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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 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., (© Penerbit Universiti Sains Malaysia, 2023.)

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., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.