Use of supplements and novel ingredients to improve Pacific whiteleg shrimp Litopenaeus vannamei feed formulations.

Abstract

World shrimp production has rapidly increased in the past 20 years. A number of factors have driven the development of shrimp culture, with proper nutrition being a key factor. However, shrimp production expenses impede further development of the sector, especially with majority of expenses being associated with shrimp feeding behavior and the high price of feed ingredients. Accordingly, there is a need to explore new diets formulated with affordable ingredients with potential to improve shrimp feeding, growth, and economic returns. A variety of protein sources have been incorporated in low or fishmeal-free shrimp diets and demonstrated good growth. However, palatability issues rise from certain ingredients, which exacerbates the amount of feed wasted and worsens feed conversion. Accordingly, the use of certain feed effectors along with alternative protein sources could provide a happy medium between cost-effective feed and minimum feed wastage by increasing feed palatability and stimulating feed consumption. However, despite the need for alternative protein sources, some of them are available and relatively inexpensive yet often overlooked in aquaculture. Hydrolyzed feather meal (HFM) is a good example; it has a high protein content and could complement other protein sources to balance the amino acid composition of the feed. If used, HFM can serve as an inexpensive source of protein and contribute to decreasing the cost of production. Other options include functional feed additives such as bacterial biomasses, which could be supplemented to low-fishmeal diets to boost shrimp growth and feed consumption. Regardless of the efforts to use alternative ingredients, certain ingredients such as cholesterol are limited in many ingredients and remain indispensable for animal growth and survival, yet their inclusion as purified supplements increases feed cost. Fortunately, phytosterols of plant origin are structurally similar to cholesterol. Given the similarity in structure, phytosterols have the potential to serve as an inexpensive partial or complete substitute for cholesterol in shrimp diets. To validate each of the aforementioned hypotheses and explore sustainable feed ingredient options, a series of trials were performed at E.W. Shell Fisheries Center in Auburn, AL. The first trial was performed to assess how the use of a chemosensory feed effector with attractive properties can affect shrimp feeding behavior, growth performance, and salinity stress tolerance. Nine diets were formulated to contain either poultry meal (6%), or fishmeal (6% or 12%) as animal protein source, with feed effector supplemented at 0, 0.1, and 0.2%. Results indicated that shrimp produced significantly more “clicks” when the poultry meal-based diets were supplemented with the feed effector, and consumption then became similar to the fishmeal-based diets. No significant differences were observed in terms of growth, FCR, or survival. However, shrimp exhibited significantly better survival when offered diets supplemented with the feed effector, regardless of the level of inclusion. Such results suggest that the feed effector improves palatability and shrimp acceptance of poultry meal-based diets and improves shrimp tolerance to salinity fluctuations. Another trial was performed to evaluate HFM, with (HFM-CCB) and without coagulated chicken blood (HFM-WCCB), as dietary ingredient for shrimp. Seven diets were formulated, where HFM-CCB or HFM-WCCB partially replaced soybean meal at 3, 6, and 9% of the formulation. Results of the 42 days study suggested that shrimp diets can include up to 9% HFM without significant effects on shrimp growth or survival. Significant yet limited differences were observed in FCR and apparent net protein retention (p < 0.05). Thus, HFM can serve as an inexpensive nutritious ingredient for shrimp, ensuring good shrimp growth by complementing other proteins sources and recycling nutrients. A third trial was performed to evaluate the effects of supplementing a high ash, low protein marine bacterial biomass to low fishmeal diets on shrimp feeding behavior, growth, proximate composition, hemolymph biochemistry, and digestive enzyme gene expression. Six diets were prepared to include graded levels (0, 2.5, 5, 7.5, 10, and 20% of the diet) of a commercial bacterial biomass. Feed intake and behavior were assessed using passive acoustic monitoring prior to a 42-days growth assessment. Results suggest that supplementing shrimp feed with 10% of the commercial bacterial biomass studied would lead to better growth, feed consumption, and feed conversion without adverse effects on hemolymph, overall health or digestion. Lastly, a fourth trial evaluated the use of phytosterols as substitute for cholesterol in shrimp diets. Twelve diets were formulated, with the basal one being deficient in cholesterol. The remaining diets were similarly formulated but systematically supplemented with increasing levels of cholesterol (0.04, 0.08, 0.10, 0.12, and 0.16%) or phytosterols (0.04, 0.08, 0.10, 0.12, 0.16, and 0.20%). Results of the 42-days trial indicated significant differences in terms of growth, feed conversion, and survival, with plasma cholesterol analysis demonstrating significant differences among treatments in a dose response fashion. Similarly, tail muscle cholesterol levels significantly increased with the increase in dietary cholesterol but not phytosterols, and vice versa with respect to dietary phytosterols. Results suggest that phytosterols can be a viable cost-effective alternative to cholesterol in practical shrimp feed, despite having a slightly lower bioavailability than cholesterol. Data from the present dissertation offer solutions and suggest alternative ingredients that can be incorporated in shrimp feed. Use of such ingredients and supplements can help improve shrimp feeding behavior, feed consumption, and minimize feed-related expenditures.