Agri Kultuur December / Desember 2018 - Page 8

Tilapia rendalli feed predominantly on aquatic plants found around the margins of lakes and dams. They are well adapted to feeding on these larger plant forms and have robust pharyngeal teeth for triturating or grinding up these food items. The type of aquatic plants eaten by this species varies considerably but includes almost all true submerged hydrophytes, many floating hydrophytes and even terrestrial grasses which are flooded during the rainy season. Nutrient Requirements of Tilapia: As the tilapia sector expands and technology development continues, traditional extensive culture is being replaced by semi-intensive and intensive production systems. In semi- intensive farming systems, supplemental feeds that consist of locally available, low-cost single feedstuffs such as rice bran, corn meal, copra meal, coffee pulp, brewery by-products and/ or their combination are generally used as supplements to natural food. These feeds are high in energy, low in protein and deficient in micronutrients such as vitamins and minerals. It is assumed that the deficient nutrients will be provided by natural food organisms. As stocking rate increases, the contribution of natural food decreases and more nutritionally complete feeds are needed. In intensive culture systems such as in ponds, raceways, cages, and tanks, feed is the most expensive item, often ranging from 30 to 60 percent of the total variable expenses, depending on the intensity of the culture operation. Thus, the availability of least-cost, nutritionally well- balanced feeds is one of the most important requisites for successful and sustainable tilapia production. Data on nutrient requirements, among other information, are needed for least-cost feed formulation. Nile tilapia requires the same ten essential amino acids as other finfishes. Protein AgriKultuur |AgriCulture requirements for optimum growth are dependent on dietary protein quality/source, fish size or age and the energy contents of the diets and have been reported to vary from as high as 45-50 percent for first feeding larvae, 35-40 percent for fry and fingerlings (0.02-10 g), 30-35 percent for juveniles (10.0-25.0 g) to 28-30 percent for on-growing (>25.0 g). The best protein digestibility occurs at 25 °C and the optimum dietary protein to energy ratio was estimated in the region of 110 to 120 mg per kcal digestible energy respectively for fry and fingerling. Tilapia brood fish require about 40-45 percent protein for optimum reproduction, spawning efficiency and for larval growth and survival. The lipid nutrition requirement of farmed tilapia has been reviewed by various researchers. The minimum requirement of dietary lipids in tilapia diets is 5 percent but improved growth and protein utilization efficiency has been reported for diets with 10-15 percent lipids. Both n-3 and n-6 polyunsaturated fatty acids (PUFA) have been shown to be essential for maximal growth of hybrid tilapia (O. niloticus x O. aureus). For Nile tilapia the quantitative requirement for n-6 PUFA is around 0.5-1.0 percent. Unlike marine fish species, tilapia appear not to have a requirement for n-3 highly unsaturated fatty acids (HUFAs) such as EPA (20:5n-3) and DHA (22:6n-3) and its n-3 fatty acid requirement can be met with linolenic acid (18:3n-3). The exact carbohydrate requirements of tilapia species are not known. Carbohydrates are included in tilapia feeds to provide a cheap source of energy and for improving pellet binding properties. Tilapia can efficiently utilize as much as 35-40 percent digestible carbohydrate. Carbohydrate utilization by tilapia is affected by several factors, including carbohydrate source, other 8