2. Materials and methods
2.1. Broodstock rearing
The experiment was located in the field research facility of the
Department of Aquaculture, Faculty of Fisheries and Marine Science,
Bogor Agricultural University, Indonesia. Male and female tilapia
broodstock were obtained from the Wanayasa Nila Nirwana Development
Center, the Department of Fisheries ofWest Java Province (BPBIAT
Wanayasa,West Java, Indonesia). The fishwere acclimatized to the local
rearing conditions for two weeks before the start of the experiment.
During this period, female and male fish were kept separately in three
outdoor tanks (3m× 2m× 0.7 m) previously filled with 3000 L chlorinated
and aerated water at a density of 40 fish per tank for female
broodstock and 20 fish per tank for male broodstock.
As a start of the experiment, 2 concrete rectangular outdoor tanks
with a dimension of 3 m × 2 m × 0.7 m and a working water volume
of 3 m3 were stocked with 25 brood fish at a female:male ratio of
4:1. The two tanks were maintained in a different way, one without
organic C addition (control) and one with organic C addition (biofloc
technology or BFT). Aeration was provided using an air blower. Commercial
floating feed (Sinta Feed, Indonesia) was provided twice daily
in each tank at a feeding level of 2.5%/day on fish biomass. Molasses
(53% C) was used as the organic C source in the BFT treatment and
was added daily at an estimated C/N ratio of 10 as described in De
Schryver et al. (2008).
2.2. Larval growth experiment
A growth experimentwas performed using tilapia at late larval stage.
Eight weeks after placing the parental generation in the broodstock
tanks, about 1000 larvae were collected from each tank and graded
according to size. Out of each batch, 120 larvae of similar size were selected
for use. The average body weight and average body length were
23 ± 4 mg and 10.3 ± 0.8 mm, and 20 ± 4 mg and 10.0 ± 0.8 mm for
the larvae from the control tank and the BFT tank, respectively (further
called “origin of the larvae”). The larvae were subsequently randomly
distributed in 2 L plastic tank, previously filled with 1.5 L of water
from either the BFT tank or the control tank (further called “culture
water”) at a density of 15 fish/tank (10 fish/L). Feeding was performed
using a commercial feed (40% protein) (PT. Matahari Sakti, Indonesia)
at a level of 40% on the initial fish biomass per day, spread over 4
times a day. For the tanks containing BFT water, molasses (53% C) was
added daily at an estimated C/N ratio of 10. Artificial light was provided