Influence of Drying Techniques on the Physicochemical, Nutritional, and Morphological Properties of Bighead Carp (Hypophthalmichthys nobilis) Fillets

Different experiment analyses were performed to evaluate the influence of two drying techniques (oven drying and microwave drying) on the fillets of bighead carp fish (Hypophthalmichthys nobilis). The processed and fresh samples were subjected to the chemical analysis of (amino acids, minerals, volatile compounds, fatty acids, and vitamins) as well as scanning electron microscopy, thermal analysis, and color measurement, in order to identify nutritional components that can be additives or supplementary in food industries. The drying techniques increased the protein content significantly. Amino acids were identified, and the level of essential amino acid (EAA) was higher under the microwave treatment compared with the oven drying process. The Ca+2 and K+1 were presented in high values, followed by Na+1 and Mg+2. In addition, the drying techniques showed and released more volatile compounds in the processed samples compared with the unprocessed samples. Under the drying process, polyunsaturated fatty acids were increased in the processed fillets, whereas the level of saturated and monounsaturated fatty acids reduced. Thermal degradation occurred from 100 to 150 °C. However, the processed samples were subjected to an intensive endothermic response, but remained stable until 100 °C. Therefore, the microwave technique showed some enhancements in the nutritional value and has the potential to be applied as an effective preservation method of bighead carp fish. Furthermore, dried fillets could be an alternative source of bighead carp fish for the food industry.

Updated Genome Assembly of Bighead Carp (Hypophthalmichthys nobilis) and Its Differences Between Male and Female on Genomic, Transcriptomic, and Methylation Level

Cyprinidae is one of the largest family in freshwater fishes, and it is most intensively cultured fish taxon of the world. However, studies about sex determination in this large family is still rear, and one of the reasons is lack of high quality and complete genome. Here, we used nanopore to sequence the genome of a male bighead carp, obtaining contig N50 = 24.25 Mb, which is one of the best assemblies in Cyprinidae. Five males and five females were re-sequenced, and a male-specific region on LG19 was confirmed. We find this region holds many male-specific markers in other Cyprinidae fishes, such as grass carp and silver carp. Transcriptome analyses of hypothalamus and pituitary tissues showed that several sex-specific differentially expressed genes were associated with steroid biosynthesis. The UCH64E gene, located in the male-specific region on LG19, showed higher expression levels in male than female tissues of bighead carp. The methyl-RAD of hypothalamus tissues between males and females indicated that the sexual methylation differences are significant in bighead carp. We also compared the methylation sites recognized using methyl-RAD and nanopore raw reads and found that approximately 73% of the methylation sites identified using methyl-RAD were within nanopore CpG sites.

Application of rosemary essential oil (Rosmarinus officinalis Linnaeus, 1753) for anesthesia and transport of bighead carp (Hypophthalmichthys nobilis Richardson, 1845) fingerlings

The aim of the present research is to study the efficacy of rosemary oil as an anesthetic for bighead carp (Hypophthalmichthys nobilis Richardson, 1845) and as an anesthetic used for transport of fingerlings. The fish used in the experiment have an average body weight (BW, g) of 42.13±17.90 and an average total length (TL, cm) of 16.54±2.32. Five treatments are conducted with five experimental concentrations: 0.20 ml.l-1, 0.30 ml.l-1, 0.40 ml.l-1, 0.50 ml.l-1 and 0.60 ml.l-1. For each concentration 10 fish are used or a total of 50 fish. For the transport experiment, 3 concentrations are used: 0.06 ml.l-1, 0.08 ml.l-1 and 0.10 ml.l-1. The applied stocking density is 3 fish/l. A total of 60 fish are used for each concentration or a total of 180 fish. The established results, for the first experiment, show that at concentration of 0.60 ml.l-1 the induction of anesthesia is the fastest (3.46 min). From all tested concentrations the recovery time is the shortest at the lowest concentration – 2.16 min (p≤0.001). The concentration of 0.10 ml.l-1 of rosemary oil can be used for transport of bighead carp fingerlings for a period from 1 to 2 hours. The concentration of 0.08 ml.l-1 can be applied when the duration of the transport is from 1 to 3 hours.

Variation in inhibitor effects on qPCR assays and implications for eDNA surveys

Aquatic environmental DNA (eDNA) surveys are sometimes impacted by polymerase chain reaction (PCR) inhibitors. We tested varying concentrations of different inhibitors (humic, phytic, and tannic acids; crude leaf extracts) for impacts on quantitative PCR (qPCR) assays designed for eDNA surveys of bighead and silver carp (Hypophthalmichthys nobilis and Hypophthalmichthys molitrix). We also tested for inhibition by high concentrations of exogenous DNA, hypothesizing that DNA from increasingly closely related species would be increasingly inhibitory. All tested inhibitors impacted qPCR, though only at very high concentrations — likely a function, in part, of having used an inhibitor-resistant qPCR solution. Closer phylogenetic relatedness resulted in inhibition at lower exogenous DNA concentrations, but not at relatively close phylogenetic scales. Inhibition was also influenced by the qPCR reporter dye used. Importantly, different qPCR assays responded differently to the same inhibitor concentrations. Implications of these results are that the inclusion of more than one assay for the same target taxa in an eDNA survey may be an important countermeasure against false negatives and that internal positive controls may not, in the absence of efforts to maximize inhibition compatibility, provide useful information about the inhibition of an eDNA assay.