High stocking density alters growth performance, blood biochemical profiles, and hepatic antioxidative capacity in gibel carp (Carassius gibelio).

This study investigated the effect of stocking density on growth performance, blood biochemical profiles, antioxidative capacity, and muscle quality of gibel carp (Carassius gibelio). Gibel carps (initial body weight 57.04 ± 1.89 g) were reared at high stocking density (HSD, 10.85 kg m-3), medium stocking density (MSD, 5.06 kg m-3), and low stocking density (LSD, 1.47 kg m-3) for 60 days. The LSD group exhibited the highest growth rate, while HSD significantly inhibited fish growth. The muscular compositions of crude fat, crude ash, and moisture were significantly changed by stocking density, but crude protein content did not differ significantly. The stocking density altered the muscular texture profiles of gibel carp. Compared to either the HSD group or the MSD group, the highest levels of resilience and springiness occurred in the LSD group. Significant differences were observed in the levels of plasma glucose, alanine aminotransferase, aspartate aminotransferase, cholesterol, and creatinine among three groups. The fish exhibited the highest level of plasma cortisol as well as the lowest levels of triiodothyronine and thyroxine in the HSD group. The fish stocked in the LSD group showed the highest activities of superoxide dismutase, glutathione peroxidase, and catalase as well as the highest content of glutathione in liver. The significant highest total antioxidant capacity occurred in the fish stocked in the LSD group. The results showed that HSD resulted in chronic crowding stress, and exerted negative impact on growth performance, muscle quality, and antioxidative capacity of gibel carp.

Sugar transporter genes in grass carp (Ctenopharyngodon idellus): molecular cloning, characterization, and expression in response to different stocking densities.

Glucose and fructose play a central role in the metabolism and cellular homeostasis of organisms. Their absorption is co-mediated by two families of glucose transporters, Na+-coupled glucose co-transporters (SGLTs) and facilitative Na+-independent sugar carriers (GLUTs), in the intestine. However, limited information has been available on these transporters in fish. Therefore, we studied glut2, sglt1, and sglt4 genes in grass carp (Ctenopharyngodon idellus). The full-length cDNAs of glut2 was 2308 bp, with an open reading frame (ORF) of 503 amino acids (AAs). The full-length cDNAs of sglt1 was 2890 bp, with an ORF of 658 AAs. Additionally, the full-length cDNAs of sglt4 was 2090 bp, with an ORF encoding 659 AAs. The three deduced AA sequences showed high homology between grass carp and other cyprinid fish species. Based on homology modeling, three-dimensional models of GLUT2, SGLT1, and SGLT4 proteins were created and transmembrane domains were noted. glut2, sglt1, and sglt4 were abundantly expressed in the anterior and mid intestine. In particular, glut2 was markedly expressed in liver (P < 0.05). Additionally, the results indicated that different stocking densities (0.9 or 5.9 kg m-2) did not alter intestinal section-dependent expression patterns of the three transporter genes. However, high stocking density impacted segmental mRNA expression levels. This work demonstrated that mRNA expression of sugar transporter genes in the fish intestine was segment specific, and crowding stress may affect the activity of intestinal sugar transporters. These results provided new insights into the relationship between crowding stress and intestinal sugar transporters in fish.

Visualizing primordial germ cell migration in embryos of rice field eel (Monopterus albus) using fluorescent protein tagged 3' untranslated regions of nanos3, dead end and vasa.

In rice field eel (Monopterus albus), germ cell development in the developing gonad has been revealed in detail. However, it is unclear how primordial germ cells (PGCs) migrate to the somatic part of the gonad (genital ridge). This study visualized PGC migration by injecting a chimeric mRNA containing a fluorescent protein fused to the 3' untranslated region (3'UTR) of three different genes, nanos3 of zebrafish (Danio rerio) and dead end (dnd) and vasa of rice field eel. The mRNAs were injected either alone or in pairs into embryos at the one-cell stage. The results showed that mRNAs containing nanos3 and dnd 3'UTRs labeled PGCs over a wider time frame than those containing vasa 3'UTR, suggesting that nanos3 and dnd 3'UTRs are suitable for visualizing PGCs in rice field eel. Using this direct visualization method, the normal migration route of PGCs was observed from the 50%-epiboly stage to hatching stage for the first time, and the ectopic PGCs were also visualized during this period in rice field eel. These findings extend our knowledge of germ cell development, and lay a foundation for further research on the relationship between PGCs and sex differentiation, and on incubation conditions for embryos in rice field eel.