Evaluation of local feed resources for hybrid catfish (Clarias macrocephalus x C. gariepinus) in smallholder fish farming systems in central Vietnam

摘要

The aim of this thesis was to examine the current feeding situation for fresh water fish in Central Vietnam, to evaluate the potential nutritive value of locally available feed resources for hybrid catfish (Clarias macrocephalus x C. gariepinus) and Nile tilapia, to determine the dietary requirement of lysine for hybrid catfish, to estimate the requirements for the other essential amino acids (EAA) by using ideal protein concept, and finally to evaluate the suitability of cassava leaf meal and shrimp head meal as a partial replacement for fish meal in the diet, without or with lysine supplementation, for hybrid catfish fingerlings. The survey indicated that, in total, 22 feed ingredients were used by the farmers. The main ingredients were cassava root meal, rice bran, cassava residue, groundnut meal, soybean meal and fish meal. Furthermore, several more unconventional feedstuffs were also commonly used, such as cassava leaves, coconut meal, shrimp head meal, sesame husk and squid by-product. The combination of ingredients used in farm-made fish feeds varied among farms and districts leading to a large variation of nutrient composition and energy content. The fish yield varied among districts and ranged from 0.8 to 6.5 t ha-1. The digestibility trial showed that the apparent digestibility (AD) of dry matter (DM), organic matter (OM) and crude protein (CP) in cassava leaf meal was significantly lower than in groundnut meal, soybean meal, sesame husk meal and shrimp head meal in both hybrid catfish and Nile tilapia. The AD of DM and OM in cassava leaf meal was higher in hybrid catfish than in Nile tilapia. Most EAA in the selected feedstuffs were equally well utilized by the two fish species. In the third experiment, the dietary lysine requirement of hybrid catfish fingerlings was found to be 56 g kg-1 of CP, corresponding to 16.8 g kg-1 of dry diet. In the feeding trial with hybrid catfish, replacing fish meal with shrimp head meal had no effect on final weight (FW) and specific growth rate (SGR), while replacing fish meal with cassava leaf meal led to impaired FW and SGR. Supplementing cassava leaf meal and shrimp head meal diets with lysine improved FW and SGR.