- Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences
Sustainable development of marine aquaculture in Cambodia was studied in this thesis, using Asian seabass as the target species. An initial survey mapped current production practices, geographical occurrence and production volumes of Asian seabass farming in coastline provinces in Cambodia (Preah Sihanoukvill, Kampot and Koh Kong). Tolerance to different salinities and alternative local feed sources were then assessed in studies conducted at Marine Aquaculture Research and Development Centre (MARDeC) in Preah Sihanoukvill and at An Giang University, Vietnam. A small digestibility study of all feed sources tested was also conducted at An Giang University. The survey revealed that fish farming was conducted both in marine and brackish water and that the most common feed used was trash fish. Commercial dry pellets were only used when fish were reared in ponds or for small fish, mainly due to high costs, which were a major constraint preventing farmers from changing from feeding trash fish to pellets. A series of experiments including two life stages of Asian seabass (fry and fingerlings) and graded levels of salinity found no significant differences in weight gain (WG, g), feed conversion ratio (FCR), daily weight gain (DWG, g day-1), specific growth rate (SGR) or condition factor (CF) in fry or fingerlings at different levels of salinity (fry treatments: 0, 5, 10 and 20 practical salinity units (psu); fingerling treatments 10, 20 and 30 psu). Experiments on including graded levels of brewer's yeast to replace dietary fishmeal (at 0, 20, 37 and 47 % based on dry matter, denote BY0, BY1, BY2 and BY3), performed in hapa and tanks, indicated only slight, non-significant differences in survival rate (SR, %). Body weight (BW, g) and DWG decreased towards the end of the experimental period, but with no differences between treatments (p=0.89 and p=0.26). However, the fish tended to display increased feed intake (p=0.61 and p=0.93) and FCR (p=0.54 and p=0.33) in hapa and tank respectively with higher level of yeast inclusion, indicating that fish on high levels of yeast need to eat more feed per unit weight gain. In the tank experiment, there was no significant difference in CF or SR, but BW increased around four-fold in all treatments. The main difference between the tank and hapa experiments was in FCR, possibly due to feed losses through the net in the hapa base, while the fish in tanks could feed on the bottom. A study on using cricket and black soldier fly (BSF) full-fat meal to replace fishmeal in the diet of Asian seabass revealed two major problems: i) The fish were accustomed to floating pellets and the experimental feed was sinking pellets, which reduced feed intake in all treatments (including control) and resulted in fish weight only doubling. Fish kept on floating commercial pellets in a parallel system performed well, with a four-fold weight increase. A longer adaptation period of the fish to sinking pellets could improve the outcome. ii) The fishmeal used as high-quality protein control was spiked with non- protein nitrogen, indicating that analysis discriminating between protein and non-protein nitrogen should be performed before feed formulation. Overall, the results indicated that both BSF and cricket full-fat meal are potential replacers of fishmeal, and thus also of trash fish, in the diet of Asian seabass. Digestibility analysis confirmed their feed value.
Asian seabass; brewer's yeast; cricket; black soldier fly; trash fish
Acta Universitatis Agriculturae Sueciae
2019, number: 2019:49
ISBN: 978-91-7760-416-7, eISBN: 978-91-7760-417-4
Publisher: Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences
Animal and Dairy Science