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In this study, several kinds of endocrine cells which produce neuropeptides and hormones have been identified and located in the digestive tract of milkfish (Chanos chanos) by the immunohistochemical technique. The oesophagus, stomach (cardiacus, fundic and pyloric regions), pyloric caeca, intestine (anterior, middle and posterior regions) and rectum were divided from the digestive tract of milkfish. The distribution and frequency of the endocrine cells produced these neuropeptides and hormones including gastrin, cholecystokinin, leuenkephalin, neuropeptide Y and somatostatin were described in these segments. Endocrine cells containing all neuropeptides and hormones immunoreactivities were present in the anterior intestine region, but no reaction was found in oesophagus. Only a few L-ENK-and SST-immunoreactive cells were detected in the pyloric caeca. Large numbers of SST-immunoreactive cells were observed in the stomach with no immunoreactivities to other neuropeptides and hormones. Two different types of endocrine cells were founded in the intestine and pyloric caeca. These results indicate that the anterior intestine region may be the main region of food digestion and absorption, and the neuropeptides and hormones regulate the food intake process by different ways in milkfish.

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The threadfin sea catfish (Arius arius) belongs to the genus Arius in Ariidae. In this paper, we initially determined the complete mitochondrial genome of Arius arius. The mitochondrial genome is 16, 711 bp in length, with the base composition on the heavy strand: A -29.67%, T -25.38%, C -29.70% and G -15.25%. It has the typical vertebrate mitochondrial gene arrangement, including 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a control region. Phylogenetic analysis showed that A. arius was clustered into the order of Siluriformes, and closely related to species in the family of Siluridae. The present study would contribute to genetic resources conservation and systematics study of A. arius.

Toxabramis houdemeri belongs to the genus Toxabramis in the subfamily of Cultrinae (Cyprinidae). We first determine the complete mitochondrial genome of T. houdemeri in this study. It is 16 618 bp in length, with the base composition on the heavy strand: 30.79% A, 16.61% G, 27.29% C, and 25.31% T. It has the typical vertebrate mitochondrial gene arrangement, including 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a D-loop region. Phylogenetic analysis showed that T. houdemeri was clustered into one branch of the subfamily of Cultrinae, and closely related to Hemiculter leucisculus. The present study will contribute to genetic resources conservation of T. houdemeri and studying its population genetic structure and phylogenetic relationships.