2.2. Larval growth experiment
A growth experiment was 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 at a photoperiod of 24 h light. The growth experiment consisted of 4
treatments, each performed in quadruplicate:
1 BFT/BFT: fish larvae collected from the BFT broodstock tank and
transferred to BFT water (with molasses addition).
2 BFT/C: fish larvae collected from the BFT broodstock tank and transferred
to control water (without molasses addition).
3 C/BFT:fish larvae collected fromthe control broodstock tank and transferred
to BFT water (with molasses addition).
4 C/C: fish larvae collected from the control broodstock tank and transferred
to control water (without molasses addition).
No water exchange was applied during the experiment. Freshwater
was, however, regularly added to replace loss due to evaporation.
Growth parameters were determined after 14 days of larval rearing in
the 2 L tanks. The survival was expressed as the percentage of surviving
larvae over initially stocked larvae. The specific growth rate (SGR) was
calculated according to Huisman (1987) using the equation:
SGR ¼
ffiffiffiffiffiffiffiffi
wt
wo
t
r
−1
!
100
with SGR = specific growth rate (%/day), wt = final average fish body
weigh (g), wo = initial average fish body weight (g), t = experimental
period (day).
The condition factor (k) was calculated according to Ali et al. (2008)
using the equation:
k ¼ W
L3
100
with k = condition factor,W = average body weight (g), L = average
body length (cm).
The relative standard deviation of the fish total length per treatment
was calculated as the percentage of the standard deviation over the
mean of the total length.