International Journal of Aquaculture, 2017, Vol.7, No.10, 71-78
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3.2.3 Under sewage-fed pond condition in net cages
Sewage-fed pond reared
C. catla
recorded the highest serum IGF-1 (2.34±0.36 ng/ml) followed by
L. rohita
(2.06
±0.03 ng/ml) and
C. mrigala
(1.07±0.06 ng/ml). There existed significant differences (P<0.05) in the IGF-1 levels
of
L. rohita
and
C. mrigala
as well as
C. catla
and
C. mrigala
(Table 3).
Cirrhinus mrigala
recorded the lowest serum IGF-1 levels under all culture conditions during the 21 days of
confinement. Significant differences (P<0.05) existed in the IGF-1 levels of net-caged
C. mrigala
of normal and
sewage-fed ponds as well as captive reared and sewage-fed pond. The difference in the IGF-1 levels of
C. mrigala
of normal farm and captive-reared was insignificant (Table 3).
4 Discussions
Among the various factors available for assessing the growth, serum IGF-1 is the most promising candidate as a
measure of instantaneous growth in fish (Picha et al., 2012). As there were no reports on the levels of serum
IGF-1 in IMCs, quantification of IGF-1 levels of IMCs cultured under varied conditions was attempted in this
study. The serum IGF-1 levels of IMCs varied with culture conditions despite the pellet feeding of uniform
nutritional status. Variations in serum IGF-1 levels were noticed between the species and within the species
analysed, possibly due to the feed availability, and physiological and nutritional status of fish, which regulate the
IGF receptor (Planas et al., 2000). In the present study,
C. catla
recorded the highest serum IGF-1 levels under
captive and sewage-fed pond conditions. Though the level was slightly higher in the sewage-fed pond than in
captive condition, the difference was insignificant (P>0.05). While in normal pond,
L. rohita
recorded the highest
serum IGF-1 level. The serum IGF-1 levels of
L. rohita
were almost constant ranging from 2.04±0.08 ng/ml in
captive to 2.10±0.19 ng/ml in normal pond condition. Likewise, the serum IGF-1 levels in
C. catla
ranged from
1.99±0.17 ng/ml in normal pond to 2.34±0.36 ng/ml in sewage-fed pond, but the differences were insignificant
(P>0.05). Also, the serum IGF-1 levels of sewage-fed pond grown
C. catla
and
L. rohita
differed insignificantly
(P>0.05), which indicated that the growth of
C. catla
and
L. rohita
is unaffected despite growing in sewage-fed
pond and the adverse environmental conditions such as high ammonia level (0.48±0.21 mg/L) and other
parameters (Table 2). In composite fish culture and/or polyculture systems, IMCs are considered due to their
compatibility for habitat preference and food to utilize ecological niches of culture system.
Catla catla, L. rohita
and
C. mrigala
feed on the foods available in the surface, column and bottom layers of the pond, respectively
(ICAR 2006). In fact, sewage-fed pond condition favoured the growth of
C. catla
, possibly because of the
abundant availability of natural foods, particularly zooplankters in the surface layer of the water body. Contrarily,
the growth rate of
L. rohita
was reportedly higher than that of
C. mrigala
in polyculture practice (FAO, 2012) and
C. catla
in a culture condition that received organic manure, inorganic fertilizer and supplementary feed (Abbas et
al., 2010).
Picha et al. (2012) suggested that IGF-1 could provide an accurate indication of the long-term effects of stress on
growth so also the results of the present study.
Cirrhinus mrigala
, a bottom dweller and detritus feeder, recorded
the lowest serum IGF-1 levels under all culture conditions. The observed significant differences in the IGF-1
levels of bottom dwelling
C. mrigala
of normal farm and sewage-fed farm, as well as captive reared and
sewage-fed farm indicated that the growth of
C. mrigala
is adversely affected by sewage, possibly due to the
long-term exposure, and prevailing water quality and unfavourable pond bottom conditions. The results further
corroborate the observations of Sahoo et al. (2005), who recorded better health status of
L. rohita
and
C. catla
than
C. mrigala
in aquaculture conditions on the basis of respiratory activity. Hayat et al. (2007) reported
significantly lower weight increments in
C. mrigala
among IMCs exposed to sub-lethal concentrations of heavy
metals, viz., Fe, Zn, Pb, Ni, Mn and their mixture for 90 days culture. The observed high serum IGF-1 levels in
L.
rohita
and/or
C. catla
than
C. mrigala
might have contributed to their tolerance in captive and sewage-fed pond
condition.
Further, the serum IGF-1 levels of IMCs were markedly lower than those recorded in channel catfish, 4-12 ng/ml
(Silverstein et al., 2000), in transgenic coho salmon, 35-400 ng/ml (Devlin et al., 2004), coho salmon, 17 ng/ml
