GROWTH PERFORMANCE OF BASIL IN A SMALL-SCALE COUPLED AQUAPONIC SYSTEM WITH THE PRODUCTION OF TILAPIA Oreochromis niloticus AND AFRICAN CATFISH Clarias gariepinus
Introduction
Aquaponics requires knowledge from a wide range of different research areas. Among others, it is important to analyze the influence of different fish species on the system stability of coupled aquaponic systems (Palm et al., 2014a). As described by Palm et al. (2014b) and Knaus and Palm (2017a,b), the production of Nile tilapia (Oreochromis niloticus), African catfish (Clarias gariepinus) and Common carp (Cyprinus carpio) resulted in differences in dissolved oxygen of the applied system and causing different system performance.
With regard to diversification of aquaponic systems, the exact influence of fish species on plant yield is of particular interest. As demonstrated by Palm et al. (2014b) and Knaus and Palm (2017a) plant yield of basil (Ocimum basilicum) was better in the O. niloticus system compared to the aquaponics with C. gariepinus. However, the exact extent was not tested for significance. In contrast, fish growth of O. niloticus was lower compared with C. gariepinus. This opposing yield correlation was also found for other fish and plant combinations including parsley (Petroselinum crispum), lettuce (Lactuca sativa), cucumber (Cucumis sativus) and tomato (Solanum lycopersicum), expressed by the Aquaponic Growth Factor (AGF) in Knaus and Palm (2017a). Following these results it might be advantageous to combine different types of fish in one system, called polyponics according to Knaus & Palm (2017b).
To describe the exact difference of growth performance of basil in a coupled aquaponic system combined with African catfish and Tilapia, two experiments were conducted in 2016 and 2017, each lasting 75 days, in the aquaponic experimental facility "FishGlassHouse" (University of Rostock). The growth of basil (Ocimum basilicum) was compared with the O. niloticus and C. gariepinus in two consecutive experiments (EXP I and EXP II, respectively). The applied new system design included a control group using conventional fertilizer, allowing comparison of the results under exclusion of environmental factors (EF, e.g. light and season). These two experiments are the first step to provide detailed information on polyponic production to potential users.
Material and Methods
The experiments were conducted inside one plant unit (50m2) of the recently established FishGlassHouse in two recirculating units (coupled aquaponic unit - AU; control hydroponic unit - HU). The AU (volume of 7.7m³) consisted of two fish-rearing tanks in succession (glass fibre tank: 2.05x2.05x0.93m, volume 3.90m³, with tank I filled with appr. 2.090l and tank II with 1.970l), one sedimentation tank (1.00m3, IBC, filled with 680l) one biofilter tank (1.00m³, IBC, 680l, filled with 28.6kg of Biocarrier KNS media substrate) and six raft hydroponic troughs, arranged into three hydroponic modules (2.50x1.20x0.47m) with a maximum water level of 38cm (332l) and a sump where a single pump lifts the water continuously back to the first fish rearing tank. The HU unit consisted of three identical raft hydroponic troughs (volume of 1.08m³) positioned aside the AU hydroponic units. In the HU system, an identical single pump located in the HU sump delivered water back to the raft hydroponic troughs, at a same water exchange rate compared with the AU.
In EXP I fish tanks of AU were stocked with 53 x O. niloticus 169.1g (±72.9) mean weight (7.7kg fish biomass) in tank I and 48 x O. niloticus 177.0g (±68.0; 7.6kg) in tank II; in EXP II 53 x C. gariepinus 134.2g (±53.7) mean weight (7.5kg) in tank I and 54 x C. gariepinus 122.2g (±53.9) in tank II (7.5kg). In EXP I O. niloticus were fed 50g per day and tank of Skretting (Meerval 44-14) and in EXP II C. gariepinus with Skretting (Meerval Top 42-13).
Basil plants (Ocimum basilicum, Kiepenkerl, Germany) were planted with 14 plants per trough (AU=84, HU=42) on hydroponic rafts. The hydroponic control group HU was adjusted to an electric conductivity (EC of 1,000μscm-1) using conventional fertiliser only (Universol Orange 16-5-25+3.4MgO+TE). For the comparison of the respective plant growth parameters, a quotient of the HU parameters (environmental factor=EF) was developed (HU EXP I / HU EXP II) and multiplied with the plant growth parameters in EXP II. All values were statistically evaluated with SPSS 22 (IBM), at normal distribution with t-test, otherwise with the Mann-Whitney test (p<0.05).
Results and Discussion
The statistical analysis of both HU groups (EXP I and II with EF) showed no significant differences. Thus, the influence of environmental parameters (e.g. light + temperature) was reduced to a non-significant level. The comparison of the plant growth parameters of both AU groups (EXP I and EXP II) showed significant differences in basil performance (Table I, p <0.05). Plant growth was lower in the AU group with C. gariepinus in Tank I & II (EXP II) between 18.5-30.9%. Consequently different fish species produce a distinctly different plant yield, confirming the results by Palm et al. (2014b) and Knaus and Palm (2017a). This effect was also evident in an experiment with Common carp (Cyprinus carpio, Knaus and Palm, 2017b), though this must be confirmed in a subsequent experiment. We demonstrate the importance of the best fish and plant combination, and the future potential to apply POLYPONICS in order to achieve economic sustainability of coupled aquaponics.
Acknowledgements
We would like to thank COST Action FA1305 "Aquaponics Hub", EIP-AGRI operational groups and the Ministry of Agriculture, Environment and Consumer Protection of Mecklenburg Western Pomerania (Germany) for supporting our research in aquaponic fish and plant production.
References
Knaus, U., Palm, H.W., 2017a. Effects of fish biology on ebb and flow aquaponical cultured herbs in northern Germany (Mecklenburg Western Pomerania). Aquaculture, 466, 51-63.
Knaus, U., Palm, H.W., 2017b. Effects of the fish species choice on vegetables in aquaponics under spring-summer conditions in northern Germany (Mecklenburg Western Pomerania). Aquaculture, 473, 62-73.
Palm, H.W., Seidemann, R., Wehofsky, S., Knaus, U., 2014a. Significant factors influencing the economic sustainability of closed aquaponic systems. Part I: system design, chemo-physical parameters and general aspects. AACL Bioflux 7(1), 20-32.
Palm, H.W., Bissa, K., Knaus, U., 2014b. Significant factors affecting the economic sustainability of closed aquaponic systems. Part II: fish and plant growth. AACL Bioflux 7(3),162-175.
