Effects of p-nitrophenol on enzyme activity, histology, and gene expression in Larimichthys crocea.

p-Nitrophenol (PNP) is one type of environmental pollutant, which is difficult to degrade and soluble in water. To investigate the effects of PNP on economically important marine fish species, we subjected Larimichthys crocea juvenile to five different concentrations of PNP for 96 h, and the semi-lethal concentration (LC50) was 6.218 mg/L. Then we collected the liver, kidney, and gill tissues to determine enzyme activity and gene expression levels, and analyzed histological changes. In histological analysis, the gills showed curling of lamella, epithelial lifting and hyperplasia; the parenchymal structure of hepatocytes was significantly damaged, with severe vacuolation and loss of original structure. The renal cells were damaged too, with congestion and renal tubular necrosis. Catalase and superoxide dismutase both showed an up- and down-tendency with the rise of concentration in the three tissues, and GSH-px had similar trend in the kidney, which decreased at 8 mg/L in the liver but showed no significant differences in the gills. Malondialdehyde of three tissues was increased with an increase in PNP concentration. The expression of four detoxification (cyp450, gst, gpx, hsp70) and one immune-related (mhc II) genes was induced at low PNP concentrations but inhibited at high PNP concentrations in the kidney. In liver, cyp450, hsp70 and mhc II showed similar trend but gst and gpx didn't increase at low PNP concentrations. Our results indicate that the fish possesses the ability to detoxify PNP; however, at high concentrations, PNP still causes serious damage to them. Our data not only help in understanding the ability of L. crocea to detoxify PNP but also should serve as a basis for the study of toxic effects of nitrobenzenes on marine fish.

Effects of formaldehyde on detoxification and immune responses in silver pomfret (Pampus argenteus).

Formaldehyde can effectively control ectoparasites in silver pomfret (Pampus argenteus). However, there is limited information on the effects of formaldehyde treatment at a molecular level in fishes. In the present study, transcriptome profiling was conducted to investigate the effects of formaldehyde treatment (80 mg/L, bath for 1 h every day for three consecutive days) on the liver and kidney tissues of silver pomfret. A total of 617959982 clean reads were obtained and assembled into 265760 unigenes with an N50 length of 1507 bp, and the assembled unigenes were all annotated by alignment with public databases. A total of 2204 differentially expressed genes (DEGs) were detected in the liver and kidney tissues, and they included 7 detoxification- related genes and 9 immune-related genes, such as CYP450, GST, MHC I & II, and CCR. In addition, 1440 DEGs were mapped to terms in the GO database, and 1064 DEGs were mapped to the KEGG database. The expression of 4 detoxification-related genes and 6 immune-related genes in three days formaldehyde treatment were analyzed using RT-qPCR, and the antioxidant enzyme levels were also determined. The results indicate differential expression of detoxification- and immune-related genes during the three days formaldehyde treatment. Our data could provide a reference for the treatment of parasites to avoid high mortality and help in understanding the molecular activity in fishes after formaldehyde exposure.

Transcriptome sequencing of olfactory-related genes in olfactory transduction of large yellow croaker (Larimichthy crocea) in response to bile salts.

Fish produce and release bile salts as chemical signalling substances that act as sensitive olfactory stimuli. To investigate how bile salts affect olfactory signal transduction in large yellow croaker (Larimichthy crocea), deep sequencing of olfactory epithelium was conducted to analyse olfactory-related genes in olfactory transduction. Sodium cholates (SAS) have typical bile salt chemical structures, hence we used four different concentrations of SAS to stimulate L. crocea, and the fish displayed a significant behavioural preference for 0.30% SAS. We then sequenced olfactory epithelium tissues, and identified 9938 unigenes that were significantly differentially expressed between SAS-stimulated and control groups, including 9055 up-regulated and 883 down-regulated unigenes. Subsequent Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses found eight categories linked to the olfactory transduction pathway that was highly enriched with some differentially expressed genes (DEGs), including the olfactory receptor (OR), Adenylate cyclase type 3 (ADCY3) and Calmodulin (CALM). Genes in these categories were analysed by RT-qPCR, which revealed aspects of the pathway transformation between odor detection, and recovery and adaptation. The results provide new insight into the effects of bile salt stimulation in olfactory molecular mechanisms in fishes, and expands our knowledge of olfactory transduction, and signal generation and decline.

Transcriptomic and cortisol analysis reveals differences in stress alleviation by different methods of anesthesia in Crucian carp (Carassius auratus).

Stress response has negative effect on fish in aquaculture and research, which can be alleviated with anesthetic. To determine the optimal anesthetic, we investigated the physiological response of crucian carp (Carassius auratus) treated with three different anti-stress treatments: MS-222, eugenol and percussive stunning. Stress responses were evaluated by analyzing serum cortisol level and gene expression in blood. We determined the optimal concentrations of MS-222 (100 mg L-1) and eugenol (20 mg L-1) by dose selection. We found that the control group had significantly higher cortisol levels (172.78 ±â€¯19.95 ng mL-1) compared to the MS-222 treated group (46.85 ±â€¯3.22 ng mL-1), the eugenol treated group (72.78 ±â€¯9.07 ng mL-1), and the stunning treatment group (82.78 ±â€¯8.16 ng mL-1). Transcriptome analysis revealed 1572 differentially expressed genes (DEGs), including 155 DEGs related to the stress response, mainly involved in oxidative-stress response, heat shock proteins, and cold shock domain-containing protein. The heat shock protein genes were the primary DEGs in response to stress. RT-qPCR analysis confirmed differential expression of Hsps. We analyzed the function of the DEGs, which were enriched in genes involved in cellular response to stress and antigen processing and presentation. Combining the results from biochemical, transcriptome, and gene expression analysis, our data suggest that eugenol is more effective than MS-222 and percussive stunning in alleviating stress in crucian carp.