1. Introduction
Fish feed is the most expensive input in aquaculture operations. The shortage and high cost of pelleted feed severely constrain the development of low-cost aquaculture systems suitable for small-scale farmers in developing countries. It would therefore be more economical to utilise plant protein in fish feeding than high-cost animal protein materials. In the natural environment, agricultural and aquaculture waste materials are available in large quantities. These materials are not wastes but waste resources, because they contain nutrients at varying levels. A variety of substances, including many waste materials from the agriculture, food and rendering industries, are recycled into feed for food-producing animals (Hao et al., 2006; Krishna, 1999).
Efficient and judicious utilisation of these waste materials as feed ingredients in aquafeed through microbial technology certainly paves the way for better management of these waste materials, which in turn reduces the pollution menace due to the disposal of these waste materials (Tovar-Ramírez et al., 2004). Hence, the present study was taken up to investigate the effect of probionts and feed additives on growth response and biochemical composition in pearl spot, Etroplus suratensis.
2. Materials and Methods
Healthy E. suratensis were collected from Rajakkamangalam, Kanyakumari district, Tamil Nadu. The collected fish were kept in the laboratory for up to 2 days, with the temperature and pH maintained. The fish were fed mainly on freshly made pellet diets, and 50% of the water was exchanged daily. The branded feed ingredients, such as fish meal, groundnut oilcake, wheat bran, soya meal, tapioca powder, vitamin, mineral mix and cod liver oil, were purchased from commercial merchants. Three different types of diets (Diet A, Diet B and Diet C) with 40% protein were compounded separately by mixing different ingredients in various proportions with 2% potato peel powder (Diet A), 2% sugarcane bagasse powder (Diet B) and 2% CMC (Diet C). The probiont Bacillus was then added as a feed additive at 1% to experimental Diet A and Diet B. Diet C was used as the control, without the addition of probionts.
3. Results and Discussion
After acclimatisation, the healthy fish were weighed individually (15.00±0.20 g). They were reared at a density of 3 fish per 12 L of water and fed ad libitum. During the experiment, which lasted 91 days, water quality was maintained.
3.1. Growth Response
During the experimental period of 91 days, the specific growth rate (SGR) of E. suratensis fed on Diet A was high (0.73±0.27%) and low in those fed the control diet (Diet C). The consumption rate of E. suratensis fed on the control diet was the highest (38.62±0.86 mg/g/day) (Table 1). The production rate of E. suratensis was high in the group fed the probiont-supplemented Diet A (14.2±0.17 mg/g/day), whereas it was low in the group fed the control Diet C (10.8±0.26 mg/g/day). The present observation is in congruence with the findings of Paulmony (1996), who reported that a probiont yeast-supplemented diet significantly influenced the growth, food conversion ratio and specific growth rate of Cyprinus carpio. Olukunle (2006) also reported that sweet potato meal was the best feed additive for growth in fish production.
| Parameters | Growth responses | ||
|---|---|---|---|
| Diet A | Diet B | Diet C | |
| Initial wt (g) | 15.0±0.60 | 15.00±0.70 | 15.00±0.20 |
| Final wt (g) | 29.2±0.45 | 26.70±0.18 | 25.8±0.75 |
| Production (g) | 14.2±0.17 | 10.20±0.35 | 10.8±0.26 |
| Food consumed (g) | 29.70±0.83 | 30.13±0.45 | 38.62±0.86 |
| FCE (%) | 30.96±0.76 | 33.85±0.45 | 27.96±0.65 |
| SGR (%) | 0.73±0.27 | 0.57±0.72 | 0.59±0.32 |
| FCR | 2.09±0.45ab | 2.90±0.24ab | 3.53±0.23a |
3.2. Biochemical Composition
The overall results on variation in biochemical composition indicated that it was much influenced both by variation in Bacillus supplementation and by the additives. The protein, carbohydrate and lipid contents of fish fed on Diet A were higher than those of fish fed on Diet B and Diet C (Table 2). The biochemical constituents analysed in the muscle, gill and gut samples did not differ much between fish fed with Diet A and Diet B, and were lower in fish fed with Diet C (Table 2). Valiño et al. (2004) studied the influence of the addition of a mutant strain of Trichoderma viride to sugarcane bagasse to improve its digestion through the cellulase enzyme system. The addition of probionts and feed additives to the diet increased the growth rate by accelerating the secretion of certain enzymes in fish (Das, 1975).
Sogaard and Suhr-Jessen (1990) reported that the introduction of probionts, particularly Bacillus, results in variations in the gut microbial composition. These changes, in relation to the flora’s capacity to prevent infections, must be regarded as a favourable increase in the Lactobacillus concentration, a reduction in E. coli and an increase in the levels of organic acids. In the present study also, the same phenomenon was observed in fish fed the experimental diets containing probiotic Bacillus and the feed additives potato peel and sugarcane bagasse, after a feeding duration of 91 days.
| Biochemical composition | Fish samples | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Muscle | Gill | Gut | |||||||
| Diet A | Diet B | Diet C | Diet A | Diet B | Diet C | Diet A | Diet B | Diet C | |
| Protein | 40.96±0.14 | 35.14±0.15 | 33.46±0.20 | 32.45±0.14 | 29.15±0.13 | 27.15±0.12 | 27.36±0.17 | 25.20±0.12 | 23.36±0.14 |
| Carbohydrate | 4.73±0.01 | 3.09±0.01 | 3.06±0.01 | 3.42±0.01 | 2.05±0.01 | 2.00±0.01 | 3.12±0.02 | 2.10±0.01 | 2.25±0.01 |
| Lipid | 3.53±0.02 | 2.23±0.01 | 2.86±0.02 | 3.12±0.02 | 1.96±0.01 | 2.08±0.12 | 2.34±0.01 | 1.70±0.01 | 1.82±0.01 |
4. Conclusion
The present work proved the effect of various bacterial probionts and vegetable waste on the increased growth of E. suratensis. The results will be further used in the aquaculture industry for large-scale production of E. suratensis under controlled environmental conditions. Furthermore, this work can be extended to various other fishes using different sources of food waste.
References
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