Suwat Tanyaros

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.

The 2004 Indian Ocean Tsunami: Impact on and Rehabilitation of Fisheries and Aquaculture in Thailand

Southern Thailand, also known as Peninsular Thailand, lies between latitudes 50 and 110 N, and longitudes 980 and 1020 E. It covers an area of 7,153,917 ha and has over 2,705 km of shoreline, with the western coastline facing the Andaman Sea and the eastern coastline facing the Gulf of Thailand – see Figure 2. The result of the phenomenal growth of tourism and fishing is that much of the mangrove and beach forest along the coastal shores have been replaced by human-built infrastructures, such as aquaculture industries and tourist resorts (UNEP, 2005). As a consequence, the coastal areas of southern Thailand have become particularly vulnerable to natural disasters (Thanawood et al., 2006). The earthquake that created the tsunami was the world’s fifth largest, with a magnitude of 9.15 to 9.3 on the Richter scale. It occurred at 00:58:53 (GMT) on Sunday, 26 December, 2004, with the epicenter, at a depth of 30km, just off the west coast of North Sumatera, Indonesia (Harinarayana & Hirata, 2005); see Figure 1. The sudden vertical rise of the seabed by several meters during the quake displaced massive volumes of water, resulting in a devastating tsunami. This seismic sea wave traveled thousands of kilometres across the Indian Ocean, and ravaged the Andaman coast of southern Thailand at 9.30 am local time. The earthquake was the largest since the 1964 Alaska quake, and the fourth biggest this century. The tsunami that ensued was among the five largest recorded, as measured in tsunami magnitude – see Table 1. The waves that hit the Andaman coast were, in some places, as high as 20 metres. The Indian Ocean tsunami was the first in living memory to strike the shorelines of southern Thailand. The tsunami caused extensive damage to life and property in six southern coastal provinces along the Andaman coast of Thailand (Figure 2). The people suffered a total of 5,395 deaths, 8,457 injured and 3,144 missing. The severely affected areas included 292 villages in 78 sub-

Exploring hidden diversity in Southeast Asia’s Dermogenys spp. (Beloniformes: Zenarchopteridae) through DNA barcoding

Members of the freshwater halfbeak genus Dermogenys are hard to identify to the species level, despite several previous attempts to isolate fixed meristic, morphometric and colour pattern differences. This has led to ongoing confusion in scientific literature, records of species occurrence, and entries in museum collections. Here, a DNA barcoding study was conducted on the genus to gain further understanding of its taxonomic status across the Southeast Asian region. Fish were collected from 33 localities, spanning freshwater and brackish habitats in Malaysia, Western Indonesia, Thailand and Vietnam. In total, 290 samples of Dermogenys spp. were amplified for a 651 base pair fragment of the mitochondrial cytochrome oxidase c subunit I (COI) gene. Analysis was able to successfully differentiate the three species: D. collettei, D. siamensis, D. sumatrana; reveal the presence of a new putative species, Dermogenys sp., that was sampled in sympatry with D. collettei at three locations; as well as uncovering two genetic lineages of a fifth species, D. bispina, that display non-overlapping geographical distributions in drainages of northern Borneo; Kudat and Sandakan. This study expands the barcode library for Zenarchopteridae, demonstrates the efficacy of DNA barcoding techniques for differentiating Dermogenys species, and the potential thereof in species discovery.

Baker’s yeast as a substitute for microalgae in the hatchery rearing of larval and juvenile tropical oyster (Crassostrea belcheri, Sowerby 1871)

ABSTRACT In this study, baker’s yeast, Saccharomyces cerevisiae, was used as a partial substitute for microalgae in the hatchery rearing of larval and juvenile tropical oyster (Crassostrea belcheri). Dietary microalgae were replaced with graded levels (0%, 25%, 75%, and 100%) of untreated and treated yeast in the feed of oysters from the early umbo (6 days postfertilization) to the eyed larval stage (18 days postfertilization); then the same diets were formulated with untreated barker’s yeast and fed juvenile oysters for 3 weeks. The results showed that a partial substitution of microalgae with untreated or treated baker’s yeast is unsuitable for feeding oyster larvae up to the eyed stage. With juvenile oysters, there were nonsignificant differences (P > 0.05) in mean shell width and length during the study period. The replacement of 25% microalgae with baker’s yeast showed mean daily growth rates (DGR) as high as that obtained with 100% microalgae, while the other treatments showed lower DGR (P > 0.05). Nonsignificant differences were found among the treatments in terms of mean percentages of survival at the end of the experiment (P > 0.05). The percentage of juvenile oysters larger than 0.75 cm was highest (P < 0.05) when 25% microalgae was replaced with baker’s yeast, while the highest percentage of juvenile oysters smaller than 0.32 cm was observed with diet where 75% microalgae was replaced with baker’s yeast (P < 0.05). From the experiments, it was concluded that a partial substitution of microalgae with untreated or treated baker’s yeast was unsuitable for feeding oyster larvae, while a 25% substitution with untreated yeast could be used for rearing juvenile oysters.