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Commercial culture of channel catfish (Ictalurus punctatus) occurs in earthen ponds that are characterized by diel swings in dissolved oxygen concentration that can fall to severe levels of hypoxia, which can suppress appetite and lead to suboptimal growth. Given the significance of the hypothalamus in regulating these processes in other fishes, an investigation into the hypothalamus transcriptome was conducted to identify specific genes and expression patterns responding to hypoxia. Channel catfish in normoxic water were compared with catfish subjected to 12 h of hypoxia (20% oxygen saturation; 1.8 mg O2/L; 27°C) followed by 12 h of recovery in normoxia to mimic 24 h in a catfish aquaculture pond. Fish were sampled at 0-, 6-, 12-, 18-, and 24-h timepoints, with the 6- and 12-h samplings occurring during hypoxia. A total of 190 genes were differentially expressed during the experiment, with most occurring during hypoxia and returning to baseline values within 6 h of normoxia. Differentially expressed genes were sorted by function into Gene Ontology biological processes and revealed that most were categorized as "response to hypoxia," "sprouting angiogenesis," and "cellular response to xenobiotic stimulus." The patterns of gene expression reported here suggest that transcriptome responses to hypoxia are broad and quickly reversibly with the onset of normoxia. Although no genes commonly reported to modulate appetite were found to be differentially expressed in this experiment, several candidates were identified for future studies investigating the interplay between hypoxia and appetite in channel catfish, including adm, igfbp1a, igfbp7, and stc2b. NEW & NOTEWORTHY: Channel catfish are an economically important species that experience diel episodic periods of hypoxia that can reduce appetite. This is the first study to investigate their transcriptome from the hypothalamus in a simulated 24-h span in a commercial catfish pond, with 12 h of hypoxia and 12 h of normoxia. The research revealed functional groups of genes relating to hypoxia, angiogenesis, and glycolysis as well as individual target genes possibly involved in appetite regulation. Listen to this article's corresponding podcast at https://apspublicationspodcast.podbean.com/e/channel-catfish-transcriptomic-response-to-hypoxia/. [ABSTRACT FROM AUTHOR]

There is a need to optimize production protocols to improve the efficiency of embryo production in commercial catfish hatcheries for hybrid catfish (female Channel Catfish Ictalurus punctatus × male Blue Catfish I. furcatus). The present study compared two methods of handling broodfish from a Channel Catfish population while they are being transferred from pond to hatchery. Sexually mature females (average weight = 3.9 kg/fish) were seined and transported in a hauling truck to the hatchery prior to being injected with hormones. The fish that were placed in soft mesh bags (confined) were compared with fish that were allowed to swim freely (nonconfined) in the hauling truck and raceway in the hatchery. The fish were bled at seining (0 h), after transport to the hatchery (1 h), and while in the raceway at 4 and 24 h, respectively, and plasma levels of cortisol were measured. The broodfish that were suspended in soft mesh bags were monitored for ovulation and strip‐spawned to determined their relative fecundity (eggs/kg of body weight) and fry/kg body weight. The results showed that cortisol levels were high after seining in both groups. The cortisol concentrations were significantly lower (P < 0.05) at 1 and 4 h in the nonconfined than in the confined group. By 24 h, the cortisol levels had decreased in both of the treatment groups. The average relative fecundity (9,617 versus 8,576) and the number of fry/kg body weight (3,039 versus 2,710) were significantly higher (P < 0.05) for the nonconfined fish than for the confined fish. Minimizing handling and confining stress of gravid Channel Catfish after seining during transport to the hatchery and holding them in hatchery tanks for 4 h prior to hormone injection appears to be beneficial to the hatchery production of hybrid catfish fry. [ABSTRACT FROM AUTHOR]

Abstract Cortisol is a glucocorticoid hormone which is an endocrine signaling molecule in all vertebrates and acts through intracellular glucocorticoid receptors (GRs). Cortisol affects many biological functions including immunity, stress, growth, and reproduction. The objective of this study was to investigate the ontogeny of the cortisol and GR stress response in channel catfish (Ictalurus punctatus) at several early life stages. To accomplish this, resting and stress-induced levels of tissue cortisol and the two catfish GRs (GR-1 and GR-2) expression were measured. Resting cortisol levels in newly fertilized eggs averaged 2.4 ± 0.2 ng/egg and decreased to 0.4 ± 0.01 ng/egg by day 5. Cortisol levels in newly fertilized eggs subjected to an acute stress (lowered dissolved oxygen from 6.5 mg/L to 1.8 mg/L) averaged 2.3 ± 0.1 ng/egg and decreased to 0.3 ± 0.03 ng/egg by day 5. At hatching, resting cortisol levels were 24 ± 1.0 ng/0.1 g tissue while levels increased to 83 ± 2.0 ng/0.1 g tissue in fry subjected to an acute stress (P <.05). Four days post-hatch, resting cortisol levels were 83 ± 1.0 ng/0.1 g tissue while levels increased to 149 ± 4.0 ng/0.1 g tissue in fry subjected to an acute stress (P <.01). There was no significant difference between GR-1 and GR-2 mRNA in stressed and unstressed newly hatched fry. Four days post-hatch, GR-1 mRNA increased 3-fold while GR-2 mRNA increased 2-fold in fry that were subjected to low dissolved oxygen conditions (P <.05). These results indicate that cortisol biosynthesis, integration and maturation of the hypothalamic-pituitary-interrenal (HPI) axis can be observed in channel catfish at hatching. The upregulation of GR-1 and -2 mRNA in stressed fry supports roles for both transcripts in integrating the channel catfish stress response. Highlights • Ontogeny of the cortisol and glucocorticoid receptor stress response in channel catfish and several early life stages. • Cortisol biosynthesis, integration and maturation of the HPI axis can be observed in channel catfish at hatching. • Upregulation of GR-1 and -2 mRNA supports roles for both transcripts in integrating the catfish stress response. [ABSTRACT FROM AUTHOR]

Abstract: This study evaluated the efficacy of an oral live‐attenuated Edwardsiella ictaluri vaccine against enteric septicemia of catfish (ESC) in channel and hybrid catfish. The vaccine was delivered one time orally by feeding fish a diet coated with an attenuated E. ictaluri isolate at four doses to deliver between 4 × 106 to 3.2 × 107 viable vaccine cells/g wet feed. Thirty‐five days postvaccination, control and vaccinated fish were challenged with virulent E. ictaluri and mortality was examined for 30 d postchallenge. Mortality of nonvaccinated hybrids (85%) and nonvaccinated channel catfish (73%) was similar but significantly greater than all groups of vaccinated fish. In channel catfish, a trend toward increasing mortality with decreasing dose was observed. Mortality of channel catfish vaccinated with the lowest dose (26.6%) was significantly higher than fish vaccinated with the highest dose (14.1%) but similar to fish vaccinated at the intermediate doses (17.5 and 19.4%). In contrast, mortality of four doses of vaccinated hybrid catfish was similar and ranged between 10.4 and 14.0%. The data demonstrate that the attenuated E. ictaluri vaccine at all four doses tested is effective at reducing ESC‐related mortalities in hybrid and channel catfish. [ABSTRACT FROM AUTHOR]

The microbiota of teleost fish has gained a great deal of research attention within the past decade, with experiments suggesting that both host-genetics and environment are strong ecological forces shaping the bacterial assemblages of fish microbiomes. Despite representing great commercial and scientific importance, the catfish within the family Ictaluridae, specifically the blue and channel catfish, have received very little research attention directed toward their gut-associated microbiota using 16S rRNA gene sequencing. Within this study we utilize multiple genetically distinct strains of blue and channel catfish, verified via microsatellite genotyping, to further quantify the role of host-genetics in shaping the bacterial communities in the fish gut, while maintaining environmental and husbandry parameters constant. Comparisons of the gut microbiota among the two catfish species showed no differences in bacterial species richness (observed and Chao1) or overall composition (weighted and unweighted UniFrac) and UniFrac distances showed no correlation with host genetic distances (Rst) according to Mantel tests. The microbiota of environmental samples (diet and water) were found to be significantly more diverse than that of the catfish gut associated samples, suggesting that factors within the host were further regulating the bacterial communities, despite the lack of a clear connection between microbiota composition and host genotype. The catfish gut communities were dominated by the phyla Fusobacteria, Proteobacteria, and Firmicutes; however, differential abundance analysis between the two catfish species using analysis of composition of microbiomes detected two differential genera, Cetobacterium and Clostridium XI. The metagenomic pathway features inferred from our dataset suggests the catfish gut bacterial communities possess pathways beneficial to their host such as those involved in nutrient metabolism and antimicrobial biosynthesis, while also containing pathways involved in virulence factors of pathogens. Testing of the inferred KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways by DESeq2 revealed minor difference in microbiota function, with only two metagenomic pathways detected as differentially abundant between the two catfish species. As the first study to characterize the gut microbiota of blue catfish, our study results have direct implications on future ictalurid catfish research. Additionally, our insight into the intrinsic factors driving microbiota structure has basic implications for the future study of fish gut microbiota. [ABSTRACT FROM AUTHOR]

The present research evaluated targeted gene expression panels and microbiota analysis to provide greater insight into the effects of alternatively-sourced dietary ingredients on production indices, gut health, changes in the gut microbiota and genes involved in the regulation of appetite, growth, metabolism, and intestinal inflammation. Four dietary formulations were based primarily on distinguishing protein sources: (D1-MFM) menhaden fishmeal (control), (D2-MBM) porcine meat and bone meal, (D3-SBM) soybean meal, and (D4-CSM/CGM) cottonseed meal/corn germ meal, respectively, and fed to channel catfish for 12 weeks. Differences in feed conversion ratio (FCR), specific growth rate, feed intake, body condition, weight gain, proximal intestine histology, intestinal microbiota composition, and quantitative gene expression were analyzed. FCR was significantly ( P  < 0.05) increased in D2–4 relative to D1-MFM; however, other production indices were unaffected by treatment. Dietary treatment also had no effect on intestinal histology ( P  < 0.05). Effects of alternative dietary formulations on the gut microbiota were minimal, although when using Chao1, a significant effect of dietary treatment was detected ( P  = 0.0497) on gut-associated microbiota richness estimates. D3-SBM caused diet-specific differences ( P  < 0.05) in the expression of neuropeptide Y, peptide YY, and D2-MBM, D3-SBM, and D4-CSM/CGM resulted in differences in α-amylase, insulin receptor-a, glucose-6-phosphate-dehydrogenase, glucocorticoide receptor 1, and glucocorticoide receptor 2, relative to D1-MFM. These changes likely relate to differences in diet-mediated regulation of appetite and glucose metabolism, and perhaps the modulation of gut passage rate. By evaluating the molecular regulation of these pathways, as well as surveying the gut-associated microbiota, effects not detectable in short-term feeding trials may be elucidated which explain subtle differences in performance, such as FCR, as observed in the present study. [ABSTRACT FROM AUTHOR]

Abstract: Juvenile channel catfish (5.6 g/fish) were fed a basal diet that contained major protein (soybean meal, cottonseed meal) and energy (ground corn grain, wheat middlings) ingredients that were derived from plant sources. The basal diet was supplemented with three levels of crystalline taurine to provide 1, 2 and 5 g/kg taurine. In addition, a fifth diet that contained 80 g/kg menhaden fishmeal formulated with the same plant‐source ingredients was included as the positive control diet. Fish were fed the five diets once daily for 12 weeks. Weight gain was highest in catfish fed taurine at 2 g/kg (47.8 g/fish) compared to catfish fed the control basal diet (40.8 g/fish) and 80 g/kg fishmeal diet (41.1 g/fish) (p < .05). Among the taurine‐supplemented diets, weight gain was lowest in catfish fed taurine at 5 g/kg. Feed conversion ratio (FCR) was significantly improved in fish fed diets supplemented with taurine at 2 g/kg compared to all other treatments (p < .01). Survival during the growth study ranged from 98.0 to 99.0% (p > .05) for all treatments. The results suggest taurine supplementation to juvenile channel catfish may improve weight gain and FCR. [ABSTRACT FROM AUTHOR]

Aquaculture recently overtook capture fisheries as the largest producer of food fish, but to continue increasing fish production the industry is in search of better methods of improving fish health and growth. Pre- and probiotic supplementation has gained attention as a means of solving these issues, however, for such approaches to be successful, we must first gain a more holistic understanding of the factors influencing the microbial communities present in the intestines of fish. In this study, we characterize the bacterial communities associated with the digestive tract of a highly valuable U.S. aquaculture species, channel catfish Ictalurus punctatus, over the first 193 days of life to evaluate temporal changes that may occur throughout ontogenetic development of the host. Intestinal microbiota were surveyed with high-throughput DNA sequencing of 16S rRNA V4 gene amplicons derived from fish at 3, 65, 125, and 193 days post hatch (dph), while also characterizing the environmental microbes derived from the water supply and the administered diets. Microbial communities inhabiting the intestines of catfish early in life were dynamic, with significant shifts occurring up to 125 dph when the microbiota somewhat stabilized, as shifts were less apparent between 125 to 193 dph. Bacterial phyla present in the gut of catfish throughout ontogeny include Bacteroidetes, Firmicutes, Fusobacteria, and Proteobacteria; with the species Cetobacterium somerae and Plesiomonas shigelloides showing the highest abundance in the catfish microbiota after 3 dph. Comparisons of the gut microbiota to the environmental microbes reveals that the fish gut is maintained as a niche habitat, separate from the overall microbial communities present in diets and water-supply. Although, there is also evidence that the environmental microbiota serves as an inoculum to the fish gut. Our results have implications for future research related to channel catfish biology and culture, and increase our understanding of ontogenetic effects on the microbiota of teleost fish. [ABSTRACT FROM AUTHOR]

Large-scale, gene expression profiling methods allow for high throughput analysis of physiological pathways at a fraction of the cost of individual gene expression analysis. Systems, such as the Fluidigm quantitative PCR array described here, can provide powerful assessments of the effects of diet, environment, and management on physiological pathways affecting production parameters. A targeted microfluidic PCR array was designed and validated, for channel catfish ( Ictalurus punctatus ) representing key pathways involved in appetite, growth, metabolism, and intestinal inflammation for their potential to provide insight into the effects of diet and dietary supplements on these important physiological processes regulating feed efficiency and growth. With few exceptions, PCR primers were designed from Ictaluridae gene sequences published in GenBank. PCR amplicons from primers designed outside of Ictaluridae were sequenced to verify gene identity. All target gene primers were initially validated via conventional real-time qPCR (RT-qPCR). Combined hypothalamus/pituitary, hepatic, stomach, and intestinal tissue were used validate a 48.48 microfluidic PCR array to analyze multitissue gene expression. Use of the Fluidigm array resulted in reliable cycle threshold levels (Ct), efficiencies (E), and quality threshold scores (QS) for all but eight genes examined. Of the potential reference genes included in the panel, alpha-tubulin (TUBA) had a high QS, E, and acceptable Ct. The high throughput application of this technology, relative to conventional RT-qPCR, for assessing dietary effects on these pathways is demonstrated. Development of this targeted multi-tissue microfluidic array paves the way for the rapid evaluation of regulatory pathways in response to alternative feeding strategies, dietary formulations, and supplementation, as well as environmental and management effects for improving channel catfish culture and validates a cost-effective, dynamic, gene expression platform for use with other cultured fishes. [ABSTRACT FROM AUTHOR]

This study evaluated the efficacy of an oral live attenuated Edwardsiella ictaluri vaccine against enteric septicemia of catfish in 20 full-sib fingerling channel catfish families. The vaccine was delivered orally by feeding fish a diet coated with an attenuated E. ictaluri isolate. Sixty-nine days postvaccination, control and vaccinated fish were challenged with virulent E. ictaluri and mortality was examined for 21 d postchallenge. Vaccinated fish had significantly lower mortality than nonvaccinated fish following challenge ( P < 0.001). Mortality of vaccinated fish was 1.7 ± 1.4% as opposed to 47.8 ± 28.7% in nonvaccinated fish. Relative percent survival ranged from 87.7 to 100% with an average of 95.2 ± 4.0% (± SE) among the 20 families of fish. There were significant differences in mortality among families in nonvaccinated fish ( P < 0.01) while there were no differences among vaccinated families of fish. Results indicate that the live attenuated E. ictaluri vaccine is effective at reducing mortality in channel catfish exposed to virulent E. ictaluri. These data demonstrate that genetic differences among healthy families of channel catfish are not major considerations in developing an effective vaccination program utilizing the oral vaccination platform described in this study. [ABSTRACT FROM AUTHOR]

ABSTRACT Innate immune proteins mannose-binding lectin ( MBL) and lysozyme were studied in channel catfish, Ictalurus punctatus, during two consecutive years at 2, 4, 6, 9, and 12 mos of age. Both groups maintained in indoor tanks in light/dark photoperiod at mean temperature 27 C. Dot-blot enzyme linked immunosorbent assay (ELISA) for MBL and turbidometry lysozyme assay done to quantify the two innate proteins and means determined for two consecutive years. An increase in mean MBL was seen in 4-mo catfish (26.9 ± 0.8 µg/mL) when compared with all other age groups. A decrease in mean MBL was seen in 6- and 9-mo catfish when compared with all other age groups. Both 2-mo (21 ± 1.4 µg/mL) and 12-mo (19.9 ± 0.4 µg/mL) catfish were very similar in mean MBL concentrations. The greatest increase in mean lysozyme was seen at 4 mo (15 ± 5.0 µg/mL). Juvenile channel catfish could produce lysozyme at 2 mo equivalent to lysozyme concentrations found in 9- and 12-mo catfish. The greatest increases for MBL and lysozyme were seen in 4-mo catfish. Mean total protein of 26.7 mg/mL and mean albumin/globulin ratio of 0.7 were found for the two groups of channel catfish sera. [ABSTRACT FROM AUTHOR]

A study was conducted to investigate the effect of a phytogenic feed additive (Digestarom ® P.E.P. MGE; containing the essential oils carvacrol, thymol, anethol, and limonene) on growth performance and disease susceptibility to Edwardsiella ictaluri . Two hundred and fifty juvenile channel catfish, Ictalurus punctatus (7.2 ± 0.1 g) were allotted into the following treatments: Control (floating diet) and EO (floating diet supplemented with essential oils). The fish were fed their respective diets for 6 weeks. At the end of the study, all fish were exposed to virulent E. ictaluri by bath immersion (1.9 × 10 7 cfu/mL; final concentration). Plasma and tissue samples were taken to quantify protein and mRNA expression levels of mannose binding lectin (MBL). Weight gain and food conversion ratio were similar between treatments. After exposing fish to virulent E. ictaluri and monitoring mortality for 21 days, survival was 43% higher (69.5 vs 48.4%) in fish fed EO compared to fish not treated with EO (P < 0.05). One day after challenge, plasma MBL levels were down-regulated in the non-treated fish compared to non-challenged fish. In the EO fish, MBL levels were similar to non-challenged fish but significantly higher than non-treated fed fish (P < 0.001). By d 7, plasma MBL levels increased in non-treated fed fish to levels observed in the EO and non-challenged fish. On d 14, MBL mRNA levels were upregulated 15-fold in fish fed EO compared to non-treated fed fish and non-challenged fish (P < 0.001). The results demonstrate that essential oils improved survival of channel catfish challenged with E. ictaluri . Mechanisms through which essential oils improve survival may involve MBL. [ABSTRACT FROM AUTHOR]

We investigated the effects of a phytogenic feed additive (Digestarom® P.E.P. MGE) on growth performance, processing yield, fillet composition, and survival of pond-raised channel catfish. Fifteen 0.4 ha ponds were stocked with 14,820 catfish (126 g/fish) per ha. Fish in control ponds were fed a 32% crude protein commercial floating diet whereas fish in test ponds were fed the same diet supplemented with Digestarom P.E.P. MGE at 200 g/ton. In a second study, ten 0.04 ha ponds were stocked at a similar density with fish that averaged 68 g/fish. At the end of the 6-mo study, there was no significant difference in the amount of feed fed or the amount of weight gained between the control and Digestarom P.E.P. MGE fed fish. Food conversion ratio, net yield, and survival were also similar between the two groups. Carcass, fillet, and nugget yield were similar. Fillet proximate analysis revealed that fillet fat was lower ( P < 0.01) whereas fillet protein tended to be a little higher ( P < 0.10) in treated fish. In conclusion, there was a significant reduction in the amount of fillet fat in Digestarom P.E.P. MGE fed fish. Improved fillet composition (higher protein and lower lipid) is of commercial importance. [ABSTRACT FROM AUTHOR]

The use of monosex populations for aquaculture is becoming widely used for several species. The current studies determined if there were any differences between male and female channel catfish, Ictalurus punctatus, in disease susceptibility to Edwardsiella ictaluri, one of the most important pathogenic bacteria in catfish culture. Disease challenge experiments were carried out on fingerling channel catfish fed 17β-estradiol or testosterone before the challenge, and on all male and on sibling all female fingerlings. All male populations were produced by mating YY males with normal XX females. Sibling females were produced by hormonally sex reversing a subpopulation of six of the all male families. Weight gain or specific growth rate did not differ in fish fed testosterone or estrogen. Fish fed the highest dose of estrogen (50 mg/kg) had a significant higher mortality ( P < 0.05), while mortality was similar in catfish fed 10 and 50 mg/kg of testosterone compared to controls. There were no differences in mortality between sibling males and females. These data indicate no increased disease susceptibility to E. ictaluri between males and females or due to exogenous sex hormones. Production of all male catfish for culture can proceed without concern for disease susceptibility to E. ictaluri. [ABSTRACT FROM AUTHOR]

Abstract: Ghrelin (GRLN), cocaine and amphetamine regulated transcript (CART), neuropeptide Y (NPY), and cholecystokinin (CCK) are neuropeptides involved in the regulation of appetite and feeding in vertebrates. We examined pre- and postprandial changes in the expression of plasma GHRL and mRNAs encoding GRLN, CART, NPY, and CCK in channel catfish. Fish were entrained to eat at 0900h for 2 weeks. Fish were then sampled at 0700, 0800, and 0900h. Remaining fish were either offered feed at 0900h (Fed) or fasted (Unfed). Fish sampling continued at 0.5, 1, 2, and 4h post feeding. Feeding increased abundance of whole brain CART mRNA out to 4h with no effect observed in unfed fish. Whole brain NPY expression peaked at 0.5h in both treatments. NPY expression then declined in fed fish but remained elevated in unfed fish. No differences in plasma or stomach GRLN expression were observed. Two separate cDNAs for CCK were identified. Brain CCKa and CCKb expression increased after feeding. These results suggest CART, NPY, and CCK play roles in the regulation of channel catfish feeding. Taken together, these results provide new insights into the neural and gastroenteric mechanisms regulating appetite in channel catfish. [Copyright &y& Elsevier]

A study was conducted to determine the clearance time of yellow pigments lutein and zeaxanthin in channel catfish at various temperatures. Fish of initial weight of 13.4 g were stocked into flow-through aquaria and fed daily with a pigment-enhanced diet for 11 wk when yellow color became visible in the flesh. All fish were then transferred into tanks in three recirculating systems that were assigned one of the three temperatures (10, 20, and 30 C). During the pigment clearance period, fish were fed a control diet without added pigments daily to satiation for 12 wk. Every 4 wk, fish from three randomly chosen tanks per temperature were euthanized and fillets were analyzed for yellow color intensity (Commission Internationale de I'Eclairage [CIE] b*) and lutein and zeaxanthin concentrations. The b* values of fillets of fish reared at 20 and 30 C decreased linearly as time progressed. There was no significant linear regression of b* value against time for fish raised at 10 C. The rate of pigment clearance was similar for fish reared at 20 and 30 C. Results demonstrate that about 8 wk were needed for catfish to "purge most of yellow pigment at warm temperatures (20 and 30 C). A longer period of time (>12 wk) was required at 10 C. [ABSTRACT FROM AUTHOR]

We validated a whole-body cortisol extraction technique for channel catfish, Ictalurus punctatus, fry. Three volume enhancement methods were tested: CAL method (zero calibrator A diluent added to lipid extract), PBS method (phosphate buffered saline added to lipid extract), and VO method (food grade vegetable oil added to lipid extract). The volume enhancement extracts were evaluated using a commercial radioimmunoassay kit. Sensitivity, accuracy, precision, reproducibility, and parallelism could not be determined for the PBS method as cortisol levels were not detected in any of the extracted samples. Intra-assay coefficient of variation (CV) for the CAL and VO methods were 7.3 and 8.3%, respectively, while inter-assay CV were 9.6 and 10.6%, respectively. Based on the sensitivity, accuracy, precision, reproducibility, and parallelism results, we conclude that the CAL method is the most appropriate method for volume enhancement of catfish fry lipid extract. Using the CAL method to detect cortisol in catfish fry, fish were stressed daily for 2 weeks. Fry weights were similar throughout the study while whole-body cortisol levels were higher ( P < 0.01) in stressed fish after 1 day of stress. These data show the CAL method can effectively measure whole-body cortisol in catfish fry. [ABSTRACT FROM AUTHOR]

The article examines whether feeding yeast-derived mannans in the form of Bio-Mos could improve growth, feed efficiency, and improve resistance of channel catfish challenged with Edwardsiella ictaluri (E. ictaluri). E. ictaluri is a bacterium that causes enteric septicemia of catfish. The results show that the addition of Bio-Mos to catfish diet does not improve weight gain, but may improve resistance to E. ictaluri.

The article compares four genetic groups of channel catfish for growth, body composition, and stress responses. They include the U.S. Department of Agriculture (USDA) 103 line of channel catfish, the USDA403, a fast growing line of catfish, and an industry pool line of catfish. At the end of the eight-week study, the USDA line of catfish was larger at stocking compared to the industry pool.

Abstract: Cocaine-and Amphetamine-Regulated Transcript (CART) is a potent hypothalamic anorectic peptide in mammals and fish. We hypothesized that increased food intake is associated with changes in expression of CART mRNA within the brain of channel catfish. Objectives were to clone the CART gene, examine tissue CART mRNA distribution, and changes in the amount of CART mRNA in relation to changes in food intake in channel catfish. Our results showed that channel catfish CART was highly similar to those of other fish species, particularly in the biologically active portion of the peptide. Expression of CART mRNA was detected in the brain and testis but not in other somatic tissues. Thirty days of fasting decreased (P <0.05) the amount of CART mRNA within the brain of channel catfish, while refeeding for 15 days restored its amount to a level similar to the fed control. In a separate 7 week feeding study, CART mRNA expression was lower in fish that consumed more food and gained more weight (P <0.05). These results suggest that CART is involved in regulation of food intake in channel catfish, similarly as it has been reported in other fish and mammals. [Copyright &y& Elsevier]

Channel catfish Ictalurus punctatus do not feed well at low temperatures. It is generally thought that a diet containing fish meal enhances feed palatability at low temperatures since fish meal is highly palatable to fish. There is a lack of information on the effects of fish meal levels on the growth performance of channel catfish reared at low temperatures. Therefore, a study was conducted in a recirculating system to examine the effects of fish meal levels on the feed consumption, weight gain, and feed efficiency of juvenile channel catfish reared at various temperatures. Fish with an initial weight of 9.6 ± 0.1 g were stocked in 23-L clear polycarbonate tanks maintained at approximately 17, 21, or 27 °C. The fish were fed with diets containing 0, 4, or 8% menhaden Brevoortia spp. fish meal for 9 weeks. There was a significant interaction between water temperature and fish meal level with respect to weight gain. At 27°C, fish fed diets containing 4% and 8% fish meal gained significantly more weight than fish fed the all-plant-protein diet. However, the level of fish meal had no significant effect on the weight gain of fish at 17°C or 21°C. This suggests that the olfactory and gustatory responses of channel catfish to fish meal (up to 8% in the diet) may not be as sensitive at low temperatures as at optimum temperatures. The results also indicate that more than 4% fish meal in the diet is not beneficial for the optimum growth and feed efficiency of channel catfish fingerlings raised at 27°C. [ABSTRACT FROM AUTHOR]

Sixty-eight families of USDA303 channel catfish Ictalurus punctatus were evaluated for growth performance for 30 d. The fastest- and slowest-growing channel catfishfamilies were further evaluated to examine the hypothesis that genes or gene products associated with the growth regulatory and stress axes can be used to describe differences in growth performance. Research examined mRNA levels of genes involved in the growth hormone-insulin-like growth factor (GH-IGF) network in fast- (family A) and slow-growing (family H) USDA303 catfish. Fish (59.0 ± 2.4 g) were fed for 7 weeks, weighed, and had tissues for RNA extraction. The remaining fish were subjected to an acute 10-min dewatering stress. Insulin-like growth factor-II mRNA was higher in the muscle of fast-growing fish, while the levels of IGF-I receptor (IGF-IR) and IGF-I1 receptor (IGF-II) were similar. Muscle IGF-IIR mRNA was two-fold higher than muscle IGF-IR mRNA. There were no differences in liver and muscle IGF-I and GH receptor mRNA or pituitary GH mRNA between the fast- and slow-growing fish. Fast-growing fish consumed 135% more feed than slow-growing fish, though the abundances of ghrelin mRNA in the gut and neuropeptide Y mRNA in the hypothalamus were similar. Cortisol levels were negatively correlated to weight gain. These results suggest that the variation in growth between fast- and slow-growing USDA303 catfish is explained, in part, by the variation in the GH-IGF and stress axes. The relationship between cortisol and weight gain warrants further investigation for possible exploitation in our selective breeding program. [ABSTRACT FROM AUTHOR]

The channel catfish Ictalurus punctatus is an important aquaculture species in the United States and has received considerable research attention in efforts to improve production. Three traits of importance to the U.S. farm-raised channel catfish industry are disease resistance, growth, and reproduction. While many factors affect these three traits, a fish's response to stress can have a substantial impact on production attributes. Understanding the relationships between the stress response and components of that response, such as plasma cortisol concentration, is important to the development of better management and breeding practices to maximize production. Although much of the data regarding the fish physiological consequences of stress and elevated plasma cortisol has been collected from studies of salmonids, recent advances have been made toward understanding these relationships in channel catfish. The present review synthesizes the research conducted over the past several years regarding the effects of stress and cortisol on disease susceptibility, growth, metabolism, and reproduction of channel catfish in the context of how stress and cortisol affect economically important production traits for aquaculture. [ABSTRACT FROM AUTHOR]

A 6-wk feeding study was conducted to determine the effect of feeding frequency on growth rate of juvenile Norris and NWAC103 channel catfish, Ictalurus punctatus, reared under laboratory conditions. Four replicate groups of Norris and NWAC103 catfish (average weight of 4.0 ± 0.2 g/fish, SEM) were fed to visual satiety at different feeding frequencies (one, two, or three times daily). The percent of total daily food consumed for Norris catfish fed three times daily (0800, 1200, and 1600 h) was 44.4, 27.7, and 27.9%, respectively, while NWAC103 catfish consumed 42.9, 26.7, and 30.4%, respectively. Specific growth rate and feed intake were higher in fish fed three times daily compared to fish fed once and twice daily for both strains. Feed efficiency was reduced in NWAC103 fed three times daily compared to fish fed once or twice, while feed efficiency was similar among the Norris treatments. Gastrointestinal (GI) tract index ([weight of GI tract/weight of fish] × 100) decreased in NWAC103 catfish as feeding frequency increased, while a similar nonsignificant trend was also observed in Norris catfish. The results of this study demonstrate that aquarium-reared Norris and NWAC103 catfish fed three times a day consume more feed and gain more weight than catfish fed once or twice a day. The observed decrease in the GI index as a result of feeding more frequently demonstrates that the size of the GI tract increases, relative to body weight, when catfish are fed only once a day. Under laboratory conditions, the number of times a day the fish are fed should be considered when trying to maximize growth of NWAC103 and Norris strains of catfish. [ABSTRACT FROM AUTHOR]

Abstract: A 3×3 factorial experiment was conducted in flow-through aquaria to evaluate effects of diets, containing 0%, 4%, or 8% menhaden fish meal, on growth performance, body composition, and insulin-like growth factor-I (IGF-I) of juvenile channel catfish of Mississippi “normal” (MN), NWAC103 [formally known as USDA103], or USDA303 strains. Twenty fish with an average weight of 4.7±0.1 g fish−1 (±S.D.) were stocked into each of 36, 110-l aquaria (four aquaria per treatment). Fish were fed 28%-protein diets containing various levels of fish meal to approximate satiation twice daily for 9 weeks. Regardless of fish strain, fish fed diets containing 4% or 8% fish meal had higher diet consumption, final weight, and feed efficiency (FE) than fish fed an all-vegetable diet. Regardless of fish meal level, NWAC103 and USDA303 channel catfish consumed more diet, gained more weight, and converted diet more efficiently than MN fish. No differences were observed in diet consumption, final weight, and FE between NWAC103 and USDA303 strains. There was an interaction in specific growth rate between fish strain and fish meal level. Specific growth rate was greater for MN fish fed diets containing 4% or 8% fish meal than fish fed the all-vegetable diet, whereas there were no differences in specific growth rate for NWAC103 and USDA303 fish fed various diets. Fillet protein was lower and fillet fat was higher for NWAC103 and USDA303 strains than for the MN strain. Plasma IGF-I levels were greater in NWAC103 and USDA303 channel catfish than in MN fish. Levels of IGF-I were similar between NWAC103 and USDA303 fish. The addition of fish meal to the all-vegetable diet for the three strains did not affect levels of IGF-I. Mean plasma IGF-I concentration was positively correlated to specific growth rate. Results from the present study indicated that the optimum inclusion level for fish meal was 4% of a soybean meal-based diet (fish meal levels higher than 8% were not evaluated in the present study). Including 4% fish meal in the diet improved the performance more for the MN strain than for NWAC103 and USDA303 strains, suggesting that a genotype-diet interaction exists in juvenile channel catfish. Performance of the NWAC103 and USDA303 channel catfish fed the all-vegetable diet was better than MN fish fed the same diet. Plasma IGF-I concentration may be a good indicator for channel catfish growth. [Copyright &y& Elsevier]

Abstract: Responses of toll-like receptors (TLR3 and TLR5), lysozyme, and insulin-like growth factor-I (IGF-I) to experimental challenge with virulent Edwardsiella ictaluri were measured in back-cross hybrid (F1 male (blue×channel)×female channel) catfish. The resistance levels to E. ictaluri and host response mechanisms of back-cross hybrids are unknown. Fish were challenged with virulent E. ictaluri and sampled pre-challenge, 2h and 2, 5, 8, 14, and 21 days post-challenge. Levels of mRNA expression of two toll-like receptors (TLR3 and TLR5) in liver, kidney, spleen, and stomach, plasma lysozyme activity, and circulating IGF-I levels were measured at each timepoint. Throughout challenge, TLR3 was expressed at higher levels than TLR5 in liver (P =0.0011) and kidney (P =0.0007) whereas TLR5 was more highly expressed than TLR3 in stomach (P =0.0032). TLR3 was upregulated in comparison to non-exposed controls in liver (P =0.0015) and stomach (P &#60;0.0001) on day 14 and TLR5 was upregulated in liver (P =0.0175) on days 2 through 8. Plasma lysozyme activity peaked on day 5 (P &#60;0.001) and IGF-I levels significantly decreased on days 2 through 14 (P &#60;0.0001). TLR expression patterns suggest that both TLR3 and TLR5 may play a role in host response to bacterial challenge. Plasma lysozyme activity also increased and circulating IGF-I decreased in response to the presence of the pathogen. [Copyright &y& Elsevier]

Abstract: Glucocorticoids are known to hinder somatic growth in a number of vertebrate species. In order to better understand the mechanisms through which they may act in channel catfish, we examined the effects of feeding cortisol on the growth hormone (GH)/insulin-like growth factor-I (IGF-I)/IGF-binding protein (IGFBP) network. Fish (30.6±3.0g) were fed once daily for 4 weeks and treatments included: (1) High-cortisol (dietary cortisol provided at 400mg/kg feed), (2) Low-cortisol (dietary cortisol provided at 200mg/kg feed), and (3) Control (commercial catfish feed). Fish fed diets with cortisol weighed approximately 50% less than Controls. Feed intake was reduced by approximately 30% in both treatments of cortisol fed fish compared to Controls. A ∼20-kDa IGFBP was observed in plasma from High- and Low-treated fish while it was not detected in Control fish plasma. High-cortisol treatment increased pituitary GH mRNA expression approximately 10-fold while liver IGF-I mRNA expression was not different between cortisol-treated fish and Controls. Cortisol treatments decreased plasma levels of IGF-I. These data indicate that feeding cortisol for 4 weeks reduces weight gain, feed intake, and plasma levels of IGF-I and induces a ∼20-kDa IGFBP. One mechanism through which cortisol may impede growth of catfish is through an increase in a low molecular weight IGFBP which may lead to inhibitory effects on the action of IGF-I. [Copyright &y& Elsevier]

Abstract: Insulin-like growth factors-I and-II (IGF-I and IGF-II) play important roles in growth and development of mammals. Toll-like receptors (TLRs) are pattern recognition molecules that orchestrate the induction of early innate immune response by recognition of specific sequences. Evidence is growing that suggests a relationship between growth and immune function. The objective of the study was to examine changes in gene expression of IGF-I, IGF-II, TLR3, and TLR5 during embryogenesis and early larval development in hybrid (channel catfish×blue catfish) and channel catfish. Egg samples were taken pre- and post-fertilization; embryos were collected at two stages of embryogenesis, at hatch, and at swim-up. All genes were detected in unfertilized catfish eggs. Expression levels of TLR5 and IGF-I mRNA in channel catfish and expression levels of TLR3, IGF-I, and IGF-II mRNA in hybrids increased over time (P &#60;0.01). Effect of time was not significant for expression of IGF-II or TLR3 mRNA in channel catfish and for TLR5 mRNA in hybrid catfish. Results of this study suggest growth (IGF-I and IGF-II) and immune (TLR3 and TLR5) associated genes could be functional and play important roles during embryogenesis and early development of hybrid and channel catfish. [Copyright &y& Elsevier]

Research was conducted to examine growth rates, circulating concentrations of IGF-I, and mRNA abundance levels of IGF-I and IGF-II in channel catfish (Ictalurus punctatus) given recombinant bovine ST (rbST; Posilac, Monsanto Co., St. Louis MO). In the first study, juvenile catfish (5.5 ± 0.5 g) were randomly assigned to one of three treatments: 1) sham-injected control (one needle puncture per week); 2) rbST (30 μg·g BW-1·wk-1; Posilac); and 3) nonhandled control (control). At the end of the 6-wk study, the fish were weighed, measured for length, and G:F was determined. Compared with sham and control treatments, rbST-treated fish had 48% greater final BW, 14% greater total length, and 52% greater G:F (P < 0.001). In the second study, juvenile catfish (41.1 ± 1.5 g) were assigned randomly to one of two treatments: 1) sham or 2) rbST. Eight fish per treatment were sampled on d 0, 1,2,7, 14, and 21 for blood, muscle, and liver. Relative expression of IGF-I and IGF-II mRNA was determined by real-time PCR and plasma concentrations of IGF-I were measured using a validated fluoroimmunoassay. Circulating concentrations of IGF-I were increased (37.9 ± 5.5 vs. 22.0 ± 6.6 ng/mL; P < 0.05) in rbST-injected fish compared with sham-injected controls by d 14. Liver IGF-I and IGF-II mRNA was increased 4.3- and 14.4-fold, respectively, by d 1 in rbST-injected fish compared with controls (P < 0.05); however, abundance of liver IGF-I and IGF-II mRNA did not differ from controls on d 0, 2, 7, 14, and 21. Abundance of muscle IGF-I and IGF-II mRNA did not differ in rbST-injected fish compared with controls throughout the study. Results of the first study demonstrated that rbST improves growth performance of channel catfish. Results of the second study showed that the growth-promoting effects of rbST were not mediated by the expression of IGF-I or IGF-II mRNA in the muscle. Instead, the results suggest that rbST promotes growth by stimulating plasma IGF-I release, possibly through its direct effect on the liver or on local tissues to synthesize IGF-I. The changes in mRNA abundance and plasma concentrations of IGF-I support the role of IGF-I in growth regulation of channel catfish. [ABSTRACT FROM AUTHOR]

Abstract: A time-resolved fluoroimmunoassay (TR-FIA) was established and validated that allows for the determination of plasma concentrations of insulin-like growth factor I (IGF-I) in three domestically cultured fishes: channel catfish (Ictalurus punctatus), hybrid striped bass (Morone chrysops×M. saxatilis), and rainbow trout (Oncorhynchus mykiss). Sensitivity of the assay was 0.20ng/ml. Intra- and inter-assay coefficients of variation (CV) were <7 and <12%, respectively. Serial dilutions of plasma from each species were parallel to the standard curve. Recovery of IGF-I from spiked plasma samples was >90% for all three species of fishes. The IGF-I TR-FIA was biologically validated via its use to determine the effect of fasting on circulating IGF-I levels in channel catfish. Fasting-induced changes in plasma growth hormone (GH), hepatic IGF-I mRNA expression, and pituitary GH mRNA expression were also determined. Fasted channel catfish lost 5.6 and 15.6% body mass after 2 and 4 weeks of fasting, respectively. Plasma IGF-I concentrations were depressed (P<0.05) relative to fed controls following 2 and 4 weeks of fasting. Plasma GH concentrations were not different (P>0.05) in fasted fish after 2 weeks, but significantly increased (P<0.05) by 4 weeks of fasting. Hepatic IGF-I mRNA expression after 2 and 4 weeks of fasting was reduced (P<0.05) relative to fed controls. Pituitary GH mRNA expression was similar (P>0.05) between 2-week-fasted catfish and fed controls, but was increased (P<0.05) in 4-week-fasted catfish. The IGF-I TR-FIA was sensitive, accurate, and precise for all three species of fishes, and provided a low-cost, and non-radioisotopic method for quantifying plasma IGF-I levels in fed and fasted channel catfish. [Copyright &y& Elsevier]

Abstract: The objective of this study was to examine insulin-like growth factor (IGF)-I and IGF-II mRNA levels in fast and slow growing families of catfish. Relative levels of IGF-I and IGF-II mRNA were determined by real-time PCR. Family A exhibited a specific growth rate (SGR) of 3.6 and was designated as fast growing, while family H exhibited a SGR of 3.1 and was designated as slow growing (P=0.017). Levels of IGF-II mRNA were 3.3-fold greater (P=0.006) in muscle for the fast growing family compared to the slow growing family. Levels of IGF-II mRNA were 1.8-fold greater (P=0.049) in liver for the fast growing family compared to the slow growing family. Levels of IGF-II mRNA from both fast and slow families were 12.2-fold greater (P<0.001) in muscle and 5.8-fold greater (P=0.021) in liver, respectively, compared to levels of IGF-I mRNA. Muscle and liver levels of IGF-I mRNA were similar between families. Elevated levels of IGF-II mRNA in muscle and liver compared to IGF-I mRNA, as well as differences in levels of IGF-II mRNA between fast and slow growing families of fish suggests a role of IGF-II in growth of channel catfish. [Copyright &y& Elsevier]

The effects of recombinant bovine growth hormone (rbGH; Posilac®) on growth rate, feed efficiency, body composition, and insulin-like growth factor binding proteins (IGFBPs) were investigated in Norris and NWAC103 strains of channel catfish. Three hundred and twenty fish from each strain were assigned randomly to four treatments with four replicates each. The treatments were (1) Sham-injected control (needle puncture per 3 weeks); (2) Low (30 μg g−1 BW per 3 weeks, Posilac®); (3) Medium (60 μg g−1 BW per 3 weeks, Posilac®); and (4) High (120 μg g−1 BW per 3 weeks, Posilac®). Fish were reared in 76-l tanks supplied with 26.0 °C flow-through well water for 9 weeks. Fish were fed a 36% CP commercial diet twice each day to apparent satiation. Feed consumption increased (P<0.05) 15% with rbGH treatment in the Norris strain while no significant increase in feed consumption was observed in rbGH-treated NWAC103 catfish. Compared to sham controls, all treatments (Low, Medium, and High) increased final weights (P<0.05) (168±13.2 vs. 144±10.0 g) (average weight of the three treatments), but no overall improvement in feed conversion ratio (FCR) was observed in NWAC103 fish. In the Norris strain, the High treatment increased (P<0.05) final weight (135±6.2 vs. 106±8.7 g) but no improvement in FCR was observed when compared to sham controls. rbGH treatments increased (P<0.05) total length in both strains, but no difference in condition factor (CF), hepatosomatic index (HSI), or body composition was observed. On day 63, levels of a 45-kDa IGFBP (catfish-IGFBP-3) were similar between treated and untreated fish in both strains. Results of this study indicate the Low treatment was as effective in promoting growth as the High treatment in the NWAC103 strain. Results of the body composition analysis suggest that the increase in weight gain was not due to an increase in fat deposition. The observed increase in length suggests rbGH enhances linear growth in channel catfish. Similar levels of cf-IGFBP-3 between treated and untreated fish may reflect “steady state” levels of cf-IGFBP-3 in growing fish. Identifying other endogenous growth factor(s) responsible for the observed increase in growth rate will be crucial in our understanding of improving growth in cultured channel catfish. [Copyright &y& Elsevier]

The effects of fasting on IGF-binding proteins (IGFBPs), glucose, and cortisol in channel catfish were examined. Fed fish (controls) were compared to 14-, 30-, and 45-day fasted fish and 45-day fasted fish refed for 15 additional days. Body length and weight changes, condition factor (CF), hepatosomatic index (HSI), and plasma glucose and cortisol were assessed to determine growth and metabolic status. Body length and growth rates were inhibited (P<0.05) after 14, 30, and 45 days of fasting. The 14-, 30-, and 45-day fasted fish exhibited hypoglycemia and reduced CF and HSI. Cortisol levels were increased (22.8±15.2 ng/ml versus 4.7±3.9 ng/ml) in 30-day fasted fish compared to fed controls (P<0.05). Associated with the increase in cortisol in fasted fish was a concomitant increase in plasma levels of a 20-kDa IGFBP through day 45. A 35- and a 45-kDa IGFBP were also identified but were similar between fed and unfed fish throughout the experiment. At the end of 15 days of refeeding, 20-kDa IGFBP, glucose, and cortisol levels were similar to fed controls. Refeeding also caused an increase in growth rates. These results suggest the existence of a catfish counter part to mammalian IGFBP-1, similar to lower molecular mass IGFBPs reported in other species of fish. These results also suggest that a 20-kDa IGFBP is upregulated during fasting-induced growth inhibition of channel catfish and provide additional evidence of the conserved nature of the IGF-IGFBP-growth axis in fish. [Copyright &y& Elsevier]

Highlights: [•] Flavobacterium columnare, columnaris, is a widespread aquatic pathogen. [•] We used RNA-seq to profile resistant and susceptible catfish gill mucosal immunity. [•] We captured dramatic basal differences in immune and mucin-related factors. [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the effects of diets (32/4 or 36/6 percent protein/fat) and six channel catfish families for growth performance characteristics. Two families with fast- (C) and slow- (D) growth rate and with low and high feed efficiency (FE) were selected for analyses of mitochondrial complex enzymatic activities (I, II, III, and IV) and gene expression (ND1, CYTB, COX1, COX2, ATP6) levels in liver, muscle, and intestine. There were significant differences in growth rate and nutrient retention among the families. Mitochondrial enzymatic complex activities (I-V) in the tissues were all lower in family C. Four of the five genes were down-regulated in the liver and up-regulated in the muscle for the fast growing family C. There were significant differences between diets for some mitochondrial respiratory chain enzyme activities and gene expression levels. Significant diet×family interactions were observed for some enzyme activities and gene expression levels. Changes in mitochondrial respiratory chain enzyme activities and gene expression levels provide insight into the cellular mechanisms of fish with differences in growth rate and feed efficiency. Results also suggest that genotype×diet interactions should be accounted for when considering strategies for using mitochondrial function as a criteria in channel catfish selection programs for improved growth performance characteristics. [Copyright &y& Elsevier]

Abstract: Leptin is a key pleiotropic cytokine involved in regulation of energy homeostasis and immunity in mammals. In channel catfish, the presence of a partial messenger RNA sequence that encodes a leptin-like peptide (LLP) has been identified and investigated. The objectives of the present studies were to clone and characterize full-length catfish LLP gene, examine tissue expression of LLP mRNA, and determine effects of prolonged fasting and exposure to Edwardsiella ictaluri (E. ictaluri), the bacteria that causes enteric septicemia in catfish, on LLP mRNA expression. Full-length catfish LLP gene was sequenced by genome walking and by 5′- and 3′-RACE. Catfish LLP gene contained three exons with the coding region located in exons 2 and 3. The amino acid sequence of the channel catfish LLP shared very low sequence similarities with leptin of other fish species or the mammalian leptin (24–49%). Using real-time polymerase chain reaction, LLP mRNA expression was detected in various tissues including brain, stomach, spleen, heart, liver, and trunk kidney and was especially high in the liver and trunk kidney. Expression of LLP mRNA in liver and brain was similar between fish that were fasted for 30days and those that received feed daily for 30days (P >0.10). Expression of LLP mRNA was increased in liver, spleen, and trunk kidney within 48h post-exposure to E. ictaluri compared to unexposed fish (P <0.05). Based on the results of the current studies, amino acid sequence of catfish LLP is highly dissimilar to mammalian and fish leptin. Unlike in most mammals, catfish LLP expression is independent of energy status. However, the expression of catfish LLP is increased after exposure to pathogenic bacteria, which is similar to mammals. Further investigations are required to clearly define the biological function and regulation of catfish LLP. [Copyright &y& Elsevier]

Abstract: Real-time PCR is a highly sensitive, relatively easy to perform assay for quantifying mRNA abundance. However, there are several complexities built into the assay that can affect data interpretation. Most notably, the selection of an appropriate internal control for normalization is essential for expression data interpretation. In this study we investigated the suitability of seven commonly used genes [18S ribosomal RNA (18S), alpha tubulin (TUBA), beta actin (ACTB), beta-2 microglobulin (B2M), embryonic elongation factor-1 alpha (EEF1A), glyceraldehyde phosphate dehydrogenase (GAPDH), and RNA polymerase II polypeptide B (POLR2B)] as potential quantitative references for normalizing real-time PCR data generated in the study of channel catfish physiology. Gene expression and stability were evaluated among 15 channel catfish tissues and within physiologically-relevant tissues in response to experimental manipulation (i.e. LHRH injection, fasting, and acute stress). Expression of the seven candidate reference genes varied across all tissue types tested, indicating that none of the genes could suitably serve as reference genes for cross tissue comparisons. Experimentally altering the physiological state of the fish differentially affected expression of the various reference genes depending on experimental design and tissue type, with 18S unaffected by the experimental treatment in all tissues examined. For example, the selection of a differentially expressed gene, GAPDH, as opposed to 18S, to normalize hepatic growth hormone receptor during fasting resulted in misinterpretation of the data. These results reveal the importance of providing comprehensive details of reference gene validation when publishing real-time PCR results, with this manuscript serving as a basic guideline for reference gene selection in channel catfish research. [Copyright &y& Elsevier]

Abstract: The objective of this study was to assess the effects of food deprivation and exogenous cortisol administration on somatic growth of channel catfish, Ictalurus punctatus, and examine the resultant changes in circulating insulin-like growth factor-I (IGF-I) concentrations and growth hormone receptor (GHR) gene expression. Integral to this objective, we report the isolation, sequence, and characterization of channel catfish GHR. Sequence analysis and characterization results indicate sequence identity and tissue distribution similar to GHRs in other teleost fish and several functional characteristics conserved in known vertebrate GHRs. The effects of food deprivation and dietary exogenous cortisol administration were assessed as part of a 4-week study. Growth was significantly reduced after 4 weeks in cortisol-fed fish compared to fed-control fish, and fasting resulted in weight loss. At the end of the 4-week study, both IGF-I plasma concentrations and hepatic GHR mRNA abundance were significantly reduced in fasted and cortisol-fed catfish. Levels of hepatic GHR mRNA were positively correlated to circulating IGF-I levels. These results suggest that a reduction in hepatic GHR gene expression might serve as a mechanism for the reduction of circulating IGF-I and growth in channel catfish during periods of food deprivation and stress. [Copyright &y& Elsevier]

Abstract: The insulin-like growth factor I (IGF-I) gene was characterized in channel catfish. Partial cDNA sequence, missing exon 1 and part of exon 2, was obtained in 5′- and 3′-RACE experiments. Direct sequencing of two bacterial artificial chromosome clones revealed gene structure and provided sequence from 640 bp upstream of the initiator methionine to 136 bp beyond the polyadenylation site. Genomic sequence contained a putative TATA box 506 bp upstream of the initiator methionine. The 477-bp reading frame within five exons encoded a 159-amino acid (aa) pre-propeptide highly similar to IGF-I in higher vertebrates. The sequence encoding the signal peptide was unique in catfish and contained 70% G+C content with the potential for a stable stem–loop structure. Full-length cDNA was only maintained in recombination-deficient (DH10B) strain E. coli. Levels of IGF-I mRNA were highest in liver, followed by brain and muscle, then heart and kidney (P <0.05). A CT/GA dinucleotide microsatellite in intron 1 was highly polymorphic in commercial channel catfish, and permitted placement of the IGF-I gene on the catfish genetic map. However, specific IGF-I alleles were not correlated with differences in growth rate from 100 to 130 days post-hatch in USDA103 line catfish. [Copyright &y& Elsevier]