3. Results and discussion
3.1. Aquaponics performance
During the study period, no fish mortality or plant disease was
observed. One batch of tomato, and three batches of pak choi were
harvested, because of the short growth period of pak choi. Table 1
shows the performance of tomato and pak choi in aquaponics.
More fish feed consumption and higher fish biomass increase were
obtained in tomato-based aquaponics, mainly because of better
water quality (discussed in Section 3.2). The feed conversion ratio
(FCR) of tomato- and pak choi-based aquaponics were 1.6 and 2.0,
respectively, both within the range of conventional aquaculture
system (i.e., 1–3) (Naylor et al., 2000). Both aquaponics successfully
achieved simultaneous production of two cash crops, i.e., fish
and vegetable.
It is worth noting that a large amount of fresh water was used to
replenish the water losses, which were mainly due to plant evapotranspiration.
Higher water replenishment of tomato-based aquaponics
was resulted from its larger leaf surface exposed to air. In
recirculating aquaculture system (RAS); daily exchange of 5–10%
with fresh water is part of the operation routine, although some
RAS have been operated successfully without water exchange in
recent years (Hu et al., 2014). With daily water exchange of 5%
as per the present study (i.e., 200 L fish tank), 1400 L of fresh water
would be needed to run a RAS continuously for 139 days. Thus,
aquaponics doesn’t seem to have obvious advantage in fresh water
conservation, especially for plants with large exposed leaf surface