Effects of thermal stress responses in goldfish (Carassius auratus): growth performance, total carotenoids and coloration, hematology, liver histology, and critical thermal maximum.

The present study aimed to investigate the effect of thermal stress on growth, feed utilization, coloration, hematology, liver histology, and critical thermal maximum (CTmax) in goldfish (Carassius auratus) cultured at three different acclimation temperatures including 27 °C, 30 °C, and 34 °C for 10 weeks. Goldfish were assigned randomly to tanks with a quadruplicate setup, accommodating 20 fish per tank. The result showed that fish acclimated to different temperatures did not significantly differ in weight gain (WG) and specific growth rate (SGR). However, increasing temperature significantly decreased feed efficiency ratio (FER), protein efficiency ratio (PER), and protein productive value (PPV), but significantly increased feed conversion ratio (FCR) (P < 0.05). The coloration parameters significantly decreased by high temperature in the trunk region with increasing temperature (L* and a* at week 5; L*, a*, and b* at week 10; P < 0.05). Total carotenoid contents in serum, fin, muscle, and skin also significantly decreased with increasing temperature (P < 0.05). Total protein, albumin, and globulin levels exhibited a notable decrease, while the albumin: globulin ratio showed a slight insignificant increase, with increasing temperature. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), total cholesterol, and triglycerides significantly increased with increasing temperature (P < 0.05). While, high-density lipoprotein cholesterol (HDL-c) decreased linearly (P < 0.05). Glucose and cortisol levels linearly increased with increasing temperature, the highest levels being observed in the 34 °C group. Liver histology showed swollen hepatocytes, nuclei displacement, and infiltration of inflammation in fish cultured at 34 °C. Goldfish acclimated to 34 °C displayed a higher CTmax of 43.83 °C compared to other groups. The present study showed that temperature should be kept below 34 °C for goldfish culture to prevent high FCR, fading coloration, and liver damages.

Effects of long-term exposure to high temperature on growth performance, chemical composition, hematological and histological changes, and physiological responses in hybrid catfish [♂Clarias gariepinus (Burchell, 1822) ×♀C. macrocephalus (Günther, 1864)].

The anthropogenic and climate-driven rise in water temperature is expected to have an effect on the physiological functions of ectothermic species. In the present study, hybrid catfish were subjected to three different temperatures (27, 32, and 37 °C) for 50 days to examine the effect of long-term exposure to high temperatures on growth and physiological parameters. The results showed that acclimation temperature improves growth and feed utilization with a quadratic effect (P < 0.05). The highest performance was observed at 32 °C, but fish acclimated at 37 °C decreased growth and feed utilization. In addition, skin darkening was observed in fish acclimated with increasing temperatures. Fat content of whole-body, liver, and dorsal muscle of fish was decreased by increasing temperatures (P < 0.05). Higher temperature levels significantly increased in all blood parameters (P < 0.05), except for high-density lipoprotein cholesterol, which was quadratically decreased (P = 0.004). Fish acclimated with increasing temperature also altered gill and liver histology such as gill shortening, hyperplasia and edema in the connective tissue, severe hyperplasia of epithelial cells, and desquamation, hepatocyte vacuolization, nuclei displacement, and pyknotic hepatic cells. While mucus cells were periphery distributed in the subcutaneous skin. In addition, cuboidal shape-like of club cells and melanophores were also observed in fish acclimated at 37 °C resulting in increased epithelial layer thickness. After fish subjected to increasing temperature exhibited an increase in the number of operculum movement and number of gasping for air (P < 0.05) in all acclimated groups. While fish challenged at 37 °C showed higher critical thermal maximum (CTmax, 41.33 °C) than those of the other groups. Overall, the maximum temperature (37 °C) may rick to hybrid catfish. To prevent physiological damage to the fish, as well as reduction of growth and productivity, the temperature in the aquaculture setting should be kept below 37 °C.

First Detection and Genomic Insight into mcr-1 Encoding Plasmid-Mediated Colistin-Resistance Gene in Escherichia coli ST101 Isolated from the Migratory Bird Species Hirundo rustica in Thailand.

Background: This study aimed to investigate the occurrence of mcr-1 encoding plasmid-mediated colistin-resistance gene in Escherichia coli isolated from migratory birds in Thailand. Materials and Methods: A total of 178 cloacal swabs from migratory birds was sampled and isolated from 2016 to 2017 in Nan, Trang, and Bangkok, Thailand. The multiplex polymerase chain reaction was used to screen the resistance genes. After screening, a disk diffusion assay and the minimum inhibitory concentration were investigated. The draft genome sequence of isolate 2A85589 was obtained using an Illumina HiSeq X-Ten platform. The genome was assembled using SPAdes 3.0.0. Antimicrobial resistance genes were identified using ResFinder 3.1. Results: We reported E. coli ST101 of isolate 2A85589, an mcr-1-carrying resistance gene isolated from the migratory bird species Hirundo rustica in Thailand. The draft genome of 2A85589 was 4,621,016 bp in size. IncHI1A plasmid was identified using PlasmidFinder with high coverage. In silico analysis detected the presence of eight putative acquired resistance genes, namely blaTEM-1B, mcr-1, mef(A), mef(B), QnrS1, sul3, tet(A), and tet(B), which conferred resistance to ß-lactam, colistin, macrolide, quinolone, sulfonamide, and tetracycline. Conclusion: This study underlines the potential risk of the environmental contamination of mcr-1-carrying E. coli isolated from the migratory bird. The long range migration of birds can result in dissemination of mcr-1-carrying bacteria globally. Therefore, plasmid-mediated colistin is an urgent need to be addressed in both human and veterinary medicine for disease control and prevention.

Molecular characterization and homology modeling of liver X receptor in Asian seabass, Lates calcarifer: predicted functions in reproduction and lipid metabolism.

Liver X receptor (LXR) is a ligand-activated transcription factor that plays vital roles in maintaining cholesterol and lipid homeostasis. Much work has been done on mammalian LXRs, but the role of LXR in fish remains unclear. In the present study, LXR gene was identified from adult Asian seabass, Lates calcarifer, and its predicted protein structure was docked with several cholesterol derivatives at the binding site. The LXR cDNA consisted of 1495 bp encoding a putative LXR protein of 494 amino acids. The Asian seabass LXR retained many important structural features found in LXRs of other fishes and mammals, such as putative signal peptide, activation function-1 (AF-1) domain, DNA-binding domain (DBD), ligand-binding domain (LBD), activation function-2 (AF-2) domain, and eight conserved cysteine residues. The deduced amino acid sequence of LXR shared significant identity with those of other species ranging from 65.7 to 95.8%. The homology modeling and in silico molecular docking demonstrated that Asian seabass LXR could interact with cholesterol derivatives at amino acid residues Phe274 and Ile312. Real-time PCR further revealed that LXR transcripts are ubiquitously expressed in all tissues examined, with the highest levels detected in the gonad followed by the liver. Given the well-known importance of cholesterol-mediated signaling in these tissues, Asian seabass LXR may reasonably be involved in reproduction and lipid metabolism.

Different effects of growth hormone and fasting on the induction patterns of two hormone-sensitive lipase genes in red seabream Pagrus major.

Growth hormone (GH) increases phosphorylation and mRNA levels of hormone-sensitive lipase (HSL) in the livers of some marine teleosts. The hepatic GH-HSL axis appears to play important roles in fasting-induced lipolysis. However, it is not known whether GH exerts similar effects on HSL in fish adipose tissues. Functional differentiation of two fish-specific HSL isoforms (HSL1 and HSL2) also remains unclear. The present study seeks to address two unanswered questions about fish lipolysis using red seabream (Pagrus major): (1) Does GH increase phosphorylation and mRNA levels of HSL in adipose tissue? (2) How do GH and fasting affect mRNA levels of two HSL isoform genes in the liver and adipose tissue? To this end, we first cloned HSL1 and HSL2 cDNAs and investigated their tissue distribution. Transcripts of both HSLs and HSL1 proteins were abundant in the visceral adipose tissue, gonads, and liver, suggesting the important role of HSL in adipose tissue lipolysis. HSL2 transcript levels were 20-65% those of HSL1 except in the skin, and HSL2 proteins were not detected by our in-house antisera. Ex vivo administration of GH increased HSL1 phosphorylation, non-esterified fatty acid (NEFA) release, and levels of HSL1 and HSL2 mRNA in both the liver and visceral adipose tissue. Hepatic HSL2 mRNA was particularly sensitive to GH administration and sometimes exceeded HSL1 mRNA levels with up to 13-fold induction. In contrast, fasting for 4 and 7d increased HSL1 mRNA levels, but had only marginal effects on HSL2 mRNA levels in both adipose tissue or liver. We concluded that GH would increase HSL mRNAs during adipose tissue lipolysis in red seabream; however, GH and fasting result in different induction ratio of two HSL isoform genes, suggesting that other hormone(s) also contributes to fasting-induced lipolysis.

Diversity of Lipid Distribution in Fish Skeletal Muscle.

Adipose tissue is a lipid storage organ characterized by the pronounced accumulation of adipocytes. Although adipose tissues are found in various parts of the vertebrate body, it is unclear whether these tissues have a common ancestral origin or have evolved in several phylogenetic lineages by independent adipocyte accumulation events. To gain insight into the evolutionary history of vertebrate adipose tissues, we determined the distribution of adipocytes by oil red O staining in skeletal muscle of 10 teleost species spanning eight orders: Tetraodontiformes, Pleuronectiformes, Spariformes, Salmoniformes, Clupeiformes, Beloniformes, Osmeriformes, and Cypriniformes. Accumulation of adipocytes in the myoseptum was observed in many species, including red seabream, rainbow trout, Pacific herring, Pacific saury, zebrafish and giant danio. We also found some order-, species-, and swimming mode-specific distribution patterns of adipocytes: 1) almost complete absence of intramuscular adipocytes in the order Tetraodontiformes (torafugu and spotted green pufferfish), 2) clear adipocyte accumulation in the inclinator muscles of fin in Japanese flounder, 3) a large intramuscular adipose tissue at the root of the dorsal fin in ayu, and 4) thick lipid layers consisting of subcutaneous adipose tissue and red muscle lipids in pelagic migratory fish (Pacific herring and Pacific saury). Of note, Pacific herring and Pacific saury are phylogenetically distinct species sharing a similar niche and swimming mode, suggesting that their analogous adipocyte/lipid distribution patterns are the consequence of convergent evolution. The potentially heterogeneous origin of adipose tissues has significant implications for the interpretation of their functional diversity.

Differences in lipid distribution and expression of peroxisome proliferator-activated receptor gamma and lipoprotein lipase genes in torafugu and red seabream.

Lipid content is one of the major determinants of the meat quality in fish. However, the mechanisms underlying the species-specific distribution of lipid are still poorly understood. The present study was undertaken to investigate the mechanisms associated with lipid accumulation in two species of fish: torafugu (a puffer fish) and red seabream. The lipid content of liver and carcass were 67.0% and 0.8% for torafugu, respectively, and 8.8% and 7.3% for red seabream, respectively. Visceral adipose tissue was only apparent in the red seabream and accounted for 73.3% of its total lipid content. Oil red O staining confirmed this species-specific lipid distribution, and further demonstrated that the lipid in the skeletal muscle of the red seabream was mainly localized in the myosepta. We subsequently cloned cDNAs from torafugu encoding lipoprotein lipase 1 (LPL1) and LPL2, important enzymes for the uptake of lipids from blood circulation system into various tissues. The relative mRNA levels of peroxisome proliferator-activated receptor gamma (PPARγ) and the LPLs of torafugu were determined by quantitative real-time PCR together with their counterparts in red seabream previously reported. The relative mRNA levels of PPARγ and LPL1 correlated closely to the lipid distribution of both fish, being significantly higher in liver than skeletal muscle in torafugu, whereas the highest in the adipose tissue, followed by liver and skeletal muscle in red seabream. However, the relative mRNA levels of LPL2 were tenfold lower than LPL1 in both species and only correlated to lipid distribution in torafugu, suggesting that LPL2 has only a minor role in lipid accumulation. In situ hybridization revealed that the transcripts of LPL1 co-localized with lipids in the adipocytes located along the myosepta of the skeletal muscle of red seabream. These results suggest that the transcriptional regulation of PPARγ and LPL1 is responsible for the species-specific lipid distribution of torafugu and red seabream.