Evaluation of Nutritional Values of Food Waste-Based Feed Pellets and Common Feeding Materials for Culturing Freshwater Fish

Abstract

There are 3,600 tonnes of food waste (FW) disposed at landfill sites daily, and the existing landfills in Hong Kong will be successively exhausted by 2020. Recycling of FW can partially ease the disposal pressure. This study aims at investigating the feasibility of using FW-based feed pellets for culturing freshwater fish, with a focus on nutritional values. Freshwater fish such as grass carp (Ctenopharyngodon idella), Nile tilapia (Oreochromis niloticus), and grey mullet (Mugil cephalus) have relatively lower dietary protein requirements than carnivorous fish. Local freshwater fish farmers prefer to use unconsumed food, agricultural by-products or leftovers from household kitchens as feed in order to reduce their operation costs. The nutritional values (essential amino acid [EAAs], crude protein, crude lipid, crude carbohydrate, total phosphorous) of Napier grass, breads, rice bran, instant noodles, soybean dregs, a commercial fish feed pellet (Jiefeng® 613) and two FW-based feed pellets were compared. FW-based feed pellets consist of meals of recycled cereal, meat, vegetable, and bone which account for 70% (w/w) of the ingredients. Formulation A (FWA) is mainly composed of 53% cereals as the major protein sources, while Formulation B (FWB) has a more balanced ratio of meat (25%) and cereal (28%). The amino acid scores of feed items for grass carp and Nile tilapia were calculated to validate whether they contained sufficient amounts of EAAs. The results demonstrated that common fish feeds are insufficient in terms of nutrient content, in particular the lysine content (except for Jiefeng® 613), crude protein (except for Jiefeng® 613 and soybean dregs) and lipids (except for the two noodle samples). In contrast, FWA and FWB contain sufficient amounts of lysine and crude protein, indicating their suitability for low trophic level fish. The result was also confirmed by the growth performance of the fish fed with different diets.