Identification and Distribution of Wedge Clams (Donacidae: Bivalvia) in Thailand by Geometric Morphometric and Molecular Analysis.

The phylogenetic relationship of living Thai Donacidae was herein studied. Two methodologies, geometric morphometrics (GM) and genetic analysis of COI sequences, were combined and applied to identify the valid taxa and explain biodiversity and the distribution pattern in this family. A total of 587 living specimens were tested to analyze the shape and size patterns by Elliptic Fourier Analysis (EFA). Shell identification and GenBank sequences were added to construct the phylogenetic relationship and haplotype network. Centroid size was used to identify the specimens to the subgenus level. Donax (Hecuba) scortum, was easily distinguished from other species by Principal Component analysis (PCA) of shell size and shape. Donax (Dentilatona) incarnatus and Donax (Deltachion) semisulcatus semisulcatus were identified using Canonical Variates Analysis (CVA). Pairwise comparison of EFA was used for species level recognition, particularly shape overlap was observed for medium and small shell size. Based on genetic distance and haplotype network of COI sequences, Donax (Latona) faba and D. (Latona) solidus could be grouped in the same clade. Intraspecific and interspecific genetic data variation of some common species in different geographical localities of Thailand was observed. Three distribution patterns of Donax species were observed along the two-marine system of Thailand.

Feeding-regimen of ß-glucan to enhance innate immunity and disease resistance of Nile tilapia, Oreochromis niloticus Linn., against Aeromonas hydrophila and Flavobacterium columnare.

ß-glucan is one of the most potent immunostimulants enhancing innate immune activity, disease resistance and growth performance of many aquatic organisms. Nevertheless, there are few studies on feeding regimens of ß-glucan that correlate to immune response and disease resistance and are important considerations for practical ß-glucan utilization. Thus, the effect of ß-glucan and feeding duration on innate immunity and disease resistance was investigated to establish an optimal feeding regimen of ß-glucan for Nile tilapia (Oreochromis niloticus Linn.). A variety of ß-glucan feeding regimens were evaluated, including: i) feeding for 2 weeks, ii) feeding for 4 weeks, and iii) feeding every-other-week, with the objective of establishing the optimal feeding regimen that enhanced innate immunity and disease resistance. Innate immunity parameters were determined every week for eight weeks. Alternative complement activity of all ß-glucan groups was significantly (P < 0.05) increased at the end of the first week, and then fluctuated but was not significantly (P > 0.05) different to the control until the end of the trial. Increased lysozyme activity was only detected at the end of the second week in all ß-glucan-treated groups, and then decreased to the control level during most of the sampling periods. Phagocytosis percentage was increased and prolonged by ß-glucan feeding, while the phagocytic index was not. Apart from innate immunity, ß-glucan-fed fish demonstrated enhanced disease resistance against Aeromonas hydrophila and Flavobacterium columnare challenge at only the end of the fourth week of the trial. The growth performance of ß-glucan-fed fish was not significantly (P > 0.05) different among the experimental groups and control. Taken together, the result indicated that all ß-glucan-feeding regimens resulted in quite similar outcomes with respect to innate immunity stimulation, disease resistance and growth performance. This novel result suggests that an every-other-week regimen is the optimal choice for Nile tilapia cultivation as an economic cost saving benefit. This is the first study to determine the optimal feeding-regimen of ß-glucan to enhance innate immunity and increase resistance to infection by pathogenic bacteria in Nile tilapia.

Morphology and taxonomy of Isognomon spathulatus (Reeve, 1858), a cryptic bivalve from the mangroves of Thailand.

Isognomon spathulatus (Reeve, 1858) is redescribed based on type material and original collections from Kungkrabaen Bay, Thailand. The species agrees with previously described isognomonids in most conchological and anatomical features, but possesses a suite of diagnostic characters, including a comma-shaped outline of the nacreous border, an uncoiled ventral diverticulum of the stomach, and the thickened mantle lobes with granulated cells. This study is the most comprehensive morphological analysis to date for any species of Isognomonidae Woodring, 1925 (1828). It describes and illustrates a number of previously unrecognized or underutilized anatomical characters of potential phylogenetic significance: the morphology of the byssal threads (cross-sectional shape, plumate rootlets, and the shape of adhesive disks), the presence and extent of the interdemibranchial buttresses, the presence of secretory cells in the central zone of the mantle, the shape of the ventral diverticulum of the gastric chamber, the presence of the typhlosolar guard ridge, and the position of the renal pore. A comparison is made between I. spathulatus and morphologically similar Isognomon ephippium (Linnaeus, 1758) with which it has been previously synonymized. Pearls of both species are described and illustrated. Individuals of I. spathulatus inhabit mangroves, where they attach by byssus to prop roots, typically in parapatry with individuals of I. ephippium that occupy adjacent mudflats. The spacial distribution and diverging adaptive strategies (pertaining to physical stabilization and response to predation) displayed by the two isognomonid species are considered in the light of the ecological speciation theory.

Ecology of Endolithic Bivalve Mollusks from Ko Chang, Thailand.

Cheewarat Printrakoon, Thamasak Yeemin, and Paul Valentich-Scott (2016) The objective of this study was to examine the ecology of coral boring bivalves from four islands southeast of Ko Chang, Trat Province, Thailand. A total of 11 bivalve families containing 18 species were recorded in the survey, including six reported for this first time in the region. Members of the Mytilidae comprised the highest bivalve diversity with five species recorded. The five most abundant species were Leiosolenus lima (Jousseaume in Lamy), Lithophaga teres (Philippi), Botula cinnamomea (Gmelin), Coralliophaga coralliophaga (Gmelin), and Gastrochaena cuneiformis Spengler. Ecological analysis showed that Ko Bai Dung had the highest density of boring bivalves, with 196.29 ± 118.24 individual/ m2. Density of coral boring bivalves was variable; the highest density was recorded for Coralliophaga coralliophaga (85.18 ± 74.35 individual/m2) at Ko Bai Dung. The highest diversity of boring bivalves was found on Ko Phrao Nok, and in dead coral. Multivariate analyses did not reveal a clear differences in the boring bivalve community composition between sites, or with coral age, or with coral species, however dead coral was well-grouped at 50% similarity. The number of species and number of specimens of boring bivalves in this study was significantly positively correlated with coral age. The maximum number of boring bivalve specimens was found in the oldest coral (11 years old) and in dead Porites host corals. Following the same trend of all dominant boring bivalves, corals more than nine years old showed the highest frequency distribution and the largest shell length. The distribution of shell height frequency showed Leiosolenus lima and Lithophaga teres had more variation in shell height than the other five dominant boring bivalve species. Endolithic bivalves are one of the main bioeroders in the coral biome. The ecologic data presented in this study can be used as one indicator of coral reef status, including bioerosion and nutrient recycling in coral ecosystems.