Reducing feed costs in aquaculture: are we feeding our fish too much?

Feed costs are the highest recurring costs in semi-and intensive aquaculture. In general, a 30-to 40% of deposition of nitrogen in the diet into fish flesh is considered as very acceptable and good.More often than not, the general approach to reducing feed costs has been to look for ways and means of substituting, either wholly or partially, the commonly used ingredient supplying the bulk of the dietary protein content-fishmeal-with low-cost, agricultural and or animal industry by-products.However, past experience shows that only very insignificant proportion of research findings on the latter areas get translated into industry practices. Fore example, apart from the wide spread use of soybean meal in fish diets, and to a lesser extent replacement of fish oil in diets with other suitable vegetable oils, the vast amount of research findings on agricultural by-products literally remain shelved. The likely reasons for this are discussed.Consequently, it leaves to search for other pragmatic solutions to the problem of tackling the issue on feed costs. It is suggested that it is best approached through a series of questions and search for available answers, such as are the diets used commonly contain more protein that is required for obtaining an positive economic outcome; is feeding the same high protein diet to fish meaningful and if not what are the alternatives? Data available to date suggest that such strategies could be adopted without compromising growth and or profits, and more over will enable a reduction in nitrogen and phosphorous in the effluent.Finally, are the diets available in the market place conform to the specifications given. In the above regard the concepts on "economically optimal dietary protein content" and "mixed feeding schedules" are presented and advantages and disadvantages in their use in day to day culture practices discussed. Examples are presented to indicate that some diets in the market, particularly in Asia, fall far below the expectations and the specifications that these are sold under.