Comparison of growth performance among channel-blue hybrid catfish, ccGH transgenic channel catfish, and channel catfish in a tank culture system.

Fish is an essential source of high-quality protein for people worldwide. The present study was designed to compare the growth performance among the channel-blue hybrid catfish, channel catfish transgenic for the channel catfish growth hormone (ccGH) cDNA driven by the antifreeze protein promoter from an ocean pout Zoarces americanus (opAFP-ccGH), and non-transgenic channel catfish control. Mean body weight of channel-blue hybrid catfish was 15.80 and 24.06% larger than non-transgenic channel catfish control at 4 and 18 months of age, respectively. However, transgenic opAFP-ccGH channel catfish were 5.52 and 43.41% larger than channel-blue hybrid catfish and 22.19 and 77.91% larger than their controls at 4 and 18 months of age, respectively. Significant differences in mean body weight between the sexes within all genetic types were found. Males were larger than females (P < 0.001). However, mean body weight of non-transgenic males was not larger than transgenic opAFP-ccGH females or male and female hybrid catfish. Condition factor of transgenic opAFP-ccGH channel catfish was higher (P < 0.05) than that of full-sibling, non-transgenic channel catfish and hybrid catfish. The mean percentage body weight gain of GH transgenic channel catfish was 559%, the channel-blue hybrid catfish was 384.9% and their non-transgenic controls channel catfish was 352.6%.

Direct and pleiotropic effects of the Masou Salmon Delta-5 Desaturase transgene in F1 channel catfish (Ictalurus punctatus).

Channel catfish (Ictalurus punctatus) is the primary culture species in the US along with its hybrid made with male blue catfish, I. furcatus. In an effort to improve the nutritional value of channel catfish, the masou salmon Δ5-desaturase like gene (D5D) driven by the common carp beta-actin promoter (ßactin) was inserted into channel catfish. The objectives of this study were to determine the effectiveness of ßactin-D5D for improving n-3 fatty acid production in F1 transgenic channel catfish, as well as examine pleiotropic effects on growth, proximate analysis, disease resistance, and other performance traits. Transgenic F1 channel catfish showed a 33% increase in the relative proportion of n-3 fatty acids coupled with a 15% decrease in n-6 fatty acids and a 17% decrease in n-9 fatty acids when compared to non-transgenic full-siblings (P < 0.01, P < 0.01, P < 0.01). However, while the relative proportion of n-3 fatty acids was achieved, the total amount of fatty acids in the transgenic fish decreased resulting in a reduction of all fatty acids. Insertion of the ßactin-D5D transgene into channel catfish also had large effects on the body composition, and growth of channel catfish. Transgenic channel catfish grew faster, were more disease resistant, had higher protein and moisture percentage, but lower fat percentage than full-sib controls. There were sex effects as performance changes were more dramatic and significant in males. The ßactin-D5D transgenic channel catfish were also more uniform in their fatty acid composition, growth and other traits.

Chronic exposure to environmental cadmium affects growth and survival, cellular stress, and glucose metabolism in juvenile channel catfish (Ictalurus punctatus).

Anthropogenic activities have led to the enrichment of cadmium in freshwater systems where it is a contaminant of concern for fisheries and aquaculture as it has no known biological function and is toxic at trace concentrations. Yet, knowledge gaps remain regarding effects of chronic exposure to environmentally relevant concentrations on freshwater fish. Thus, the objectives of the current study were to assess chronic impacts of cadmium on channel catfish (Ictalurus punctatus) including how tissue-specific bioaccumulation patterns relate to functions of those tissues over time. We focused on liver and kidneys, and expression of genes related to cellular stress, glucose metabolism, and steroidogenesis. Catfish were exposed to concentrations of 0.5 (control), 2 (low), and 6 (high) µg L-1 Cd from fertilization to six months. Cadmium exposure negatively impacted channel catfish growth and was linked to bioaccumulation of tissue Cd, which followed a dose-related response, where concentrations in trunk kidney > liver = head kidney >> muscle. Differences in tissue Ca, Cu, Fe, and Zn concentrations were also observed between treatments. Following 3 months of exposure, expression of metallothionein (MT) and heat shock proteins (HSP) 70 & 90 increased relative to controls; however, no differences were detected at 6 months, suggesting compensation. Conversely, there were no differences in expression patterns for key genes in steroidogenesis, steroidogenic factor 1 (SF1), steroidogenic acute regulatory protein (StAR), and cytochrome P450scc (P450), which supports the observation that Cd did not affect the secondary stress response, evaluated via plasma cortisol and glucose concentrations following a low water stress event. As a function of length and weight, the high Cd treatment yielded fish that were significantly smaller than controls. In addition to the cellular responses in MT and HSPs noted, reduced growth in the high Cd treatment was likely due, at least in part, to elevated energetic demands. This is supported by observations of the upregulation of genes necessary for glucose metabolism. Hexokinase (HK), glucose-6-phosphatase (G6P), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were significantly elevated in the high treatment relative to controls at 3 months of exposure. Over the study period, exposure also reduced survival of channel catfish from 3 to 6 months. Reduced fitness, as a consequence of cadmium exposure, could be visible at the population level through altered life histories and growth patterns.

Sublethal effects of salinity and temperature on non-native blue catfish: Implications for establishment in Atlantic slope drainages.

The distribution and further range expansion of non-native blue catfish Ictalurus furcatus in coastal waters throughout the United States Atlantic slope depend, in part, on the salinity tolerance of the fish. However, temperature-mediated sublethal effects of increased salinities on blue catfish biology are not yet known. We assessed the effects of salinity and temperature on growth, body condition, body composition and food consumption of juvenile blue catfish in a controlled laboratory experiment. Temperature and salinity had an interactive effect on blue catfish biology, although most fish survived 112 days in salinities up to 10 psu. At salinities ≤7 psu, mean growth rate, body condition and consumption rates were higher at 22°C than at 12°C. Mean consumption rates declined significantly with increasing salinities, yet, salinities ≤7 psu were conducive to rapid growth and high body condition, with highest growth and body condition at 4 psu. Fish at 10 psu exhibited low consumption rates, slow growth, low body condition and lower proportions of lipids. Habitats with hyperosmotic salinities (>9 psu) likely will not support the full lifecycle of blue catfish, but the fish may use salinities up to 10 psu for foraging, dispersal and even growth. Many oligohaline and mesohaline habitats in U.S. Atlantic slope drainages may thus be vulnerable to establishment of invasive blue catfish, particularly given the increasing temperatures as a result of climate warming.

Deep Transcriptomic Analysis Reveals the Dynamic Developmental Progression during Early Development of Channel Catfish (Ictalurus punctatus).

The transition from fertilized egg to larva in fish is accompanied with various biological processes. We selected seven early developmental stages in channel catfish, Ictalurus punctatus, for transcriptome analysis, and covered 22,635 genes with 590 million high-quality RNA-sequencing (seq) reads. Differential expression analysis between neighboring developmental timepoints revealed significantly enriched biological categories associated with growth, development and morphogenesis, which was most evident at 2 vs. 5 days post fertilization (dpf) and 5 vs. 6 dpf. A gene co-expression network was constructed using the Weighted Gene Co-expression Network Analysis (WGCNA) approach and four critical modules were identified. Among candidate hub genes, GDF10, FOXA2, HCEA and SYCE3 were involved in head formation, egg development and the transverse central element of synaptonemal complexes. CK1, OAZ2, DARS1 and UBE2V2 were mainly associated with regulation of cell cycle, growth, brain development, differentiation and proliferation of enterocytes. IFI44L and ZIP10 were critical for the regulation of immune activity and ion transport. Additionally, TCK1 and TGFB1 were related to phosphate transport and regulating cell proliferation. All these genes play vital roles in embryogenesis and regulation of early development. These results serve as a rich dataset for functional genomic studies. Our work reveals new insights of the underlying mechanisms in channel catfish early development.

Functional identification and characterization of IpMSTNa, a novel orthologous myostatin (MSTN) gene in channel catfish Ictalurus punctatus.

Channel catfish (Ictalurus punctatus) are one of the most important commercial freshwater fish in the world. China has been the major producer and consumer of channel catfish following the rapid development in the past three decades. In the present study, a novel orthologous myostatin gene, IpMSTNa, of channel catfish was identified based on homology cloning and genome locating. Multiple sequence alignments and gene structure analyses showed that the IpMSTNa gene and its deduced protein presented similar architectures to other known vertebrates. Phylogenetic and synteny analyses indicated that IpMSTNa belongs to MSTN1 orthologues. Pro-IpMSTNa protein is a typical disulphide-linked homodimer, with each chain containing an N-terminal pro-domain and a C-terminal unmatured GF domain, while pro-IpMSTNa present some significant differences in secondary structure and three-dimensional substances with pro-IpMSTNb. Relative expression level of the IpMSTNa gene upregulated rapidly and decreased dramatically during the embryonic and larval developmental stages, respectively. In addition, IpMSTNa displayed remarkably higher expression at most developmental stages compared to IpMSTNb. Tissue distribution analysis indicated that the IpMSTNa gene had a significantly higher level of expression than IpMSTNb in all selected tissues, with abundantly greater expression in the liver, muscle, gill and spleen, and moderately greater expression in the kidney, intestine, and head kidney. ISH analysis demonstrated that the expression signals of IpMSTNa and IpMSTNb at the selected developmental stages are consistent to qRT-PCR tests. Our study suggested that the IpMSTNa gene may have more biological functions, which have yet to be determined compared to the IpMSTNb gene.

Growth, health aspects and histopathology of brown bullhead (Ameiurus nebulosus L.): replacing fishmeal with soybean meal and brewer's yeast.

A ten-week feeding trial was carried out to investigate the effects of replacing fishmeal (FM) with soybean meal (SBM) and brewer's yeast (BY) on growth performance, blood parameters, oxidative stress and micromorphology of liver and intestines in brown bullhead (Ameiurus nebulosus L.). Fish were fed nine feeds in which FM was replaced with 25%, 50%, 75% and 100% SBM (K1, K2, K3 and K4) and 17% + 8%, 42% + 8%, 67% + 8% and 92% + 8% of SBM/BY combination (K5, K6, K7, K8). Growth indices showed greater outcomes for the K2 group in comparison to all other groups. A decrease in plasma cholesterol and triglycerides concentrations was found after FM replacement. Activity of SOD was higher in groups K4, K7 and K8. The early inflammatory indications with abnormal vacuolization of lamina propria and basal epithelium were present in diets K4 and K8. Hepatocytes were irregular in shape with signs of inflammatory reaction in diet K8. A decreased perimeter of hepatocyte nuclei was detected in all experimental diets when compared with the control. This study demonstrates that the optimal replacement of FM with SBM/BY in brown bullhead diets contains up to 50% of FM replaced with SBM in order to obtain advantageous growth performance and adequate health condition.

Non-synonymous polymorphisms in candidate gene associated with growth traits in Channel catfish (Ictalurus punctatus, Rafinesque, 1818).

Resequencing of Myostatin, Growth Hormone, Follistatin-A-like, Insulin-like Growth Factor I (IGF-I) and Myogenin (MYOG) genes was completed to discover novel genetic variations and assess non synonymous (ns) polymorphisms (SNPs) effect on growth related traits of channel catfish. Wild and farmed animals were used as a discovering population. Resequencing lead to the identification of 59 new variants in the five analyzed genes; 66% found in introns and 34% in coding regions. From coding regions, 14 variants were synonyms and six were ns variations. A mutation rate of one in 129 bp was estimated. Four ns variations were selected for validation and association analysis. In IGF-I two ns polymorphisms, at IGF-I19 the G wild type allele was fixed in population and for IGF-I63 the C allele had a frequency of 0.972 and for mutate allele G of 0.027. In MYOG two ns SNPs were assessed. MYOG131 presented a frequency of alleles T and A, of 0.754 and 0.246, respectively and MYOG233, with a frequency of G and C of 0.775 and 0.225, respectively. Only MYOG131 (g.529T>A) was significantly associated (P < 0.04) to some growth traits. Results suggest MYOG131 g.529T>A as candidate locus for genetic enhancement of growth traits in channel catfish.

Ontogeny of the cortisol stress response and glucocorticoid receptor expression during early development in channel catfish, Ictalurus punctatus.

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 ±â€¯0.2 ng/egg and decreased to 0.4 ±â€¯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 ±â€¯0.1 ng/egg and decreased to 0.3 ±â€¯0.03 ng/egg by day 5. At hatching, resting cortisol levels were 24 ±â€¯1.0 ng/0.1 g tissue while levels increased to 83 ±â€¯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 ±â€¯1.0 ng/0.1 g tissue while levels increased to 149 ±â€¯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.

The relation between polychlorinated biphenyls and population metrics of 4 species of fish from the upper Hudson River, New York, USA.

In the upper Hudson River, New York, USA, fish were exposed to polychlorinated biphenyls (PCBs) from the 1940s to 1977, and PCBs still persist in this environment. Yellow perch (Perca flavescens), brown bullhead (Ameiurus nebulosus), smallmouth bass (Micropterus dolomieu), and largemouth bass (M. salmoides) were collected annually from 2003 to 2009 from 1 control site upstream of the PCB discharge locations and from 2 sites downstream from where PCBs were released. Fish PCB concentrations were estimated, and 3 population metrics were examined: 1) relative abundance, 2) weight-to-length ratio, and 3) growth. Normalized lipid-based PCB concentrations at the 2 PCB exposure pools averaged approximately 100 to 600 µg/g. Estimated relative abundances with electrofishing were higher for largemouth bass, smallmouth bass, and brown bullhead at PCB exposure sites compared to the control site; but yellow perch were more abundant at the control site. Weight to length ratios varied among sites and species, but no consistent pattern was evident in relation to PCBs at the population level or for individual fish. Growth rates for yellow perch and brown bullhead were similar among sites. Largemouth bass growth was slightly higher at the control site compared to the 2 PCB sites, but smallmouth bass growth was much higher at the PCB sites compared to the control site. We could not detect any relation or influence of PCBs on the 3 population metrics that we examined. the present results corroborated those of previous investigations concerning the effects of PCBs on fishes. We recommend stronger consideration of the biological impacts of PCBs at the population level when conducting risk assessments. Environ Toxicol Chem 2019;38:329-339. © 2018 SETAC.

Exposure to environmentally relevant cadmium concentrations negatively impacts early life stages of channel catfish (Ictalurus punctatus).

Cadmium is a persistent contaminant of surface waters. The effects of cadmium on early life stages of fish are not well understood, although they are often disproportionately affected by contaminants. The objectives of this study were to examine effects of chronic exposure to environmentally relevant concentrations on growth, development, cellular stress, and glucose metabolism of channel catfish, Ictalurus punctatus. Eggs were wet-fertilized in treatment water at concentrations of 0.4 (control), 2.2 (low), or 8.5 (high) µg L-1 and monitored through swim-up, black fry stage. Eggs and fry accumulated cadmium dose-dependently. Fertilization rates were unaffected, yet hatch rate was significantly reduced in the high treatment. Survival to black fry and overall size and condition factor were not affected; however, differences in yolk sac size, and presumably energetics of yolk fry, was detected. Physiological pathways were also affected, demonstrated by altered gene expression, most notably in genes related to carbohydrate metabolism. Elevated expression of HK and G6PD, rather than G6P and GADPH, suggests glucose may be shunted towards the pentose-phosphate pathway. Overall, observations indicate cadmium negatively affects development in early life stages of channel catfish, which could lead to shifts in population structure and life history patterns in exposed populations of wild fish.

Bacterial diversity and community structure of the intestinal microbiome of Channel Catfish (Ictalurus punctatus) during ontogenesis.

The acquisition of gut microbes does not occur randomly and is highly dependent on host factors, environmental cues, and self-assembly rules exerted by the microbes themselves. The main objective of this project was to characterize how the gut microbiome develops during the early life stages of Channel Catfish and to identify i) which bacteria are the main constituents of the gut microbiome at different ontogenesis stages, and ii) at which time point(s) the gut microbiome stabilizes. High-throughput Illumina Miseq DNA sequencing of the V4 domain of the 16S rRNA gene was used to assess the microbial community composition during the life stages of Channel Catfish along with water and feed samples. Microbiomes from fertilized eggs, sac fry, swim up fry, pre-fingerlings, and fingerlings were all significantly distinct. OTUs analyses showed that the phylum Proteobacteria, Firmicutes, Fusobacteria and Cyanobacteria dominated the Channel Catfish gut microbiome. During the early stages of ontogenesis, the fish microbiome was dynamic and highly diverse, with significant shifts occurring between fertilized eggs to sac fry (6dph), and from sac fry to swim up fry (15dph). The gut microbiome stabilized between the pre-fingerlings and fingerlings stage (≤90dph) with an observed reduction in species richness. Feed had a more significantly contribution to the microbial colonization of the gut than water. We have identified the period in which the gut microbiome changes rapidly from 15dph until 21dph before stabilizing after 90dph.

Oxytetracycline does not cause growth promotion in finfish.

Until recently, use of antibiotics to enhance terrestrial animal growth performance was a common, U.S. Food and Drug Administration (FDA)-approved, but controversial practice. There are no FDA-approved production claims for antibiotic drug use in fish, but it is a common misconception that antibiotics are widely used for this purpose in U.S. aquaculture. Antibiotics are not thought to be effective growth promoters in fish, but there is little quantitative data available to address whether there are growth-promoting effects that might incentivize the use of antibiotics in this way, despite legal prohibitions. Therefore, this study was conducted to determine if oral administration of oxytetracycline, an antibiotic with known growth-promoting effects in terrestrial livestock, has a similar effect when applied to channel catfish Ictalurus punctatus, hybrid striped bass Morone chrysops × M. saxatilis, Nile tilapia Oreochromis niloticus, or rainbow trout Oncorhynchus mykiss. Oxytetracycline products with production claims are typically applied at doses substantially lower than the approved therapeutic doses for the same products. Medication (0, 0.24, or 1.2 g oxytetracycline dihydrate kg-1 feed) and feeding rates (3% BW d-1) were selected to achieve target daily doses of 0, 16, or 80 mg kg-1 fish representing control, subtherapeutic, and therapeutic treatments. Replicate groups of fish (N = 4) were fed accordingly for 8 wk. Overall, oral administration of oxytetracycline did not affect survival or promote growth of the selected taxa, with no significant differences observed for weight gain, feed conversion ratio, or specific growth rate (P > 0.05 in all cases). Few differences were observed in organosomatic indices and in the frequency of tissue abnormalities; where present, these differences tended to suggest a negative effect of long-term dietary exposure to oxytetracycline. These data demonstrate that there is no benefit to dietary supplementation with oxytetracycline for nontherapeutic purposes in a range of economically important finfish species. As such, our results indicate there is little incentive to misuse oxytetracycline products for purposes of growth promotion in U.S. aquaculture.

A modified von Bertalanffy growth model dependent on temperature and body size.

Fish growth models are widely used in fisheries as well in aquacultures and ecology. Water temperature is one of the most important factors determining the growth of fish. In the present study, we propose a growth model that includes the effect of water temperature on the growth in the von Bertalanffy growth model. Our model was applied to fit the growth data of bullhead (Cottus gobio), brown trout (Salmo trutta L.), juvenile salmon (Salmo salar), and Araucanian herring (Strangomera bentincki). The model reproduces the growth patterns of each species and fits a set of appropriate parameter values for each species. Moreover, the model reflects the seasonal growth rates quite well.

DExD/H-box RNA helicase genes are differentially expressed between males and females during the critical period of male sex differentiation in channel catfish.

DExD/H-box RNA helicases are motor proteins participating in nearly all aspects of cellular processes, especially in RNA metabolism. In this study, a total of 54 DExD/H-box RNA helicase genes including 37 DDX (DEAD-box) and 17 DHX (DEAH-box) genes were characterized in channel catfish (Ictalurus punctatus), and annotated through phylogenetic and syntenic analyses. All the catfish RNA helicases contained conserved helicase signature motifs, demonstrating that the RNA helicase gene family was highly conserved. Analysis of the relative rates of synonymous (dS) and nonsynonymous (dN) substitutions revealed that the RNA helicase genes were subjected to strong negative (purifying) selection. Meta-analysis was conducted to determine expression of the RNA helicase genes during the critical period (90-110days post-fertilization, dpf) of male gonad differentiation. At 90dpf, 24 RNA helicase genes were highly differentially expressed in the gonad tissues between the males and females; similarly, 24 and 18 RNA helicase genes were found highly differentially expressed in the gonad tissues between the males and females at 100 and 110dpf, respectively (p<0.01). In general, the vast majority of the RNA helicase genes (31) were expressed at higher levels in females than in males. In the male gonad, a set of 8 RNA helicases were expressed at a significantly higher level at 110dpf than at 90dpf. These findings suggested that RNA helicases may play important roles in sex development and differentiation in teleosts.

Taste receptors and gustatory associated G proteins in channel catfish, Ictalurus punctatus.

Taste sensation plays a pivotal role in nutrient identification and acquisition. This is particularly true for channel catfish (Ictalurus punctatus) that live in turbid waters with limited visibility. This biological process is mainly mediated by taste receptors expressed in taste buds that are distributed in several organs and tissues, including the barbels and skin. In the present study, we identified a complete repertoire of taste receptor and gustatory associated G protein genes in the channel catfish genome. A total of eight taste receptor genes were identified, including five type I and three type II taste receptor genes. Their genomic locations, phylogenetic relations, orthologies and expression were determined. Phylogenetic and collinear analyses provided understanding of the evolution dynamics of this gene family. Furthermore, the motif and dN/dS analyses indicated that selection pressures of different degrees were imposed on these receptors. Additionally, four genes of gustatory associated G proteins were also identified. It was indicated that expression patterns of catfish taste receptors and gustatory associated G proteins across organs mirror the distribution of taste buds across organs. Finally, the expression comparison between catfish and zebrafish organs provided evidence of potential roles of catfish skin and gill involved in taste sensation.

Impact of oral and waterborne administration of rhamnolipids on the susceptibility of channel catfish (Ictalurus punctatus) to Flavobacterium columnare infection.

Flavobacterium columnare is the causative agent of columnaris disease and causes tremendous morbidity and mortality of farmed fish globally. Previously, we identified a potential lectin-mediator (a rhamnose-binding lectin; RBL1a) of F. columnare adhesion and showed higher RBL1a expression in susceptible channel catfish under basal conditions and following infection. Exposure of challenged fish to the carbohydrate ligand l-rhamnose just prior to a challenge substantially decreased columnaris mortality and pathogen adherence via the down-regulation of RBL1a. While highly effective in protecting fish from columnaris, l-rhamnose is prohibitively expensive, underscoring the need for alternative cost-effective sources of rhamnose for disease control. One such alternative may be microbially produced glycolipid compounds termed rhamnolipids (RLs), which feature abundant l-rhamnose moieties and are readily available from commercial sources. In the present study, we examined whether commercially available RLs (administered either by immersion or via feed) would function similarly to l-rhamnose in affording host protection against F. columnare. A four-week feeding trial with basal and RL top-coated diets (basal diet + RLs) was conducted in channel catfish fingerlings. Surprisingly, columnaris challenges revealed significantly lower survival following the 10 d challenge period in RL diet fed fish when compared with the basal treatment group (p < 0.001). In fish fed RLs, we observed a rapid and large-scale upregulation of RBL1a immediately after challenge combined with a suppression of mucin and lysozyme transcripts. Similarly, fish that were briefly pre-exposed to RLs by immersion and then challenged exhibited lower survival as compared to unexposed fish during a 4 d trial. In conclusion, RLs do not represent an alternative to rhamnose as an experimental treatment for protecting catfish from columnaris mortality. Further research is needed to find other affordable and efficacious alternative sources of l-rhamnose.

Differential abundance of muscle proteome in cultured channel catfish (Ictalurus punctatus) subjected to ante-mortem stressors and its impact on fillet quality.

The effects of environmental and handling stress during catfish (Ictalurus punctatus) aquaculture were evaluated to identify the biochemical alterations they induce in the muscle proteome and their impacts on fillet quality. Temperature (25°C and 33°C) and oxygen (~2.5mg/L [L] and >5mg/L [H]) were manipulated followed by sequential socking (S) and transport (T) stress to evaluate changes in quality when fish were subjected to handling (25-H-ST; temperature-oxygen-handling), oxygen stress (25-L-ST), temperature stress (33-H-ST) and severe stress (33-L-ST). Instrumental color and texture of fillets were evaluated, and muscle proteome profile was analyzed. Fillet redness, yellowness and chroma decreased, and hue angle increased in all treatments except temperature stress (33-H-ST). Alterations in texture compared to controls were observed when oxygen levels were held high. In general, changes in the abundance of structural proteins and those involved in protein regulation and energy metabolism were identified. Rearing under hypoxic conditions demonstrated a shift in metabolism to ketogenic pathways and a suppression of the stress-induced changes as the severity of the stress increased. Increased proteolytic activity observed through the down-regulation of various structural proteins could be responsible for the alterations in color and texture.

Bioconcentration and endocrine disruption effects of diazepam in channel catfish, Ictalurus punctatus.

Recently, the detection of pharmaceuticals in surface waters has increased worldwide. Pharmaceuticals are typically found in the environment at concentrations well below therapeutic levels in humans; however, their mechanisms of action may be largely unknown in non-target organisms, such as teleost species. Thus, chronic exposure to these types of compounds warrants further investigation. The goal of this study was to examine the potential for diazepam, a model benzodiazepine drug, to bioconcentrate in tissues of channel catfish and to examine its ability to interact with the endocrine system through modulation of steroid hormones and/or steroidogenic genes. To investigate the bioconcentration potential of diazepam, channel catfish (Ictalurus punctatus) were exposed to 1 ng/mL diazepam for seven days, followed by clean water for another seven days, using an abbreviated OECD 305 Fish Bioconcentration Test study design. This concentration of diazepam is well below environmentally relevant concentrations of diazepam (ng/L). To evaluate steroidogenic effects, fish were exposed to 1 ng/mL diazepam for seven days only. Steroid hormone concentrations were analyzed for various tissues, as well as expression of selected steroidogenic genes. Calculated bioconcentration factors for diazepam were well below regulatory threshold values in all tissues analyzed. No changes in steroid hormone concentration were detected in any tissue analyzed; however, the steroidogenic gene cytochrome P450 side chain cleavage (P450scc) was significantly down-regulated at day 5 and 3ß-hydroxy steroid dehydrogenase (3ß-HSD) was significantly down-regulated at day 7 in the gonad. These results indicate that although diazepam does not significantly bioconcentrate, low-level chronic exposure to diazepam may have the potential to interact with endocrine function by altering gene expression.

Explosive development of pectoral muscle fibres in large juvenile blue catfish Ictalurus furcatus.

As part of an effort on scaling of pectoral spines and muscles, the basis for growth was examined in six pectoral muscles in juvenile blue catfish Ictalurus furcatus, the largest catfish in North America. Fibre number increases slowly in fish from 13.0 to 26.4 cm in total length, doubles by 27.0 cm and remains stable in larger individuals. Simultaneously, mean fibre diameter decreases by half, caused by the addition of new small fibres, before increasing non-linearly in larger fish. The orders of magnitude disparity between the size at hatching and the size of large adults may have selected for rapid muscle fibre addition at a threshold size.