Ictalurid Catfish Research Articles

Acoustic Variation in Ictalurid Catfishes

More than 35,000 ray-finned fish (Actinopterygii) species are potentially using acoustic communication. However, of the approximately 1200 known soniferous fish species, few include North American freshwater fish. To help fill this knowledge gap in fish acoustic communication, which holds great promise for conservation monitoring, I document acoustic measurements (duration 90%, bandwidth 90%, number of pulses, center frequency, and peak time) across 4 species (Ameiurus nebulosus, Ameiurus natalis, Noturus flavus, Ictalurus punctatus) from 3 genera of the North American catfish family, Ictaluridae. This was done by recording 10 trials of disturbance calls from 28 individuals and analyzing 1294 sounds using Raven Pro 1.6 software. I hypothesized that: 1) more phylogenetically/morphologically related species would have more similar acoustic features, 2) acoustic features would correlate with one another, and 3) acoustic features would correlate with standard length (cm). For hypothesis 1, I instead found that Ameriurus nebulosus was the most acoustically dissimilar, despite having the highest level of phylogenetic/morphological similarity with Ameirus natalis. However, only Ameriurus nebulosus' number of pulses were significantly different from other species. For hypothesis 2, it was found that many acoustic measurements were correlated with one another as predicted. For hypothesis 3, only the number of pulses was found to be significantly correlated with standard length, but minimally so. These findings further support that pulsation measurements may contain a high level of phylogenetic signal, given that it is the most crucial characteristic to differentiate species.

Effect of Brooder Age and Size on Fry Size Variation in Channel Catfish

AbstractVariation in harvest size of ictalurid catfishes can be problematic for both catfish producers and processors, ultimately reducing profitability for both. Although harvesting and grading techniques can reduce this variation, the biological underpinnings of these size discrepancies remain unknown. Fry from Channel Catfish Ictalurus punctatus brooders that were 2–5 years old were measured to determine the amount of naturally occurring variation in body mass among sac fry and swim‐up fry. Over two spawning seasons, older brooders consistently produced larger sac fry (38–54% larger) and swim‐up fry (42–51% larger) than their younger counterparts. However, within‐spawn fry size variation was similar among all brooder ages measured. Regression modeling indicated that broodstock body mass did not influence fry body mass, whereas broodstock age was a significant predictor. These data reveal that brooder age is an important determinant of fry size and that initial fry body mass variation could be relevant to understanding fingerling size variation and may play a role in improving the production of ictalurid catfishes.

Copper Toxicity to the Ghost Rams‐Horn Snail Biomphalaria havanensis

AbstractAvian piscivores cause direct economic losses to the aquaculture industry through predation, as well as indirect losses through transmission of digenetic trematodes. Bolbophorus damnificus is a trematode parasite associated with significant losses in catfish aquaculture. The complex life cycle involves the American white pelican Pelecanus erythrorhynchos, planorbid snails, and ictalurid catfish. With no approved therapeutics for B. damnificus in catfish Ictalurus spp. and federal protections on American white pelican, management is restricted to controlling snail hosts. Two snail species, marsh rams‐horn snail Planorbella trivolvis and ghost rams‐horn snail Biomphalaria havanensis, are common inhabitants of commercial catfish ponds and known to transmit B. damnificus. Previous work evaluated copper sulfate toxicity on marsh rams‐horn snails; however, data are lacking for ghost rams‐horn snails. Herein, laboratory‐reared adults of ghost rams‐horn snails and marsh rams‐horn snails were exposed to copper concentrations ranging from 0.16 to 3.38 mg/L Cu to evaluate 24‐, 48‐, and 72‐h acute toxicity. Additionally, sequential low‐dose treatments ranging from 0.1 to 0.8 mg/L Cu were evaluated on eggs, juveniles, and adults of ghost rams‐horn snails as a potentially safer treatment regime for ponds. Acute toxicity was similar between snail species for all exposure times. A 72‐h exposure produced an LC50 of 0.10 and 0.37 mg/L Cu for ghost rams‐horn snails and marsh rams‐horn snails, respectively. The LC50 values increased to 1.1 mg/L Cu for both species with 48‐h exposure. However, in the multiple low‐dose study, a single dose of 0.4 or 0.8 mg/L Cu was lethal to all adult snails after 1 week, as was 0.2 mg/L Cu after two doses. Four doses of 0.1 mg/L Cu or greater killed all ghost rams‐horn snail juveniles. Results indicate that marsh rams‐horn snails and ghost rams‐horn snails have similar sensitivity to copper, and multiple low‐dose treatments were effective against all life stages of ghost rams‐horn snails. These data indicate that copper can be an effective treatment for snail control in commercial catfish ponds.

Length-weight-relationship of two Ictalurid catfish species from an artisanal fishery in central México

Length-weight-relationship of two Ictalurid catfish species from an artisanal fishery in central México

First Observations of Movements of Invasive Flathead Catfish (Pylodictis olivaris) in the Tidal Delaware River Based on Acoustic Telemetry

Pylodictis olivaris (Flathead Catfish) is a large piscivorous ictalurid catfish that has been introduced widely outside of its native range. Introduced Flathead Catfish are recognized as invasive in many locations and have contributed to declines in native fishes. Flathead Catfish were first documented in the mainstem Delaware River in 2001 and now occupy at least 200 km of tidal and non-tidal habitats. This paper describes the movements of 2 Flathead Catfish opportunistically tagged with acoustic transmitters in the tidal Delaware River. The first Flathead Catfish, tagged in November 2005 and tracked for 1055 days, occupied a 26-km reach of the upper tidal river and evidenced 3 cycles of seasonal movement between the same areas of the river. The second Flathead Catfish, tagged in January 2020 and tracked for 340 days, occupied a 49-km reach of the lower tidal Delaware River and was detected for an extended period in the lower Christina River. This catfish also demonstrated seasonal downriver and upriver movements, but exhibited weaker site fidelity than the other individual. Both Flathead Catfish tended to move at night or in the morning, which is typical for the species, although daylight movements were also observed. The annual ranges of river occupied by the Flathead Catfish in this study were larger than previously described for introduced populations, and suggest that any program of management or control would have to be at a watershed scale. This study is the first to describe seasonal movements of Flathead Catfish in the Delaware River, documents a 17-km downriver expansion of the species' range, and provides the first record of Flathead Catfish in the Christina River.

MYXOZOAN COMMUNITY COMPOSITION AND DIVERSITY IN CLINICAL CASES OF PROLIFERATIVE GILL DISEASE IN MISSISSIPPI CATFISH AQUACULTURE.

An abundance of morphologically variable Henneguya species complicates the understanding of disease relationships between ictalurid catfish and myxozoan (Phylum: Cnidaria) parasites on North American aquaculture operations. Henneguya ictaluri, the cause of proliferative gill disease (PGD) in channel and hybrid catfish, is arguably the most important parasite of commercial catfish aquaculture in the southeastern United States. While research indicates arrested development and limited sporogenesis of H. ictaluri in channel (Ictalurus punctatus) × blue (Ictalurus furcatus) hybrid catfish, incidents of PGD persist in hybrid production systems. This work investigated the influence of fish host on myxozoan community composition and diversity within naturally infected gill tissues from diagnostic case submissions to the Aquatic Research and Diagnostic Laboratory in Stoneville, Mississippi, from 2017 to 2019. Gills collected from farm-raised catfish with clinical PGD were subjected to metagenomic amplicon sequencing of the myxozoan 18S SSU rDNA gene diagnostic variable region 3 (DVR3). Myxozoan community composition significantly differed between channel and hybrid catfish PGD cases, with channel catfish having more diverse community structures. Channel catfish gills had a greater relative abundance of H. ictaluri in 2017 and 2019, while no differences were observed in 2018. Importantly, H. ictaluri was present in all channel and hybrid catfish PGD cases across all years; however, H. ictaluri was not the most abundant myxozoan in almost half the cases examined, suggesting other myxozoan species may also contribute to PGD pathology. The detection of numerous known and unclassified myxozoan sequences in addition to H. ictaluri provides evidence PGD may involve mixed species infections. Furthermore, the presence of numerous unclassified myxozoan sequences in gill samples from clinical PGD cases indicates the number of described species from U.S. farm-raised catfish vastly underestimates the true myxozoan diversity present within the varied pond microcosms associated with catfish aquaculture.

Identification and Characterization of Differentially Expressed IgM Transcripts of Channel Catfish Vaccinated with Antigens of Virulent Aeromonas hydrophila

Channel catfish (Ictalurus punctatus) is the top species produced in US aquaculture and motile Aeromonas septicemia, caused by virulent Aeromonas hydrophila (vAh), is one of the most severe diseases that afflict catfish farms. Previously, vaccination of fish with extracellular proteins (ECP) of vAh was shown to produce a robust antibody-mediated immune response against vAh infection. In this study, we analyzed IgM transcripts that were differentially expressed in the head kidney and liver of ECP-immunized and mock-immunized (control) fish with emphasis on a variable domain of heavy chain. Quantitative PCR analysis indicated that immunized fish produced significantly more IgM transcripts than control fish. Full-length IgM heavy chain cDNA was cloned, which encoded typical IgM peptide, including signal peptide, variable domain (VH), constant domain (CH), and carboxyl terminal peptide. Great sequence diversity was revealed in a VH segment, with the third complementarity diversity region (CDR3) being most variable. Using germline VH gene grouping method, variants (clones) of VH characterized in this study belonged to nine VH families. The most unique variants (approximately 49%) were found in the VH2 family. Vaccinated fish apparently had more unique variants than in the control fish. There were 62% and 79% of unique variants in the head kidney and liver of vaccinated fish, respectively, while 44% and 27% unique variants in the head kidney and liver of control fish, respectively. Among the unique variants in VH2 family, approximately 87% of them were found in vaccinated fish. Two-dimensional gel electrophoresis of semi-purified IgM protein confirmed that matured IgM protein was as variable as IgM transcripts identified in this study, with isoelectric points crossing from 6 to 10. Results of this study provided insight into the molecular and genetic basis of antibody diversity and enriched our knowledge of the complex interplay between antigens and antibodies in Ictalurid catfish.

Establishment and characterization of a cell line from ictalurid catfish

AbstractThe catfish industry is integral to the economy of the southern United States contributing >70% of the total U. S. finfish production. Intensive catfish production systems are more vulnerable to infectious disease outbreaks resulting in significant economic losses. Viruses are a major concern especially in the hatchery and nursery phases of catfish rearing. These infectious agents require host cell machineries to replicate. The ability to propagate fish viruses in vitro using cell cultures is imperative in advancing virus research and facilitating disease management strategies. Several viruses show host‐ or even tissue‐specificity. Scarcity of host‐specific fish cell lines forces researchers to rely on general cell lines that might not be conducive for the replication of some viruses, thus hindering their isolation, identification, and characterization. The ictalurid cell line (channel catfish ovary [CCO‐ATCC® CRL‐2772]) previously available from cell repository (ATCC) has recently been reported as cross‐contaminated by brown bullhead (BB) cells. Lack of host‐specific cell cultures and contamination issues necessitated initiation of cell cultures from the fin tissues of hybrid catfish (♀ channel catfish × ♂ blue catfish). A combination approach involving tissue explantation and enzymatic digestion methods were used to develop catfish fin cell cultures. These cultures were passaged over 100 times and transitioned into an established cell line. The hybrid catfish fin (HCF) cell line was characterized, growth conditions optimized, species of origin molecularly authenticated, and the susceptibility to fish viruses evaluated. This catfish cell line could serve as an efficient tool for virus studies, antiviral agent screening, and vaccine development benefitting catfish aquaculture.

An investigation into the pathogenesis of blue catfish alloherpesvirus in ictalurid catfish

AbstractIntensive aquaculture production systems often encounter infectious viral disease outbreaks causing substantial fish mortalities and associated economic losses. Blue catfish alloherpesvirus (BCAHV) is an Ictalurid herpesvirus with limited information on pathogenesis. To determine the host‐specificity and potential host range of BCAHV, the virus was inoculated onto various fish cell lines belonging to families Ictaluridae, Cyprinidae, Centrarchidae, and Clariidae. Viral replication and exhibition of cytopathic effects (CPEs) were restricted to cell lines from the family Ictaluridae indicating the host preference of BCAHV. Subsequently, fish challenges were conducted to evaluate intrinsic and extrinsic factors influencing BCAHV infection. Mortality because of BCAHV infection was significantly higher in blue catfish and least in channel catfish further specifying the host preference of the virus. Histopathological assessment of the BCAHV infected fish revealed splenitis with severe erythrophagia. Host susceptibility to BCAHV differed with age with fish at 60 days post hatch being more susceptible. Temperature had a significant role in the activation and pathogenesis of BCAHV. Fish exposed to BCAHV at a sustained high temperature had significantly low mortality suggesting the likelihood of virus inactivation. Virus exposure in tanks with high stocking density resulted in significantly high fish mortalities indicating horizontal transmission is a key element in BCAHV pathogenesis. The heightened pathogenicity of BCAHV in blue and hybrid catfish as observed in this study validates its potential to be a significant pathogen in catfish production.

Effectiveness of Cathelicidin Antimicrobial Peptide against Ictalurid Catfish Bacterial Pathogens.

One of the major goals in aquaculture is to protect fish against infectious diseases as disease outbreaks could lead to economic losses if not controlled. Antimicrobial peptides (AMPs), a class of highly conserved peptides known to possess direct antimicrobial activities against invading pathogens, were evaluated for their ability to protect Channel Catfish Ictalurus punctatus and hybrid catfish (female Channel Catfish × male Blue Catfish I. furcatus) against infection caused by the fish pathogen Aeromonas hydrophila ML09-119. To identify effective peptides, the minimum inhibitory concentrations against bacterial pathogens Edwardsiella ictaluri S97-773, Edwardsiella piscicida E22-10, A. hydrophila ML09-119, Aeromonas veronii 03X03876, and Flavobacterium columnare GL-001 were determined invitro. In general and overall, cathelicidins derived from alligator and sea snake exhibited more potent and rapid antimicrobial activities against the tested catfish pathogens as compared to cecropin and pleurocidin AMPs and ampicillin, the antibiotic control. When the peptides (2.5µg of peptide/g of fish) were injected into fish and simultaneously challenged with A. hydrophila through immersion, increased survival rates in Channel Catfish and hybrid catfish were observed in both cathelicidin (alligator and sea snake) treatments as compared to other peptides and the infected control (P<0.001) with alligator cathelicidin being the overall best treatment. Bacterial numbers in the kidney and liver of Channel Catfish and hybrid catfish also decreased (P<0.05) for cathelicidin-injected groups at 24 and 48h after challenge infection. These results show the potential of cathelicidin to protect catfish against bacterial infections and suggest that an approach overexpressing the peptide in transgenic fish, which is the long-term goal of this research program, may provide a method of decreasing bacterial disease problems in catfish as delivering the peptides via individual injection or feeding would not be economically feasible.

Strategic Planning for Catfish Angling in the Future: An Example from Urban Iowa

AbstractIctalurid catfish have a long history of popularity in Iowa fisheries, but recent changes have highlighted the need to investigate catfish angling interest and potential for future growth. Ictalurid catfish were superseded by other taxa for the first time in recent statewide angler surveys, putting their importance into question. Ongoing urbanization in Iowa was associated with reduced interest in angling and specifically in catfish angling. We sought to determine demographic characteristics, preferences, and constraints of potential anglers, lapsed catfish anglers, active catfish anglers, and non‐catfish anglers and to predict where catfish angling had the greatest potential for growth. A survey of urban areas was conducted in 2018; questions included interest and past experience fishing in Iowa, target species, characteristics of an ideal fishing trip, interest in various programs, and constraints to fishing participation. A total of 693 responses were obtained, yielding a 27.7% response rate. Catfish anglers were predominantly male, middle aged, and White, and interest in catfish angling was best explained by gender, age, and rurality (i.e., urban/rural background). Interest level (i.e., potential, lapsed, active, or non‐catfish angler) was related to ideal trip factors, program preferences, and constraints, with active catfish anglers being significantly different in numerous aspects from lapsed, potential, and non‐catfish anglers. Based on their description of an ideal fishing trip, some potential anglers were predicted to be similar to active catfish anglers, while others would be similar to lapsed anglers. Spatial prediction of interest based on Tapestry segment composition revealed patterns of interest in both Channel Catfish Ictalurus punctatus and Flathead Catfish Pylodictis olivaris, which were repeated across cities. Our findings suggested numerous differences between active catfish anglers and those who may be recruited or reactivated; these differences translate into dissimilar management actions and interventions. We conclude that catfish angling can grow in Iowa’s urban centers, but recruitment and retention strategies should be specific to both audience and place.

Evaluation of Microhabitat Conditions Used by Noturus stanauli (Pygmy Madtom) in the Clinch River, Tennessee

Noturus stanauli (Pygmy Madtom) is an endangered ictalurid catfish species endemic to the Clinch and Duck rivers within the Tennessee River system. Little is known regarding the species' habitat preferences due to its rarity, small body size, and the challenging level of collection difficulty in its mainstem riverine environment. In the Clinch River during July, September, and November of 2017, we (1) quantified microhabitat conditions in 1.5-m2 quadrats where we collected Pygmy Madtoms by kick-seining methods and (2) evaluated environmental covariates associated with Pygmy Madtom occupancy and detection using a single-season occupancy-modeling approach. We collected 13 Pygmy Madtoms in July (n = 1) and November (n = 12), with no individuals seen in September. Pygmy Madtoms occupied quadrats with a mean depth of 27 cm, column water velocity of 52 cm/s, water temperature of 12 °C, and substrates dominated by gravel- or pebble-sized particles. Most quadrats with Pygmy Madtom present were located either 1–2 m or 4–5 m away from the nearest bank. Pygmy Madtom occupancy estimates were high (0.498 for the top candidate model) but were not significantly associated with any environmental characteristics. However, the likelihood of Pygmy Madtom detection was significantly related to water temperature (-), with water column velocity (+) and distance to bank (-) playing supportive roles in top candidate models. Our results inform recovery efforts by providing the first quantitative evaluation of Pygmy Madtom microhabitat associations in the Clinch River.

Tapeworms (Cestoda) of Ictalurid Catfishes (Siluriformes) in North America: Redescription of Type Species of Two Genera and Proposal of Essexiellinae n. Subfam.

Ictalurid catfishes (Siluriformes) in North America harbor proteocephalid tapeworms of the subfamily Corallobothriinae. Type species of 2 of 3 genera of these tapeworms from ictalurids are redescribed, based on museum and newly collected material. Essexiella fimbriata (Essex, 1928) is typified mainly by a wide, umbrella-shaped scolex with a metascolex formed by numerous folds of tissue, anteriorly directed suckers without sphincters, vitellarium bent inwards posteriorly, "flower-shaped" uterus (with anterior, lateral, and posterior diverticula), and a conspicuously pre-equatorial genital atrium. Verified host records of this cestode are only from 3 species of Ictalurus Rafinesque, 1820. Megathylacoides giganteum (Essex, 1928), which seems to be specific to the channel catfish (Ictalurus punctatus), possesses a globular scolex, with a weakly developed metascolex formed by tissue folds posterior to the suckers, anterolaterally directed suckers with large semilunar sphincters, proglottids that are widest at the level of the genital atrium at the anterior third of the proglottid, and uterine diverticula that do not reach the vitelline follicles laterally. A new subfamily, Essexiellinae Scholz and Barčák, is proposed to accommodate species of EssexiellaScholz, de Chambrier, Mariaux and Kuchta, 2011 (type genus), MegathylacoidesJones, Kerley and Sneed, 1956, and CorallotaeniaFreze, 1965 from ictalurid catfishes in the Nearctic Region. These tapeworms possess a metascolex, medullary genital organs, uterus lined with numerous chromophilic cells, pre-equatorial genital atrium, and uterine development of type 2. The new subfamily was monophyletic in all molecular phylogenetic analyses, being most closely related to 3 Neotropical proteocephalids from the redtail catfish, Phractocephalus hemioliopterus (Bloch and Schneider, 1801), but distant from all remaining proteocephalid tapeworms from freshwater fishes in North America.

Off‐flavors in pond‐grown ictalurid catfish: Causes and management options

AbstractIctalurid catfish grown in ponds often acquire undesirable off‐flavors prior to harvest. Off‐flavors develop when odorous, lipophilic substances in food or water are absorbed across gut or gill epithelium and concentrated in edible tissues. The most common causes of catfish off‐flavors are two nontoxic secondary metabolites of planktonic cyanobacteria: geosmin (causing an earthy off‐flavor) and 2‐methylisoborneol (causing a musty off‐flavor). Off‐flavored fish are unacceptable for processing, and harvest must be postponed until the source of the odorous compound disappears and the compound purges from edible fish tissue. Harvest delays caused by episodes of off‐flavor increase production time, interrupt cash flow, and increase the risk of fish loss. Catfish farmers consider off‐flavor to be one of their most important production‐related problems. This paper reviews the causes of off‐flavor in catfish, pharmacokinetics of uptake and loss of odorous compounds in catfish, seasonality and prevalence of off‐flavors, farm‐ and industry‐level impacts, the ecology of cyanobacteria in catfish ponds, and various strategies for preventing or treating cyanobacterial (and other) off‐flavors. A decision‐making system based on knowledge gained from research is presented as a guide to effective use of the limited tools available to manage off‐flavors.

Evaluation of a field protocol for internally-tagging fish predators using difficult-to-tag ictalurid catfish as examples

Tagging protocols that result in high tag retention will benefit fisheries professionals who use telemetry data. Ictalurid catfish historically have had very poor telemetry tag retention. Here, we use these difficult-to-tag taxa to address two research objectives. First, we evaluated our field-based internal tagging methodology by quantifying six tag retention metrics using data from 48 acoustically-tagged blue catfish (Ictalurus furcatus) released into Milford Reservoir, KS, USA. Second, to better understand the results of this field evaluation, we evaluated tag retention and survival in the hatchery for the closely-related channel catfish (I. punctatus). Field and hatchery studies provided complementary information. Eighty percent of tagged blue catfish were detected at the end of our 5-mo field study (1,139,402 = total detections; 24,243 = average detections per fish). A 13-week hatchery evaluation of our field methodology also had high tag retention (100%). Hatchery treatments that used a lateral-ventral incision had higher tag retention and survival than those treatments that included a mid-ventral incision. Time invested in training, protocol refinement, and field organization were also important. Furthermore, monitoring the surgical history and recovery of individual fish allowed us to correct problems before mortality occurred. Because a need exists for a range of internal tagging methodologies that are effective on an assortment of fish species tagged under a variety of circumstances, our high tag retention methodology may be useful to the expanding research community that studies native and non-native catfish, as well as, other telemetry researchers who seek beneficial refinements to their tagging protocols.

The Mexican Blindcat Project: new discoveries and future efforts

The endangered Mexican blindcat (Prietella phreatophila, Carranza 1954) is one of only four described stygobitic ictalurid catfish in North America. Members of two monotypic genera (Satan eurystomus and Trogloglanis pattersoni) are known from the Edwards Aquifer in Texas and, until recently, Prietella (represented by P. lundbergi and P. phreatophila) was only known to occur in Mexico (northern Coahuila to southern Tamaulipas). The recent discovery of P. phreatophila in a cave on the Amistad National Recreation Area in Val Verde County, Texas is the result of decades of sporadic effort on both sides of the US/Mexican border and has stimulated a renewed effort to investigate the distribution, ecology, evolutionary history, and conservation status of this species. Collaborative efforts among The San Antonio Zoo, The University of Texas at Austin, Zara Environmental, and The National Park Service are currently focused on habitat surveys in Texas as well as captive husbandry and propagation. Ongoing efforts with collaborators from the Comisión Nacional de Áreas Naturales Protegidas, Área de Protección de Recursos Naturales Sabinas and the Laboratorio de Genética para la Conservación, Centro de Investigaciones Biológicas del Noroeste, La Paz include expanded fieldwork in Mexico, hydrogeologic studies, and surveys using environmental DNA.

Comparison of Channel Catfish and Blue Catfish Gut Microbiota Assemblages Shows Minimal Effects of Host Genetics on Microbial Structure and Inferred Function.

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.

Evaluation of Unbaited Hoop Nets for Simultaneously Assessing Channel Catfish and Flathead Catfish populations in the Minnesota River

AbstractFisheries managers desire efficient sampling methods with sufficient precision for monitoring ictalurid catfish populations. For this study, I conducted single unbaited hoop‐net surveys in the Minnesota River to evaluate the efficacy of simultaneously assessing stock‐size (≥280‐mm) Channel Catfish Ictalurus punctatus and quality‐size (≥510‐mm) Flathead Catfish Pylodictis olivaris populations. I compared catch rates and length‐frequency distributions among months (April–September) and used resampling procedures to estimate the number of hoop‐net samples needed to achieve desirable precision of catch rate estimates and adequate statistical power. Catch rates (mean ± SE) were 2.1 ± 0.3 fish/net‐night for Channel Catfish and 0.8 ± 0.1 fish/net‐night for Flathead Catfish. Resampling procedures demonstrated that desirable precision (i.e., relative SE ≤ 25) and adequate statistical power (≥0.80 with α = 0.10) to detect 50% reductions in mean catch rates with two‐tailed t‐tests could be achieved for both species with as few as 68 hoop‐net samples during August. Unbaited hoop nets are effective for simultaneously assessing Channel Catfish and Flathead Catfish populations in the Minnesota River, and conducting surveys during August provides the best balance between catch rate and precision while minimizing perceived environmental and behavioral biases. However, the amount of sampling effort needed to detect small population changes (&lt;50%) and to collect sufficient sample sizes for age and growth analyses may be logistically prohibitive. This study emphasizes the importance of evaluating precision and statistical power of sampling methods so that fisheries managers can identify the most suitable methods for their specific objectives.

Resolving evolutionary changes in parasite life cycle complexity: Molecular phylogeny of the trematode genus Alloglossidium indicates more than one origin of precociousness

The evolutionary causes and consequences of changes in complex life cycles are of central importance in parasitology. However, data remain limited because in part, knowledge on phylogenetic relationships among species that differ in life cycle patterns remains scarce. We present a molecular phylogeny of the trematode genus Alloglossidium, which contains several species that display precocious (a.k.a., progenetic) life cycles (i.e., maturation in what is typically regarded as an intermediate host). The molecular phylogeny contrasts with previous morphological and life-history based phylogenetic hypotheses. In particular, a precocious life cycle wherein leeches are used as final hosts evolved early in the history of the genus. Among the remaining species, which are a separate clade, a three-host life cycle using ictalurid catfishes is ancestral. Furthermore, there are at least two additional independent evolutionary events that lead to a precocious life cycle where a catfish host is lost and a crustacean is used as a final host. We conclude with a discussion on how existing hypotheses on the evolution of precociousness, and parasite life cycle complexity in general, may or may not relate to the patterns observed in genus Alloglossidium.

Dissolved Oxygen and Aeration in Ictalurid Catfish Aquaculture

AbstractFeed‐based production of ictalurid catfish in ponds is the largest aquaculture sector in the USA. Feed has an oxygen demand, and increases carbon dioxide, ammonia nitrogen, and phosphate inputs to ponds. Major sources of oxygen in ponds are phytoplankton photosynthesis and mechanical aeration; the major sink for oxygen is respiration by fish and by microorganisms in the water column and sediment. Dissolved oxygen concentrations decline when respiration exceeds photosynthesis, and the most crucial time for low dissolved oxygen concentration is at night. Mechanical aeration is applied to avoid nighttime dissolved oxygen concentrations from falling below the critical level for catfish of 3 mg/L. Electrically powered paddlewheel aerators are used by most catfish producers. The oxygen‐transfer efficiency of these aerators is known, but calculations of aeration requirement from stocking and feeding rates are not reliable because of variation in phytoplankton abundance and in weather conditions. Dissolved oxygen concentrations must be monitored, and when measurements suggest that nighttime dissolved oxygen concentration will be unacceptably low, tractor‐powered emergency aerators must be operated to supplement dedicated aeration. Dissolved oxygen concentration also is important in hatcheries, and small aeration systems have been developed for hatchery application.