BACHELOR’S THESIS IN BIOLOGY
15 hp
VT2020
Rearing of Nile tilapia in Bio-RAS approach compared
to traditionally biofloc technique.
The future of Aquaculture!
Mattias Djurstedt
mattias.djurstedt@hotmail.com
Swedish supervisor: Per-Erik Olsson
Indonesian supervisor: Julie Ekasari
Examiner: Håkan Berg
Örebro University 2020
Abstract
Aquaculture is important towards the accomplishment of the Sustainable Development Goals, especially goal 14 and rural economic development in developing countries, but today
aquaculture still has many unsustainable factors both in water use and organic waste. Biofloc (aggregation of microorganisms) technology is a potential aquaculture system which could make the industry more economic viable and more sustainable. In biofloc technology the reared species is together with microbes in the same water body and the toxic nitrogen species (NH4+) is converted into microbial protein. This gives both better growth performance and feed utilization, but also less water use. However, there are some problems in biofloc technology when the reared species and the microbes both has their own biological
preferences towards feed, water parameters and water turbulence. These problems limit the production of the system. In Bio-RAS (term created by A. Kiessling and S. Zimmermann (RAS means Recirculating aquaculture system)) approach the water body is separate between the reared species and the microbes, therefore both organisms can be handled towards their own biological preferences. In this study Bio-RAS approach is tested and compared towards traditionally biofloc technology, where the Bio-RAS results was significant better in both growth performance and feed utilization. The conclusion is that Bio-RAS may be the future “tree branch” for the technology to follow for both economical and sustainability reasons
Table of content
1 Introduction ... 1 1.1 Background of aquaculture ... 1 1.2 Aquaculture in Indonesia ... 2 1.3 Tilapia ... 2 1.4 Biofloc Technology ... 3 1.5 Bio-RAS ... 4 2 Objectives ... 6 2.1 Aim ... 6 2,2 Hypothesis ... 63 Material and Methods ... 7
3.1 Experimental design ... 7
3.2 Fish and feed ... 9
3.3 Sample collection and calculation ... 10
3.3 water quality monitoring ... 10
4 Results ... 11
4.1 Growth performance, feed utilization and survival rate ... 11
4.2 Water quality ... 15
5 Discussion ... 16
5.1 Bio-RAS compared to traditionally biofloc technology, not CW-RAS ... 16
5.2 Density of fish capacity important for the future of Bio-RAS approach. ... 16
5.3 Bio-RAS and the sustainable development goals ... 17
Conclusion ... 19
Acknowledgements ... 20
1 Introduction
1.1 Background of aquaculture
Aquaculture is the process where humans cultivate aquatic animals and plants either in costal, marine or inland areas. A wide variety of fish and plant species can be cultivated. Aquaculture have a high relevance towards fulfilment of the agenda for sustainable development and its 17 sustainable development goals, especially goal 14 (Conserve and sustainably use the oceans, seas and marine resources for sustainable development) (FAO, 2018). However, aquaculture must first solve some of its unsustainable problems to reach its fully potential, therefore research in this area is very important for the sustainable development goals fulfillment
2016 global fish production was 171 million tons. 47 % of this amount was produced from aquaculture and figure 1 shows that during the last decade aquaculture production is responsible for suppling the global demands of fish when the stocks of fish in the seas are stagnated. Aquaculture is the fastest growing food production sector, it had double digit numbers of annual growth in the 1980s and 1990s but has decreases to an average about 5,8% annual growth between 2000-2016 (FAO, 2018).
Figure 1: Diagram showing the difference in world captured fish and aquaculture production during the last decade. Orange is Aquaculture and blue is captured fish. Based on (FAO, 2018),
(http://www.fao.org/3/i9540en/i9540en.pdf). 92,2 89,5 90,6 91,2 92,7 90,9 61,8 66,4 70,2 73,7 76,1 80 0 20 40 60 80 100 2010 2011 2012 2013 2014 2015 2016 2017 Prod u ctio n Ton n e s Year
There have been problems with husbandry practices in aquaculture which led to harmful impacts of local environments and created outbreaks of diseases. For the future development of aquaculture there is a need for better technology and husbandry practices (FAO, 2020a). In this study a new further developed aquaculture technique is tested, which has the potential to make the aquaculture industry more sustainable and contribute in aquacultures potential towards helping in the global development goals.
1.2 Aquaculture in Indonesia
With the 26,6 million hectares of potential aquaculture area, Indonesia is suitable for aquaculture and is considered important for reducing unemployment and supporting rural economic development (FAO, 2020b). Aquaculture is practiced in both marine, brackish and fresh water in Indonesia but only 0,03 percent, 39,25 percent and 11,22 percent, respectively, of the potential area is used. Therefore, aquaculture has the potential to both expand and help the economic development of Indonesia. The most reared species in Indonesian aquaculture is common carp (Cyprinus carpio), catfish (Clarias spp., Pangasius spp.) and Nile tilapia (Oreochromis niloticus) (FAO, 2020b). Nile tilapia was first imported to Indonesia in 1967 and last decades the production has expanded because of huge export demands, mostly china, and strong government support. Between 1999 and 2003 the production increased from 31 217 tons to 71 789 tons (FAO, 2020b). Therefore, the relevance of the Nile tilapia species in the Indonesia aquaculture has increased a lot last decades.
1.3 Tilapia
In this study Nile tilapia (Oreochromis niloticus) was used as the biological system as it is one of the most reared fish species in aquaculture worldwide. With origins from Africa, Nile tilapia is a tropic fish species and prefers water temperatures between 31-36 °C. It is an omnivore which means that it can survive both on animal and plant diet. Nile tilapia can also “filter feed” microorganisms like phytoplankton, bacteria and mucous (FAO, 2020c).
Egyptian tombs confirm that Nile tilapia has been grown in closed systems by humans over 4000 years, but it was not before the 1960s when the fish was introduced to the rest of the world, Thailand 1965, Brazil 1971, United states 1974, China 1978 (FAO, 2020c). Since then the production of Nile tilapia has increased enormously worldwide, as shown in figure 2.
Figure 2: Diagram showing the global production of Nile Tilapia last decades. Based on (FAO, 2020c), (http://www.fao.org/fishery/culturedspecies/Oreochromis_niloticus/en).
The pros of using Nile tilapia in aquaculture is mostly because it can be farmed intensely and economically. However, the species also tolerate feed with lower total protein content and a higher total plant protein count, which makes it cheaper compared towards for example cultivating salmon that need high animal protein feed. Tilapia also tolerate diseases and different water qualities good (FAO, 2020c). The cons of Nile tilapia are their high breeding rate and they will over-reproduce inside the ponds. Therefore, preferably only monosex populations of male tilapia is grown, which also gives similar growth rates. To achieve this often hormone treatment is utilized, but the current trend of the industry is to obtain
genetically male Nile tilapias without hormone treatment (FAO, 2020c).
1.4 Biofloc Technology
The problem that arise with inland aquaculture, where you intensively grow fish in a defined compartment, is the accumulation of ammonium (NH4+), nitrite (NO2+) and nitrate (NO3+). Ammonium is the most toxic one and different techniques exists to solve this problem. Traditionally aquaculture uses frequently water exchange to get rid of the toxic ammonium. However, frequently exchange water gives economical expensed by pumping the water,
0 500 000 1 000 000 1 500 000 2 000 000 2 500 000 3 000 000 3 500 000 4 000 000 4 500 000 1 9 7 5 1 9 8 0 1 9 8 5 1 9 9 0 1 9 9 5 2 0 0 0 2 0 0 5 2 0 1 0 2 0 1 5 2 0 2 0 Prod u ctio n Ton n e s Year
GLOBAL AQUACULTURE PRODUCTION OF
NILE TILPAIA
higher probability of introducing pathogens and recent decades environmental regulations has prohibit release of nutrient rich water into the environment (Avnimelech, 1999). Biofloc technology is another strategy to remove ammonium. Biofloc is an aggregation of
microorganisms. Carbohydrates are added into the fish tank, which triggers heterotrophic microorganisms to grow and ammonia is converted into microbial protein (Avnimelech, 1999). If a fish species that can digest microorganisms is used, example Nile tilapia, the microbial protein serves as an extra feed and reduces feed costs. (Avnimelech, 2007). The feed contribution from the biofloc technology was showed to be near 50% (Avnimelech, 2007) and 25% (Avnimelech & Kochba, 2009) of the protein requirement for Nile tilapia.
Aquaculture is considered as one of the big factors for achieving the sustainable development goals (FAO, 2018). Applying the biofloc technology gives a more sustainable aquaculture industry where the technology gives a higher production but in the same time a small
environmental impact, compared to traditional aquaculture (Bossier & Ekasari, 2017). Biofloc technology increases the production around 8-43% compared to traditional aquaculture
(Ekasari, 2014), gives a higher resistance towards diseases (Ekasari et al., 2014) and reduce the water exchange (Bossier & Ekasari, 2017).
In the report by Bossier and Ekasari (2017) it is noted that Biofloc Technology enables a lower total protein content and a higher plant-based protein content in the feed, but also increasing the feed efficiency and reducing the amount of nitrogen (N) and phosphorus (P) waste levels. A lot of the nitrogen and phosphorus is excreted in the feces, but in the biofloc technology the feces are converted into microbial protein and when fed to the cultivated organism nutrient waste is reused.
1.5 Bio-RAS
Bio-RAS is a concept created by professor Anders Kiessling, (SLU) and Sergio Zimmermann. “The term, Bio-RAS, describes the combined system of BFT and RAS designed to provide the optimal environment for both the reared species and microbes” (Nhi et al., 2018) (BFT: biofloc technology, RAS: recirculation aquaculture system). Bio-RAS is a further developed technique based on the traditional biofloc technique. The concept was successfully tested for
the first time by Nguyen Huu Yen Nhi, a cooperation between the Swedish University of Agriculture and An Giang University in Vietnam (Nhi et al., 2018). However already in 2008 there were conclusions made that more research should investigate a hybrid technology between the RAS and biofloc technology, both for promising production and sustainability factors (Azim & Little, 2008).
Problems in traditionally biofloc technology arise when both the fish and microorganism is reared in the same water body. It gives a competitive challenge where the fish and microbes both has their own specific biological preferences regarding to feed, water quality parameters and turbulence of the water. Another problem is that dead microorganism gives non-digested material, sludge, formation and can give formation of the very toxic metabolite SH2.
In Bio-RAS the fish farming unit is connected to an external biofilter unit, allowing separation in treatment of fish and the microbial community, but there are exchange of microorganisms to the farming unit and return of non-digested and fecal matter, sludge, back to the biofilter unit. In the biofilter unit sludge is broken down by the microorganisms and by pumping water from selected parts, a biological separation can be made and therefore the accumulation of sludge and risk of SH2 is avoided. The biological separation also allows to fulfill the specific biological preferences for both the fish and the microbial community.
In Nhi´s study “Comparative evaluation of Brewer's yeast as a replacement for fishmeal in diets for tilapia (Oreochromis niloticus), reared in clear water or biofloc environments” a conclusion is made that bio-RAS approach gives greater growth performance and feed utilization then CW-RAS approach. CW-RAS is a clear water recirculation aquaculture system that is often used in tank rearing aquaculture. Nhi also points out that the bio-RAS technique has the potential to carry as high densities of fish that conventional RAS can do, but with the beneficial effects of the biofloc technology.
The Bio-RAS concept was in this report tested for the second time in a cooperation between Indonesia, IPB University and Sweden, Örebro University. Supervisor from Örebro
University was professor Per-Erik Olsson and the supervisor in Indonesia was doctor Julie Ekasari. Anders Kiessling and Sergio Zimmermann was aiding the project as consultants.
2 Objectives
2.1 Aim
The aim of this study was to evaluate production of Nile tilapia in the new concept Bio-RAS approach compared to traditionally biofloc technology.
2,2 Hypothesis
Main hypothesis: Rearing Nile Tilapia in bio-RAS approach compared to traditionally biofloc technology gives better growth performance, feed utilization and survival rate
Part hypothesis: Weight gain, specific growth rate and average daily growth of Nile tilapia would be higher in Bio-RAS approach, and the feed conversion ratio and death rate were hypothesized to be lower in Bio-RAS approach, compared towards traditionally biofloc technology.
3 Material and Methods
3.1 Experimental design
The bio-RAS system was built up as following: three 5000 m3 tank was used as farming units rearing Nile tilapia, called B1, B2, B3 and one 5000 m3 tank used as a biofilter, called BF with only microorganisms inside. For oxygen aeration each tank had 6 air stones, where B1, B2 and B3 had one joint air blower (230W, 200L/min) connected towards the air stones and BF had one air blower (230W, 200L/min) on its own. Separate pipes from B1, B2 and B3 was connected towards the BF and Resun SP7500 75W pumps in the bottom of B1, B2 and B3 was used both for internal circulation and transferee of water towards the BF. In the BF tank one Resun SP9600 230W pump was used for internal circulation located in the bottom of the tank, and a SWP180EA 180W pump, near the water surface, was used for transferring BF water back to B1, B2 and B3, the distance was connected by a joint pipe. The transferred BF water was released on the water surface in B1, B2 and B3. This setup allowed controlled water flow from the farming units towards the biofilter and vice versa. By pumping water from the bottom in the farming units and a return of surface water in the biofilter, sludge is transferred from the farming units towards the biofilter and clear water is transferred back. For better understanding look at figure 3. Each day after feeding around 9:00 AM 15% of the total water volume from B1, B2 and B3 was transferred towards the BF, to break down the sludge. No water exchange was done from the biofilter until 5:00 PM when the same water volume was transferred back from BF to B1, B2 and B3. 15 minutes before the BF water was transferred towards B1, B2, B3 internal circulation and aeration of the BF was stopped, to obtain sedimentation.
Figure 3: Schematic picture of the bio-RAS setup that was used in this experiment.
The traditionally biofloc technology system was built up as following: three 5000 m3 tanks was used and called C1, C2 and C3. Nile tilapia was reared together with the biofloc and no separation was created. For aeration all three tanks were connected towards a joint air blower (230W, 200L/min) where each tank had 6 air stones separately. Each tank had a Resun SP3200 80W pump on the bottom of the tank for the internal circulation, and the internal circulation was built up in the same way as in the BF tank, see figure 4. All tank even in the bio-RAS setup was in tropical outdoor environment without any roof above them and the experiment was executed at Indonesia, IPB University of Bogor, Faculty of Fisheries and Marine Science.
Figure 4: Schematic picture of the traditionally biofloc technology setup that was used in this experiment.
There was a disease outbreak in the beginning of the experiment, therefore the first month of data was excluded in the experiment because it would become a big error. The fish arrived 24 of February 2020, but the data that was used started to be collected 23 of Mars 2020 and collection of data stopped 4 of May 2020.
3.2 Fish and feed
Initially 250 Nile tilapias (Oreochromis niloticus) was transferred towards each tank except the BF tank. The approximated initially bodyweight was 109,89 g/fish and gives an initially density of 5,5 kg fish/m3. The fish was bought at the fish store Iwake Cinangneng, Bogor, West Java and transported by a car in 0.5 m3 plastic bags, the water was oxygen-saturated and contained 1 kg of fish/bag. The population was not monosex and the water used for farming came from a nearby lake. At the initial transferring of the fish potassium permanganate KMnO4 was transferred towards the water to calm down the fish and the fish was left for 2 weeks to acclimatize to the new water. The fish was feed daily until saturation at 8:00 AM and 4:00 PM. The fish feed used was produced on site from the University’s own mill, the feed was 3 mm and contained protein (30,54%), fat (4,37%), water (11,16%), ash (8,57%), crude fiber (1,77%). The carbon source used as feed for the microbes in the biofilter was molasses with a carbon profile about 40%. The first week of the experiment there were a lot
of dead fish with symptoms of whirling, purulens and exopthalmia, but no disease
identification was done. There was a peak of dead fish in the first week, but there where cases of diseased and dead fish the entire first month. After 23 of Mars there were no more disease symptoms on the fish. The 6 of April a partial harvest was conducted, where the density of fish was decreased towards 25 kg/tank (5kg/m3), only fish that weighted more then 190g was taken away.
3.3 Sample collection and calculation
Every second week length and weight were measured on 30 random selected Nile tilapias from each tank. The parameters that was analyzed was the feed conversion ratio (FCR), specific growth rate (SGR), average daily growth (ADG), weight gain (WG) and survival rate (SR). The parameters were calculated with these formulas:
FCR = feed given (g)/ fish weight gain (g)
SGR (%/day) = [(ln final weight−ln initial weight)/days] × 100 ADG (g/day) = body weight gain (g) / days
WG (g) = Final fish weight – initial fish weight
SR (%) = (Total number of fish harvested/ Total number of fish initially) × 100.
3.3 water quality monitoring
At the start of the experiment 0,14 g probiotics was added to each tank (Sano life PRO-W. Company INVE (Thailand) Ltd, Strains, Bacillus subtilis and bacillus licheniformis, 5x1010 cfu/g), and after a heavy rain same amount was added again. The carbon:nitrogen ratio, C:N, in the bio-RAS system was 15:1 and the C:N ratio in the traditionally biofloc technology system was 10:1. To achieve these C:N ratios molasse as a carbon source was added. To start the microbial growth in the biofilter, ammonium chloride NH4Cl was added as a nitrogen source, only in the beginning, (company Himedia Laboratories PVT Ltd).
Twice a day, morning and evening, temperature, PH, and dissolved oxygen: DO, was measured. Total acid number: TAN, nitrite, nitrate and alkalinity were supposed to be
measured once every week, but because of the Covid 19 pandemic the labs where closed and not much water quality analysis could be done. Biofloc volume was measured once a day and was kept under 20g biofloc/ L water.
4 Results
4.1 Growth performance, feed utilization and survival rate
In table 1 the data of feed conversion ratio, FCR, specific growth rate, SGR, and average daily growth, ADG from tank B1, B2 and B3 is presented. In table 2 FCR, SRG and ADG collected from C1, C2 and C3 is presented. FCR, SRG and ADG was calculated every second week in al the tanks. A higher average in FCR, SGR and ADG could be seen in the Bio-RAS approach compared towards traditionally biofloc technology.
Table 1: Growth performance and feed utilization of the bio-RAS approach.
Feed conversion ratio, FCR, Specific growth rate, SGR, and average daily growth, ADG.
Bio-RAS FCR
SGR
(%/day) ADG (g/day)
sample 1 B1 1,7 0,71 1,29 sample 1 B2 2,78 0,47 0,85 sample 1 B3 0,93 1,43 2,84 sample 2 B1 1,36 1,29 2,95 sample 2 B2 1,11 1,32 3,01 sample 2 B3 1,18 1,22 2,77 sample 3 B1 0,82 2,04 5,89 sample 3 B2 1,11 1,35 3,71 sample 3 B3 1,2 1,24 3,36 Average 1,354444 1,23 2,963333333 SD 0,59068 0,443057558 1,440546771 Variance 0,348903 0,1963 2,075175
Table 2: Growth performance and feed utilization of the traditionally biofloc technology. Feed conversion ratio, FCR, Specific growth rate, SGR, and average daily growth, ADG.
Traditional
Biofloc FCR SGR (%/day) ADG (g/day)
sample 1 C1 1,81 0,95 1,75 sample 1 C2 1,47 0,97 1,77 sample 1 C3 1,42 0,87 1,6 sample 2 C1 1,12 1,12 2,54 sample 2 C2 1,25 1,17 2,63 sample 2 C3 1,06 1,19 2,7 sample 3 C1 1,62 0,97 2,55 sample 3 C2 1,55 1,14 3,02 sample 3 C3 1,62 0,97 2,56 Average 1,435555556 1,038888889 2,346666667 SD 0,249454961 0,11591424 0,503587132 Variance 0,062227778 0,013436111 0,2536
In table 3 weight gain, WG, and survival rate, SR, data is presented from tanks B1, B2 and B3 and in table 4 WG, and SR data is presented from tanks C1, C2 and C3. There were a higher average weight gain and survival rate in the Bio-RAS system compared towards the
traditionally biofloc technology, but no significant T.test could be done on that data.
Table 3: Weight gain and survival rate of bio-RAS approach.
Measured and calculated at the end of the experiment in each tank B1, B2 and B3. (The T.test was negatively affected by the small amounts of samples.)
Bio-RAS Weight gain (g)
Survival rate (%) B1 158,83 100 B2 125,34 98,6 B3 114,5 98,6 Average 132,89 99,06666667 SD 23,10928601 0,808290377 Variance 534,0391 0,653333333 T.test (p-value) 0,120926403 0,127070332
Table 4: Weight gain and survival rate of the traditionally biofloc technology.
Measured and calculated at the end of the experiment in each tank C1, C2 and C3. (The T.test was negatively affected by the small amounts of samples.)
Traditional
Biofloc Weight gain (g)
Survival rate (%) C1 108,34 97,8 C2 116 99 C3 109 98 Average 111,1133333 98,26666667 SD 4,244824299 0,642910051 Variance 18,01853333 0,413333333
To know if the results in table 1 and table 2 was significant or not, a one-tailed unpaired T.test was done. The null-hypothesis was that in bio-RAS samples specific growth rate, SGR, and average daily growth, ADG, should be higher than the traditionally biofloc technology samples and that the feed conversion ratio, FCR, should be lower in the bio-RAS samples compared to the traditionally biofloc technology. The T.test gives a p-value and to be significant the p-value should be under 0,05, this mean that there is only 5% chance that the result is obtained by a coincidence and 95% chance that the results was obtained because the null-hypothesis is correct. As can be seen in table 5 the p-values was over 0,05 and therefore the results is not significant, there is to high chance that the results is only a coincidence, but if sample 1 B2 in table 2 is taken away the T.test gives significant values on both FCR, SGR and ADG as can be seen in table 6. A t-test was also done on table 3 and table 4, and gave no significant difference in weight gain, WG, and survival rate, SR, between the two systems.
Table 5: T.test FCR, SRG and ADG.
T.test P-value
T.test FCR 0,355847834
T.test SGR 0,120929454
Table 6: T.test for FCR, SRG and ADG.
(Without sample 1 B2, because it was an outliner).
T.test, no sample 1 B2 p-value
T.test FCR 0,0292601
T.test SGR 0,0320089
T.test ADG 0,0514635
To determine if sample 1 B2 is an outlier and therefore acceptable to take away from the data an outlier detection program called Graph Pad Prism was used. The program confirmed that sample 1 B2 was an outlier. The results are therefore that bio-RAS approach has a higher growth performance and feed utilization compared towards traditionally biofloc technology. Feed conversion ratio, FCR, is significant (P<0,05) lower in bio-RAS approach, Specific growth rate, SGR, is significant (P<0,05) higher in bio-RAS approach and average daily growth, ADG, is significant (P=0,05) higher in bio-RAS approach, but no significant (P≈0,12) difference in weight gain, WG, and survival rate, SR, could be seen between the two systems
4.2 Water quality
The water quality parameter did not differ that much between the two systems, the main difference that can be seen in table 7 was dissolved oxygen, DO, bio-RAS approach has a higher average, and a higher minimum value compared to traditionally biofloc technology.
Table 7: Water quality parameters from both bio-RAS and traditionally biofloc technology. DO: dissolved oxygen, TAN: Total acid number
Water parameters Bio-RAS Traditional Biofloc
Temperature, max, °C 33 32,8 Temperature, min, °C 25,5 25,7 Temperature, average, °C 28,4 28,7 Ph, max 8,1 8 Ph, min 5,9 5,8 Ph, average 7,1 7 DO, max, mg/L 5,98 5,55 DO, min, mg/L 3,06 2,13 DO, average, mg/L 4,8 4,5 TAN, max, mg/L 1,89 1,98 TAN, min, mg/L 0,18 0,19 TAN, average, mg/L 0,67 0,7 Nitrite, max, mg/L 3,06 2,42 Nitrite, min, mg/L 0,07 0,01 Nitrite, average, mg/L 1,47 1,55 Nitrate, max, mg/L 5,79 5,54 Nitrate, min, mg/L 0,01 0,07 Nitrate, average, mg/L 2,04 1,6
Alkalinity, max, mg CaCO3 /L 212 168
Alkalinity, min, mg CaCO3 /L 40 40
Alkalinity, average, mg CaCO3 /L 100,3 93,6
Floc volume, max, g/L 13 18
Floc volume, min, g/L 0 0
5 Discussion
5.1 Bio-RAS compared to traditionally biofloc technology, not CW-RAS
This study shows that bio-RAS approach gives a higher growth performance and feed
utilization compared towards the traditionally biofloc technique, and is partially supported by the first novel experiment done on bio-RAS (Nhi et al., 2018) which also showed conclusions of bio-RAS approach giving greater growth performance and feed utilization. However, Nhi compared her study towards a clear water recirculation aquaculture system (CW-RAS) commonly used all over the world in tank-based aquaculture. The big difference between this experiment and Nhi’s experiment is therefore that this study compared bio-RAS towards the traditionally biofloc technology and not the CW-RAS, in this regard this experiment is also novel and therefore there is small amounts of material that can support the findings of this experiment.
Bio-RAS approach was chosen to be compared towards traditionally biofloc technology instead of being compared towards a CW-RAS, because bio-RAS is augmented in Nhi’s study (2018) to be a better further developed technique from the traditionally biofloc technology, but no experiment has been done to prove that statement. This study was therefore created towards providing proof that bio-RAS indeed is a better system then the traditionally biofloc technology and therefore may be the right “tree branch” for the biofloc technology to go in the future for both economical and sustainability reasons. In some regards it feels like this study should have been done firstly, to verify Nhi’s statement and the next step would have been to compare bio-RAS towards a CW-RAS.
5.2 Density of fish capacity important for the future of Bio-RAS approach.
In Nhi’s study she mentions that the bio-RAS technique has the potential to carry as high densities of fish that a CW-RAS can do, but with the beneficial effects of the biofloc technology. This is where future research must be done. The downside with the bio-RAS approach is that water volume that could potentially been used to farm fish is used towards rearing microorganism inside a biofilter. Therefore, the main goal of the biofilter is to take up as little water volume as possible, and leave as much volume as possible to grow fish in. The
perfect ratio between biofilter volume and fish rearing volume needs more research, you want as much water volume as possible to grow fish in, but in the same time a big enough volume for the biofilter to be able to clean the water. Anders Kiessling and Sergio Zimmermann (creators of the term bio-RAS) gave the advice to have a volume ratio between the biofilter and farming unit at 1:1. If this advice would have been followed this experiment would had 3 biofilter tanks connected towards the 3 farming units, but because of limited space and resources only one biofilter tank was used towards 3 farming units, this gave a
biofilter:farming-unit ratio of 1:3. Because of the small biofilter volume the transferring of water in this experiment was only 15% per tank and only one transfer per day, this to prevent overflooding of the biofilter. The optimal idea of the bio-RAS approach would have a 30% water exchange every day from each farming units and a constant water flow between the biofilters and farming units. If the optimal ratio between the biofilter and farming unit would be 1:1 (but more research is needed in that topic) it means that half of the water volume would be used towards rearing microorganisms. To be able to compete with the traditionally biofloc technology where all the water volume is used towards rearing fish, the maximum fish density tolerated by the bio-RAS approach must be at least twice as high compared to the traditionally biofloc technology. This to be able to compete with it, and getting a similar total yield of fish produced.
5.3 Bio-RAS and the sustainable development goals
Aquacultures future is to help achieving the sustainable development goals, especially goal 14 (Conserve and sustainably use the oceans, seas and marine resources for sustainable
development) (FAO, 2018), but also important for rural economic development in the
developing countries like Indonesia (FAO, 2020b). For aquaculture to reach its fully potential it needs to solve unsustainable problems and the biofloc technology may be the answer (Bossier & Ekasari, 2017). Biofloc technology increases the production around 8-43 % compared to traditional aquaculture (Ekasari, 2014), gives a higher resistance towards
diseases (Ekasari et al., 2014), reduce the water exchange (Bossier & Ekasari, 2017), enables a lower total protein content and a higher plant-based protein content in the feed (Bossier & Ekasari, 2017), contributing around 25-50% towards the total protein requirement of Nile tilapia (Avnimelech, 2007 ; Avnimelech & Kochba, 2009) and both increasing the feed
efficiency and reducing the amount of nitrogen (N) and phosphorus (P) waste levels (Bossier & Ekasari, 2017). However, biofloc technology also has some problems with rearing
microorganism and fish in the same water body, which limits the production capacity of the system. Bio-RAS approach is a further developed technique from the traditionally biofloc technology which solves a lot of the problems in the traditionally biofloc technology and significantly increases the growth performance and feed utilization of Nile tilapia. Therefore bio-RAS approach may be the future of the biofloc technology and may in the long turn help in the achievement of the sustainable development goals.
Conclusion
Bio-RAS approach gives significant higher growth performance and feed utilization both compared to traditionally biofloc technology and the CW-RAS, but there is a need of more research both in the topic of volume ratio between the biofilter and farming units and the maximum fish density tolerance of the bio-RAS approach, to fully evaluate its economic advantage. Bio-RAS approach solves a lot of the problems in the traditional biofloc technology and may be the future tree branch for the technology to follow for both economical and sustainability reasons.
Acknowledgements
Firstly, I want to thank the Swedish International Development Agency (SIDA) that funded this study through a MFS-Student scholarship and I also want to thank IPB University of Bogor, Faculty of Fisheries and Marine Science for allowing me to conduct this study with their own equipment and facilities on site.
Foremost I want to give my sincere gratitude towards my local supervisor Dr. Julie Ekasari, both for helping and arranging my arrival to Indonesia and later for the competent support throughout the hole experiment.
I would like to give my special thanks to my consultants Professor Anders Kiessling and Docent Sergio Zimmerman for their interest in myself as a future entrepreneur and for their extraordinary base of competence towards aquaculture.
I also would like to thank my supervisor professor Per-Erik Olsson from Örebro University, both for his positive support towards my abroad-study and for the support he gave during the writing process of this thesis.
I am also greatly indebted towards my local co-worker/student Achtus D Napitupulu, you deserve a special thanks for finishing the experiment without me when I was forced to return to Sweden because of the Covid 19 pandemic.
Finally, but by no means least important, I would like to express my thanks towards Örebro University, all lectures and all friends I have met during my scholar years. It has been a wonderful journey full of joy, knowledge and memories for life, but now I will try my wings as an aquaculture entrepreneur.
References
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FAO (2020a). Governance of aquaculture. Food and agriculture organization of the United nations. http://www.fao.org/fishery/governance/aquaculture/en
FAO (2020b). Indonesia. Food and agriculture organization of the United nations. http://www.fao.org/fishery/countrysector/naso_indonesia/en
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Comparative evaluation of Brewer's yeast as a replacement for fishmeal in diets for tilapia (Oreochromis niloticus), reared in clear water or biofloc environments. Aquaculture, 495, pp. 654-660.
