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.

Comparative digestive biology between the ponyfishes from the Pranburi River estuary, Thailand.

We investigated the digestive biology of two prevalent leiognathid species in Pranburi River estuary, Thailand: the decorated ponyfish (Nuchequula gerreoides) and the splendid polyfish (Eubleekeria splendens). A total of 632 samples collected from February to April and September to November 2017 were analysed using morphological and histological approaches. The overall structures were similar between the species: a short mucous-cell-rich oesophagus region, a well-developed gastric gland uniformly present across the stomach's mucosal layer, and three finger-like pyloric caeca between the stomach and intestine. However, there were marked differences in the mouth, gill raker, and intestinal coefficient (IC). N. gerreoides had a relatively longer mouth, smoother gill rakers, and an IC of 1.08 ± 0.01, similar to those of other carnivorous fish. In contrast, the gill raker of E. splendens had more villiform teeth that can filter-feed better, and their IC was 2.16 ± 0.02 (i.e., longer intestine). Although digestive structures were generally similar between the ponyfishes, these differences suggest that N. gerreoides is relatively carnivorous with stronger suction, whereas E. splendens may be an omnivorous or herbivorous filter-feeder.

Histological structure of the digestive tract, liver, and pancreas of Ambassis nalua (Hamilton, 1822) with ultrastructural details of the gastric gland.

The scalloped perchlet Ambassis nalua is one of the dominant fishes in the Estuarine Pranburi River, Thailand. It is suggested that this fish is in the secondary trophic level with a carnivorous nature. Studies on digestive system will help us further identify the niche of this species in the food web/food chain. The present study therefore aimed to report the detailed structure and ultrastructure of A. nalua digestive system. Fish samples (n = 30) with a total length of 5.7 ± 0.5 cm were obtained using beach seines from the Estuarine Pranburi River. Their digestive tract length and intestine coeficient were 3.6 ± 0.07 cm and 0.91, respectively. Light microscopic observation showed that the digestive wall comprised four layers, namely mucosa, submucosa, muscularis, and serosa. The prominent mucous-secreting cells were found in the mucosal oesophagus. The stomach had many gastric folds, with height and width being 649.76 ± 85.15 and 370.30 ± 68.56 µm, respectively. Gastric glands were found in the anterior stomach but not in the posterior stomach. Each gastric gland was made up of a single type of columnar cells. The gastric cells were ultrastructurally characterized by numerous mitochondria and well-developed secretory granules of varying sizes. A few small vacuoles were also identified in the apical area of the gastric cells. The intestine had two regions (anterior and posterior intestines), and pyloric caecum was absent. The density of the goblet cell was significantly higher in the posterior intestine. These results provide basic knowledge of the digestive system of A. nalua, and the low intestine coefficient and the absence of pyloric caecum suggest the carnivorous feeding habit of this species.

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.

Comprehensive Structure of the Female Marine Water-Strider Asclepios annandalei Distant, 1915 from Pranburi River Estuary, Thailand: New Information for the Genus Asclepios.

The objective of this study was to describe the structure and histochemistry of the systemic organs in the female marine water-strider Asclepios annandalei from Pranburi river estuary, Thailand. Results from this study revealed for the first time that the integumentary system of this species consisted of three layers including epicuticle, exocuticle and endocuticle. The muscular system apparently contained only skeletal muscle along the body. In the urinary system, we observed well-developed Malpighian tubules, each of which was covered with the simple cuboidal epitheliums. These epitheliums also contained the secretory granules that were reacted positively with periodic acid Schiff (PAS). The digestive system of this species was composed of three distinct parts including foregut, midgut and hindgut. The respiratory system was composed of the respiratory organ, which was rarely found near the integument system. This organ was lined with a simple squamous epithelium. Two regions of nervous system, i.e., frontal ganglion connected to the eye structure and ventral nerve cord, were found. Each ganglion basically consisted of two layers, outer cortex and inner medullae. The outer cortex contained three types of cells, including neurosecretory cells, neuroglial cells and neurons. The cytoplasmic inclusion of neurosecretory cells contained secretory granules, which reacted positively with PAS, indicating the presence the glycoprotein. The neuroglia and neuron were also observed in the inner medullae layer. The female reproductive system (the ovarian structure, the reproductive tract and the accessory organ) of this gerrid species was seen under histological sections. The well-developed integument system and Malpighian tubule as well as the abundant respiratory organ is a characteristic of this species, which might be useful for the adaption to the estuarine condition.

An update on the evolutionary origin of aglomerular kidney with structural and ultrastructural descriptions of the kidney in three fish species.

The kidney of fish contains numerous nephrons, each of which is divided into the renal corpuscle and renal tubules. This glomerular structure is the filtration unit of the nephron and is important for the kidney function, but it has been reported that the renal corpuscle was lost in at least four independent linages of fish (i.e., aglomerular kidney). In this study, the authors newly described renal structures for three species by histological and ultrastructural observations: two aglomerular kidneys from a seahorse Hippocampus barbouri and a toadfish Allenbatrachus grunniens and a glomerular kidney from a snake eel Pisodonophis boro. The renal development of H. barbouri was also described during 1-35 days after birth. In all species tested, the anterior kidney was comprised of haematopoietic tissues and a few renal tubules, whereas the posterior kidney contained more renal tubules. Although the glomerular structure was present in P. boro, light microscopic observations identified no glomeruli in the kidney of H. barbouri and A. grunniens. Ultrastructurally, abundant deep basal infoldings with mitochondria in the renal tubules were observed in A. grunniens compared to H. barbouri and P. boro, suggesting the possible role of basal infoldings in maintaining the osmotic balance. By integrating the results from the three species and comprehensive literature search, the authors further showed that 56 species have been reported to be aglomerular, and that the aglomerular kidney has evolved at least eight times in bony fishes.

The sbGnRH-GTH system in the female short mackerel, Rastrelliger brachysoma (Bleeker, 1851), during breeding season: implications for low gamete production in captive broodstock.

The short mackerel (Rastrelliger brachysoma) is one of the most economically important fish in Thailand; it is also a prime candidate for mariculture but unfortunately is plagued by reproductive problems that cause low production of gametes in captivity. An understanding of how the brain, pituitary, and gonad axis (BPG) from the neuroendocrine system are involved in the reproductive activity of wild and captive R. brachysoma should help clarify the situation. In this study, we investigated changes in the sea bream gonadotropin-releasing hormone (sbGnRH)-gonadotropin (GTH) system in the female short mackerel, Rastrelliger brachysoma (Bleeker, 1851), during breeding season. sbGnRH-immunoreactive (ir) cell bodies were detected in the nucleus preopticus-periventricularis including nucleus periventricularis (NPT), nucleus preopticus (Np), and nucleus lateralis tuberis (NLT). Additionally, the sbGnRH-ir fibers protruded into the proximal par distalis (PPD) where GTH (FSH and LH) cells were detected. The number of sbGnRH-ir cell bodies and GTH cells and level of LH mRNA were significantly higher in the breeding season than those in the non-breeding season. Moreover, the number of sbGnRH-ir cell bodies and GTH cells and levels of sbGnRH and GTH (FSH and LH) mRNA were significantly higher in the wild fish than those in the cultured broodstock. It is suggested that the wild fish tended to have better reproductive system than hatchery fishes. This could be related to the endocrinological dysfunction and the reproductive failure in the hatchery condition. Moreover, the changes of all of the hormonal level could potentially be applied to R. brachysoma aquaculture.

Correction to: The sbGnRH-GTH system in the female short mackerel, Rastrelliger brachysoma (Bleeker, 1851), during breeding season: implications for low gamete production in captive broodstock.

The published online version of this article contained outdated Figs. 4 and 5. The original article has been corrected.