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/lp/wiley/biofloc-and-green-water-condition-improves-reproductive-traits-and-P0emWNN255
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- Wiley
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- © 2023 The Authors. Aquaculture, Fish and Fisheries published by John Wiley & Sons Ltd.
- eISSN
- 2693-8847
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- 10.1002/aff2.89
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- See Article on Publisher Site
Abstract
INTRODUCTIONThe brine shrimp Artemia is a crustacean that typically colonizes in extremely saline aquatic environments, such as coastal lagoons, inland lakes, and saltworks all over the world (Persoone & Sorgeloos, 1980; Turcihan et al., 2021). Artemia is a highly nutritious live food resource with tremendous value in aquaculture as the first diet for fish larvae (Sorgeloos, 1980). Artemia provides digestive enzymes for fish larvae, whose rudimentary digestive tract cannot digest inert diets (Sorgeloos & Tackaert, 1991). The nutrition value of Artemia can be improved through encapsulation techniques to attain the required levels needed by cultured animals (Fernández, 2001; Dhont & Sorgeloos, 2002; Sorgeloos et al., 2001). Due to these characteristics, Artemia has facilitated the expansion of global aquaculture production of finfish and crustaceans.To enhance the supply of Artemia cysts in global hatcheries, Artemia has been integrated into various saltworks (Van Stappen et al., 2020). In Kenya, Artemia was inoculated in Malindi area about 4 decades ago (Rasowo & Radull, 1986). However, optimization of the Artemia biotope for local aquaculture initiatives is yet to take place due to a lack of sufficient data on reproductive characteristics and nutritive value of the local Artemia biotope, to inform mass production procedures. Artemia is adapted to produce dormant cysts, which can remain viable over a long period with good hatching efficiency when good conditions return. Artemia cysts can be used as direct food for larvae with the help of the ‘cyst decapsulation’ technique (to remove the thick outer shell of the cyst) to facilitate ingestion and allow for its digestion (Van Stappen, 1996). Despite the economic and biological significance of Artemia in aquaculture, a regular supply of Artemia nauplii is stressful to many hatcheries, primarily due to the high cost of producing microalgal paste, which is the preferred Artemia diet. Therefore, studies are needed to develop low‐cost but nutritious diets as a relevant priority for aquaculture.Artemia is an obligatory nonselective particle filter feeder (Dhont & Sorgeloos, 2002). Feed reported to date include bioflocs (i.e., bacteria, protozoa, organic detritus, and other particulate matter of biological origin) and green water (i.e., nonfilamentous algae cells) (Eryalcin, 2018; Van Stappen, 1996). Newly hatched Artemia do not feed because their mouth and anus are not fully developed. A few hours after hatching, Artemia molts into the second larval stage (instar II), which can filter small food particles from 1 to 50 μm, including bacteria. The nauplii grow and progress through 15 molts before reaching adulthood in about 8 days. Due to filter‐feeding behaviour, Artemia is useful in salt works as they feed on algae particles, hence eliminating salt contamination, leading to first‐class salt quality production (Faruque et al., 2010).Biofloc condition yields huge densities of algal cells (dinoflagellates and diatoms), fungi, ciliates, flagellates, rotifers, copepods, nematodes, metazoans, and heterotrophic bacteria cells such as Pseudomonas and Aeromonas family that conglomerate together under optimum carbon/nitrogen (C/N) ratio and adequate aeration (Avnimelech, 2003; Manan et al., 2016). Bacteria, and by extension the microbial loop is known to play important roles as recycling pathways for C and N in food webs (Azam et al., 1983). Bioflocs have good nutrition including fatty acids, which are essentially transferred to Artemia when feeding on them. Usually, an optimum C/N ratio ensures the immobilization of inorganic nitrogen into huge bacterial proteins (biomass) and restores good water quality by removing toxic ammonia (Azim & Little, 2008). This study explores the feasibility of promoting the simultaneous growth of highly dense bacterial biomass and Artemia in the same culture facilities, where Artemia feeds directly on the microbial flora.Green water technology encourages the growth of high Tetraselmis sp. algal densities (Toi et al., 2013). The algal density is promoted by chicken manure, which contains nutrients, especially nitrogen which is useful for algal growth. Chicken manure also contains different hormones such as 17β‐estradiol and testosterone that are important for culturing zooplankton communities (Finlay‐Moore et al., 2000; Hakk et al., 2005; Shemesh & Shore, 1994). These hormones influence the population growth, mixis induction, and body size of zooplankton species (Preston et al., 2000; Yang & Snell, 2010). Therefore, a hypothesis about whether chicken manure extract (CME) and biofloc technology (BFT) can influence the growth, reproductive traits, and fatty acid composition of Artemia was formulated and tested in this study.MATERIALS AND METHODSSource of artemia cystsArtemia was first inoculated on the Kenyan coast, around Malindi area about 4 decades ago courtesy of the Kenya‐Belgium Project (KBP), implemented by the Kenya Marine and Fisheries Research Institute (KMFRI) and University of Ghent, Belgium (Rasowo & Radull, 1986). The Artemia species have since then adapted to local conditions and developed permanent populations in Malindi area (Ogello et al., 2013, 2014). Artemia is currently being used by salt companies and the local community to purify salt. For this study, Artemia cysts were sourced from Khadzuhoni salt pans in Malindi.Experimental designTo establish sufficient Artemia nauplii for the experiment, Artemia hatching was achieved by the use of natural seawater in a 5‐L glass bottle, to which 10 g of cysts was added, and placed on a rotor at four cycles min−1 for 24 h under constant illumination using fluorescent lamps (2000 lux). Freshly hatched instar I nauplii were harvested for the experiment. About 1000 nauplii were batch cultured in each 1‐L glass jar containing 500 ml of natural seawater (i.e., stocking density of 2 nauplii/ml). Artemia was cultured under laboratory conditions using three treatments, that is, green water technology (GWT), biofloc technology (BFT), and normal algal conditions (control‐C). The composition of each treatment is described in Table 1.1TABLEComposition of each treatment used for the experimentTreatmentCompositionQuantity appliedReferencesControl (C)Tetraselmis spp.7.0 × 106 cells ml−1 dailyHagiwara et al. (1994)GWTCME + C0.5 g l−1 of CMEOgello et al. (2015)BFTGWT + Molassesdepending on TANAbbreviations: BFT, biofloc technology; CME, chicken manure extract; GWT, green water technology; TAN, total ammonium nitrogen.Management of the treatmentsMolasses were regularly added to BFT based on total ammonium nitrogen (TAN) concentration to maintain a C/N ratio of 10 from the 5th day of culture. During the first 2 days after stocking, Artemia was fed with fresh Tetraselmis tetrathele algae, for conditioning, after which each treatment was applied. Artemia cultures were maintained at 28.0 ± 1°C using an electrically heated water bath with constant aeration and light (2000 lux) for 30 days. An inoculum of T. tetrathele was obtained from the laboratory of zoology at Maseno University, Kenya, and the algae were cultured following a standard protocol (Coutteau, 1996), where a continuous culture method was used. Fertilized seawater was continuously pumped into the T. tetrathele growth chamber at a steady, predetermined rate and the excess culture was simultaneously washed out, allowing maintenance of the culture close to the maximum growth rate.Survival studiesUpon hatching, 50 instar I nauplii were transferred into different cylindrical shaped vials (45 ml) filled with natural seawater and were fed with three replicated treatments described in Table 1 throughout the tests. No artificial aeration was used, but to ensure sufficient oxygen levels, one‐third of water renewal was done upon survival determination every 2 days. Final survival was determined at the end of the experiment by counting the number of live Artemia in each culture flask.Survival activity index (SAI) experiments were performed to determine Artemia nauplii survivability during starvation. Here, cysts harvested from each treatment were hatched in the laboratory using the protocol and conditions described above. About 20 Artemia nauplii from each treatment were placed in a 200 ml beaker containing 100 ml of natural seawater at 28 ± 1°C in total darkness, without aeration and feeding. Dead Artemia nauplii were counted and removed every 24 h until total larval mortality was reached. Triplicate observations were used to calculate the SAI using the equation of Shimma and Tsujigado (1981):SAI=1N∑i=1KN−hi×i,$$\begin{equation*}{\rm{SAI}} = \frac{1}{N}\sum_{i = 1}^K {\left( {N - hi} \right)} \times i,\end{equation*}$$where N is the total number of examined larvae, hi is the cumulated mortality by i‐th day, and K is the number of days elapsed until all larvae died due to starvation.Growth studiesArtemia growth data was measured in terms of length, which was started from the 5th day after stocking and then repeated every 2 days. A sample of 10 Artemia was taken randomly from each jar. Artemia was first treated with Lugol's solution before taking total body length measurements from the tip of the head to the end of the telson through a dissecting microscope. As the animals grew, a dissecting microscope was used for measurement with the aid of a digitizer (KD 4300, Graphtec corp., Japan).Population densityArtemia population density was monitored daily from the batch cultures described above. Each day, three‐1 ml of culture water was sampled from each glass jar, fixed with Lugol's, and then Artemia numbers were counted under a stereo microscope at ×25 magnification to estimate population density. In the first exponential growth phase, partial harvesting was done by replacing 50% of the culture medium with new seawater and diet. Artemia was left to regenerate without additional inoculation.Specific growth rateThe specific growth rate (SGR) was calculated as follows: r = [ln Nt – ln No]/t, where, No is the initial population density, Nt is the population density after the time (t), and t is the time in days (i.e., day 16). To determine the stability of the cultures, the coefficient of variation (CV) of the mean SGR was computed as standard deviation (SD)/mean SGR. The CV was calculated on day 16 for each diet.MicrobiologyThe Artemia culture medium was separately screened for bacteria under sterile conditions. The medium was serially diluted up to 10−4 after filtering out Artemia and residues using the 10 μm net. For platting, the Zobell marine agar (Difco™ 2216; Becton, Dickinson & Co. France) was used. Then, 0.1 ml of the respective diluted samples was inoculated over the surface of the solidified agar in triplicates. The plates were incubated upside down (to avoid vapour condensation on the agar) at 32°C for 48 h. The bacterial colony‐forming units (CFU) were calculated as CFU ml−1 = (No. of colonies × dilution factor)/inoculated volume (ml).Reproductive testsThe mass batch culture was carried out until the pre‐adult stage was reached in a similar set‐up as indicated above. When riding couples were seen, it was noted as the time in days when sexual maturity was attained at the earliest in those animals. Immediately when couples were observed, 10 couples from each treatment were removed from the mass culture bottle and every single couple was transferred into a 50 ml Falcon tube for closer examinations. The Artemia couples were exposed to the same conditions as in the culture bottle. The number of cysts and/or nauplii released per female was counted and recorded daily. The data collected were used to determine the pre‐reproductive and reproductive period, total offspring per female, offspring per female per day, the total number of broods per female, oviparous and ovoviviparous brood size, and brood interval in days.Fatty acid analysisTo obtain substantial biomass for fatty acid analysis, mass cultures were up‐scaled into 20‐L glass aquariums using similar treatments for 60 days. Artemia biomass was regularly harvested from each treatment and weight was measured. A total of 300 g of freshly harvested Artemia biomass from each treatment was preserved under frozen conditions and transported to Polucon Company Ltd., Mombasa, Kenya, for fatty acid analysis. Fatty acid methyl esters (FAME) were prepared using the AM/C/107 method in which the sample methanolysis was prepared at 100°C for 2 h after the addition of 2 M hydrogen chloride methanol. FAME was extracted by n‐hexane. Gas chromatography analysis was performed using a GC‐2010 (Shimadzu Scientific Instruments, Inc.) equipped with an HR‐SS‐10 column (Shinwa Chemical Industries, Ltd.). The column temperature was regulated at 150–220°C. Individual fatty acids were quantified utilizing the response factor of 15:0 fatty acids as the internal standard (Folch et al., 1957). The analysis essentially followed protocols by Laakso on fatty acid analysis. The fatty Acid values were expressed as g/100 g artemia dry weight.Data analysisThe data were analyzed using R statistical software (version 3.2.1 of the R Foundation for Statistical Computing Platform © 2015). The Bartlett test was used to test for the homogeneity of variances. One‐way analysis of variance (ANOVA) was used to test the effects of each diet on water quality, Artemia population densities, growth (length), and reproductive traits. Where significant differences were detected, Tukey's HSD Post hoc test was performed to locate the differences at p < 0.05. Only one sample was analyzed per treatment.RESULTSSurvivalAs shown in Figure 1, Artemia survived in all treatments for 30 days. There was a significant effect of treatments on Artemia survival (p < 0.05), with Artemia cultured in BFT having a higher survival (87.1 ± 3.2%) than those cultured in GWT (66.2 ± 2.9%) and Control (57.9 ± 1.3%). There was a significantly higher survival activity index (SAI) of Artemia nauplii hatched from cysts harvested in BFT (8.23 ± 0.33 days) than in GWT (6.34 ± 0.11 days) and Control cultures (5.24 ± 0.42).1FIGUREThe proportion of surviving Artemia cultured in green water technology (GWT), biofloc technology (BFT), and Control using normal seawater for 30 days. Values are presented as means ± SE (n = 3).GrowthThere was a significant effect of the treatments on Artemia size (p < 0.05), with Artemia cultured in the BFT treatment having a higher length than those grown in GWT and control from day 10 to 30 (Figure 2). The final mean lengths were 12.1 ± 0.2, 10.1 ± 0.4, and 7.5 ± 0.1 mm for Artemia cultured in the BFT, GWT, and Control cultures, respectively.2FIGUREGrowth curves of Artemia cultured in green water technology (GWT), biofloc technology (BFT), and Control using normal seawater for 30 days. Values are presented as means ± SE (n = 3).Population densityThere was a significant effect of treatments on Artemia population density (p < 0.05). The population density of Artemia cultured using BFT was higher than those cultured in GWT and Control on days 14, 16 and 20 (Figure 3). At the end of the experiment, the population densities were 45.4 ± 2.3, 26.3 ± 3.1 and 15.1 ± 4.2 nauplii/ml in BFT, GWT and Control cultures, respectively. The Artemia‐specific growth rates (SGR) were 0.16, 0.12, and 0.11 individuals /day in BFT, GWT, and control, respectively. Meanwhile, the CV was 5.04%, 10.81%, and 10.86% in BFT, GWT, and Control cultures, respectively.3FIGUREPopulation density (individuals/ml) of Artemia cultured in green water technology (GWT), biofloc technology (BFT), and Control using normal seawater for 30 days. Partial harvesting was done on day 17 by replacing half of the culture medium with new media as indicated by the dotted lines. The values represent mean ± SD. Different letters each day denote significant differences at p < 0.05, n = 3.BiomassThere was a significant effect of treatments on Artemia biomass (p < 0.05), with Artemia cultured in the BFT having higher cumulative biomass than those cultured in GWT and Control. At the end of day 60, the biomass (wet weight) was 722.45 ± 39.33, 577.98 ± 67.34, and 474.23 ± 62.43 g in BFT, GWT, and Control cultures, respectively. Artemia productivity was estimated at 36.2, 28.5, and 23.7 g/L after 60 days in BFT, GWT, and control cultures, respectively.MicrobiologyThe colonies are shown in Figure 4. The treatments significantly affected the CFUs (ml−1) (one‐way ANOVA, F = 24.11, p = 0.01), where the Artemia cultured in the BFT had higher CFU (1.38 × 107 CFU/ml) than those cultured in GWT (1.11 × 107 CFU/ml) and control‐rotifers (7.3 × 106 CFU/ml) (Figure 5).4FIGUREGrowth cultures of bacteria isolated from (a) biofloc technology (BFT), (b) green water technology (GWT), and (c) control culture mediums5FIGUREThe bacterial colony‐forming units (CFU/ml) in the culture medium from biofloc technology (BFT), green water technology (GWT), and control at ×104 dilution rate. Different letters indicate significant differences between treatments, n = 3.Reproductive traitsThere was a significant effect of treatments on the Artemia reproductive traits as shown in Table 2. Artemia cultured in the BFT unit had a shorter pre‐reproductive period (15.6 ± 0.6 days) and a longer reproductive period (20.9 ± 2.6 days) compared to those cultured in GWT and control (Table 2). The BFT‐cultured Artemia had higher total broods per female per day (4.3 ± 0.3) than GWT (3.5 ± 0.2) and Control (2.5 ± 0.3). There was a higher ovoviviparous reproduction in BFT (4.4 ± 0.5 broods/female) than in GWT (2.5 ± 0.3) and control (2.4 ± 0.4). However, the control treatment showed higher oviparous reproduction (1.4 ± 0.2 broods/female) than BFT (0.5 ± 0.1) and GWT (0.7 ± 0.2). The total number of offspring per female was significantly higher in the Artemia cultured in the BFT unit (73.5 ± 6.1) than those cultured in GWT (66.2 ± 7.9) and Control (42.6 ± 12.1). There was a significantly shorter brood interval in BFT (1.6 ± 0.3 days) than in GWT (1.7 ± 0.3) and control (2.5 ± 0.4).2TABLEReproductive traits of Artemia cultured using the biofloc technology (BFT), green water technology (GWT), and the control treatments in normal seawater for 30 daysReproductive traitsGWTBFTControlFemale pre‐reproductive period (days)21.8 ± 0.7b15.6 ± 0.6a22.0 ± 0.5bFemale reproductive period (days)16.4 ± 2.3b20.9 ± 2.6a15.8 ± 1.9bTotal broods per female per day3.5 ± 0.2b4.3 ± 0.3a2.5 ± 0.3cOvoviviparous broods per female2.5 ± 0.3b4.4 ± 0.5a2.4 ± 0.4bOviparous broods per female0.7 ± 0.2c0.5 ± 0.1a1.4 ± 0.2bTotal offspring per female66.2 ± 7.9a73.5 ± 6.1a42.6 ± 12.1bBrood interval (days)1.7 ± 0.3b1.6 ± 0.3b2.5 ± 0.4aNote: Values are presented as means ± SE (n = 3).Fatty acid compositionThe fatty acid composition of Artemia was significantly higher in the BFT system than in the GWT and control culture systems. The compositions of myristic C14:0n‐8, palmitic C16:0n‐3, heptadecanoic C17:1n‐7, oleic, C18:1n‐9, and linoleic C18:2 n‐6 and linolenic C18:3 n‐3 acids were significantly higher in the BFT culture system than in the GWT and control systems. The compositions of heptadecanoic acid C17:0n‐7, palmitoleic acid C16:1n‐7, stearic acid C18:0 n‐4, and arachidic acid C20:0 n‐6, on the other hand, did not differ significantly between the experimental culture systems as shown in Table 33TABLEFatty acid composition (%) in total lipids of dried Artemia biomass cultured using the biofloc technology (BFT), green water technology (GWT), and the control treatments in normal seawater for 30 daysFatty AcidFormulationGWTBFTControlUnits (g/100 g)Myristic acidC14:0 n‐822.6438.829.51Pentadecanoic acidC15:0 n‐70.220.540.12Palmitic acidC16:0 n‐39.4314.316.47Palmitoleic acidC16:1n‐7<0.01<0.01<0.01Heptadecanoic acidC17:0 n‐70.020.030.01Stearic acidC18:0 n‐4<0.01<0.01<0.01Oleic acidC18:1n‐921.9830.666.31Linoleic acidC18:2 n‐67.119.384.33Linolenic acidC18:3 n‐34.235.242.22Arachidic acidC20:0 n‐62.012.131.32The absence of the eicosapentaenoic acid 20:5 n‐3 (EPA) which can constitute up to 4%–5% of fatty acids in artemia (based on) can be explained by the lack of capacity at our lab to conduct the analysis. Further explanation is given in Section 4. Only one sample was analyzed per fatty acid due to a lack of capacity at our laboratory to process the samples, resulting in a high cost of sample analysis by the private company.DISCUSSIONWith the current growth of the aquaculture sector expected to continue in the next few decades, Artemia availability will play a critical role in the improvement of aquaculture, especially the culture of fish and shrimps with high economic returns, such as sea bass (Lates calcarifer), sea bream (Sparus aurata), Penaeus monodon, Penaeus indicus, and Penaeus japonicus (Dhont & Van Stappen, 2003; Lim et al., 2003). This study has demonstrated that integrated BFT and GWT condition influences the growth and fatty acid composition of Artemia under limited algal conditions. In normal situations, Artemia is fed on algal pastes, which have become expensive and fragile to culture in many local fish and shrimp hatcheries. The results of this study indicate that Artemia can be cultured using waste‐generated bacteria as food for Artemia.There was a higher survival and SAI in the BFT than GWT and control (Figure 1). Higher SAI is an indication that Artemia cultured under BFT can withstand longer periods of starvation, which is important for ensuring maximum larval fish feeding in hatcheries. This could be attributed to the presence of huge bacterial biomass in the BFT compared to other treatments. The higher bacterial biomass in the BFT was facilitated by molasses. Being a filter feeder, Artemia can feed on a variety of non‐algal particles including micro‐algae, microbial organisms, protozoa as well as small detritus particles (Fernández, 2001). In addition, the cultures contained minimal algal particles, which presented supplemental food resources for Artemia in the BFT treatment. Food shortage causes interactions in Artemia populations through competition for the available nutrients, which results in stress, slow growth rate, and eventually mortalities are experienced (Hoa et al., 2021).The higher Artemia growth and population density in BFT could have been a synergistic effect of CME and bacterial biomass within the BFT cultures. It is plausible that CME and molasses in the biofloc system stimulated the growth of algal communities and microorganisms (protozoa and bacteria), respectively, which are direct supplemental feed for Artemia. CME is an excellent substrate for bacterial and algal growth associated with organic matter, which promotes the development of a dense population of protozoa (Schroeder, 1980). Further, the addition of a carbon source promotes the generation of sufficient microbial proteins and energy which is very essential for active swimming thus increasing hunting chances for food and obtaining the appropriate oxygen for their metabolism.Artemia cultured in the BFT unit showed higher regeneration and culture stability (coefficient of variation of 5.04%) after partial harvesting (Figure 3). With more stable cultures, several Artemia generations can be cultured in ponds while conducting partial harvesting at production peaks (every 2 weeks), without need for fresh inoculations. Higher Artemia culture stability is usually a factor of limited pathogenic microorganisms in cultures that would cause culture crush. BFT is known to stabilize cultures by maintaining good water quality and provision of biosecurity advantages (Nootong et al., 2011). However, further studies should be done to determine the ability of BFT‐grown Artemia to resist pathogenic bacteria. The BFT provided a rich food environment (i.e., bioflocs and algae) that stimulated a faster growth and regeneration of Artemia after partial harvesting. This is an important strategy to ensure constant mass production of Artemia biomass especially when optimal conditions for oviviparous reproduction are maintained. However, other studies have reported that increased proliferation of bioflocs raises water viscosity, which may reduce Artemia swimming activities, food utilization, and higher energy consumption for locomotion, resulting in retarded growth (Toi et al., 2013).The population density of Artemia was higher in the BFT due to ovoviviparous reproduction loop. The high Artemia biomass recorded in the BFT cultures shows that the application of BFT is a more efficient technology for Artemia biomass production compared to the GWT and control. The high biomass in BFT could be a result of the massive growth of a highly nutritious bacterial community stimulated by the added molasses. Toi et al. (2013) confirmed that an adequate amount of bacteria could be a good source of feed for Artemia. This study, therefore, demonstrates that the stimulation of microbial protein through the addition of molasses in BFT could enhance the production of Artemia biomass, especially in cases of food shortage. This is because molasses stimulates microbial development in the culture water, thus providing supplemental feed to Artemia, leading to high Artemia biomass in BFT. In addition, most microbial organisms contain carotenoids mostly found in Haloferax (Chen et al., 2006), glycoprotein, and exopolysaccharides (López‐Ortega et al., 2020), which nutritionally might modulate the health of Artemia, leading to better performance in terms of biomass and length.The results of the present study reveal that the BFT treatment improved the reproductive performance of Artemia. The provision of mixed diets with microalgae, bacteria, or protozoa microorganisms promotes growth and high rates of mature females obtaining better nauplii due to their nutritional quality. High food abundance in a culture unit is also important because survival and the number of nauplii produced depend on it (Wayne & Maciej, 2001). Earlier research has confirmed that Artemia can efficiently feed on bioflocs produced from animal wastes (Sui et al., 2013; Verma et al., 2011). The utilization of CME to stimulate the production of feed for Artemia is an attractive alternative due to its low cost. Further, the feeding of Artemia with bioflocs may be a promising method of directly providing probiotics to the digestive tract of the target aqua species (Suzer et al., 2008). In addition, microbial organisms are considered a good source of activating enzymes that enhance the activation of food items (Toi et al., 2014). This, therefore, justifies the significantly higher total number of offspring per female in the Artemia cultured in the BFT unit than those cultured in GWT and Control.According to Browne et al. (1984), Artemia has reproductive modes including ovoviviparity and oviparity, and the occurrence of each depends on various environmental conditions, such as variation in temperature, salinity, stress, and the availability of food. Oviparity mostly happens when the Artemia have challenges with their living conditions or when the living condition is out of their stand (N. V. Hoa et al., 2007). In the present study, the BFT treatment facilitated the ovoviviparous mode of reproduction, while the control treatment favoured oviparous reproduction. A shorter brood interval in BFT than in control was reported in this study, which could be due to the presence of nutritional microbial feed leading to the fast growth of the Artemia, thus reaching sexual maturity within a shorter period compared to Artemia reared in GWT and control. The nutrition of the female (fatty acids, ascorbic acids, vitamins, amino acids, and overall food availability), physiological factors (mobilization of energy reserves, and hormones), and ecological factors (environmental conditions such as food availability, water quality, and salinity) are some of the factors that have been confirmed to trigger reproduction (Rocha, 2008). Some of the factors listed above could therefore have contributed to the higher reproductive performance recorded in the BFT treatment in comparison to GWT and control. Bioflocs also not only have a considerable amount of protein but also have highly unsaturated fatty acids (HUFA) and vitamin C which enhances gonadal maturation and high quantity and quality offspring (Crab et al., 2012; Ekasari et al., 2010). This could be the reason for the higher fecundity recorded in the BFT compared to the GWT and control.During Artemia culture, Artemia wastes and organic matter accumulate in the culture medium polluting the environment. It is therefore essential to improve the culture environment to promote higher growth performance of the Artemia and enhance the production of biomass as a whole. There are various methods of controlling nitrogenous wastes; however, the stimulation of microbial organisms to grow has been reported to be the best (Avnimelech, 2012). BFT has in earlier studies been reported to improve water quality, biosecurity, and yield of the cultured species through the conversion of nitrogenous compounds to microbial protein, stabilizing the bacterial organisms and lowering the cost of production (De Schryver et al., 2008; Nootong et al., 2011). The addition of molasses as a carbon source which is easily absorbed by heterotrophic bacteria quickly lowers TAN levels through the formation of stable bacterial flocculations.The presence of HUFA is an important factor that is used in the determination of the nutritional value and marketing of Artemia for utilization in the aquaculture industry (Mana et al., 2014). The high levels of mysteric, palmic, linoleic, and oleic fatty acids of the Artemia reported in this study confirm earlier studies that have reported the same fatty acids to be the major fatty acids found in bioflocs (Anand et al., 2014; Crab et al., 2010; Emerenciano et al., 2012; Magondu, 2012; Toledo et al., 2014). The absence of the eicosapentaenoic acid 20:5 n‐3 (EPA), which can constitute up to 4%–5% of fatty acids in artemia (based on Cabanes, 1992; Tizol‐Correa et al., 2006), can be explained by the lack of capacity at our lab to conduct the analysis. The samples were therefore analyzed at a private company (Palucon Company Ltd. in Mombasa, Kenya). The company for some reason failed to test for EPA. The authors acknowledge, however, that this fatty acid could not have been missed in the Artemia had the samples been analyzed for it.In aquaculture, these fatty acids are very essential in cell synthesis, immune function, reproduction, and endocrine function (Emerenciano et al., 2012; Glencross, 2009). In this context, bioflocs appear to supplement such important fatty acids through natural production which are unavailable in the control and GWT. The fatty acids improve certain effectors of the immune system, including respiratory bursts and coagulation (Aguilar et al., 2012). This influences the resistance of the cultured organisms to infectious organisms including bacteria, viruses, fungi, and parasites (Trichet, 2010), leading to high survival rates. Through bioaccumulation processes, Artemia can accumulate fatty acids in their gut, making it a perfect diet for the larviculture of fish and shrimp (Castro et al., 2009; Dhont & Sorgeloos, 2002; Zadehmohseni et al., 2020). However, the BFT developed in this study promises a major leap towards developing a cheap and nutritionally rich diet for Artemia. Based on the food value of the bioflocs, the BFT culture fluid can be considered a cheaper enrichment medium for low‐quality larval fish foods, for example, bakers’ yeast, and may reduce the need for the expensive enrichment emulsions (Ogello et al., 2018). Other homemade emulsion products have been produced using fish oil and egg yolk as cheap ways of enriching Artemia cultures, but these products are prone to oxidation and have a short shelf life that limits their application in aquaculture. The bacteria‐held polyunsaturated fatty acids (PUFAs) in BFT are more protected against oxidation and provide a variety of other natural nutrients that meet the species‐specific nutritional requirements of the Artemia, and the larval fish that feed on them.CONCLUSIONIntegrated BFT conditions provide an enhanced environment for better Artemia survival, growth, reproductive traits, and amino acid composition. This technology promises a major leap towards developing a cheap and nutritionally rich diet for the mass production of Artemia biomass compared to algal pastes, which are costlier and more fragile to produce. The BFT condition ensures stable Artemia cultures, producing up to 20–40 nauplii/ml biweekly. This presents self‐sustaining biotechnology for the production of high density of nutrient‐rich Artemia without microalgae for aquaculture. BFT reduces the female pre‐reproductive period, extends the reproductive period, and promotes oviviviparity of Artemia; hence, it is suitable for mass production of Artemia biomass.AUTHOR CONTRIBUTIONSConceptualization, funding acquisition, resources, and writing—original draft: Erick O. Ogello. Writing—review and editing: Nicholas O. Outa. Data curation: Bramwel O. Mukaburu. Methodology and writing—review and editing: Mavindu Muthoka.ACKNOWLEDGEMENTSThis study was funded by the WIOMSA‐MASMA project grant No. MASMA/OP/2020/02 awarded to Erick O. Ogello of Maseno University, Kenya. 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Journal
Aquaculture Fish and Fisheries – Wiley
Published: Feb 1, 2023
Keywords: Artemia franciscana; biofloc technology; carbon‐nitrogen ratio; chicken manure extract (CME); green water technology