Growth Performance, Feed Intake and vegf121 Gene Expression Feature of Dwarf Cyprinus carpio rubrofuscus

Abstract

To explore the molecular mechanism of dwarf fish formation in the cultured population of Cyprinus carpio rubrofuscus and the functions of vascular endothelial growth factor (VEGF) in fish growth, the features of growth trait, feed intake, and feed utilization of dwarf fish were detected and analyzed. Vegf121 cDNA was amplified and sequenced in this study. The expression levels of vegf121 were analyzed by quantitative real time PCR (qRT-PCR) in 11 tissues of normal fish, and in the heart, pituitary, brain, muscle, and hypothalamus of dwarf fish. The results showed that under the culture condition in ponds, the body length distribution of the typical five-month-old C. carpio rubrofuscus population with dwarf individuals showed two obvious independent normal distribution curves. Furthermore, the dwarf individuals formed a small population that distinguished it from the normal and fast-growing fish in terms of body size. The results of the feeding experiment showed that the daily feed intake (DFI) and the weight gain rate (WGR) of fish in the dwarf group were significantly lower than those in the normal group, whereas the feed conversion rate (FCR) showed no significant difference between the two groups. Meanwhile, vegf121 was found to be differentially expressed in C. carpio rubrofuscus. The partial cDNA sequence of vegf121 gene was 1, 235 bp with an open reading frame of 432 bp encoding 144 amino acids. According to the predicted amino acid sequence, the protein belongs to the VEGF121 isoform and has a relatively high sequence identity to the VEGF121 proteins of 11 known fish with the lowest identity of 79.86% aligned to Denticeps clupeoides. However, the identities to VEGF121 isoforms to those of Homo sapiens and Mus musculus were lower, at only 51.02% and 52.74%, respectively. The low homology and different spatial and temporal distribution of VEGF121 isoforms between animals and fishes may be related to breathing regulators and the differences in vascularization patterns in the respiratory system. The qRT-PCR results of the expression levels of vegf121 mRNA detected in the tissues of the normal growth fish showed that the relative expression levels were the highest in the muscle, followed by those in the heart, gill, brain, stomach, pituitary, eye, liver, kidney and spleen, and the lowest in the hypothalamus. This suggested that vegf121 has different regulatory functions in the development of blood vessels in different tissues of C. carpio rubrofuscus. Comparing the expression of vegf121 in the five tissues between the dwarf and normal-growth fish group revealed that the expression levels of vegf121 mRNA in the hypothalamus of the dwarf fish group were significantly higher than those of the normal fish group. The hypothalamus, as a high-level nerve center regulating endocrine and metabolic activities in humans and fish, may undergo some pathological changes under the action of certain environmental or genetic factors. The higher expression of vegf121 in the hypothalamus may have disrupted hormone secretion in C. carpio rubrofuscus and subsequently destroyed the metabolic balance in the body, resulting in a decrease in the appetite and feeding ability of fish. However, there was no significant change in the expression of vegf121 mRNA in two other neural tissues, the brain and pituitary, between the two groups. While the expression levels of vegf121 in the both muscle and heart were slightly lower than those in the normal-growth group. The abnormally higher expression of vegf121 in the hypothalamus indicated angiogenesis or lesions in the hypothalamus, which may have affected the feed intake regulation pathway signals in the fish body. This study provides a scientific basis to further explore the mechanism leading to dwarfism in C. carpio rubrofuscus. Genetic studies on the reasons leading to dwarf individuals in cultured economic fish populations can help increase the yield and productivity in aquaculture.

Keywords

• cyprinus carpio rubrofuscus
• vascular endothelial growth factor
• dwarf
• feed intake