A growth comparison among three commercial Tilapia species in a biofloc technology system in South Africa

[摘要] ENGLISH ABSTRACT: With environmental conservation playing a growing role in decision making today, the aquaculture industry has sought new innovative ways to reduce the impact on the environment, and maximize efficiency. Much of the focus of such developments has included lower water usage and better feed utilization, with the emergence of biofloc technology systems addressing such needs. Tilapia has been identified as a fish for the future, with its production having already risen to make it an important food fish globally, and an increase in its market share is predicted going forward. Although it is common around the world, the production of tilapia has failed to take off in South Africa, with the reasoning being put forward including; legislative restrictions, unfavourable climate, incorrect species choice and shortage of expertise and supporting industry.The major aims of this study were to address the main constraints and uncertainties facing the local tilapia industry in terms of species choice, and to investigate the biofloc technology concept under local conditions. Being restricted to the use of the Mozambique tilapia (Oreochromis mossambicus), and with the recent changes allowing the use of the Nile tilapia (Oreochromis niloticus), the question whether O. niloticus will in fact outperform O. mossambicus under South African conditions, was raised. With the production of the Three Spot tilapia (Oreochromis andersonii) also prevalent in southern Africa, this species was also included in the study. The secondary aim of the study was to create a profile of key water quality parameters during the start-up period of the biofloc technology system prior to fish being introduced, and throughout the course of the trial.With the biofloc technology concept being expected to play a role in the development of the South African tilapia industry, the study was conducted in a biofloc technology system. Twelve tanks, connected through airlift pumps to homogenize the water quality, were stocked with fish. Each of the three species were stocked randomly into four tanks with each tank being considered an independent replicate. The growth trial was conducted within a greenhouse, and commenced at the start of the summer grow out period for tilapia in South Africa, in October 2014, running for 10 weeks. Fish were sampled fortnightly from the system, with the mass data being used to fit a linear regression. Water quality measurements were taken from the start-up period in mid-September, for 12 weeks.Profiles for temperature, dissolved oxygen, pH, salinity, electro-conductivity, total dissolved solids, floc volume, total ammonia nitrogen, nitrite, nitrate, orthophosphate, total suspended solids and turbidity were successfully documented over the trial period. Two spikes in total ammonia nitrogen and nitrite were recorded, one during start-up, and one following a water loss event during the trial. A regression fitted to the mass data showed O. niloticus to have the highest growth rate with an average daily gain of 0.693±0.018 g/day, followed by O. mossambicus of 0.405±0.025 g/day, and then O. andersonii of 0.185±0.025 g/day, with significant difference between all three species. The lowest feed conversion ratio was also recorded for O. niloticus being 1.00±0.05, followed by O. mossambicus of 2.24±0.16, and O. andersonii with 2.53±0.28. These results suggest that of the three species investigated, O. niloticus performs best in a biofloc technology system in South African conditions. It is recommended that this species should therefore be used in biofloc technology systems as they develop in South Africa.

[发布机构] Stellenbosch University