Observation of the middle intestinal tight junction structure, cloning and studying tissue distribution of the four Claudin genes of the grass carp (Ctenopharyngodon idellus).

To confirm the existence of the tight junction (TJ) in middle intestine and obtain the genetic information of Claudin-3, Claudin-15a, Claudinb and Claudinc of grass carp, we observed the physical structure of TJ by transmission electron microscopy and cloned the partial cDNAs of the four Claudins using reverse transcriptase PCR technique. The four partial cDNAs consist of 1,261, 490, 776 and 662 bp encoded 131, 150, 195 and 171 amino acids, respectively. Homology analysis showed that the grass carp Claudin shared high homology with other teleost species, especially with Danio rerio and Carassius auratus. Multi-alignments of the four Claudin amino acid sequences have seen the two conserved cysteines existing in the first extracellular loop of Claudin-15a, Claudinb and Claudinc, and the sequence diversity of the four Claudins mainly lies within the C-terminal tails, which usually end with the -Y-V motif, except the -F-V motif in Claudinb. Tissue distributions of the four Claudins were measured by applying quantitative real-time PCR technique. Results showed that Claudin-3 was mainly expressed in liver and middle intestine and Claudinb was ubiquitously expressed with a higher expression in middle intestine while Claudin-15a and Claudinc were mainly expressed in middle intestine. Our study revealed the existence of the TJ in the middle intestinal and obtained the genetic information of Claudin-3, Claudin-15a, Claudinb and Claudinc of grass carp, aiming to found the molecular biology basis for the further study of the intestinal barrier function of grass carp.

Oxygen consumption and ammonia excretion of black carp (Mylopharyngdon piceus Richardson) and allogynogenetic crucian carp (Carassius auratus gibelio female x Cyprinus carpio male) fed different carbohydrate diets.

Oxygen consumption and ammonia excretion of black carp (Mylopharyngdon piceus Richardson) (4.6±0.3 g) and allogynogenetic crucian carp (Carassius auratus gibelio ♀×Cyprinus carpio ♂) (5.7±0.5 g) were examined when fish fed two types of carbohydrate (dextrin and glucose) at two levels (20 and 40%) each. The diets were isonitrogenous (40% dry matter) and isocaloric at 18.5 kJ g(−1) (dry matter) by adjusting the oil content to 10.1 and 1.5%, respectively. In black carp, the interactions between the carbohydrate type and level were found in oxygen consumption at 3 and 6 h and in ammonia excretion at 6 h after feeding. At 20% carbohydrate, no significant difference was observed between dextrin and glucose in oxygen consumption. However, at 40% carbohydrate, oxygen consumption in fish fed glucose was significantly higher than that in fish fed dextrin at 3 and 6 h after feeding. Within the dextrin diets, no significant differences in both oxygen consumption and ammonia excretion were detected between the two carbohydrate levels. Within the glucose diets, however, fish fed 40% glucose showed significantly higher oxygen consumption than those fed 20% glucose at 3 and 6 h after feeding. Ammonia excretion in black carp fed 40% glucose was higher than that in black carp fed 40% dextrin at 6 h and also found higher than those in the other three treatments at 24 h after feeding. The postprandial oxygen consumption and the ammonia excretion in crucian carp fed 40% glucose were the highest, but no significant differences were observed. Our data indicate that the escalation of glucose to 40% in a fish diet results in high oxygen consumption and ammonia excretion in black carp, suggesting that the efficiency of glucose as an energy source for this fish is compromised by the high metabolic expenditure after feeding. Crucian carp, on the other hand, have a better ability to cope with dietary carbohydrates.