A partial substitution of microalgae with single cell detritus produced from seaweed (Porphyra haitanensis) for the nursery culture of tropical oyster (Crassostrea belcheri)

Oyster seed production in hatchery and nursery systems has relied on the production of microalgae, which is cost effective, but often unpredictable. The development of a satisfactory substitute diet would greatly reduce production costs of hatchery operations. Single cell detritus (SCD) production from seaweed (Porphyra haitanensis) may have great potential as a partial substitute for microalgae. In this experiment, a technique for producing SCD was developed and the product was used as a partial substitute for microalgae for the nursery culture of juvenile tropical oysters (Crassostrea belcheri) in a hatchery setting. A reverse osmosis technique was used on ground seaweed (particle size <200 μm) immersed in freshwater and placed on a shaker at 100 rpm for 2 h before being returned to seawater. This technique was shown to be highly effective for SCD production with a density of 33.7 ± 7.0 × 10⁴ cell mL^?1 and the percentage of SCD particle diameter <20 μm was 89.2%. A partial replacement of microalgae with SCD was found to be unsuitable for nursing oyster larvae. For juvenile oysters (shell width 1.85 ± 0.03 mm and shell length 1.78 ± 0.06 mm) substituting 75% of microalgae with SCD showed lower absolute shell growth, and lower daily yields and survival rates when compared to rates substituting 50% or lower substitution with SCD, or 100% microalgae (P < 0.05). It was found that substituting 50% of the traditional microalgae with SCD produced from seaweed (P. haitanensis) can be used as a partial microalgae substitute for the nursery culture of the juvenile tropical oyster.     

Post-tsunami rehabilitation of fish cage farms on the Andaman coast of Thailand

A post-tsunami rehabilitation of cage culture along the Andaman Sea coast of Thailand was carried out in five provinces (Ranong, Phang-nga, Krabi, Trang and Satun) from September 2007 to February 2008. Based on the survey conducted, the money compensated subsequently used to buy materials for cage re-construction and cage repair accounted for 28.1% of the total, and to buy seed, feed and chemicals for culture operations, 15.8%. A surprising finding is that 56.1% of compensated money was used for other purposes. The analysis showed that the quality and quantity of equipment, seeds and feeds invested in aquaculture farms were increased in comparison with the pre-recovery period. Importantly, the farm area, growth rate, amount of product and revenue were improved during the post-tsunami rehabilitation period. Additionally, the area and quality of houses, household consumption, household infrastructures, health care and education were also improved. The satisfaction level of cage farmers in regard to the recovery programs was high (weigh average index = 3.88). The results from this study showed that the net economic profit (NEP) achieved was 41,030.49 baht/crop (33.9 baht = 1 US$) for sea bass culture, while NEP for grouper culture was 59,529.98 baht/crop. The result from the present study indicated that the economic value of cage culture farms was profitable. However, the seed shortage, high cost of trash fish, disease outbreak and marketing were among key problems and constraints encountered. In this study, we also found that the knowledge about fish marketing and culture techniques was poor. Therefore, technical, marketing and financial support are required for the future.     

Evaluation of flocculated concentrates from intensive shrimp pond water as a substitute for microalgal concentrates in the nursery culture of juvenile oyster (<Emphasis Type="Italic">Crassostrea belcheri</Emphasis>)

Intensive shrimp pond water typically contains high densities of microalgae and may have a great potential as a substitute for microalgae in the nursery culture of juvenile oysters as this stage needs large amount of microalgae. Two experiments with different phytoplankton composition in flocculated concentrates from shrimp pond water were investigated to compare the effect on preservation and use of flocculated concentrates from intensive shrimp pond as a partial substitute for microalgae concentrates for the nursery culture of juvenile oysters (Crassostrea belcheri) was evaluated. The results show that total crude protein content in flocculated concentrates mostly contain unidentified nanocyanobacteria preserved in refrigerator at 4 °C gradually decreased from the first week in experiment 1, while a slight decrease in crude protein content appeared after the third week in flocculated concentrates dominated by the Bacillariophyceae and unidentified nanocyanobacteria groups in experiment 2. The pheophytin a:chlorophyll a ratio suddenly increased during the third week of storage and most of the fatty acid composition was absent after four weeks of storage in both experiments. Substituting 75 % of microalgal concentrates in feed with flocculated concentrates from shrimp pond water showed no significant differences in growth performance in experiment 1, but higher growth performance in experiment 2 in comparison with control treatment (100 % microalgal concentrates). Our findings indicate that a partial substitution of flocculated concentrates of up to 75 % from shrimp pond water for microalgal concentrates would lead to better growth in juvenile oysters.     

Evaluation of Agronomic Traits in Chromosome Segment Substitution Lines of KDML105 Containing Drought Tolerance QTL under Drought Stress

Drought is a major abiotic constraint to rice production in rainfed lowland and insufficiently irrigated areas.The improvement of drought tolerant varieties is one of the strategies to reduce the negative effects of drought.Quantitative trait loci(QTLs) for primary and secondary traits related to drought tolerance(DT) on chromosomes 1,3,4,8 and 9 that determined from double haploid lines derived from a cross between CT9993 and IR62266 were introgressed and dissected into small pieces in the genetic background of Khao Dawk Mali 105(KDML105) to develop chromosome segment substitution line(CSSL) population.The CSSLs were evaluated at the reproductive stage for their agronomic performance and yield components under drought stress,and results were compared with irrigated condition.The flowering of CSSL lines was 6 to 7 d earlier than KDML105.The mean values of grain yields in the CSSLs were higher than KDML105 under drought and irrigated conditions.At irrigated condition,the grain yields of introgression lines carrying DT-QTLs from chromosomes 4 and 8 were higher than that of KDML105,whereas other traits showed little difference with KDML105.Analysis indicated that grain yield has positive correlation with plant height,tiller and panicle number per plant,and total grain weight per plant under drought stress while negatively correlated with days to flowering.As mentioned above,CSSLs showing good adaptation under drought stress can be used as genetic materials to improve drought tolerance in Thai rainfed lowland rice breeding program,and as materials to dissect genes underlying drought tolerance.     

Effect of Water Flow Rate and Stocking Density on Nursing Hatchery-Reared Juvenile Oysters,Crassostrea belcheri in a Semi-Closed Recirculation System

Juveniles of hatchery-reared oysters (Crassostrea belcheri) were grown in a semi-closed recirculation system at water flow rates of 0.5, 1, 2, and 4 l min^?1. Growth rate increased with increasing water flow rate (P < 0.05) over four weeks. No significant differences in survival were found among water flow rates (P > 0.05). Four stocking density treatments were compared: 4, 8, 12, and 16 juveniles cm^?2. Stocking density affected the growth of animals, with higher growth rates obtained at the lower densities. Optimum stocking density based on growth rate was obtained for oysters at 12 juveniles cm^?2. Survival of oysters declined with increasing density (P < 0.05) over four weeks. Among the treatments tested, a water flow rate of 4 l min^?1 and stocking density of 12 juveniles cm^?2 are suitable for nursing hatchery-reared juvenile oysters (C. belcheri) in a semi-closed recirculation system.