-145.01 ng N g−1 h−1, respectively. The absolute copy numbers of nitrogen functional genes and total bacterial 16S rRNA were 1.59×105-1.39×109 and 1.55×1010-2.55×1010copies g−1, respectively, with the dominant phyla, i.e., Proteobacteria, Actinobacteriota, Chloroflexi, Cyanobacteria, and Firmicutes. The relative abundances of the genera related to nitrification and denitrification, varied from 0.01% to 0.79% and from 0.01% to 15.54%, respectively. The potential nitrification rate was positively related to the sediment TOC concentration; and the potential denitrification rate had a positive correlation with sediment nitrate concentration. The genera Bacillus positively correlated with sediment NO3‐-N concentration, whereas Flavobacterium and Shewanella positively correlated with sediment NH4+-N concentration, which could be the functional bacteria for nitrogen removal. These findings may shed light on quantitative molecular mechanisms for nitrogen removal in zero-water exchange ponds, providing a sustainable solution to nitrogen pollution problem in the freshwater aquaculture ecosystems.

Variation of dietary protein/lipid levels used in postlarvae of freshwater prawn Macrobrachium rosenbergii cultured in a biofloc system

A 70-day experimental trial was performed to evaluate the contribution of biofloc to the nutrition of Macrobrachium rosenbergii 15 days old postlarvae (PL) (average 82.00 ± 19.71 mg) fed different crude protein (P) and lipids (L) levels in zero-water exchange culture tanks. Six biofloc treatments (BFT) as experimental diets with 15, 20, or 25% P levels and 5 or 8% L levels were managed: BFT-15/5; BFT-15/8; BFT-20/5; BFT-20/8; BFT-25/5; BFT-25/8, and a clear-water control without biofloc fed with 25% P and 8% L (CW-25/8). The experiment was done in triplicate in 21-60 L plastic tanks containing 10 prawns tank-1. At the end of the experiment, survival of prawns was above 66%, with no significant differences among experimental groups (P &gt; 0.05). The best growth performance was observed in the experimental prawns maintained in BFT-20/5, BFT-20/8, BF-25/5, and BFT-25/8 compared to the control (P &lt; 0.001). The feed conversion rate of the prawns in BFT-20/5 was significantly lower than that in control (P &lt; 0.001); the best P efficiency ratio and productive P value were observed in all BFT compared to control prawns (P &lt; 0.001). Results showed that it is feasible to use low concentrations of P (20%) and L (5%) in diets to grow giant freshwater prawn PL in a biofloc system. Results also demonstrated that biofloc contributes to the P and L requirements of cultured freshwater prawn PL, as indicated by improved feed utilization, P retention, and growth performance.

Effect of Stocking Density on Growth, Water Quality Changes and Cost Efficiency of Butter Catfish (Ompok bimaculatus) during Seed Rearing in a Biofloc System

Biofloc technology is a modern-day high-density fish culture system employing heterotrophic conversion of nitrogenous waste into useful flocs for water quality control and improved welfare. However, optimization of the stocking density for the target species during seed rearing is the key to a successful farming operation. The study evaluated the effect of different stocking density on the growth, feed utilization, digestive physiology and economics in a biofloc-based seed rearing of butter catfish, O. bimaculatus. Advanced fry (1.21 ± 0.08 g) was reared in a zero-water exchange biofloc system for 90 days at stocking densities of 0.5 g/L(T1), 1.0 g/L(T2), 1.5 g/L(T3) and 2.0 g/L(T4). The observed water quality indicates a reduction in DO and pH in T4, while the total ammonia nitrogen and nitrite levels remained low in T1. Among the groups, highest weight gain was noticed in the lowest stocking density (0.5 g/L) (p &lt; 0.05), which coincides with a better feed conversion ratio. Similarly, the digestive enzyme (protease, amylase, and lipase) secretion was higher in T1. Profitability assessment describes the possibility of low profit in T4, in the case where the fish’s sale price is based on harvested size. T1 showed higher individual growth and higher profit. Overall, a low stocking density of 0.5 g/Lis optimum for augmenting growth, feed utilization, physiological function and economic performance of O. bimaculatus. The study provides direction for a low-stocking oriented ecological and economically sustainable method of seed production of butter catfish in a biofloc system.

Effect of Zero Water Exchange Systems for Litopenaeus vannamei Using Sponge Biocarriers to Control Inorganic Nitrogen and Suspended Solids Simultaneously

The traditional shrimp farming mode, which mainly uses water exchange to dilute toxic nitrogenous compounds, not only brings risks of disease infections and outbreaks but also results in waste of water resources and has a negative impact on the environment. In this study, zero water exchange systems for Litopenaeus vannamei were constructed by using sponge biocarriers with precultured biofilms (SBBFs), and the effect of SBBFs on controlling inorganic nitrogen, suspended solids and on the performance of L. vannamei was determined. The experiment consisted of four treatments: (1) SBC (control, SB 5% (v/v) + aeration); (2) SBBF2.5a (SBBF 2.5% (v/v) + aeration); (3) SBBF5a (SBBF 5% (v/v) + aeration); and (4) SBBF5 (SBBF 5% (v/v)). The results showed that the concentrations of TAN and NO2−-N in the SBBF treatments were significantly lower than those in the SBC treatments, while the SBBF treatments registered higher NO3−-N concentrations. After the adsorbates were removed by regular cleaning to regenerate the adsorption capacity of the SBs, the turbidity was reduced by 47.8%~71.5%. The shrimp grown in the SBBF treatments exhibited a higher mean final weight, survival and productivity than those grown in the SBC treatments. This work found that the use of SBBFs can maintain the low levels of TAN, NO2−-N and suspended solids while improving the performance of the L. vannamei under the strict requirement of zero water exchange.

Production of Pacific white shrimp under different stocking density in a zero-water exchange biofloc system: Effects on water quality, zootechnical performance, and body composition

This experiment was conducted to compare water quality, growth performance, body composition, and insulin growth factor gene expression of Pacific white shrimp, Litopenaeus vannamei, reared under different stocking densities (100, 200, 300, and 400 shrimp m−3) in a biofloc system with zero-water exchange for nine weeks. The results demonstrated that all the water quality variables remained within the acceptable range that are presumed to be safe levels for Pacific white shrimp farming. The weight gain ratio and specific growth rate of shrimp reduced by increasing the stocking density to the lowest values of 2800.00 ± 105.32 % and 5.34 ± 0.11 % d−1, respectively, in shrimp reared under the highest stocking density (400 shrimp m−3). The highest feed conversion ratio was also obtained under the highest stocking density of shrimp (P < 0.05). A significant decreasing trend of the insulin growth factor-1 gene expression was observed by increasing the shrimp stocking density (P < 0.05). The final yield of shrimp in the present study significantly increased by increasing the shrimp stocking density and reached the maximum value of 3.05 ± 0.21 kg m−3 at the highest stocking density. There was no significant difference in the carcass composition of the shrimp among the experimental treatments (P < 0.05), except for lipid content which was significantly higher in shrimp reared under the lowest stocking density (100 shrimp m−3) (P < 0.05). Findings of the current study confirmed a clear effect of stocking density on growth performance of the Pacific white shrimp with the recommended density of 400 shrimps m−3 to achieve the maximum yield, while the stocking density of 100 shrimps m−3 is feasible to reach the highest weight gain and probability of Pacific white shrimp cultured in a biofloc system with zero-water exchange for the present experimental condition, genetics used and nutrition supplementation.

Effects of carbon-nitrogen ratio manipulation on the growth performance, body composition and immunity of stinging catfish Heteropneustes fossilis in a biofloc-based culture system

A 10-week indoor culture study was done to evaluate the effects of varying C/N ratios on growth performance, body composition, immunity, and haematology of stinging catfish Heteropneustes fossilis cultured in zero-water exchange culture tanks. Biofloc-based tanks with four levels of C/N ratio (12, 15, 18, 21) via the addition of carbohydrate referred to as ‘CN12′, ‘CN15', 'CN18' and 'CN21', and freshwater tanks operated with the facility of water exchange and without the addition of carbohydrate referred to as 'Control' (CN10). Fish (average weight 0.60 g) were stocked in 15 experimental tanks with 300 L water capacity and fed a commercial diet containing 30 % crude protein. The water quality parameters (pH, temperature, total ammonia nitrogen, nitrite nitrogen, dissolved oxygen, total suspended solids, and total dissolved solids) were monitored throughout the experiment. There was no significant (P > 0.05) difference among the treatments in the case of DO and temperature. The pH, total ammonia nitrogen, and nitrite nitrogen contents decreased with increasing C/N ratio, whereas the total dissolved solids and total suspended solids increased with gradually increasing the C/N ratio. Compared to the control, the treatment CN15 resulted in a 72 % and 34.4 % higher percent weight gain and specific growth rate, respectively. CN15 treatment resulted in improved feed utilization, as measured by feed conversion ratio (1.32 ± 0.07) and protein efficiency ratio (1.36 ± 0.10), which were 36.2 % lower and 54.5 % higher, respectively, than control. However, there were no differences in growth performance and feed utilization data between CN15 to CN21. Increasing the C/N ratio increased the body protein and ash contents and decreased the moisture and lipid contents compared to control. In the serum lysozyme test, the lysozyme value increased with a gradually increasing C/N ratio, and a better result was found in the CN15-CN21 treatments (15.58–15.74 µg ml−1) compared to the control (12.45 µg ml−1). At the end of the rearing period, fish were subjected to a challenge test with Aeromonas hydrophilla to determine the mortality rate where mortality was the lowest in CN15 treatment. Furthermore, increasing the C/N ratio from 15 to 21:1 showed better results for haemoglobin, white blood cells, red blood cells and hematocrit values. Overall, the manipulation of the C/N ratio from 15 to 21:1 revealed suitable for the feed utilization, growth performance, body composition, and immunity of stinging catfish. Therefore, maintaining a C/N ratio of 15:1 can be recommended for the culture of stinging catfish in the biofloc system.

Effect of Input C/N Ratio on Bacterial Community of Water Biofloc and Shrimp Gut in a Commercial Zero-Exchange System with Intensive Production of Penaeus vannamei.

Although increasing attention has been attracted to the study and application of biofloc technology (BFT) in aquaculture, few details have been reported about the bacterial community of biofloc and its manipulation strategy for commercial shrimp production. An 8-week trial was conducted to investigate the effects of three input C/N ratios (8:1, 12:1 and 16:1) on the bacterial community of water biofloc and shrimp gut in a commercial BFT tank system with intensive aquaculture of P. vannamei. Each C/N ratio group had three randomly assigned replicate tanks (culture water volume of 30 m3), and each tank was stocked with juvenile shrimp at a density of 300 shrimp m−3. The tank systems were operated with zero-water exchange, pH maintenance and biofloc control. During the trial, the microbial biomass and bacterial density of water biofloc showed similar variation trends, with no significant difference under respective biofloc control measures for the three C/N ratio groups. Significant changes were found in the alpha diversity, composition and relative abundance of bacterial communities across the stages of the trial, and they showed differences in water biofloc and shrimp gut among the three C/N ratio groups. Meanwhile, high similarity could be found in the composition of the bacterial community between water biofloc and shrimp gut. Additionally, nitrogen dynamics in culture water showed some differences while shrimp performance showed no significant difference among the three C/N ratio groups. Together, these results confirm that the manipulation of input C/N ratio could affect the bacterial community of both water biofloc and shrimp gut in the environment of a commercial BFT system with intensive production of P. vannamei. Moreover, there should be different operations for the nitrogen dynamics and biofloc management during shrimp production process under different C/N ratios.

Effects of different carbon sources and carbon–nitrogen ratios on the survival, growth, intestinal biochemical parameters, and water quality of seahorse juveniles cultured under zero-water exchange conditions

Effects of different carbon sources and carbon–nitrogen ratios on the survival, growth, intestinal biochemical parameters, and water quality of seahorse juveniles cultured under zero-water exchange conditions

Assessment of an automated IoT-biofloc water quality management system in the Litopenaeus vannamei’s mortality and growth rate

Climate change greatly influenced aquaculture in the Philippines and the deteriorating water quality; in effect, fish production reduced drastically. Thus, fish farmers and aquaculture researchers have been searching for innovative technologies to address these issues. One technology is the biofloc systems. This technology uses a zero-water exchange and accumulates microorganisms that serves as a food source. In the biofloc, water quality management is highly recommended. This study aimed to assess the technical and operational effect on the shrimp growth and survival of the developed automated water quality management internet of things (IoT) system in a biofloc system. The hardware prototype comes with a mobile application which has features namely: account management, fish/shrimp profile, water quality management, auto feeding and manual controls. This study conducts experimental research which assessed the impact of an indoor pond biofloc with the developed prototype on the Litopenaeus vannamei’s growth and survival rates. Results were favorable to the biofloc system with the developed prototype, having a 10% higher survival rate and 3.2% higher growth rate, compared to the traditional recirculating aquaculture systems. Adapting the biofloc and the IoT prototype, a fish farmer may earn P78,300 pesos for each white leg shrimp (Litopenaeus vannamei) harvesting period.

Aeration level in HDPE-lined nursery ponds that optimizes yield and production cost of preadult redclaw crayfish, Cherax quadricarinatus

The potential for commercial Australian redclaw crayfish culture is considered very significant. However, information on the effect that different water exchange and aeration levels has on growth, survival, yield and nursery production costs of redclaw is limited. We evaluated the effect of aeration levels in the yield and production cost of preadult redclaw crayfish, Cherax quadricarinatus, during the nursery phase. In a preliminary trial, 4 levels of water exchange: 0%, 2.5%, 5% and 7.5% day−1, were tested in 1.7 m diameter (2.26 m2) tanks, stocking 3.0 ± 0.2 g juveniles at a density of 15 juveniles m−2. After 60 days, the physicochemical water quality parameters were within the recommended intervals for cultivation of the species. Final weight, survival, biomass and FCR’s of pre-adult C. quadricarinatus did not show any significant differences (p > 0.05) among treatments so we conclude that adequate production of C. quadricarinatus during zero-water exchange nursing is feasible. With the previous information, 4 aeration levels (0, 6, 12 and 24 hr day−1) were evaluated in triplicate 100 m2 HDPE-lined outdoor ponds. Juveniles (3.5 ± 0.5 g) were stocked at a density of 15 juveniles’ m−2. After 84 days of cultivation, survival was not significantly different among treatments and varied within 86–87%. The highest final average weight, growth rate and biomass were obtained with 12 h of aeration per day (3.2 ton ha−1), but there were no significant differences from those obtained in ponds with continuous aeration (24 hr day−1). The feed conversion rates were within 0.72 − 0.75. We conclude that it is possible to maximize C. quadricarinatus production in HDPE-lined ponds without water exchange, maintaining aeration at a rate of at least 12 hr day−1. A cost analysis shows that, with this strategy, it is possible to reduce the electricity costs required for water pumping and aeration in 70% and 50%, respectively. With this, a reduction of 11.17% in the production cost of pre-adult C. quadricarinatus during the nursery phase is achieved, compared with the best published reports.

Impacts of water additives on water quality, production efficiency, intestinal morphology, gut microbiota, and immunological responses of Nile tilapia fingerlings under a zero-water-exchange system

The impacts of commercial probiotics as water additives to the zero-water exchange system on water quality, production efficiency, gut microbiota, antioxidant, and immunological responses of Nile tilapia (Oreochromis niloticus) were investigated. Five treatments, with three triplicates, were randomly designed, where in each replicate 150 fish (100 ± 4.5 g) were stocked in 20-m3 concrete ponds. Different water probiotics were added to ponds' water as follows: T1 (Control: no probiotic added); T2 (Prozym powder Ultra ® at 0.002 g/ m3/ day); T3 (Microban aqua ® at dose 0.002 g/ m3/ day); T4 (Aquastar ® at dose 0.0015 g/ m3/ day); and T5 (Sanolife PRO-W ® at dose 0.0010 g/ m3/ day). For eight weeks, fish in each group were fed a commercial feed (30% crude protein) up to satiety three times a day. After the experimental period, dissolved oxygen in ponds' water was significantly improved, while ammonia, nitrite, and nitrate levels were significantly lowered by water additives as compared to the control group. Compared to the control group, yield, specific growth rate, and total feed intake were significantly improved, while feed conversion ratio was not significantly changed among different treatments. Significant (p < 0.05) increases in villus height/width, and the absorption area was observed in groups that received water additives. Total Vibrio spp. counts in fish guts and ponds' water were significantly lower, while the total Bacillus spp. counts in both ponds' water and fish guts were significantly higher in probiotic-treated groups. Hematological parameters (counts of white blood cells and red blood cells as well as hemoglobin and hematocrit levels) significantly (p < 0.05) increased in probiotic-treated groups. In similar trends, antioxidant (superoxide dismutase and catalase activities) and immunity (total protein, globulin, immunoglobulin, and lysozyme activity as well as activities and index of phagocytes) were significantly enhanced in the groups treated with water probiotics. Overall, our results show that water probiotics in the current study were beneficial for reducing the nitrogenous compunds in ponds'water and improving the production efficiency, gut microbiota, antioxidant and immunological responses of Nile tilapia.

Effect of organic carbon source and stocking densities on growth indices, water microflora, and immune-related genes expression of Litopenaeus vannamei Larvae in intensive culture

The study conducted to evaluate the effect of different stocking densities in a biofloc (BF) system, with sugarcane bagasse as an organic carbon source on growth performance, immune response-related genes, and microbial biomass of shrimp larvae in a 90-days. Litopenaeus vannamei larvae (0.002 ± 0.01 g) were cultured in 12-tanks with different stocking densities (12 or 16 larvae/l), including two controls without a carbon source (12C and 16C) and two BF treatments without a commercial diet (12BF and 16BF) in triplicates. Based on the results, the total number of heterotrophic bacteria (THB) and Vibrio spp. counts (TVC) were positively affected by BF treatment. The highest THB value was recorded in treatment 12BF, whereas the lowest TVC value was recorded in 16BF. The highest (9.85 ± 1.60 g) and lowest (7.96 ± 2.72 g) weight gains were observed in 16BF and its control.Overall, the highest growth indices, survival rate and crude protein content were recorded in BF treatments. Furthermore, the expression of immunity-related genes were positively affected by BF treatment. However, the addition of agricultural by-product sugarcane bagasse as a carbon source in BF-tanks with zero-water exchange facilitated water recycling and increased the number of THB communities which could replace the commercial diet in BF-tanks and improve the growth and health of shrimp.

Growth performance and immunological response of African Catfish (Clarias gariepinus) juveniles reared in biofloc system

This study was conducted to examine the growth and immune performance of catfish ( Clarias gariepinus ) juveniles cultured in a biofloc fish farming system. To achieve this, 900 C. gariepinus juveniles (9.0 ± 0.23 g) were cultured in an intensive zero water exchange biofloc system for 72 days in 9 separate tanks (2 m 3 each) aerated by an air blower, after which growth assessment of fish was conducted. The trial consisted of three treatments in triplicates, a control without carbon source addition, and two biofloc treatments with carbon source addition of rice bran or cassava flour. The two carbon sources added had a C/N rate of 15:1 to form the floc. The results showed no significant difference between dissolved oxygen (DO), pH, and temperature in all the treatments, however, conductivity, total dissolved solids, and salinity showed significant differences between the bioflocs and control treatments and the treatment group. Nevertheless, the obtained values for the water parameters were within the range required for culturing C. gariepinus. Survival rate of catfish was significantly higher in the biofloc culture with a cassava carbon source (98.3%) compared with the control experiment (64.3 %). Weight gain of the fish was highest in rice bran based biofloc (44.9 ± 3.00 g) and lowest (37.0 ± 4.15 g) in the control treatment. The non-specific immune assay revealed that monocytes, serum lysozyme, and myeloperoxidase were higher in the biofloc treated groups compared to the control group. In contrast, neutrophils' percentage was lower in the treated groups than in the control group. Therefore, this study demonstrated the suitability of biofloc as an aquaculture wastewater purifier, growth-promoting, and immune-enhancing technology for the small-scale culture of C . gariepinus .

Effect of bioflocs on growth performance and survival of white-leg shrimp Litopenaeus vannamei raised in zero-water exchange culture tanks

A 90-day trial was conducted to evaluate the effects of three different protein levels (25%, 30% and 35% CP) and two different carbon sources (sugarcane bagasse and wheat flour) on the growth performance, feed utilization and survival rate of the white-leg shrimp Litopenaeus vannamei in zero –water exchange tanks. Six biofloc treatments and one control (45% CP) without biofloc were managed. Final body weight, weight gain, specific growth rate and protein efficiency ratio were highly affected interaction 0.05) among all treatments. There were no significant differences (P > 0.05) in moisture, crude protein and lipid among six biofloc and control treatments.