DISCUSSION
It was found that dietary supplementation of prebiotic
compound showed a positive growth performance with the
level of 10% mushroom inclusion exhibiting the greatest
weight gain (Figure 1). Among the growth performance
analysis (Table 2), Diet 2 and Diet 3 showed better growthresponse but was not significantly different (p>0.05). The
improved growth observed in the present study was in
agreement with studies done with hybrid striped bass (Li
& Gatlin 2004) and rainbow trout (Staykov et al. 2007).
However, the effect of dietary prebiotic supplementation
on aquatic organism growth exhibits negative results in
certain reports (Grisdale-Hetland et al. 2008; Mahious
et al. 2006). Fish fed with Diet 4 (20% mushroom stalk
meal supplementation) showed slight decrease in weight
gain compared with Diet 2 and 3. Reduced growth rate
was recorded in terms of weight gain and increased FCR
value that caused fish to have lower feed intake and
consequently deterioration of water quality. According
to Vetter (2007), some bioactive compounds embedded
in mushroom can potentially affect the digestibility of
nutrients. High fiber content of mushroom may explain
the result of the lower nutrient intake in the present
study. The survival rate and FCR values of all diets
were not significantly different (p>0.05). This was in
agreement with a report from Samrongpan et al. (2008)
who mentioned that mannan – oligosaccharides has not
affected the Nile tilapia fry in terms of survival rate and
feed conversion ratio.
The idea of prebiotic in aquaculture feed originated
from the observation that inulin and oligosaccharides
stimulated the growth of bifidobacteria selectively in
human nutrition. However, application of prebiotic in
aquatic organism was limited in its use due to lack of
information until earlier studies being conducted in 1995
(Hanley et al. 1995). Some reviews on potential of dietary
fiber used as prebiotic in aquaculture were done by Ringo
et al. (2010). Earlier studies in prebiotic application was
done by using the commercial prebiotic, Grobiotic that
significantly increased feeding effectiveness, improved the
survival rate, immunological response and the resistance
against pathogen in striped bass (Peng & Gatlin 2003).
Lactic acid bacteria are regarded as beneficial organism
living in the fish intestinal system. It is because they
produce bacteriocins which suppress the development
of fish potential pathogen and thereby positively affect
microflora of fish. Some reports such as Szilagyi (2002)
revealed that prebiotic compounds may promote the
existence of lactic acid-producing bacteria and can enhance
the resistance to development of potential pathogen.
There were several studies that showed feed efficiency
and protein efficiency ratio were improved in fish fed
with the diets supplemented with prebiotics. Results from
Zhou et al. (2010) indicated that prebiotic-supplemented
diets improved the height of microvilli in red drum. The
microvillus height was correlated with improvement of
growth and feed utilization of target fish by enhancing
apparent digestibility coefficient (ADC) of nutrient
uptake.
As shown in Table 3, carcass composition was not
affected by dietary treatments at the end of the feeding
trial. Crude protein, crude lipid and ash of fish carcass
were not significantly different between dietary treatments
with the exception of crude lipid of fish that exhibited
significant difference between Diet 4 and others. However,
dry matter of carcass composition showed significant
increase in comparison with the Diet 1 (control) in
all dietary treatments. Similarly, Genc et al. (2007)
found that dry matter and protein content of fish fillet
increased with increasing level of dietary MOS (mannan –
oligosaccharides).
In conclusion, the improvement of growth performance
and survival with 10% prebiotic supplemented diet (Diet 2)
may result in promising productivity in various aquaculture
enterprises leading to a beneficial return of investment.
Growth performance obtained by Diet 2 treatment was
the best and feeding with this dietary treatment with
supplementation of prebiotic compound makes fish
culture worthy because it comes with a combination of
medication treatment in the diet against infections. The
use of natural immunostimulants such as mushroom
in fish culture for prevention of fish diseases showed a
promising new development and could solve the problem
of massive use of antibiotics. The results obtained in the
present study indicated a distinct improvement of growth
with an addition of prebiotic.