Life history, fisheries and aquaculture of mudskipper (Pseudapocrytes elongatus, Cuvier 1816) in the coastal zone of the Mekong Delta, Vietnam | |
| Author | Truong Hoang Minh |
| Call Number | AIT Diss. no.AQ-09-03 |
| Subject(s) | Fisheries--Mekong River Delta (Vietnam and Cambodia) Aquaculture--Mekong River Delta (Vietnam and Cambodia) |
| Note | A dissertation submitted in the partial fulfillment of requirements for the Degree of Doctor of Philosophy in Integrated Tropical Coastal Zone management |
| Publisher | Asian Institute of Technology |
| Abstract | The mudskipper Pseudapocryptes elongatus is considered as a potential species for coastal aquaculture development in the Mekong Delta, Vietnam. Due to its high economic value and declining wild stocks, aquaculture of P. elongatus is rapidly developing in the Mekong Delta, resulting in high catch effort to supply P. elongatus juveniles for farming. At present, some important information on the biology, ecology, fishery and aquaculture of this species are not known well. In order to provide scientific information that will be useful for its fishery management and aquaculture development, research was conducted to (1) document the current status of fishery and aquaculture of P. elongatus and its economic aspect; (2) identify spatial and temporal distribution and density of juveniles; (3) determine the feeding habit, reproduction, age and growth and life-cycle of this species; (4) recommend strategic measures for fisheries management and aquaculture development of P. elongatus. This research was conducted in Bac Lieu and Soc Trang provinces, lower Mekong Delta, Vietnam from April 2006 to March 2007. The research used several methods appropriate for each of the following objectives: (1) investigation of fishery and aquaculture of P. elongatus used RRA techniques and interviews with fisherman and aquaculture farmers of the mudskipper; (2) determination of spatial and temporal distribution and density of this species through carrying out pilot study for identifying P. elongatus juveniles, monthly sampling of P. elongatus juveniles during high tide in spring tide period from toward offshore sites to interior river sites (2 km interval) in My Thanh (Soc Trang province) and Nha Mat (Bac Lieu province) estuaries, and measuring some ecological parameters such as: salinity, water current velocity, pH and transparency at each sampling site; (3) determining spawning season, life-cycle, feeding habit, and age and growth determination of P. elongatus by applying methods such as random monthly sampling for the live adults of P. elongatus during low tide in spring tide period by river bag-nets in both provinces, five bag-nets in each province. Besides, sub¬adults were caught randomly in mangrove forest areas, shallow water bodies and water pools on mudflat. These samples were used for GSI and histological analysis, gut contents analysis (n = 39 individuals), otholith and length frequency analysis (n = 1,410 inds in Bac Lieu and 1,684 inds in Soc Trang provinces) by using von Bertalanffy equation, W = a*Lb and the LFDA & FISAT II software. The distribution of the mudskipper at different sizes and habits in the nature were used to compile a life-cycle description of this species. The research revealed that P. elongatus juvenile fishing activity started in 2001. Catching P. elongatus juveniles is operated by fishermen during high tide in spring tide periods along the coast and interior river sites from May to November. Mean CPUE was 200,466 ind net⁻¹ in six months. The juvenile catch is supplied to mudskipper farms. The adults (10 - 22 cm total length) are caught during low tide period by river bag-nets. Lowest catch yield of the adults was from March to June and highest yield from September to December. The catch yields of the adults ranged from 13 kg to 18 kg bag-net⁻¹ month⁻¹. The adult catch yield has decreased 20-30%, compared to 2005. In general, mudskipper fishing activities generate good income for local fishermen. Intensive (80 - 100 ind m⁻²) and semi-intensive (15 - 30 ind m⁻²) culture systems were identified. Mudskipper farming is operated from May to December. The yield in the intensive system was much higher (6.4 tonnes ha⁻¹) than in the semi-intensive system (0.8 ton ha⁻¹). Production cost was low, i.e. US$ 967 ha⁻¹ in semi-intensive, US$ 8,696 ha⁻¹ in intensive system, and net profit was quite high, i.e. US$ 1,039 ha⁻¹ in semi-intensive and US$ 12,784 ha⁻¹ in intensive farms. Consequently, P. elongatus is considered to have a good potential for coastal aquaculture development as an alternative species to shrimp in the coastal area. The spatial, temporal distribution and density of P. elongatus juveniles were identified in this study. The smallest size of the juveniles was found in offshore and the biggest was in interior of river. Highest densities were observed in mangrove forest areas and lowest in non-mangrove areas. The juvenile density increased from offshore sites to river mouth and decreased in the interior sites of rivers. The density of juveniles increased from June to September, peaking in June and September. There was a strong correlation between density of the juveniles and season, salinity and water velocity, indicating that high density of the juveniles occurs during rainy season, in mangrove forest areas, at salinity of 10 to 15 ppt and water velocity of about 20 cm SI. Relative gut length (RGL) was determined at 1.4 and the gut content was mainly (85-86%) Chlorophyta algae. The female GSI was high from June to October. The oocytes diameter ranged from 1.82-2.67 um. Maximum maturity stage was found at secondary yolk globule stage. The later stages were not found in this study. Some basic growth parameters were identified, i.e. L~ = 20.1 cm, K = 0.89 yr⁻¹, to = - 0.05 (Bac Lieu) and L~ = 20.4 cm, K = 0.814 yr⁻¹, to = - 0.03 (Soc Trang). Four age groups were determined: age 1 at 12 cm, age 2 at 17 cm, age 3 at 19 cm and age 4 at 20 cm long. Weight and len~th relationships equations are y = 0.0092x²·⁶⁹⁶⁸ (R² = 0.85) in Bac Lieu and y = 0.0079x²·⁷³⁷⁶ (R² = 0.84) in Soc Trang province. Habitat and life cycle of P. elongatus were also determined in this study. In conclusion, this species is considered to have good potential for coastal aquaculture in the Mekong Delta. The wild juveniles and all sizes of P. elongatus face high catch pressure leading to the decline of this resource. Mudskipper fisheries and aquaculture activities generate a good income to boost the coastal people livelihood. Seed production and culture technology development, as well as better fisheries management of P. elongatus, are proposed. |
| Year | 2009 |
| 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) | Gallardo, Wenresti G.; |
| Examination Committee(s) | Bart, Amrit ;Shivakoti, Ganesh P. ;Ikejima, Kou ;Nguyen Thanh Phuong ;Macintosh, Don J.; |
| Scholarship Donor(s) | Ministry of Education and Training, Vietnam; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2009 |