MATERIALS AND METHODS

Experimental Site
The present experiment was conducted at Aquaculture Lab, Department of Fisheries, Raipur and feed analysis part was done at Department of Animal Nutrition, Anjora, Durg of Indira Gandhi Agricultural University, Raipur, Chhattisgarh, India during period of December to February, 2003-04.

Preparation of Experimental Diets
Five different nearly iso-caloric (3.6-3.7 kcal g^-1) diets with 23.96, 25, 30, 35 and 40% crude protein were formulated. D₁ to D₄ were prepared using finely powdered, mustard oil cake, rice bran, slaughter house waste, vitamin-mineral mixture and soybean oil with carboxy methyl cellulose as a binder, while control diet was prepared by mixing all the above ingredients except slaughter house waste. Slaughter house waste in the diets was incorporated at levels of 14.62, 24.32, 34.04 and 43.75% to replace equal proportion of the other ingredients in D₁ to D₄. Physiological fuel values of 3.5, 4.5 and 8.5 kcal g^-1 for carbohydrate, protein and lipid, respectively were used for dietary energy calculations (Jauncey, 1982). The composition of ingredients used for experimental diets given in Table 1. The proximate composition of the ingredients used for formulation of diets is given in Table 2. Dietary ingredients were cleaned, milled and mixed in definite proportions. Therefore, thick dough was made using luke warm water. Using a hand pelletizer, 0.5 mm thick pellets were obtained, while using in feeding experiments. The proximate compositions of the experimental diets are displayed in Table 3.

Table 1:	Composition of experimental diets
Composition of vitamin-mineral mixture: Vitamin A (as acetate) 5000 IU.; Cholecalciferol 1000 IU.;Thiamin monocitrate 10.00 mg; Riboflavin 10.00 mg; Pyridoxine hydrochloride 5.00 mg; Cyanacobalamin 15.00 g; Nicotinamide 75.00 mg; Calcium pentathenate 10.00 mg; Ascorbic acid 150.00 mg; a tocopheryl acetate 25.00 mg; Biotin 5.00 mg; Folic acid 5.00 mg; Menadione 100.00 mg; Choline chloride 50.00 mg; PABA 5.00 mg; Myoinocitol 10.00 mg; Calcium lactate 0.125 mg; Magnesium oxide 60.00 mg; Dried ferrous sulphate 30.00 mg; Copper sulphate 2.00 mg; Manganese sulphate 2.00 mg; Zinc sulphate 2.00 mg; Sodium molybdate dihydrate 0.25 mg; Sodium borate 0.80 mg; Potassium iodate 20.00 mg; Bicalcium phosphate 0.10 g; Cobalt chloride 20.00 mg

Table 2:	Proximate composition of feed ingredients used in the formulation of diets
±SEM

Table 3:	Proximate composition of the experimental diets (% on dry matter basis)

Experimental Design
Fingerlings of Labeo rohita, procured from the Fish farm, Department of Fisheries, Indira Gandhi Agricultural University were given a prophylactic dip in dilute KMnO₄ solution before stocking in glass aquaria. After 15 days of acclimation to the formulated control diet consisting of rice bran and mustard oil cake, the fingerlings were sorted out to almost identical size (Ave. wt. 1.83±0.02 g) group were stocked at a density of 10 fingerlings in each of the specially designed glass aquaria (60x30x30 cm) containing 60 L of dechlorinated bore water. Each dietary treatment consisted of four replications and the experiment continued to 49 days. The initial weight of the fish and proximate composition of the muscle were determined prior to commencement of the experiment. Each group of fish were fed with the respective diet at the rate of 4% of the total body weight twice daily at 8.00-8.30 h and 16.00-16.30 h The water from each aquarium was partly changed daily and replenished with fresh water. The fish were weighed on weekly interval and the amount of ration adjusted accordingly. Any left over food was collected after 3 h of feeding fish, separately from each aquarium and weighed after drying in an oven to determine the feed consumption. At the termination of the experiment, the fish from all the treatments were weighed individually and processed for subsequent analysis. At the end of the experiment, 4 to 5 fish from each treatment were sacrificed and analyzed for proximate composition of whole skeletal muscle.

Analytical Methods
Prior to formulation of the diets, all the feed ingredients were analyzed for their proximate composition using standard methods (AOAC, 1990). Moisture content was measured by the difference in weight after keeping the sample in oven (100°C) for 24 h Ash content was determined by incinerating the sample in a muffle furnace (600°C) for 5 h Crude protein was estimated by micro- kjeldhal method (Nx6.25), while fat was quantified by continuous Soxhlet extraction technique using petroleum ether as solvent. Crude fibre was analysed using fibra plus apparatus.

Data Collection
Absolute growth (g) = Final weight− Initial weight
Feed conversion efficiency (FCE) = Live weight (g)/ Feed consumed (g)×100
Specific growth rate (SGR) = Log_e Final wt. – Log_e Initial wt. / Experimental period (days)×100
Net protein utilization (NPU) = Fish protein gain/Quantity of protein consumed×100

Statistical Analysis
Analysis of variance (Snedecor and Cochran, 1968) followed by Duncan’s Multiple Range Test (Duncan, 1955) was employed to test the differences between the means.

RESULTS

The water quality parameters (temperature, pH, dissolved oxygen, total alkalinity and free CO₂ of the water in the experimental aquaria ranged from 18.7-26°C, 7.45-7.82, 6.65-7.20 mg L^-1, 80-100 mg L^-1 and 0.0-2.32 mg L^-1, respectively) were well within the range for fish culture.

Growth performance indicated by absolute growth, percentage live weight and Specific Growth Rate (SGR), Feed Conversion Efficiency (FCE), Net Protein Utilization (NPU) and survival rate when subjected to analysis of variance revealed significant influence of slaughter house waste (Table 4). Data indicate that the fish fed with diet D₂ having 30% protein level reflected best growth in terms of absolute growth (2.80 g), percent live weight gain (153.2%) and specific growth rate. The highest food conversion efficiency (52.72) and net protein utilization (2.48) were also obtained with the same diet. The lowest percentage live weight gain (96.26), specific growth rate (1.55%) and feed conversion efficiency (36.88) were recorded with control diet. Growth performance and feed efficiency showed significant (p<0.01) difference between control and experimental diets.

The protein and lipid in the muscle of the experimental fish increased over the initial in all the dietary treatments (Fig. 1). After the experimental period of 49 days, moisture content in fish body tissue was decreased. However, the decrease in the moisture content was not directly related to the protein content of the feed in fish body tissues. Lipid levels increases in all diet groups and highest found in D₂ and lowest in D₄. Highest value of body carcass protein was observed in fish fed on D₂ having 30 % protein level and lowest in the group feeding D₄ having 40% protein level. All these values were found to be significantly higher (p<0.01) than those with the control diet. Significantly (p<0.01) lower ash content was found in all experimental diets compared to initial value.

The highest survival rate was recorded in treatments D₂ and D₃ receiving 30 and 35% protein diet. Survival rate decreased with increased or decreased level of protein.

Table 4:	Growth and feed utilization of Labeo rohita fingerlings fed the control and test diets for 49 days
Values in the same rows with different superscripts differ significantly (p<0.01)

Fig. 1:	Initial and final carcass composition (% dry matter basis) of Labeo rohita under various diet treatments

DISCUSSION

At the end of the feeding trial, significant increase in weight gain was recorded among the various treatment groups fed diets containing slaughter house waste as compared to control diet. This indicates the efficacy of slaughter house waste as a feed ingredient for Labeo rohita. The highest percentage of live weight gain indicating best performance was noted with fish fed 30% protein diet. This points to the fact that under a given condition better performance in terms of growth, digestion, absorption and eventually better conversion of nutrients to flesh. Greater degree of protein (Jafri and Anwar, 1995) and energy (Jafri and Hassan, 1999) digestibility of goat offal by Labeo rohita justifies the performance of this diet in producing maximum live weight gain. In a review, Nandeesha et al. (1991) stated that the growth attained by carps on slaughter house waste based diet was comparable to that fed on fish meal. Hassan et al. (1999) also found best growth of Labeo rohita fingerlings with diet containing slaughter house waste. Jadhav and Rao (1991) reported that goat offal gives the best growth in carps.

The best feed conversion was noted with the group fed slaughter house waste based diets. Similarly, among all the diets, the NPU, used to compare the efficacy of different experimental feed, was found to be highest with D₂ having 30% protein level, indicating the superiority of this feed for L. rohita. Protein utilization of diets decreases with increase of protein level in diet Hassan et al. (1991).

Results on optimum protein levels for Labeo rohita are in broad agreement with those of Gangadhara et al. (1997), Chakraborty et al. (1999), Rangacharyulu et al. (2000). These authors obtained high growth and feed efficiency in fish when fed on a diet containing 30-35% crude protein.

Further, growth depressing effect of high protein levels in carps has been reported for several fish species like, rohu (Khan and Jafri, 1992; Chakraborthy et al., 1999; Nandeesha et al. 1991).

Of the various factors which govern the carcass quality, nutrient composition exerts the strongest influence. In the present experiment, although the diets were isocaloric, the influence of different protein levels on body composition was clearly seen.

The study, thus, clearly indicated that slaughter house waste is a good source of animal protein in terms of feed, protein conversion and growth efficiency and 30% protein level is optimum for growth of Labeo rohita.

ACKNOWLEDGMENTS

The authors thank Dr. S.P. Tiwari, Professor and Head, Department of Animal Nutrition, College of Veterinary Sciences and Animal Husbandry and Dr. Shailendra Shrivastava, Incharge fish farm, College of Agriculture, Indira Gandhi Agricultural University Raipur, Chhattisgarh, India for their encouragement and facilities provided.