Paradigm shift of fish nutrition and feed: the necessity revealed by the application of formulated feed in Micropterus salmoides and Larimichthys crocea farming

The research on fish nutrition and feed started in 1950s, and the paradigm in this field was established based on that of researches targeting human beings and terrestrial animals. In the past seven decades, based on the paradigm, researches on fish nutrition and feed generated a great amount of valuable data, which promoted the fast development of technology, production and industry of aqua-feed. Challenges of natural resource depletion and environmental pollution to aquaculture industry has been growing with the worldwide expansion of aquaculture scale, and farming practices always raise more and higher demands or standards on aqua-feed. It is widely noted that the formulated feed designed on basis of the research on nutrition and feed for some carnivorous fish species cannot be used in commercial fish farming with success. The fact reveals that results of fish nutrition and feed research conducted following the current paradigm cannot well meet the demand of modern finfish aquaculture. In this paper, the author reviews results of the researches about nutrient requirement and dietary fish meal replacement for Micropterus salmoides and Larimichthys crocea, two carnivorous fish species with commercial importance in inland finfish aquaculture and marine finfish aquaculture in both the world and China. The application of formulated feed in commercial farming of M. salmoides and L. crocea is full of twists and turns, and these fishes had to be fed with raw fish diet for a long period due to the formulated feed did not provide fast growth displayed by the fish fed with raw fish diet. At present, it is known the poor growth of M. salmoides and L. crocea fed with the formulated feed was attributed to the obviously underestimated dietary protein levels. Earlier studies reported that the optimal dietary protein level was 400-440 g/kg for M. salmoides, and 450-470 g/kg for L. crocea. Latter studies reassessed dietary protein requirements of these fishes, and revealed the optimal protein levels for M. salmoides and L. crocea are 480-510 g/kg and 490-520 g/kg, respectively, which are much higher than those reported in the earlier studies. Growth of M. salmoides and L. crocea fed with the formulated feed containing the optimal protein content are comparable to that of the fishes fed with raw fish diet. The story of formulated feed application in M. salmoides and L. crocea farming reveal the necessity of paradigm shift of fish nutrition and feed. The author indicates that the disadvantages in the currently used paradigm include the following: ① The paradigm emphasizes the role of food in regulating fish growth, but ignores the roles of fish genetics and environmental conditions other than food in determining growth and feed intake of fish. ② The paradigm emphasizes that individual growth of fish reflects its nutrient requirements and demand on feed quality, but ignores that individual growth of fish cannot completely represent yield and economic income of commercial fish farming. ③ The paradigm emphasizes the importance of fish growth and feed utilization efficiency as indicators in evaluating benefits of fish farming, but ignores that the negative impacts of fed aquaculture on natural resources and environment are the bottle-neck limiting sustainability of aquaculture industry. ④ The paradigm ignores the effect of basal diet formula in evaluating nutrient requirements and feed quality, and the use of unreasonable basal diet in some research results in erroneous or senseless conclusion. To diminish the aforementioned disadvantages, the author proposes to improve the concept, theory and method of the currently used paradigm. ① Emphasizing the importance of fish genetics and the environmental conditions except food in determining growth and feed intake of fish. Emphasizing that growth potential of fish determine its nutrient requirement, while emphasizing that nutrients from diets can support and modulate fish growth. ② Emphasizing the interaction between different dietary nutrients, and emphasizing that different feed ingredients play their own role in establishing nutrient balance of diet formula. ③ Emphasizing the importance of genetics and population structure of the test fish used in feeding trials. Emphasizing the magnitude of difference in growth between individual fish fed with different diets is an indicator for assessing nutrient requirement and feed quality. Emphasizing the impacts of diet formula on natural resources and environment, which are factors limiting sustainability of aquaculture industry. After the shift or improvement, the paradigm for fish nutrition and feed research will be better in accord with the situation and demand of modern aquaculture farming practices. The results of nutrition and feed research conducted following the shifted paradigm will be more reliable and accurate for diet formula design of aqua-feed, and the formulated feed will be more successful in application in commercial aquaculture farming.