Management strategies for marble goby-carp polyculture in coves based on natural food webs in Tri An Reservoir, Vietnam | |
| Author | Vu Cam Luong |
| Call Number | AIT Diss. no.AQ-04-11 |
| Subject(s) | Natural foods--Vietnam Inlets--Vietnam Fish-culture--Vietnam Fishes Food--Vietnam |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science |
| Publisher | Asian Institute of Technology |
| Abstract | Cove fish culture in Tri An Reservoir involves partitioning bays in the reservoir by barrier nets. Cove fish production depends upon natural food resources available in coves. This study was conducted in 5.24-ha Truong Dang Cove in Tri An Reservoir of Vietnam during June 2002-May 2003 to develop management strategies for marble goby-carp polyculture in coves based on natural food webs in Tri An Reservoir, Vietnam. The specific objectives of the study were: (1) to investigate hydrological and physico-chemical conditions in the cove and their effects on the natural food sources; (2) to evaluate roles of terrestrial vegetation in the drawdown area of the cove; (3) to evaluate potential natural food production in the cove; (4) to assess cove polyculture of marble goby and carps, and feeding habit of marble goby; and (5) to assess the trophic transfer efficiency and ecological relationships in the cove, and to manipulate the natural food webs for cove fish culture; and (6) to propose management strategies for marble goby-carp polyculture in coves based on natural food webs. The hydrological characteristics indicated large seasonal fluctuation of water levels in the studied cove (0-9 m), and the corresponding surface water areas varied from 0 to 7.44 ha. Such fluctuations affected significantly on fish culture practices and management as well as fluctuations of natural food production in the cove. It also created a terrestrial ecosystem that lasted from June to July, with abundant terrestrial vegetation growth (221.5 g DW/m2) in the drawdown area. Such vegetation contributed important sources of detritus and nutrients for the cove after floods. Results indicated that the cove had relatively good physico-chemical conditions with diversified natural food sources such as terrestrial vegetation, phytoplankton, periphyton, zooplankton, benthos, detritus, small wild fish and prawns. Detritus was the most abundant in the food chain with mean biomass ranging from 801 to 1,164 g DW/m2. During the fish culture period, the mean biomasses of phytoplankton, periphyton, zooplankton, benthos, small wild fish and prawn were 0.63, 1.79, 0.27, 0.45, 1.44 and 1.35 g DW/m2, while the productivity was 221.55, 66.6, 38.26, 9.23, 2.23 and 24.3 g DW/m2/crop, respectively. Considering available natural food sources, annual fish production that could be supported by phytoplankton, periphyton, zooplankton, benthos and prawns in Truong Dang Cove was estimated to be 1.66, 0.83, 2.39, 1.29 and 3.24 g DW/m2/crop, respectively. Polyculture was practiced in the cove by stocking marble goby (Oxyeleotris marmorata Bleeker), silver carp (Hypophthalmichlhys molitrix), bighead carp (Aristichthys nobilis), common carp (Cyprinus carpio) and grass carp (Ctenopharyngodon idelld) at 960, 470, 470, 470 and 170 fish/ha, respectively. After 6.5 months of culture from October 2002 to May 2003, the gross yield of marble goby was 251.1 kg/ha/crop, with mean weight of 353 g/fish, while gross yields of silver carp, bighead carp, common carp and grass carp were 90.5, 114.3, 84.6 and 35.0 kg/ha/crop, with mean weights of 333, 368, 301 and 321 g/fish, respectively. Recovery rate was 73.7 % for marble goby and 55.1-62.8 % for carps. Marble goby is typical carnivorous fish with nocturnal feeding behavior. The major food item of marble goby was small freshwater prawns, followed by small wild fish and benthos. Addition of marble goby to carp polyculture in cove gave much higher economic return, compared to that without marble goby (US$2,713.2 vs, US$260/crop). An attempt to construct four trophic models for different stages of the culture period in Truong Dang Cove was made using the Ecopath approach and software, in which the energy flows of terrestrial plant, detritus, phytoplankton, periphyton, zooplankton, benthos, small wild fish, prawns, and five cultured fish species were quantified. Those models were used to estimate the carrying capacity of the cove in terms of natural food potential to support production of cultured fish, with considerations of the entire system and interrelationships of various components. In the present study, ecotrophic efficiencies of phytoplankton, zooplankton, benthos and prawns were estimated approximately 0.955, 0.941, 0.950 and 0.941 during the entire culture period, respectively, implying these natural foods were fully utilized by higher trophic levels. The lack of plankton food sources that occurred at the middle and late stages of the culture period indicated that attention needed for food web management at the above stages. Ecotrophic efficiencies of detritus, small wild fish and periphyton were 0.098, 0.259 and 0.337 during the entire culture period, respectively, indicating that there was great potential for the production of fish based on such food items. Food web manipulation was earned out and tested using 17 sets of Ecopath models with some adjustments of fish biomass and species composition as well as diet composition. Main results indicated that: (1) planktivorous fish biomass should be reduced to balance the trophic web; (2) it would not be possible to further enhance marble goby production based on the existing natural food resources in the cove; and (3) increasing the prawn biomass by 48% for the entire fish culture period would support 50% increment of marble goby standing stock. Three management directions are open to utilize the natural food sources better in coves: (1) to stock fish based on available natural food resources and physico-chemical conditions; (2) to introduce new culture practices such as nursing activities in sub-coves or integrated cage-cum-cove culture systems; and (3) to seed natural food organisms such as prawns (Macrobrachium spp.) and benthic organisms. This study demonstrated that cove culture of marble goby in reservoirs is ecologically practical and economically gainful. |
| Year | 2004 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Aquaculture and Aquatic Resources Management (AQ) |
| Chairperson(s) | Yang, Yi;Yakupitiyage, Amararatne |
| Examination Committee(s) | Lin, C. Kwei;Clemente, Roberto;Le Thanh Hung;Macintosh, Donald John; |
| Scholarship Donor(s) | Ministry of Education and Training of Vietnam;Asian Institute of Technology;Aquaculture CRSP; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2004 |