Climatic conditions must be also similar in order to compare results and would clearly affect production in other locations. In fact, the hours of inbound radiation and the fluctuations in temperatures can limit the use of some crops and affect the growth of the plants. Water temperatures also condition the growth of the fishes. In areas such as Seville, with a clear seasonal difference in temperature and solar radiation on plant production in aquaponics, the large variations in monthly production can condition the supply of food of aquaponic origin. The results of this study in Seville, located at 37◦ of latitude and with two periods of heat and cold that could limit aquaponic production, are similar to those obtained by Somerville in the areas between Israel, Gaza and West Bank that are located at 32◦ latitude and with similar climatic conditions, although probably having less cold temperatures in autumn-winter. In another study, in Palermo,at 38◦ of latitude with a somewhat milder climate due to the influence of the sea, an average of 2250 lettuce heads were produced in 5 m2 of cropping area at a very high density. Considering an average of 165 g per lettuce head, the production per growing area unit was 74.25 kg m− 2. This harvest obtained is strikingly high,but the authors do not detail information on the annual range of water temperatures in their MAS, nor how they achieved a sufficient biomass of tilapia from October to March to maintain such a high lettuce production at low water temperatures. Love et al. produced a variety of vegetables during two years in Baltimore,using an aquaponic facility with tilapia.
They obtained a plant production of 22 kg m− 2 in the first year and 31.5 kg m− 2 in the second. Those results are more consistent with ours. Regarding the fish growth indicators, the AGR 1.3 g d− 1 in MAS1 and 1.7 g d− 1 in MAS2 was higher than that of Delaide et al.. The FCR in our study,lower than those reported by Effendi et al. ,are in line with other authors: 1.29,1.16 and 1.56. The type of stocking method proposed in this study allowed obtaining 5 harvests of tilapia in MAS1 and 4 in MAS2 over 1 year, similar to the results cited by Sommerville et al. with a staggered stocking method, stacking flower pot tower with fingerlings restocked each three months. Asciuto et al. also used the staggered stocking method, but with two rounds of stocks in 1 year, also maintaining a higher fish biomass by having 2 tanks of 500 L each. This strategy was not adopted in our study because we believe that one single fish tank with only a batch of fish makes the MAS be more easily handled. The high biomass of fish harvested in summer as a precaution against high temperatures, reduced the fish biomass too much during autumn winter, which limited the plant production and also prevented any harvest of fish in this period. A better strategy in climates like those of Seville would be to increase the aeration in the water in the fish tanks during summer, instead of reducing the biomass. This would enable reducing the second August harvest by half, to 5 kg of fish, and the remaining 5 kg would accumulate to increase biomass during autumn winter, allowing a harvest during this period. In addition, there would be a surplus biomass of tilapia that, after 1 year of growth, would not exceed 350 g. These fish could join the annual restock of another 110 fry in the second year to start a new cycle of aquaponic production with a higher biomass that maintains a higher level of nutrients in the water for the plants.The combined production of fish and vegetables also has an influence on the inputs required. For instance, the water requirements in this type of systems are much lower than those for conventional aquaculture.
The average water replenishment rate calculated in our study was lower than the 3.6 % reported by Delaide et al.,similar to that observed by P´erez-Urrestarazu et al. and in the lower part of the 0.5–10 % range determined for aquaponics by Love et al.. Considering the total plant production of the systems and all the water volume consumed, the average water footprint for the vegetal produce was 64 L kg− 1 in MAS1 and 91.3 L kg− 1 in MAS2. These values are lower than those obtained by Delaide et al. and Love et al. and well below those reported by Delaide et al.. If the fish production is also considered, 53.7 L were needed to get a kg of produce in MAS1 and 78.4 L in MAS2. P´erez-Urrestarazu et al. obtained a similar value in their best case scenario. In terms of energy consumption, the aquaponic facilities employed in our study required a very low amount of energy, as only the pumps and air compressors needed electricity. Hence, the average annual daily consumption was 0.86 kW h d− 1,very similar in MAS1 and MAS2. However, during the cold months, MAS2 presented a slightly lower daily consumption, while MAS1 increased to 0.91 kW h d− 1,due to the heaters that were sometimes necessary when the solar panel was not enough. Therefore, the energy consumed was really low: 1.6 kW h per kg of produce. In contrast, Love et al. reported an annual electricity consumption around 10,900 kW h plus 8500 kW h in propane. Considering the joint production that they obtained, 41.15 kW h of energy were required per kg of produce. In Delaide et al.’s study, a much higher energy consumption per kg of produce was observed, though the average daily consumption was lower. A value of 41.5 kW h kg− 1 was deduced from a study in much colder weather. The main difference of energy consumption between all these studies and ours was due to heating water, this being the most sensitive parameter in the aquaponic system. For example, in Delaide et al. the submersible heaters they had to use accounted for 57 % of the energy required. Conversely, Atlason et al. showed a much lower energy consumption per kg of produce,as they used waste heat from a co-generation system for heating the system. Still, it was 5.5 times higher than in our study.
In light of this, it is clear that the strategies employed in our trial were successful as they produced a vast reduction in energy consumption. This is very important as energy costs are usually one of the most important factors for the viability of aquaponic production. The labour required for the operation of these systems is not high in relative terms as an average of 14− 18 min per day were necessary. However, an annual workload of 100− 120 h has a high cost if the MAS are not self-managed.The human population worldwide currently exceeds 7 billion, and it is projected to reach 8.5 billion by 2030, and 9.7 billion by 2050. With a fast growing global population, the demand for soil and land for crop production is likely to increase, and more urban area development is projected to take place. Earth’s arable land is finite and challenges such as soil degradation, water scarcity, and urban area development need to be addressed by developing new and modified agricultural systems. Alternative food production systems that require limited land, soil, and water, and which can be developed in urban areas may play a major role in future agriculture. Hydroponics and aquaponics are soilless agricultural systems that are highly productive, suitable for urban areas, and can address the shortage of land in relation to growing demand for food production. Hydroponics is the culture of plant crops in soilless water-based systems, where nutrients come only from formulated fertilizer. Aquaponics, is an integration of hydroponics and aquaculture, where crop plants and aquatic species can be grown together in a soilless water-based system. Aquaculture is growing of aquatic animals/organisms in a designated water body. Large amounts of polluted water are produced in aquaculture systems with a potential for environmental pollution,which can be reduced by techniques such as aquaponics.
Aquaponics, a combined culture of fish and plants has been proposed as a means to decrease waste accumulation from aquatic monoculture and to increase the productivity and profitability of the system. Soilless water-based systems are commonly set-up in vertical integration systems in indoor urban settings, which addresses the limitations of soil quality and space availability. Being indoor practices, hydroponics and aquaponics are not directly affected by the changing climatic patterns and abrupt weather conditions, and hence could be effective adaptive strategies, as well. Aquaponics has several advantages over aquaculture and hydroponics. This system reduces the need for formulated fertilizers, eliminates the possibility of agricultural run-off, and cleanses the water through bio-filter treatments. The nutrients released from fish excreta and microbial breakdown of organic wastes are used by plants in aquaponic systems. This way the plant component serves as a bio-filter, and therefore a separate bio-filter is not needed unlike aquacultural systems. In addition, this bio-filter also generates income through the sale of the economic plant products. Therefore,ebb and flow the aquaponic systems develop an economically advantageous symbiotic system, where aquatic species and the plant component benefit each other and the grower receives two marketable products. In contrast, the crop plant is the only marketable product in hydroponics and it is devoid of the commercial aquatic species and associated nutrient supply. Aquaponics can also be a strategy to combat water scarcity, as it has been shown to lower overall water consumption and prolong the useful life of water by reducing turnover rates and subsequently the environmental pollution, with improved economic return. Primarily, fishes are used as the aquatic species in aquaponic studies and the potential for other commercial species such as crayfish are little known. Crayfishes have high economic importance globally, including southern United States and Southeast Asia. However, very few aquaponic studies have incorporated crayfishes and observed plant animal interaction effects. Effendi et al. observed that spinachaquaponic systems resulted 5% higher crayfish survival rates than crayfish monoculture. They concluded that plant bio-filters such as spinach, is very effective in cleansing the water resulting better crayfish survival. Crayfish can also be grown together with common fishes under aquaponic systems. In Louisiana, cultivation of crayfish and rice together increased yield for both. Gallardo-Collí et al. reported that tilapia cohabited with crayfish in an aquaponic system that produced 9.4% higher green corn fodder compared to hydroponics. Selection of plants for soilless systems is critical.
Basil is an annual herb that is commercially important and both fresh and dried leaves are used for culinary purposes. Basil is considered a medicinal herb for its diuretic and stimulating properties and also used in perfume compositions. Basil is suitable for soilless production, and several studies have used basil as aquaponic or hydroponic crop.Rakocy et al. reported that aquaponic basil produced higher yield than field basil. However, no studies have compared aquaponics and hydroponics systems for basil production. Hydroponics and aquaponics are emerging fields of alternative agriculture with the potential to address the contemporary challenges faced by traditional agriculture. However, of the few studies that have compared these two systems, mostly focused on the commercial aquaponic species and little information is available on the plant production dynamics. In addition, little is known about the potential for non-fish aquatic species such as crayfish. We conducted a greenhouse study comparing crayfish-based aquaponic systems to hydroponic systems with a focus on the basil plant. The parameters under study included basil plant growth, yield, quality, and nutrition.Water pH and water temperatures were measured twice weekly and daytime greenhouse temperature was collected daily. Water nitrogen content was measured weekly using freshwater aquarium master test kit. Weekly basil leaf chlorophyll content was measured using SPAD 502P chlorophyll meter. In each plant a lower leaf and an upper leaf were measured in full sunlight and then averaged. Leaf chlorophyll content is a reflection plant health/quality and hence, the SPAD readings are commonly used to determine the health quality of plant. Plant height was measured every week using a standard ruler. Harvesting of basil plants took place on November 19, 2015.