Histological characteristics of oocyte differentiation in the captive longnose seahorse Hippocampus trimaculatus (Leach, 1814).

This study aimed to explore the reproductive histology and oocyte differentiation of the longnose seahorse Hippocampus trimaculatus (Leach, 1814) in captivity. Five mature healthy females were histologically observed. The reproductive systems of the five specimens exhibited similar morphological characteristics with a pair of saccular creamy white ovaries merging caudally into a single gonoduct. There were two germinal ridges lined with a layer of germinal epithelium (GE). The ovarian maturation of this species was considered asynchronous. The oogenic cells were classified into oogonia and oocytes at several developmental phases based on their size and characteristics. Oogonia were identified among the connective tissue in the middle area of the GE. The stromal compartment contained oocytes that were classified into four distinct phases: the primary growth (PG) phase having two steps (perinucleolar and oil droplets-cortical alveolar steps) and the secondary growth (SG) phase with three oocyte types, including early SG oocytes, late SG oocytes, and fully grown oocytes. The atretic oocytes (AO) were observed in all stages of oogenesis. Postovulatory follicles were also seen among the ovarian connective tissue. The occurrence of postovulatory follicles suggested that the specimens analysed in this study were in the spawning period. This research provides new insights into the identification of the reproductive cycles and morphological characteristics of the ovary of H. trimaculatus.

A rapid and simple procedure for the whole-mount bone staining of small fish.

The cartilage and bone structure has provided insightful knowledge about evolution and ecology of fish, which is an important component of biological oceanography. However, the whole-body bone staining is a lengthy and complicated process that typically takes five days to several months, and the improvement of the conventional method has been one of the important issues in this field. Here we report a quick and easy whole-mount bone staining method for small fish, in which a newly designed fixative is applied. Compared to conventional methods, this novel protocol is a straightforward process that could be adopted for small estuarine fish and other small vertebrates.

Hematological Evaluation of Three Common Teleosts in Relation to The Environmental Changes from Trang Province, Thailand.

Hematological evaluation of fish is essential to the assessment of their physiological status. This study describes the morphometric analysis and comparison of blood cell characteristics in Zanarchopterus sp., Gerres filamentosus Cuvier, 1829 and Leiognathus decorus (De Vis, 1884). The species were collected at two locations off the coast of Trang Province, Thailand. A comparative hematological evaluation was made to assess the effects of environmental conditions on the blood of the fish. Ten individuals of each species were collected from a seagrass bed at Libong Island, where human activities are increasing, and from a secluded sandy beach. Their blood samples were analysed using the blood smear technique. Erythrocytes of all the studied fishes were either elliptical or oval. The morphometric data from both locations showed that erythrocytes were of similar size, except for those of Zanarchopterus sp. Fish from both stations showed several types of leukocytes, including neutrophils and lymphocytes.The highest proportion of leukocytes was made up of lymphocytes, followed by neutrophils. However, monocytes were only observed in fish from Libong Island and the erythrocytic nuclei of fish collected from Libong Island were both reniform and lobate. Our results show the potential of hematological evaluation as an early warning signal of environmental impacts on aquatic animals. The determination of baseline parameters could provide a tool for the monitoring of environmental quality.

Ecomorphological diversification of some barbs and carps (Cyprininae, Cyprinidae) in the Lower Mekong Basin of Thailand.

Morphological variation is fundamentally related to various aspects of fish ecology, including foraging, locomotion, and habitat utilisation. Twenty-six species of closely related cyprinid fish (n = 502) were analysed for patterns of morphological variations by using geometric morphometric methods. Ecological data of feeding and habitat preferences were determined by the observations in fields and laboratory together with the gathering of bibliographic information. The findings of major variation displayed in all parts of the fish body and correlated with ecological parameters. Variations of head shape especially form and position of mouthpart involved with feeding behaviours, whereas the variations of body depth and length which affected swimming patterns reflected responsiveness of water currents and habitat uses. Adaptation of head shape and body elongation was remarkably related to the feeding regime, swimming manoeuvrability and habitat utilisation of the species. Some convergent variation was observed between the tribes Smiliogastrini and Poropuntiini. Therefore, we propose that the morphological diversity of cyprinine fish is mainly affected by ecological gradients, while phylogenetic effects on morphology are minor.

Genetic variations and population structure in three populations of beardless barb, Cyclocheilichthys apogon (Valenciennes, 1842) inferred from mitochondrial cytochrome b sequences.

This study aimed to investigate the relation of dispersal barrier and genetic diversity, population structure, and demographic history of 46 samples of beardless barb, Cyclocheilichthys apogon (Valenciennes, 1842) collected from three different locations in North-eastern Thailand. The analysis of molecular variance (AMOVA) was employed in order to determine the genetic variability within and among populations of this fish. The neutrality tests and mismatch distribution analysis were additionally applied to assess the neutrality and demographic expansion of the populations, respectively. Contiguous sequences within range from 1100 to1140 bp were obtained with varying 16 different haplotypes with high-haplotype diversity (0.8773 ± 0.0327) and low-nucleotide diversity (0.00215 ± 0.00020). The variations within and among populations accounted for 98.98 and 1.02% of the total variation, respectively. The low level of pairwise Fst estimations indicated a possible gene flow among populations and a suggestion of genetic homogeneity at this geographical range. A supportive idea of having a single-maternal lineage and past demographic expansion or selection experiencing has distinctly appeared among these populations. The current data suggests that all three populations distinctly exist as a single stock unit and that is an important factor in identifying genetic variation of C. apogon in this geographical area to be used in establishing effective plans and strategies for a conservation and management.