Chanyut Sudtongkong

Stream degradation increases with high anthropogenic activity and climate variability, while declines occur in biodiversity. However, few studies have been undertaken on tropical waterways, a major impediment to biodiversity conservation. The present study was conducted on 95 relatively pristine small streams in Eastern Thailand with 10 reasonably uncommon species of balitorid fishes. Measurements were made of 21 physical and chemical factors and the substrate particle size. Stepwise regression identified the direct importance of substrate particle size and nitrate on the species’ richness of balitorids, whereas its abundance was negatively related with iron concentrations. A Canonical Correspondence Analysis identified three fish groups: the 1st group was negatively correlated with ammonia and positively correlated with dissolved silica, the 2nd group was positively correlated with substrate particle size and negatively correlated with stream ambient temperature and ammonia concentration, and the 3rd group was negatively correlated with low dissolved silica, respectively. The results of this study may indicate the vulnerability of balitorids under climate warming and anthropogenic pressure that alter the water physicochemical factors and river degradation including the substrate type. Thus, a conservation framework should be provided regarding the limits for water temperature, ammonia, and iron in Thailand’s Water Quality Criteria to better protect its freshwater ecosystem. Balitorid is a potential bioindicator for evaluating the river temperature effect in combination with ammonia nutrient stressors as long as the way-of-life habits of the species are taken into account.

The Japanese flathead, Inegocia japonica Cuvier, 1829 is a commercially important fish in small‐scale coastal fisheries in Thailand; however, an explanation of its digestive biology is missing. This study describes the digestive tract and accessory organs of I. japonica, using morphological and histological methods. The fish (10 individual fish, 24.5 ± 0.98 cm in total length) were obtained from Libong Island, Thailand. Integrated morphological and histological data showed that the digestive tract was composed of oesophagus, stomach, pyloric caeca and intestine, with accessory organs. All digestive tracts consisted of four layers, including mucosa, submucosa, muscularis and serosa. Two stomach regions were identified (cardiac and pyloric stomachs). Several clusters of gastric glands were identified in the cardiac stomach. Each gland was a unicellular structure. The apical surface of this gland contained the vacuolar cell. The intestine was lined with a simple columnar structure with goblet cells that was similar to pyloric caecum. Goblet cells were rare in the anterior intestine, in contrast to the posterior intestine where goblet cells were abundant. The numerous of hepatocyte was mostly observed in the liver, whereas an exocrine acinar cell of pancreas was also identified. The results of our observations provided the first information of the digestive tract of I. japonica and can be applied to advanced study, such as physiology and histopathology.

The health status of the zebra-snout seahorse, Hippocampus barbouri in captivity has been required for approval for aquaculture. In this study, we investigated the histopathological appearance of three vital organs including gill, kidney and liver in captive H. barbouri during its juvenile and adult stages, by using histological techniques. In juveniles from stage 14-days (100% prevalence) towards stage 30-days adults (100% prevalence), the gills exhibited intraepithelial edema and necrosis while hepatic tissue showed evidence of intracytoplasmic vacuoles. In addition, histological alteration to renal tissues was observed the degeneration of renal tubules, the presence of melanomacrophage, and the infection of trematode parasites. The parasites were found in stage 30-days adult fish in the kidney (33.3 % prevalence). Taken together, this study highlights the issue of health in captive rearing of H. barbouri, in particular histopathological alterations in gill, liver and kidney tissues, suggesting that aquaculture of this seahorse species requires improved methods and protocols for maintenance and preventing infection.

The optimal dietary protein requirement for sesarmid crabs (Episesarma singaporense) was investigated. Juvenile E. singaporense, individually reared in plastic glasses containing 250 mL sea water, were fed five fish meal-soybean meal-microbound diets variously containing dietary protein levels of 30%, 35%, 40%, 45% and 50% for six weeks. A completely randomized design was used in the experiment, comprising five treatments with 60 crabs in each. At the end of the experiment, a significant improvement in survival was observed in all treatments relative to the diet containing 30% dietary protein (p < 0.05) while the growth performance parameters did not differ across the five dietary groups. A significantly higher protein efficiency ratio was observed in the E. singaporense crabs receiving 45% dietary protein relative to the remaining treatments. The specific activities of the digestive enzymes, pepsin-like, trypsin, amylase, and lipase, and the amylase to trypsin ratio fluctuated across the five treatments, but that of chymotrypsin remained consistent, suggesting different nutritional responses to the various dietary protein levels. The crabs receiving the 45% protein diet had significantly higher in essential amino acid (EAA) profiles followed by the 40% protein diet, although some EAA values were only moderate. The pattern for the non-EAA (NEAA) was reversed, and the ΣEAA/ΣNEAA ratio was higher in the crabs receiving the 45% protein diets relative to the other treatments. Based on our investigations, the optimal dietary protein requirement achieving desirable characteristics of juvenile E. singaporense crabs was 45%. This finding would be a useful guideline in preparing artificial diets for the mariculture of this species.