International Journal of Aquaculture, 2016, Vol.6, No.21, 1
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using a digital thermometer, while pH was measured with a digital pH meter (LI-120, ELICO, India). Dissolved
oxygen, free carbon dioxide and total alkalinity were determined following standard procedures (APHA, 1992).
Plankton samples were also collected on fish sampling days, using a net made of No. 30 bolting silk cloth having
60 µm mesh size, by filtering 100 liters of water from different locations of each experimental tank. Dry weight of
plankton was determined by drying the filtrate in a hot-air oven at 80 ºC, till a constant weight was obtained.
2.4 Body indices
Hepatosomatic index (HSI) and Viscerosomatic index (VSI) of fishes was computed on termination of the
experiment using the following formulae.
HSI (%) = Weight of liver (g)/Weight of fish (g) X 100
VSI (%) = Weight of viscera (g)/Weight of fish (g) X 100
2.5 Muscle DNA and RNA
Muscle DNA was determined by the diphenylamine method of Giles and Myres (1965), while RNA was estimated
as described by Ceriotti (1955).
2.6 Proximate composition
Proximate composition of the feed ingredients (Table 2), diets and fish carcass was analyzed. Crude protein, lipid,
crude fiber and ash were determined according to AOAC (1995). NFE was obtained by the ‘Difference method’
(Hastings, 1976). The energy content was obtained by multiplying protein, fat and carbohydrate (NFE) content by
factors of 5 (Smith, 1976), 9 and 4 (Hastings, 1975) respectively and expressed in kJ/g.
Table 2 Proximate composition (% ±S.E.) of ingredients used in feed formulation
Parameter (%)
Fishmeal
Groundnut oil cake
Rice bran
Tapioca flour
Moisture
7.96 ±0.12
8.67 ±0.17
11.96 ±0.19
12.33 ±0.03
Crude protein
60.73 ±0.27
41.92 ±0.14
9.56 ±0.04
3.51 ±0.02
Lipid
9.24 ±0.06
11.09 ±0.07
9.64 ±0.06
0.92 ±0.01
Ash
18.91 ±0.17
3.58 ±0.06
25.48 ±0.18
1.67 ±0.04
Crude fiber
0.36 ±0.03
6.40 ±0.05
30.80 ±0.12
3.50 ±0.06
Nitrogen-free extract
2.79
29.01
26.46
79.05
Gross energy (kJ/g)
16.65
17.79
10.05
14.30
2.7 Digestive enzyme activity
The activity of digestive enzymes viz. protease, amylase and lipase in the pancreas and intestinal segments of the
experimental fish was analyzed on termination of the experiment by the methods of Kunitz (1947), Bernfeld
(1955) and Bier (1962) respectively. Six fish from each treatment were used to collect the tissues for enzyme
assay.
2.8 Performance indices and statistical analysis
Performance indices viz. specific growth rate (SGR), feed conversion efficiency (FCE) and net production were
calculated as follows.
Specific growth rate (SGR % day-
1
) = [(ln final weight
-
ln initial weight/Experimental duration in days)]
×100.
Feed conversion efficiency (FCE) = Fish weight gain (g)/Feed consumed (g) x100.
Net production (g) = Gain in body weight (g) x Total number of fish harvested.
Comparison among treatments for various parameters was done by one-way analysis of variance (ANOVA),
followed by Duncan’s multiple range test at P<0.05 (Duncan, 1955; Snedecor and Cochran, 1968).
