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Discoveries in Agriculture and Food Sciences - Vol. 11, No. 6
Publication Date: December 25, 2023
DOI:10.14738/dafs.116.15139.
Shimakawa, Y., Kitaya, Y., Shibuya, T., & Endo, R. (2023). Plant Growth and Nitrogen Flow in an Aquaponics System Integrating
Lettuce Hydroponics and Loach Aquaculture. Discoveries in Agriculture and Food Sciences, 11(6). 89-95.
Services for Science and Education – United Kingdom
Plant Growth and Nitrogen Flow in an Aquaponics System
Integrating Lettuce Hydroponics and Loach Aquaculture
Shimakawa, Y.
Osaka Metropolitan University, Gakuencho 1,
Naka-ku, Sakai-shi, Osaka 599-8531, Japan
Kitaya, Y.
Osaka Metropolitan University, Gakuencho 1,
Naka-ku, Sakai-shi, Osaka 599-8531, Japan
Shibuya, T.
Osaka Metropolitan University, Gakuencho 1,
Naka-ku, Sakai-shi, Osaka 599-8531, Japan
Endo, R.
Osaka Metropolitan University, Gakuencho 1,
Naka-ku, Sakai-shi, Osaka 599-8531, Japan
ABSTRACT
There is an urgent need to develop production technology that uses water and other
material resources effectively to create a stable food supply. Aquaponics combining
hydroponics and aquaculture is expected as an efficient system for producing crops
and animal proteins sustaining the reuse of water and balance of nutrient elements
between both cultures, using dissolved elements in fish excrement for plant growth.
To evaluate the possibility of aquaponics combining lettuce hydroponics and loach
aquaculture, we analyzed the growth performances of lettuce and loach and the
balance of nutrient elements, especially for nitrogen between input and output of
the whole system and nitrogen flow in the system. As a result, lettuce grew in
aquaponics with half strength standard solution as well as hydroponics with a
standard solution by the optimal combination of the number of plants and fish. In
nitrogen balance, almost 70% of nitrogen from the feed was used by growing lettuce
and about 25% of nitrogen from the feed was accumulated in loach.
keyword: aquaculture, hydroponics, sustainability
INTRODUCTION
Due to the recent growth in the global population, concerns have arisen over the stable supply
of food and water resources. Therefore, there is an urgent need to develop production
technology that uses water resources effectively to create a stable food supply (Yamada, 2015).
This study examines aquaponics, a biological production system combining hydroponics and
fish farming that has been attracting attention in recent years as a resource-recycling
production system.
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Discoveries in Agriculture and Food Sciences (DAFS) Vol 11, Issue 6, December- 2023
Services for Science and Education – United Kingdom
Aquaponics can make effective use of water and nutrients (Wongkiew et al., 2017). Sharing
water between hydroponics and aquaculture systems allows plants to utilize the fertilizer
components derived from fish excrement for growth. Therefore, food can be produced while
reusing nutrients and converting waste into high-value resources.
To date, the main focus in the field of aquaponics has been the availability, dissolved
concentration, and accumulation of nitrogen compounds (Goddek et al., 2016). This is because
plant growth depends on nitrogen supply (Xu et al., 2012). Since aquaponics is a biological
production system that combines hydroponics and fish farming, a thorough understanding of
the nitrogen balance is required to increase the production of the system.
Most studies dealing with aquaponics have used tilapia or catfish as the fish to be cultured (e.g.,
Nuwansi et al., 2016; Graber and Junge, 2009; Naznin et al.; Islam et al., 2022) because they are
edible and have a high growth rate. However, some parts of these fish are not edible, such as
the head, internal organs, and bones, which is a drawback. In contrast, loach has an edible
portion of 100% and high nutritional value (Japan Ministry of Education, Culture, Sports,
Science, and Technology). It is also a traditional Japanese ingredient. In addition, loaches are
resistant to dissolved oxygen deficiency because they can breathe using their intestines.
Therefore, loach was adopted as the fish to be cultivated in this study. Many studies have been
conducted on aquaponics cultivation with different types of plants. For this study, lettuce was
adopted as the plant to be cultivated, as it is common in plant factory cultivation.
The nitrogen balance has been the main focus of aquaponics research (e.g., Hu et al. 2015) As a
biological production system combining hydroponics and aquaculture, a thorough
understanding of nitrogen balance is necessary to increase system productivity. In this study,
we also evaluated the usefulness of components derived from fish excreta as fertilizers for plant
growth in aquaponics, using a combination of loach farming and lettuce hydroponics. In
particular, we evaluated the flow of nitrogen within the system, as it is an essential element for
plants and is abundant in fish excreta.
MATERIALS AND METHODS
Lettuce (Lactuca sativa L. 'crunch') and loach (Misgurnus anguillicaudatus) were cultivated and
bred for 21 days. Dechlorinated tap water (12 L) and loach (initial weight 2.9 g/fish) were
placed in a cultivation container, and 21-day-old lettuce seedlings (fresh weight 2.8 ± 0.2
g/plant) were planted in the holes at 5 cm intervals in a grid pattern (Fig. 1). The environmental
conditions for growing lettuce were set at a temperature of 25 °C, relative humidity of 70%, a
CO2 concentration of 1000 μmol mol-1, a photosynthetic effective photon flux density of 200
μmol m-2 s
-1, and a light period of 16 h d-1. A white fluorescent lamp (FHF32EXD HX-S NEC
Corporation) was used as the light source. Continuous aeration (3.5 L min-1) was provided to
the nutrient solution. Loaches were fed a commercially available goldfish feed (Kyorin Co., Ltd.)
once a day, 5 times a week, equivalent to 1% of their body weight (about 0.03 g / fish).
Test Group
In this study, a commercial fertilizer solution (OAT, Ohtsuka Co., Ltd.) at 1/2 the standard
prescription concentration was used as a standard nutrient solution. Separate test plots were
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Shimakawa, Y., Kitaya, Y., Shibuya, T., & Endo, R. (2023). Plant Growth and Nitrogen Flow in an Aquaponics System Integrating Lettuce Hydroponics
and Loach Aquaculture. Discoveries in Agriculture and Food Sciences, 11(6). 89-95.
URL: http://dx.doi.org/10.14738/dafs.116.15139
established with the standard nutrient solution, 0.5-fold nutrient solution, and 0.5-fold nutrient
solution with 20 loaches, respectively. Furthermore, the amount of dissolved nitrogen
discharged from 20 loaches was quantified by establishing a test plot in which only loaches
were bred in dechlorinated tap water.
Nitrogen Flow
The nitrogen content (g) of each element in the system was calculated using the following
procedure.
The amount of nitrogen contained in the nutrient solution of a test plot (“Nutrient Solution”;
Fig. 2) was calculated from the nutrient solution composition specified by the manufacturer.
The amount of nitrogen contained in the feed provided to the fish (“Feed”; Fig. 2) was calculated
by multiplying the nitrogen content (g g-1) contained in the loach feed by the total feed amount
(g). There was no leftover food. The amount of nitrogen contained in the excretion from loaches
("Excretion from loaches"; Fig. 2) is the amount of nitrogen derived from loach emissions
calculated from the total amount (g) of dissolved nitrogen components discharged by 20
loaches in 21 days in the test plot where only loaches were bred. The amount of nitrogen
remaining in the cultivation container at the end of the experiment ("Residual solution"; Fig. 2)
was calculated from the amount of dissolved nitrogen component (g) at the end of the
experiment. The amount of nitrogen accumulated in the lettuce grown during the experiment
("Lettuce"; Fig. 2), calculated using the nitrogen content of lettuce at the end of the experiment
(g g-dry-1) and the increase in the total dry weight of lettuce during the experiment (g-dry). The
amount of nitrogen accumulated in the loach body during the experimental period ("Loaches";
Fig. 2) was calculated from the nitrogen content in the loach body (g g-dry-1) and the increase
in the loach dry matter during the experimental period (g-dry).
Fig. 2: Schematic diagram of the experimental aquaponics combining lettuce hydroponics and
loach aquaculture.
Nutrient
Solution
Lettuce
Loach Pump