Effect of dietary protein level, initial body weight, and their interaction on the growth, feed utilization, and physiological alterations of Nile tilapia, Oreochromis niloticus (L.)
Introduction
The feeding of prepared diets is a principal factor in aquaculture to increase growth and production of reared fish (Thankur et al., 2004, Liti et al., 2005, Abdel-Tawwab et al., 2007). Dietary protein is an important aspect in achieving efficient fish production and its needs should accommodate fish requirements due to age/weight. Protein is the most expensive ingredient in prepared feeds and thus it should be carefully formulated to meet the needs of the cultured organism. Understanding the fish's protein requirement during the growth period is fundamental in fish culture management leading to maximized feed conversion efficiency, cost savings, and reduced nutrient loading into the aquatic ecosystem (Abdel-Tawwab and Ahmad, 2009).
The physiological status of intensively farmed fish is an integral part of evaluating their health status. Diet composition, metabolic adaptations, and variations in fish activity are the main factors responsible for seasonal changes in physiological variables (Cnaani et al., 2004, Řehulka et al., 2004). Physiological alterations might be indicative of unsuitable environmental conditions or the presence of stressing factors such as toxic chemicals, excess organic compounds, and even usual procedures in aquaculture (Barton and Iwama, 1991, Wendelaar Bonga, 1997, Barcellos et al., 2004).
Nile tilapia, Oreochromis niloticus (L.) accepts artificial feeding from hatching and typically shows high survival rates and fast growth (El-Sayed, 2006). The effect of dietary protein on the intermediary metabolism of this species, however, remains scarcely known. Assessing the nutritional demands and the effect of dietary protein on the metabolism of this species at different weights is of particular interest. Therefore, this study was carried out to assess the effect of dietary protein level, initial body weight, and their interaction on growth, feed utilization, carcass composition, and physiological alterations of Nile tilapia.
Section snippets
Fish culture technique
The experiment design was factorial, including three weight classes and three dietary protein levels, by triplicate. Healthy Nile tilapia, O. niloticus (L.) of different weights were obtained from Abbassa fish hatchery and nursery ponds, Central Laboratory for Aquaculture Research, Abbassa, Abo-Hammad, Sharqia, Egypt. Fish were acclimated in indoor tanks for 2 weeks by feeding a commercial diet containing 20% crude protein (CP). After that they were categorized according their weights into fry
Growth performance
Fish growth was significantly affected by protein level and initial weight, while their interaction significantly affected specific growth rate (SGR) only (P < 0.05; Table 2). The highest growth of fry tilapia was obtained at 45% CP, while fingerling and advanced juvenile showed optimum growth performance at 35% CP (Fig. 1). The poorest fish growth was obtained with the 25%-CP diet irrespective of fish weight. Feed intake (FI) and feed conversion ratio (FCR) were significantly affected by protein
Discussion
The present study shows that the dietary protein level markedly affects the growth, feed utilization, and physiological status of Nile tilapia in all weight classes. The optimum dietary protein required for Nile tilapia is weight dependant; fry tilapia (~ 0.5 g) required the 45%-CP diet for optimal growth; whereas, fingerling (~ 20 g) and advanced juvenile (~ 40 g) performed optimally with the 35%-CP diet. El-Sayed and Teshima (1991) found similar results in terms of the protein requirement of Nile
Acknowledgements
The authors would like to thank Mamdouh A.A. Mousa, Department of Fish Biology and Ecology, Central Laboratory for Aquaculture Research, Abbassa, Abo-Hammad, Sharqia, Egypt, for his great help in doing the physiological assays and for his valuable comments and advises during the writing of this manuscript.
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