2. Materials and methods
2.1. Experimental diets The test diets were formulated using the linear least-cost computer program ‘‘Feed-
Ž .
mania’’ Mania Software, Brisbane, Australia . With least-cost diet formulation, nutrient Ž
concentrations and ingredient contents are specified minimum andror maximum levels .
or unrestricted and then the cheapest mix of ingredients to supply the specified nutrients Ž
. are selected. For the least-cost diets formulated for this study 95LC1 and 95LC2 ,
nutrients were specified in relation to the available nutrient profile in the successful SP35. We intended 95LC1 to be similar in nutrient profile to the successful SP35
reference diet. Fish meal content was set at 10 and minimum digestible protein, energy, essential amino acids and phosphorous and linolenic series fatty acids were
restricted to within about 5 of the concentrations in SP35. In contrast, we relaxed specifications for 95LC2 to achieve a cheaper formulation. Fish meal was set at 5 and
minimum digestible protein, energy, essential amino acids and phosphorous and linolenic series fatty acids were restricted to within 15 of the concentrations in SP35. Peanut
and canola meals were excluded from 95LC1 and restricted to 5 in 95LC2. Ingredients and composition of the experimental diets are shown in Tables 1 and 2. Ingredient prices
were obtained from NSW Agriculture, Sydney Retail Feed Ingredient Prices or directly from ingredient suppliers or feed manufacturers. They do not include freight charges,
although clearly all feed mills will have to pay costs of freight for some ingredients.
The least-cost diets, 95LC1 and 95LC2, were manufactured by Ridley Agriproducts Ž
. Narangbar, Qld, Australia . The diets were ground to F 500 mm particle size, steam
Ž conditioned and were manufactured to give 3 or 6 mm diameter sinking pellets Table
. Ž
. 1 . The control diet, SP35 Diet 1, Table 1 was a commercial diet, widely used by
Ž .
industry, and was manufactured by Janos Hoey Forbes, NSW, Australia using a pellet press, without steam conditioning, and was also pressed into 3 or 6 mm diameter sinking
pellets.
2.2. Experimental fish Ž
. Silver perch
Bidyanus bidyanus were artificially bred at the Grafton Research Centre and the fingerlings were raised in earthen ponds using techniques described by
Ž .
Ž .
Rowland 1995a and Thurstan and Rowland 1995 . Before the experiment, fingerlings were fed SP35 and treated with 5 g l
y1
NaCl for 5 days to ensure they were free of Ž
. ectoparasites and to prevent fungal infection Rowland and Ingram, 1991 . Immediately
Ž
y1
. prior to stocking, fish were anaesthetised using ethyl r-aminobenzoate 20 mg l
, weighed and distributed among the nine ponds by systematic interspersion. A total of 1
Ž .
Ž
y1
. 500 silver perch mean weight 80.7 g were stocked density of 1500 fish ha
into Ž
. each 0.1 ha earthen pond Table 3 . Three replicate ponds were used for each diet.
2.3. Experimental facilities and procedures Experimental earthen ponds were 0.1 ha with a maximum depth of 2 m and an
average depth of 1.5 m. The ponds were aerated using a 1-hp paddlewheel aerator for at
Table 1 Formulation for experimental diets SP35, 95LC1 and 95LC2
a b
Ingredient Quantity in diet
Dry Protein
Assumed cost Ž
. Ž .
Ž . Ž
. gr100 g dry matter
matter content
AUDrt SP35
95LC1 95LC2
Ž .
Fish meal Danish 27.00
10.00 5.00
94.70 65.86
1500 Ž
. Meat meal lamb meal
– 21.71
36.88 97.15
52.75 325
Ž .
Blood meal ring dried 2.00
2.09 –
88.65 85.32
800 Corn gluten meal
4.00 3.77
5.19 92.90
57.68 700
Ž .
Soybean meal solvent extracted 20.00
– –
89.11 45.55
479 Canola
– –
5.00 91.74
40.00 295
Peanut meal –
– 5.00
94.75 39.00
325 Ž
Field peas Pisum satiÕum –
14.92 10.39
88.55 24.44
350 Ž
. Lupins Gungaroo dehulled
– 25.50
7.36 95.02
43.61 350
Wheat 26.85
– –
90.78 13.70
180 Sorghum
11.00 4.70
– 89.59
14.62 180
Millrun 2.00
10.00 17.70
89.67 19.62
150 Ž
. Fish oil cod liver oil
1.00 2.91
3.21 100.00
– 800
DL
-methionine 0.15
0.40 0.27
100.00 78.60
5120
c d
Vit rmin premix 4.00
4.00 4.00
100.00 –
4000 Di-Calcium phosphate
2.00 –
– 100.00
– 610
a
More information on the ingredients used here, including details of processing, nutrient composition and Ž . Ž .
digestibility are given in Allan et al., 1999; in press a , b .
b
Based on prices published by NSW Agriculture, Sydney Retail Feed Ingredient Prices, NSW Agriculture, .
Orange, NSW, 2800, Australia , or from commercial feed manufacturers, 1998.
c
Ž .
Ž . Ž
. Ž .
Ž .
IUrkg diet : retinol A , 8000; cholecalciferol D3 , 1000; a-tocopherul acetate E , 125; mgrkg diet : Ž .
Ž .
ascorbic acid C , 1000; biotin 2 , 1; calcium pantothenate, 55; calcium propionate, 250; choline chloride, Ž
. Ž
. 1500; cyanocobalamin B12 , 0.02; ethoxyquin, 150; folic acid, 4; menadione sodium bisulphite K3 , 16.5;
Ž .
Ž .
Ž .
myo-inositol, 600; nicotinamide, 200; pyridoxine B6 , 15; riboflavin B2 , 25.2; thiamin HCl B6 , 10.
d
Ž .
Mgrkg diet : calcium carbonate, 7500; manganese sulphate, 300; zinc sulphate, 700; copper sulphate, 60; ferrous sulphate, 500; sodium chloride, 7500; potassium iodate, 2.
least 13 h each day during the culture period, between 1700 and 0800 h. The ponds were static and water was added every four to five weeks to account for evaporative loss and
seepage. Up to 50 of the water in each pond was exchanged during January because of Ž
y1
. relatively high concentrations of unionised ammonia 0.3 mg l
in most ponds. Ž
. Ž
The fish were cultured for 143 days from December Summer 1995 to May Autumn .
1996 . Fish were fed by hand twice a day, seven days a week, until feeding activity appeared to cease. A maximum of 3 body weight day
y1
was delivered in two roughly equal portions at 0800 h and 1500 h. Approximately 100 fish pond
y1
were sampled monthly, the mean weight determined, the biomass estimated and the ration adjusted
accordingly. Feed rates were also readjusted mid-month based on daily growth rates from previous sampling. Fish were harvested by seine net and draining the ponds. All
fish were harvested, counted and weighed. Performances were evaluated by measuring
Ž .
survival, daily growth rate, weight gain, body composition, feed conversion ratio FCR , Ž
. w
protein efficiency ratio PER s individual wet weight gainrindividual protein intake
Table 2 Chemical composition and digestible nutrients of the experimental diets SP35, 95LC1 and 95LC2
a
Ž .
Nutrient Quantity in diet dry matter basis
SP35 95LC1
95LC2 Ž .
Digestible protein 36.08
36.41 34.01
Ž .
Digestible energy MJrkg 13.71
14.53 14.00
Ž . Fat
6.97 9.18
9.01 Ž .
Linolenic series fatty acids 1.25
1.19 1.11
Ž . Available lysine
2.24 2.10
1.97 Ž .
Available methionineqcys 1.65
1.53 1.44
Ž . Available isoleucine
1.58 1.47
1.39 Ž .
Available leucine 3.26
3.04 2.86
Ž . Available arginine
2.20 3.16
2.74 Ž .
Available histidine 0.91
0.99 0.86
Ž . Available phenylqtyro
2.98 2.90
2.72 Ž .
Available valine 1.87
1.75 1.64
Ž . Available threonine
1.57 1.53
1.39 Ž .
Available phosphorous 0.68
0.62 0.83
a
Based on previously determined composition and digestibility coefficients for each ingredient in all diets.
Ž .x
by fish dry weight , production per unit pond area and ingredient cost per unit of fish produced.
Ž .
Water quality in each pond was monitored twice daily 0800 and 1500 h at least Ž
. three days a week using methods described in Rowland 1995a .
2.4. Sensory eÕaluation of silÕer perch At the completion of the experiment, the silver perch were purged for three weeks in
tanks supplied with domestic water. Fish were not fed during this period. Whole silver perch were gutted and frozen at y188C for shipment and holding prior to sensory
evaluation. The aim of this component of the experiment was to assess odour, appear- ance, flavour and texture attributes of cooked silver perch to determine if diet composi-
Table 3 Mean performance and diet ingredient cost for silver perch fed the three expermental diets for 143 days
Diet Initial
Survival Weight
Growth rate FCR PER
Production Ingredient
y1 y1
Ž . Ž
Ž .
weight increment
g fish kg ha
cost
y1 y1
Ž . Ž .
. g
g day
AUS kg fish
a a
b a
a
SP35 80.91.5 97.51.1 314.511.9
2.230.07 2.230.03
1.330.02 5779127 1.79
b b
a b
b
95LC1 80.41.5 97.00.4 353.410.8 2.530.09
1.970.09 1.370.06 6283117
1.25
b b
a b
c
95LC2 80.81.0 96.80.5 360.97.2 2.530.03
1.930.03 1.410.02 645083
1.06 Values are meansS.E.M. for 3 replicate ponds. Means in columns which share the same superscript were not
Ž .
significantly different P 0.05; ANOVA; SNK .
Ž tion affected sensory properties of the flesh. A total of 12 tasters eight male, four
. Ž
. female assessed three samples one from each dietary treatment using a standard rating
Ž .
procedure AS2542.2.3, SAA, 1988 at each of three sessions. All fish from any
treatment were from one pond. All samples presented to each taster were matched for position within the fish, and were from fish of the same weight rank. Temperature of the
samples served was 758C. Order of tasting the treatments was balanced across the panel. Samples were served to tasters in individual booths illuminated with white light
Ž
. daylight equivalent . Purified water was freely available for palate cleansing prior and
during tasting. Tasters identified and rated the colour of internal flesh, and odour, flavour and texture characteristics on structured graphic line scales. Overall acceptability
of the flesh was also rated, and tasters were given the opportunity to record additional descriptors and add any general comments about the samples.
2.5. Biochemical analyses All chemical analyses were done in duplicate. Fish samples were analysed for dry
Ž .
Ž .
matter, ash, crude fat and energy bomb calorimetry by the AOAC 1990 procedures. Ž
. Ž Nitrogen was determined by the method of Havilah et al. 1977
crude protein s N = .
Ž .
6.25 . Amino acids were determined by the method of Cohen et al. 1989 and analysed following acid hydrolysis using high pressure liquid chromatography and Waters
Ž .
Pico-Tag Waters, Lane Cove, NSW, Australia . Sulphur amino acids were determined separately following performic acid digestion, and tryptophan, which is lost during acid
Ž .
hydrolysis, was not analysed Cohen et al., 1989 . 2.6. Statistical analysis
All experiments were designed for analysis using single-factor ANOVA. Homogene- ity of variance was assessed using Cochrans’ Test, and multiple comparison among
means using Student Newman–Keuls procedure. Mean values were considered signifi- cant at P - 0.05.
For each of the sensory variables measured, scores for each diet were compared using a randomised block analysis of variance with sessions and panellists as blocking terms.
Ž .
Where a significant P - 0.05 F ratio was found then pairwise comparisons of the
mean scores were made using the least significant difference procedure.
3. Results
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