|Weber, Gregory - Greg|
|Richman Iii, Harold|
Submitted to: Tilapias: Culture, Nutrition, and Feeding
Publication Type: Book / Chapter
Publication Acceptance Date: 7/13/2004
Publication Date: 9/27/2006
Citation: Shepherd, B.S., Weber, G.M., Vijayan, M., Seale, A., Riley, L., Rodriguez, M.F., Richman III, H., Hirano, T., Grau, G. 2006. Control of growth in tilapia: developments and prospects. Tilapias: Culture, Nutrition, and Feeding (3)73-137. Interpretive Summary: Methyltestosterone (MT) treatment and environmental salinity (seawater) appear to increase the nutritional requirements of tilapia. Available evidence suggests that the acceleration of growth by MT and salinity is supported not only by increased food consumption, but also by improved food and protein utilization and by elevations in endogenous growth-promoting hormones. The hypothesis that the actions of MT and salinity are mediated, in part, by stimulation of the GH/IGF axis finds support from evidence showing that many of the actions of MT on protein metabolism in the whole animal are similar to those produced by GH and IGF-I. To our knowledge, the actions of androgens, and hormones of the somatotropic axis, on protein and carbohydrate metabolism, have not been well studied in teleosts and warrant greater consideration. Furthermore, research efforts to integrate advanced approaches, such as use of growth promoters, selective breeding and molecular biotechnology, to growth enhancement in economically-important teleosts, should be encouraged and supported.
Technical Abstract: It is clear that MT and SW rearing directly affect the levels of endogenous growth-promoting hormones and intestinal nutrient absorption in tilapia. The influence of anabolic hormones on carbohydrate and protein metabolism suggests that an elevation in the availability of these nutrients may be required for the full effects of the growth promoters and salinity to be expressed. Until recently, a diet designed for trout has been used by us, and others, in growth experiments. Diets such as this contain a much higher protein and lipid content (and less carbohydrate) than is either required or typically used for tilapia. As the studies discussed herein have shown, such a diet is likely to fully support the anabolic actions of MT, but other less expensive formulations can achieve similar results, especially in fresh water rearing. This is an important issue to fish nutritionists and the aquaculture industry. Faced with the high cost and declining availability of fishmeal, there is strong motivation to identify and use alternative, less costly and sustainable nutrient sources in finfish feeds. However, caution must be exercised when designing feed formulations for growth-accelerated animals, since sufficient nutrients may not be supplied by diet formulations in which a higher proportion of calories is supplied by carbohydrates at the expense of protein content or have divided the source of protein inappropriately between plant and fishmeal sources. For this reason, the supplementation of feeds with high quality sources of nutrients can be justified only to the degree that the added cost yields a commensurate increase in production efficiency