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Objective: The Delta Select line of Channel Catfish Ictalurus punctatus was established in 2006 and has undergone five generations of genetic selection, specifically targeting increased growth rate and carcass yield, and was released to U.S. catfish farmers in 2020. While improvements in growth rate and carcass yield have been confirmed, performance for other important production traits has yet to be evaluated. Infectious disease, particularly bacterial infections caused by Edwardsiella spp., cause significant economic losses to catfish producers in the southeastern United States. Given the economic consequences of these bacterial pathogens, experimental infectivity trials were conducted comparing susceptibility to Edwardsiella spp. between the Delta Select line and a randomly bred line of Channel Catfish originating from the same base population (Delta Control line). Methods: Twenty‐six full‐sib families from each line were used in infectivity trials consisting of a high and a low dose of E. ictaluri (immersion challenge: high dose = 1.6 × 107 CFU/mL, low dose = 8.0 × 106 CFU/mL) and E. piscicida (intracoelomic challenge: high dose = 6.3 × 105 CFU/fish, low dose = 1.9 × 105 CFU/fish). Result: The high challenge dose resulted in the highest mortality for both pathogens (p < 0.001), regardless of selection line. There was no significant difference in cumulative percent mortality between the Delta Select and Delta Control lines following the E. ictaluri challenge at either dose (p = 0.55). Delta Selects had reduced mortality (p < 0.001) in response to E. piscicida challenge compared with the Delta Controls, regardless of dose. Conclusion: These results indicate that selection for increased growth rate and carcass yield in the Delta Select Channel Catfish line did not negatively impact resistance to E. ictaluri while potentially improving resistance to E. piscicida. Impact statementSelection for increased growth and carcass yield in the Delta Select line of Channel Catfish has not impacted susceptibility to Edwardsiella ictaluri and appears to have reduced susceptibility to Edwardsiella piscicida. [ABSTRACT FROM AUTHOR]

Enteric septicemia of catfish (ESC), caused by the gram‐negative enteric bacteria Edwardsiella ictaluri, is a significant threat to catfish aquaculture in the southeastern United States. Antibiotic intervention can reduce mortality; however, antibiotic use results in an imbalance, or dysbiosis, of the gut microbiota, which may increase susceptibility of otherwise healthy fish to enteric infections. Herein, recovery of the intestinal microbiota and survivability of channel catfish in response to ESC challenge was evaluated following a 10‐day course of florfenicol and subsequent probiotic or prebiotic supplementation. Following completion of florfenicol therapy, fish were transitioned to a basal diet or diets supplemented with a probiotic or prebiotic for the remainder of the study. Digesta was collected on Days 0, 4, 8 and 12, beginning on the first day after cessation of antibiotic treatment, and gut microbiota was characterized by Illumina sequencing of the 16S rRNA gene (V4 region). Remaining fish were challenged with E. ictaluri and monitored for 32 days post‐challenge. Florfenicol administration resulted in dysbiosis characterized by inflated microbial diversity, which began to recover in terms of diversity and composition 4 days after cessation of florfenicol administration. Fish fed the probiotic diet had higher survival in response to ESC challenge than the prebiotic (p =.019) and negative control (p =.029) groups. [ABSTRACT FROM AUTHOR]

To prevent catfish idiopathic anaemia, diets fortified with iron have been adopted as a regular practice on commercial catfish farms to promote erythropoiesis. However, the effects of prolonged exposure of excess dietary iron on production performance and disease resistance for hybrid catfish (Ictalurus punctatus × I. furcatus) remains unknown. Four experimental diets were supplemented with ferrous monosulphate to provide 0, 500, 1000, and 1500 mg of iron per kg of diet. Groups of 16 hybrid catfish juveniles (~22.4 g) were stocked in each of 20, 110‐L aquaria (n = 5), and experimental diets were offered to the fish to apparent satiation for 12 weeks. At the end of the study, production performance, survival, condition indices, as well as protein and iron retention were unaffected by the dietary treatments. Blood haematocrit and the iron concentration in the whole‐body presented a linear increase with the increasing the dietary iron. The remaining fish from the feeding trial was challenged with Edwardsiella ictaluri. Mortality was mainly observed for the dietary groups treated with iron supplemented diets. The results for this study suggest that iron supplementation beyond the required levels does affect the blood production, and it may increase their susceptibility to E. ictaluri infection. [ABSTRACT FROM AUTHOR]

Objective: Proliferative gill disease (PGD) in Channel Catfish Ictalurus punctatus and hybrid catfish (Channel Catfish × Blue Catfish I. furcatus) is attributed to the myxozoan Henneguya ictaluri. Despite evidence of decreased H. ictaluri transmission and impaired parasite development in hybrid catfish, PGD still occurs in hybrid production systems. Previous metagenomic assessments of clinical PGD cases revealed numerous myxozoans within affected gill tissues in addition to H. ictaluri. The objective of this study was to investigate the development and pathologic contributions of H. ictaluri and other myxozoans in naturally and experimentally induced PGD. Methods: Henneguya species‐specific in situ hybridization (ISH) assays were developed using RNAscope technology. Natural infections were sourced from diagnostic case submissions in 2019. Experimental challenges involved Channel Catfish and hybrid catfish exposed to pond water from an active PGD outbreak, and the fish were sampled at 1, 7, 10, 12, 14, 16, 18, and 20 weeks postchallenge. Result: Nine unique ISH probes were designed, targeting a diagnostic variable region of the 18S ribosomal RNA gene of select myxozoan taxa identified in clinical PGD cases. Partial validation from pure H. ictaluri, H. adiposa, H. postexilis, and H. exilis infections illustrated species‐specific labeling and no cross‐reactivity between different myxozoan species or the catfish hosts. After experimental challenge, mature plasmodia of H. ictaluri and H. postexilis formed in Channel Catfish but were not observed in hybrids, suggesting impaired or delayed sporogenesis in the hybridized host. These investigations also confirmed the presence of mixed infections in clinical PGD cases. Conclusion: Although H. ictaluri appears to be the primary cause of PGD, presporogonic stages of other myxozoans were also present, which may contribute to disease pathology and exacerbate respiratory compromise by further altering normal gill morphology. This work provides molecular confirmation and more resolute developmental timelines of H. ictaluri and H. postexilis in Channel Catfish and supports previous research indicating impaired or precluded H. ictaluri sporogony in hybrid catfish. Impact statementThis work implicates Henneguya ictaluri as the primary cause of proliferative gill disease, a devastating parasitic disease of U.S. catfish aquaculture, but demonstrates other myxozoan parasites can contribute to disease severity. The study better defines the developmental timeline of H. ictaluri and H. postexilis in Channel Catfish and supports research indicating impaired maturation of H. ictaluri in hybrid catfish. [ABSTRACT FROM AUTHOR]

The myxozoan Henneguya ictaluri is cited as the cause of proliferative gill disease (PGD) in Channel Catfish Ictalurus punctatus and Channel × Blue Catfish I. furcatus hybrids. Differences in host susceptibility result in decreased transmission rates, reduced sporogenesis, and lesser incidence of PGD in hybrid catfish. In experimental pond trials, continuous monoculture of hybrid catfish suppressed H. ictaluri abundance in pond systems compared to Channel Catfish monoculture. The present study examined differences in myxozoan community structure in catfish ponds stocked with Channel Catfish or hybrid catfish. Experimental ponds (0.4 ha) dedicated to Channel Catfish or hybrid catfish monoculture were maintained over three production cycles. Pond water collected during the spring of each year was subjected to metagenomic analysis by targeted amplicon sequencing of a diagnostic hypervariable region (DVR3) of the myxozoan 18S ribosomal RNA gene. Relative abundance of H. ictaluri was significantly greater in Channel Catfish ponds than in hybrid catfish ponds during years 2 and 3. In hybrid catfish ponds, H. ictaluri never exceeded 20% average relative abundance. Hybrid catfish ponds also revealed decreased myxozoan diversity and species evenness compared to Channel Catfish ponds, suggesting that myxozoan taxa associated with Channel Catfish may not be well adapted to the hybridized host. Results corroborate previous research indicating that hybrid catfish monoculture can suppress H. ictaluri compared to ponds that are devoted to Channel Catfish. These data imply that alternating catfish culture species in ponds (crop rotation) has the potential to mitigate PGD by precluding H. ictaluri from accumulating within ponds to levels associated with disease and catastrophic loss. Further, this work identified numerous previously unidentified taxa present within these systems that clustered phylogenetically with both catfish and noncatfish hosts. The impacts that these other myxozoans have on catfish health and production are unknown, but their presence indicates that myxozoan diversity within catfish aquaculture ponds has been greatly underestimated and is significantly influenced by stocking choice. [ABSTRACT FROM AUTHOR]

In the mid‐2010s, Edwardsiella tarda was reaffiliated into three discrete taxa (E. anguillarum, E. piscicida, and E. tarda), obscuring previous descriptions of E. tarda‐induced pathology in fish. To clarify ambiguity regarding the pathology of E. tarda, E. piscicida, and E. anguillarum infections in US farm‐raised catfish, channel catfish (Ictalurus punctatus), blue catfish (I. furcatus), and channel × blue catfish hybrids were challenged with comparable doses of each bacterium. The most severe pathology and mortality occurred in fish challenged with E. piscicida, supporting previous reports of increased pathogenicity in commercially important ictalurids, while E. anguillarum and E. tarda warrant only minimal concern. Acute pathologic lesions among bacterial species were predominantly necrotizing and characteristic of gram‐negative sepsis but became progressively granulomatous over time. After 100 days, survivors were exposed to the approximate median lethal doses of E. piscicida and E. ictaluri, revealing some cross‐protective effects among E. piscicida, E. anguillarum, and E. ictaluri. In contrast, no fish that survived E. tarda challenge demonstrated any protection against E. piscicida or E. ictaluri. This work supports reports of increased susceptibility of channel, blue, and hybrid catfish to E. piscicida, while highlighting potential cross‐protective affects among fish associated Edwardsiella spp. [ABSTRACT FROM AUTHOR]

Proliferative gill disease (PGD), caused by the myxozoan Henneguya ictaluri, is an important parasitic disease in U.S. catfish aquaculture. Continuous exposure of Channel Catfish Ictalurus punctatus to the actinospore stage of H. ictaluri results in a severe inflammatory response at the gills, leading to morbidity and death. Previous work indicates that the chemical cues in fish mucus that are recognized by myxozoan actinospores are not host specific. Building on these findings, the potential decoy effects of nonictalurid fish to actinospores of H. ictaluri were evaluated. Exposure of actinospores to gill mucus from multiple nonictalurid fishes resulted in actinospore activation for all fish species tested. Based on these findings, experimental transmission trials with potential interceptor fish were conducted. Individual Channel Catfish were co‐stocked with Western Mosquitofish Gambusia affinis at 0, 10, 25, or 50% of mean Channel Catfish biomass and exposed to 3,000 actinospores of H. ictaluri. Gill tissues were sampled at 24 h postchallenge, and parasite burden was estimated by H. ictaluri‐specific quantitative PCR. Results revealed that Western Mosquitofish stocked at 25% and 50% of catfish biomass reduced H. ictaluri DNA in Channel Catfish gills more than threefold. In a second study, catfish were exposed to pond water collected from an active PGD outbreak in the presence of Western Mosquitofish stocked at 25% of catfish biomass. Channel Catfish were sampled at 24 h and at 7 d after the last pond water exposure. At 24 h postexposure, catfish that were co‐stocked with Western Mosquitofish showed significantly lower H. ictaluri DNA than catfish stocked alone. This treatment effect was absent at 7 d postexposure, as parasite quantities within tissues had increased over 1,000×, with marked variability. Still, results indicate that the chemical cues that activate H. ictaluri actinospores are not specific to Channel Catfish. This work evinces a potential benefit of nonictalurid fish in combating H. ictaluri, suggesting that the presence of nonictalurid interceptor fish in catfish ponds may minimize PGD severity. [ABSTRACT FROM AUTHOR]

Edwardsiella piscicida is a growing problem for catfish aquaculture in the southeastern United States, particularly in channel (Ictalurus punctatus) x blue (I. furcatus) catfish hybrids. Research has shown E. piscicida isolates recovered from farmed catfish in Mississippi form at least five discrete phyletic groups, with no apparent differences in virulence in channel and hybrid catfish. Laboratory trials have shown a live‐attenuated E. ictaluri vaccine (340X2) cross‐protects against at least one E. piscicida isolate (S11–285) in channel and hybrid catfish, although it is unknown if this protection exists for other E. piscicida variants. To this end, channel and hybrid catfish were immunized by immersion with E. ictaluri 340X2. Thirty days later, fish were challenged by intracoelomic injection with representative E. piscicida variants from each phyletic group. Relative percent survival (RPS) for hybrids ranged from 54.7% to 77.8%, while RPS in channels ranged from 80.5% to 100%. A second study investigated whether channel and hybrid catfish exposed to heterologous E. piscicida isolates were similarly protected against wild‐type E. ictaluri. Fish were exposed by bath immersion to representative E. piscicida isolates from each phyletic group. Thirty days post‐immunization, fish were challenged by immersion with wild‐type E. ictaluri isolate S97–773. Regardless of variant, previous exposure to heterologous E. piscicida isolates significantly improved survival following E. ictaluri challenge. These findings suggest the presence of shared and conserved antigens among E. piscicida and E. ictaluri that could be exploited by application of polyvalent or cross‐protective vaccines. [ABSTRACT FROM AUTHOR]

The echinostomatid Drepanocephalus spathans (syn. Drepanocephalus auritus) parasitizes the double-crested cormorant Phalacrocorax auritus. In North America, the marsh rams-horn snail Planorbella trivolvis and ghost rams-horn snail Biomphalaria havanensis serve as snail intermediate hosts, both of which inhabit catfish aquaculture ponds in the southeastern United States. Studies have demonstrated D. spathans exposure can be lethal to juvenile channel catfish Ictalurus punctatus. Two studies were undertaken to elucidate the life cycle of D. spathans to establish a developmental time line. In both studies, D. spathans cercariae collected from naturally infected P. trivolvis individuals were used to infect channel catfish fingerlings, which were then fed to double-crested cormorants (DCCOs) that had been pharmaceutically dewormed. In study 1, laboratory-reared P. trivolvis and B. havanensis individuals were placed in aviary ponds with experimentally infected DCCO and examined bi-weekly for release of cercariae. Trematode eggs were observed in the feces of exposed birds 3 days post-infection. Birds were sacrificed 18 days post-exposure (dpe), and gravid adults morphologically and molecularly consistent with D. spathans were recovered. Snails from the aviary pond were observed shedding D. spathans cercariae 18–54 dpe. In study 2, trematode eggs were observed in the feces of exposed DCCOs beginning 8 dpe. Once eggs were observed, birds were allowed to defecate into clean tanks containing naïve laboratory-reared P. trivolvis individuals. Additionally, eggs from experimental DCCO feces were recovered by sedimentation and placed in an aquarium housing laboratory-reared P. trivolvis individuals. Birds in study 2 were sacrificed after 60 days, and gravid D. spathans specimens were recovered. Snails from the experimental DCCO tanks shed D. spathans cercariae 89–97 dpe. Lastly, trematode eggs were isolated and observed for the hatching of miracidia, which emerged on average after 16 days at ambient temperatures. No D. spathans adults were observed in control birds fed non-parasitized fish. This is the first experimental confirmation of the D. spathans life cycle, resolving previously unknown developmental time lines. In addition, the effects of fixation on adult trematode morphology were assessed, clarifying reports of pronounced morphological plasticity for D. spathans. [ABSTRACT FROM AUTHOR]

Advances in hybridization practices in U.S. catfish aquaculture have led to increased production of channel (Ictalurus punctatus) × blue catfish (Ictalurus furcatus) hybrids to capitalize on their more favorable production characteristics. However, the effects of typical channel catfish pathogens on hybrids are not well understood, including the digenean Bolbophorus damnificus, which has caused significant losses in channel catfish production. Three experiments were conducted to assess the longevity and site specificity of 2 life stages of B. damnificus impacting catfish production. The first experiment investigated the cercarial longevity and infectivity of B. damnificus over time. Channel catfish were individually challenged with 100 cercariae/fish with cercariae aged in 12-hr time intervals over 5 days (n = 5 fish/time point), with metacercarial cysts excised and enumerated 14 days postchallenge. There was a decrease in cercaria viability and encysted metacercariae over the first 36 hr, with the 12-hr time point having both the greatest cercaria survival and the highest number of metacercariae in exposed fish. The second experiment investigated the longevity of metacercariae within both channel and hybrid catfish. Fish (n = 30) were exposed to 2 treatments (75 or 150 cercariae/fish), and 2 fish from each treatment were sampled every 3 mo for 13 mo. Live metacercariae, based on motility observed after excystment, were found in both species up to 13 mo postchallenge, indicating the metacercariae of B. damnificus can persist throughout an entire growing season in both channel and hybrid catfish. The third experiment investigated the site specificity of metacercariae within both channel and hybrid catfish. Fish (n = 60/species) were challenged with 300 cercariae/fish and 9 fish/species were sampled after 90 days. Metacercariae were excised and enumerated from the anterior midsection (head and body), posterior midsection (trunk/caudal peduncle), ventral (belly), and caudal fin (tail) sections of each fish. Overall, the trunk/caudal peduncle had a 2-fold increase in the number of metacercariae excised, and although not significantly higher, results indicate this region should be the focal point of pondside assessment for the presence of B. damnificus because of ease of detection of encysted metacercariae. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The bacterium Edwardsiella piscicida causes significant losses in global aquaculture, particularly channel (Ictalurus punctatus) × blue (I. furcatus) hybrid catfish cultured in the south‐eastern United States. Emergence of E. piscicida in hybrid catfish is worrisome given current industry trends towards increased hybrid production. The project objectives were to assess intraspecific genetic variability of E. piscicida isolates recovered from diseased channel and hybrid catfish in Mississippi; and determine virulence associations among genetic variants. Repetitive extragenic palindromic sequence‐based PCR (rep‐PCR) using ERIC I and II primers was used to screen 158 E. piscicida diagnostic case isolates. A subsample of 39 E. piscicida isolates, representing predominant rep‐PCR profiles, was further characterized using BOX and (GTG)5 rep‐PCR primers, virulence gene assessment and multilocus sequence analysis (MLSA) targeting housekeeping genes gyrb, pgi and phoU. The MLSA provided greater resolution than rep‐PCR, revealing 5 discrete phylogroups that correlated similarly with virulence gene profiles. Virulence assessments using E. piscicida representatives from each MLSA group resulted in 14‐day cumulative mortality ranging from 22% to 54% and 63 to 72% in channel and hybrid fingerlings, respectively. Across all phylogroups, mortality was higher in hybrid catfish (p <.05), supporting previous work indicating E. piscicida is an emerging threat to hybrid catfish aquaculture in the south‐eastern United States. [ABSTRACT FROM AUTHOR]

The trematode Bolbophorus damnificus (Digenea: Bolbophoridae) has caused significant economic losses since the late 1990s, with deleterious effects on production efficiency in farm‐raised catfish. Previous work has demonstrated that even mild outbreaks, which may go unnoticed by producers, can result in over 60% reduction in net economic returns. Although transmission rates in Channel Catfish Ictaluruspunctatus and hybrid catfish (Channel Catfish × Blue Catfish Ictalurus furcatus) are similar in controlled studies, anecdotal industry reports imply that the impacts of B. damnificus on hybrid catfish are less severe. In this study, mortality in juvenile Channel and hybrid catfish exposed to B. damnificus was evaluated in two discrete, replicated infectivity challenges. Mortality curves in Channel and hybrid catfish were consistent with trends previously established for B. damnificus in Channel Catfish, although in both challenges cumulative mortality was significantly lower in hybrids. All exposed fish presented clinical signs consistent with B. damnificus infection—namely lethargy, exophthalmia, distended abdomens, and metacercariae grossly visible below the skin. No mortality occurred and no parasites were observed in control fish. The biological and economic implications of these findings on catfish production are unknown but suggest that hybrid catfish are less susceptible to the deleterious effects and reduced productivity elicited by B. damnificus in Channel Catfish. [ABSTRACT FROM AUTHOR]

Blue catfish alloherpesvirus (BCAHV) is a novel virus isolated from the blue catfish (Ictalurus furcatus). To date, the ultrastructure, virulence and immunogenicity of BCAHV have not been reported. Given the importance of blue catfish in producing channel ♀ (I. punctatus) × ♂ blue (I. furcatus) catfish hybrids and the increasing demand for hybrid catfish in the US catfish industry, the susceptibility of blue, channel and hybrid catfish to BCAHV was assessed. Further, the cross‐protective potential of BCAHV against Ictalurid herpesvirus 1 (IcHV1) was investigated in channel and hybrid catfish that survive BCAHV exposure. Neutralization assays revealed BCAHV is refractive (neutralization index [NI] = 0) to anti‐IcHV1 monoclonal antibody Mab 95, compared to IcHV1 (NI = 1.8). Exposure of blue catfish fingerling to 1.3 × 105 TCID50/L BCAHV produced cumulative mortality of 51.67 ± 0.70% and pathologic changes similar to those of channel catfish virus disease. No mortality was observed in channel or hybrid catfish. Twenty‐eight days post‐challenge, surviving channel and hybrid catfish were exposed to 9.4 × 104 TCID50/L IcHV1 (LC50 dose), resulting in 100% relative per cent survival compared to naïve cohorts. These data provide baseline information for BCAHV and lay the groundwork for future studies. Data also identify BCAHV as a potential vaccine candidate against IcHV1. Based on host range and immunogenicity evaluations, in addition to genome sequence data from previous studies, BCAHV should be given consideration as a new species of Ictalurivirus. [ABSTRACT FROM AUTHOR]

Multiple‐batch production is the most widely practiced method of raising channel catfish. Producers are increasingly adopting intensified production practices in multiple‐batch systems by increasing stocking density and aeration rates as a means to improve cost efficiencies. Proven stocking recommendations are required for the efficient implementation of recent developments in multiple‐batch production. Twelve 0.4‐ha ponds were understocked with 17,484, 20,612, and 26,124 fingerlings/ha (mean weight = 40 g/fish) over equal weights of carryover fish (0.46 kg/fish @ 4,589 kg/ha). Fish were fed once daily to apparent satiation with a 28% protein floating feed and aerated with a single 7.4‐kW electric paddlewheel aerator. Density‐dependent significant differences were absent for gross, net, daily net yields, marketable yields (≥0.54 kg), growth (g/day), and survival. Sub‐marketable yield (<0.54 kg) and feeding rate increased significantly with increased understocking density. Economic analysis revealed increased breakeven prices and diminished net returns with increased stocking density when sub‐marketable fish were not considered as revenue. These differences in production costs and profits among the three treatments became minimal when sub‐marketable fish were included as revenue. All three density treatments attained positive annual net cash flows. This study validates channel catfish understocking densities of 17,000–26,000 fish/ha to improve cost efficiency in intensively aerated, multiple‐batch production systems. [ABSTRACT FROM AUTHOR]

The commercial channel catfish (Ictalurus punctatus) industry is adversely impacted by enteric septicemia of catfish (ESC), caused by the Gram‐negative enteric rod Edwardsiella ictaluri. In efforts to develop more effective management strategies, the use of a live‐attenuated E. ictaluri isolate as an oral vaccine was investigated. The utility and broad application of a vaccine is dependent on the protection offered against multiple field isolates. Immunization trials, followed by bacterial challenge with archived virulent E. ictaluri isolates from the catfish farming region of the southeastern United States, were conducted over a 3‐year period. These isolates were archived from 1993 to 2016 and included representatives from nonvaccinated and vaccinated populations of diseased channel catfish in Mississippi, an isolate from nonvaccinated hybrid catfish raised in Mississippi, and an isolate from nonvaccinated channel catfish from Alabama. Molecular characterization of the isolates revealed a high degree of genetic similarity evidenced by repetitive sequence‐mediated polymerase chain reaction (rep‐PCR) fingerprinting and virulence gene amplification, suggesting that the population of E. ictaluri within catfish aquaculture in Mississippi and Alabama has been genetically stable over time. Plasmid profiling revealed the existence of at least four distinct plasmids among field isolates. Nevertheless, the E. ictaluri vaccine protected fish against all isolates, irrespective of heterogeneous or homogeneous plasmid profiles. In addition, plasmid profiles were supported by antimicrobial sensitivity testing, indicating that the E. ictaluri vaccine strain does not carry natural or plasmid‐mediated multidrug resistance to the three antibiotics approved for use in U.S. food fish aquaculture. Challenge data from this study argue against the need for multivalent E. ictaluri vaccines to account for presumed antigenic or genetic variation among wild‐type E. ictaluri isolates as the vaccine was effective against all archived isolates. [ABSTRACT FROM AUTHOR]

Azomite is a hydrated sodium calcium alumina silicate that is mined from a volcanic deposit in Utah. The product contains many micronutrients that may be beneficial in preparing catfish nursery ponds for stocking. In northwest Mississippi, a 5‐week study was conducted to compare water quality, phytoplankton populations, and zooplankton populations in Channel Catfish Ictalurus punctatus nursery ponds treated with Azomite at 0, 50, or 100 kg/ha. The study was conducted in 0.04‐ha ponds during April, when fry ponds are prepared for stocking. Azomite application did not affect ammonia concentrations. Over time, nitrite concentrations increased more in control ponds compared to Azomite‐treated ponds; however, nitrite concentrations were low in all ponds. Chlorophyll‐a concentrations were also unaffected by Azomite application. The pH did significantly increase with increasing Azomite application rate. Azomite application had no effects on phytoplankton or zooplankton populations. Overall, there were no beneficial effects of adding Azomite to Channel Catfish nursery ponds in northwest Mississippi. [ABSTRACT FROM AUTHOR]

A pond study examined the effects of long‐term restricted feeding followed by full feeding on production and processing characteristics, fillet composition, and economics of market‐size hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus. Market‐size fish averaging 674 g were stocked into 24 ponds (0.04 ha) at 17,300 fish/ha. Fish were either fed once or twice weekly for 4 months or once or twice weekly for 4 months followed by 15‐ or 30‐day daily full feeding. All fish were fed to apparent satiation on days fed. Fish fed once weekly for 4 months gained about 30% weight and those fed twice weekly gained 70% weight. Feeding once or twice weekly for 4 months followed by 15‐ or 30‐day full feeding did not significantly affect carcass yield compared with the initial sample (overwintered fish). At least 30 days of full feeding were needed to restore fillet yield to normal levels. Based on economic analysis and processing yield, it is suggested fish fed once weekly should be given full feed for 15 days or so to improve fillet yield before harvest. Fish fed twice weekly can be harvested with or without 15 days full feeding. [ABSTRACT FROM AUTHOR]

Edwardsiella piscicida has emerged as an important pathogen of channel × blue catfish hybrids cultured in the southeastern United States. With increasing popularity of hybrid catfish and growing concern over E. piscicida, the crossprotective potential of a live‐attenuated E.ictaluri vaccine was evaluated. An immunization bath of E. piscicida (3 × 107 CFU/ml) protected channel catfish against immersion challenge of wild‐type E. ictaluri (1 × 107 CFU/ml) across multiple temperatures and feeding regimens (relative percent survival [RPS]: 89–100%). Channel catfish immunized orally with a live‐attenuated E. ictaluri vaccine/feed admix (3 × 107 CFU/g of feed) were protected against intracoelomic injections of both high (HD) (7.4x105 CFU/fish; RPS = 85%) and low doses (LD) (1.5 × 105 CFU/fish; RPS = 88%) of E. piscicida. Because of limited feed consumption during vaccination, oral immunization of hybrids was followed by a 30‐min immersion bath with cultured vaccine (5 × 106 CFU/ml). Combinatory oral/bath vaccination was ineffective against HD E. piscicida but was protective against LD E. piscicida (48% RPS) and E. ictaluri (96% RPS). Finally, naïve catfish that survived LD E. piscicida injections were protected against E. ictaluri immersion challenge (2 × 107 CFU/ml; RPS: Hybrids 55%; Channels 75%). Results suggest a live‐attenuated E. ictaluri vaccine can also protect channel and hybrid catfish against E. piscicida. [ABSTRACT FROM AUTHOR]

Proliferative gill disease (PGD) caused by the myxozoan Henneguya ictaluri is one of the most damaging diseases affecting U.S. catfish aquaculture. In channel and hybrid catfish, continuous exposure to the actinospore stage of the parasite elicits a destructive branchitis, impairing osmoregulatory and respiratory function. Mortality can reach 100% in severe outbreaks. Despite similarities during acute stages of infection, research indicates arrested development in hybrid catfish, evinced by reduced H. ictaluri sporogenesis and comparably less parasite DNA in hybrid tissues across the developmental timeline. To assess these findings at the pond level, 18, 0.4‐ha ponds were stocked (3,000 fish/pond) with channel (n = 9) or hybrid (n = 9) catfish fingerlings and maintained as monoculture systems for three production cycles, with clean harvests and restocking as warranted. Water was collected monthly for quantitative polymerase chain reaction (qPCR) estimations of H. ictaluri DNA, and sentinel fish were utilized to estimate PGD severity. By the second year, H. ictaluri DNA in hybrid systems was significantly reduced, and PGD lesions in sentinel fish were negligible. Assessment of parasite loads in fish harvested at the termination of the study revealed H. ictaluri DNA in channel catfish to be an order of magnitude higher than hybrid catfish. These results support previous work suggesting that the production of hybrid catfish may reduce PGD incidence in U.S. catfish aquaculture. [ABSTRACT FROM AUTHOR]

Since its recognition in the early 1980s, enteric septicemia of catfish (ESC), caused by the gram‐negative enteric Edwardsiella ictaluri, is one of the most significant pathogens affecting catfish aquaculture. In efforts to improve disease management in U.S. catfish aquaculture, a live‐attenuated ESC vaccine and method of in‐pond oral vaccine delivery was developed. This work evaluated the efficacy of the oral delivery platform using a live‐attenuated E. ictaluri vaccine under simulated commercial conditions. Channel catfish fingerlings were orally vaccinated approximately 40–50 days poststocking by mixing the attenuated vaccine with feed using a patent‐pending mechanized delivery system. Across three discrete years under varying evaluation methods, vaccination resulted in significant improvements in survival, feed conversion ratio, feed fed, and total yield. An economic analysis of experimental data suggests a significant positive net economic benefit from vaccination. After accounting for a projected cost of vaccination, the realized improvements in survival and yield resulted in an estimated benefit exceeding $3,500/ha ($1,400/acre) on fingerling operations. These results suggest vaccinating channel catfish fingerlings against ESC is an effective strategy to mitigate ESC‐related losses and can significantly improve production efficiency and profitability on catfish operations. [ABSTRACT FROM AUTHOR]

This study evaluated dietary protein concentrations and replacing fish meal with porcine meat and bone meal (PMB) for pond‐raised fingerling channel catfish, Ictalurus punctatus. Three diets were formulated to have 28, 32, or 35% protein using soybean meal, cottonseed meal, and fish meal as the main protein sources, respectively. A fourth diet contained 32% protein with fish meal being replaced with PMB. Analyzed protein concentrations were 29.7, 31.9, 34.4, and 31.1% on 90% dry matter basis, respectively. Small fingerlings (average initial weight: 2.0 g/fish) were stocked in 20 earthen ponds (0.04 ha) at 172,970 fish/ha and were fed once daily to apparent satiation for 98 days. There were no significant differences in total diet fed, gross yield, final weight, feed conversion ratio, survival, or condition factor among diets. There were also no significant differences in ammonia‐N, nitrite‐N, chlorophyll a, or desirable zooplankton concentrations in pond water of fish receiving different diets. Results show that a diet containing about 30% protein can support optimum growth of pond‐raised channel catfish fingerlings of 2 g and larger in fertilized ponds fed once daily to apparent satiation. PMB can completely replace fish meal in a 32% protein diet. Economic analysis suggests considerable cost savings by replacing fish meal with PMB and reducing protein concentrations in channel catfish fingerling diets. [ABSTRACT FROM AUTHOR]

A study was conducted to investigate the effects of dietary azomite (0.25% or 0.50%) or sea salt (0.5% or 1.0%) on the growth performance and disease resistance of Channel Catfish Ictalurus punctatus. Channel Catfish fingerlings were fed diets that were supplemented with graded levels of azomite or sea salt for 9 weeks in trial 1 and for 5 weeks in trial 2. The growth parameters (weight gain and feed conversion ratio) and survival rate were determined at the end of the feeding trials. The resistance of the fish against Edwardsiella ictaluri infection was also evaluated in those that were fed diets containing 0.5% azomite or 1.0% sea salt in trial 2. The results showed that there was no significant difference in the growth performance of the fish that were fed azomite‐ or sea salt‐supplemented diets compared with control animals (P > 0.05). The mortality rate of Channel Catfish 28 d after the E. ictaluri challenge did not differ significantly between groups receiving different dietary treatments. The results indicate that dietary supplementation with azomite or sea salt at the tested levels had no significant effect on either growth performance or disease resistance against E. ictaluri in Channel Catfish fingerlings. [ABSTRACT FROM AUTHOR]

A pond production trial was conducted to evaluate the economics of raising Channel Catfish Ictalurus punctatus in intensively aerated ponds operated under the single‐batch cropping system. Channel Catfish fingerlings averaging 0.09 lb were stocked at 6,000, 8,000, 10,000, and 12,000 fish/acre with six replicate ponds (1 acre) per treatment. A treatment of hybrid catfish (♀ Channel Catfish × ♂ Blue Catfish I. furcatus) fingerlings stocked into five replicate ponds at 12,000 fish/acre was concurrently evaluated to compare the economic performance of hybrids and that of Channel Catfish. All ponds were provided with a fixed‐paddlewheel aerator (10 hp/acre) and were fed once daily to apparent satiation for 206 d. For Channel Catfish, the gross yield ranged from 6,562 to 9,039 lb/acre, showing nominally linear trends of increasing yield with stocking density. However, the same trend was not seen in the relationship between costs and stocking density: the highest breakeven price (US$1.07/lb) was associated with the lowest density treatment (6,000 fish/acre), and the least cost ($0.96/lb) was associated with the intermediate density of 8,000 fish/acre. Average annual net cash flows from all Channel Catfish treatments were insufficient to make the investment in intensive aeration profitable in the long run (10 years). The hybrid catfish treatment (12,000 fish/acre) outperformed all Channel Catfish treatments in terms of yield (17,542 lb/acre), which offset some of the fixed costs associated with intensively aerated ponds and resulted in a lower cost of production ($0.85/lb) and better long‐term returns (17%). This study indicated that Channel Catfish do not perform well—either biologically or economically—at densities greater than 8,000 fish/acre in single‐batch, intensively aerated ponds. The study reflects current industry trends, where integrated farms (farms with their own processing plants) with yield‐maximizing business objectives prefer raising hybrid catfish in single‐batch systems, while nonintegrated farms prefer raising Channel Catfish in multiple‐batch systems. [ABSTRACT FROM AUTHOR]

Enteric Septicemia of Catfish (ESC) is a ruinous bacterial disease affecting the U.S. catfish industry. Previous attempts to develop ESC vaccines have failed to achieve industry acceptance, largely attributed to difficulties in delivering the vaccine to immunocompetent fish. Recently, a live attenuated ESC vaccine has been developed, coupled with a mechanized platform designed to accurately deliver measured doses of vaccine with feed. This delivery scheme for vaccine-feed admixture has shown tremendous promise under controlled research settings. This study evaluated the economic effects of on-going commercial-vaccination trials on catfish fingerling operations in Mississippi. Commercial-vaccination trials for both channel and hybrid catfish demonstrated significant improvement in survival, growth, feed consumption, feed conversion and gross yield. At a realistic vaccination cost of $750/ha, the net economic benefits to channel and hybrid catfish fingerling-production phases were $3199 and $6145/ha, respectively. Whole-farm models showed additional profit ranging from $71,758 to $133,887/400-ha on farms that integrate fingerling production to their production strategies due to appropriation of more of the otherwise incumbent fingerling production acreage into foodfish production. Commercial adoption of the oral-vaccination platform would greatly enhance profitability while laying the foundation for development and delivery of polyvalent vaccines against other catfish diseases. [ABSTRACT FROM AUTHOR]

Henneguya ictaluri is the etiologic agent of proliferative gill disease (PGD) in farm‐raised Channel Catfish Ictalurus punctatus and hybrid catfish in the southeastern United States, and significant annual losses are attributed to this disease. Research suggests that H. ictaluri infection dynamics in Blue Catfish I. furcatus and hybrid catfish (Channel Catfish × Blue Catfish) differ from those in Channel Catfish. Two separate infectivity trials were conducted to investigate H. ictaluri development in Channel Catfish, Blue Catfish, and their hybrids. On two separate occasions with two different year‐classes, fish were exposed to pond water containing H. ictaluri actinospores and sampled weekly for 12 weeks (trial 1) or 14 weeks (trial 2). In trial 1, the presence of H. ictaluri was evaluated histologically and by quantitative PCR of fish tissues, including gills, blood, anterior kidney, brain, heart, liver, posterior kidney, spleen, and stomach. Henneguya ictaluri DNA was detected in significantly higher concentrations throughout multiple organ systems in the Channel Catfish compared to the hybrid catfish and Blue Catfish, with the gills having higher quantities. Myxospores were observed in Channel Catfish gill tissue at 8 weeks postexposure. No myxospores were observed in Blue Catfish or hybrid catfish. The second trial focused on gills only and yielded similar results, with Channel Catfish having significantly greater H. ictaluri DNA quantities than hybrids or Blue Catfish across all time points. Myxospores were observed in Channel Catfish beginning at 6 weeks postexposure and were found in 36% (58/162) of Channel Catfish sampled for molecular and histological analysis during weeks 6–14. Myxospores in hybrid catfish were sparse, with single pseudocysts observed in two hybrid catfish (1.2%) at 14 weeks postexposure. These results imply arrested development of H. ictaluri in hybrid catfish. As such, culture of hybrid catfish may be an effective management strategy to minimize the burden of PGD. [ABSTRACT FROM AUTHOR]

Channel Catfish Ictalurus punctatus fry farmers are interested in treating ponds to prevent trematode infections. Control strategies rely on chemical treatments to reduce snail populations and break the trematode life cycle. On a commercial catfish fingerling operation, we evaluated water quality, zooplankton, phytoplankton, and fish production in catfish nursery ponds treated with 1.02‐mg/L Cu 21 d before fry stocking. These variables were also evaluated in controlled experimental ponds treated with 1.27‐mg/L Cu 21, 14, 7, or 1 d before stocking. In the on‐farm trial, copper sulfate treatment initially reduced phytoplankton and zooplankton populations, but communities recovered to adequate numbers at stocking. However, fry survival and revenue from ponds treated with copper sulfate were reduced relative to those from untreated ponds (survival: 17.7% versus 63.0%; revenue: $10,250 versus $27,467 per hectare). In the experimental pond study, free copper concentrations at fry stocking were 0.52 mg/L for the 1‐d interval between treatment and stocking, 0.10 mg/L for the 7‐d interval, 0.04 mg/L for the 14‐d interval, and 0.02 mg/L for the 21‐d interval. Similar results were observed in the experimental study, with lower survival in all treatment groups compared to controls; the lowest survival was observed in fry stocked 1 d after copper sulfate treatment. The cause of lower survival in copper‐treated ponds is unclear. With the exception of ponds stocked 1 d after copper treatment, lower survival was likely related to effects on environmental quality rather than direct copper toxicity. Regardless of the cause, until further work evaluates copper's environmental effects, copper sulfate should not be used in Channel Catfish nursery ponds during early developmental fry stages. [ABSTRACT FROM AUTHOR]

There is a trend toward the increased incidence and prevalence of Edwardsiella piscicida septicemia in US catfish aquaculture, particularly in channel ♀, Ictalurus punctatus, × blue ♂, I. furcatus, hybrid catfish. From 2013 to 2017, a total of 3242 disease case submissions were made to the Aquatic Research and Diagnostic Laboratory (ARDL) at the Thad Cochran National Warmwater Aquaculture Center in Stoneville, MS. Of these, 1400 (43.2%) were hybrids. E. piscicida was suspected in 138 (4.3%) of cases, the majority of which (89.1%) were from hybrid catfish. A molecular survey of these isolates confirmed the majority (92.0%) to be E. piscicida. Furthermore, cases of E. piscicida from hybrids submitted to the ARDL and the Aquatic Diagnostic Laboratory of the Mississippi State University College of Veterinary Medicine in Starkville, MS, were documented for gross lesions and histological analysis. Grossly, E. piscicida presents with small dermal ulcerations, a raised fluid‐filled cranial midline lesion that is frequently ulcerated, hemorrhage in the gills, exophthalmia, and abdominal distension. Internally, lesions include splenomegaly, straw‐colored ascites, renomegaly, and occasionally hemorrhagic intestines. Histopathological examination is in agreement with gross observations, and infected fish repeatedly demonstrate a mononuclear meningoencephalitis, hemorrhagic branchitis, splenitis, ulcerative dermatitis, granulomatous interstitial nephritis, and hepatitis coupled with a hemorrhagic enteritis. [ABSTRACT FROM AUTHOR]

Two experiments were conducted in consecutive years to evaluate the responses of hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, to "superdosing" of 6‐phytase added to existing commercial catfish feeds. In each experiment, two diets with or without a phytase superdose (2500 and 5000 phytase units/kg, respectively) were compared. In Experiment 1, fingerlings (mean weight: 59 g/fish) were stocked in 17 0.4‐ha earthen ponds at 17,290 fish/ha and were fed once daily to apparent satiation for 198 d. In Experiment 2, fingerlings (mean weight: 47 g/fish) were stocked in 10 0.4‐ha ponds at 24,710 fish/ha and were fed for 128 d. In both experiments, there were no significant differences in total feed fed, gross yield, final fish weight, survival, or Blood packed cell volume between fish fed diets with or without phytase. The diets also had no significant effects on pond water column total phosphorus or chlorophyll a concentrations, but soluble reactive phosphorus concentrations were significantly higher in ponds receiving the phytase diet in Experiment 2. Phytase superdosing of nutritionally complete feeds does not appear to have additional benefits beyond the standard phytase dose on production characteristics or packed cell volume of pond‐raised hybrid catfish and had no beneficial effects on water quality. [ABSTRACT FROM AUTHOR]

Abstract: This study examined four experimental diets with different protein concentrations and sources for pond‐raised fingerling hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus. A 35% protein diet with fishmeal was used as the control diet. Test diets were 32 and 28% all‐plant‐protein diets and a 28% protein diet with porcine meat, bone, and blood meal. Small fingerlings with a mean initial weight of 2.9 g/fish were stocked into 20 earthen ponds (0.04 ha) at a density of 172,970 fish/ha. They were fed once daily to apparent satiation for 107 d. No significant differences were observed for total diet fed, gross yield, final weight, survival, or condition factor among dietary treatments. However, fish fed the 28 and 32% all‐plant‐protein diets had a significantly higher feed conversion ratio than fish fed the 35% protein diet with fishmeal. There were no significant differences in chlorophyll a and nitrite concentrations in the pond water, but ponds receiving the 35% protein diet had significantly higher ammonia than those receiving 28% protein diets. Economic analysis suggested potential cost savings by using low‐protein and all‐plant‐protein diets for hybrid catfish fingerling production. [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]

Abstract: Bolbophorus damnificus (Digenea: Bolbophoridae) causes significant economic losses in catfish aquaculture in the southeastern USA. To determine mortality trends associated with B. damnificus exposure, three separate disease challenges were conducted. The first challenge exposed channel catfish, Ictalurus punctatus, fingerlings (7–13 cm) to approximately 285 B. damnificus cercariae/L, while the second exposed fish to approximately 215 cercaria/L. Fish were monitored for morbidity and mortality for 28 d. In both studies, mortality first occurred 8 d postchallenge (PC) and peaked at 9 and 10 d PC, respectively. Mortality had subsided by 14 d PC, with only sporadic mortality occurring >15 d PC. Dead and moribund fish presented with lesions consistent with B. damnificus infection. A third challenge was performed to record histological changes associated with parasite development from initial exposure up to the cessation of mortality. Catfish (2–5 cm) were exposed as described above to a range covering 0, 35, 70, 100, 150, 175, and 215 cercariae/L. Each day, two fish were sampled from each treatment. Mortality trends were consistent with previous challenges. The mortality window coincided with parasite encapsulation, neovascularization, and development of the host‐derived cyst, suggesting that morbidity and mortality are linked to host pathophysiological changes in response to metacercariae encapsulation. [ABSTRACT FROM AUTHOR]

Abstract: Members of the genus Edwardsiella are important pathogens of cultured and wild fish globally. Recent investigations into the phenotypic and genotypic variation of Edwardsiella tarda have led to the segregation of E. tarda into three distinct taxa: E. tarda, Edwardsiella piscicida, and Edwardsiella anguillarum. In catfish aquaculture in the southeastern USA, E. piscicida has been more commonly associated with disease than E. tarda or E. anguillarum, and recent research has demonstrated E. piscicida to be more pathogenic in channel catfish than E. tarda or E. anguillarum. Anecdotal reports from industry suggest an increased prevalence of E. piscicida associated with the culture of channel (♀) × blue (♂) hybrid catfish. This work investigated the comparative susceptibility of channel catfish, blue catfish, and their hybrid cross to molecularly confirmed isolates of E. tarda, E. piscicida, and E. anguillarum. There was significantly higher mortality in hybrid catfish compared to channel catfish following intracoelomic injection of E. piscicida. To our knowledge, E. piscicida is the first bacterial pathogen to demonstrate increased pathogenicity in hybrid catfish compared to channel catfish. [ABSTRACT FROM AUTHOR]

Trematodes of the subclass Digenea are a major impediment to catfish aquaculture in the southeastern United States. Catfish production ponds are ideal feeding grounds for piscivorous birds, and given the variety of aquatic snails that inhabit these ponds, they offer a prime environment for the propagation of digenetic life cycles. In July 2014, snails morphologically consistent with Biomphalaria havanensis L. Pfeiffer, 1839, were collected from 2 different catfish production ponds in the catfish farming region of eastern Mississippi. These snails were refractory to Schistosoma mansoni Sambon, 1907, infection, and phylogenetic analyses based on internal transcribed spacer (ITS)1 and ITS2 fragments placed the snails within the B. havanensis/ obstructa complex. Some (1.5%) of these snails shed cercariae morphologically and molecularly consistent with Drepanocephalus auritus Kudlai, Kostadinova, Pulis, and Tkach, 2015 (formerly reported as Drepanocephalus spathans Dietz, 1909) , an echinostomatid parasite of the double-crested cormorant Phalacrocorax auritus Lesson, 1831, and channel catfish Ictalurus punctatus Rafinesque, 1818. Juvenile channel catfish were challenged individually with ∼275 cercariae of D. auritus per fish, resulting in limited mortality (2 out of 10 fish). Surviving fish were euthanatized 7 d postchallenge, and the presence of metacercariae was confirmed histologically. Parasite-associated pathology was consistent with previous studies. Subsequent molecular analysis of 5 different gene targets confirmed morphological identifications. Previous research has suggested the existence of discrete North American and South American haplotypes of D. auritus. Mitochondrial cytochrome c oxidase subunit 1 and nicotinamide adenine dinucleotide dehydrogenase subunit 1 sequences demonstrated that both haplotypes were released by snails in this study, suggesting a broader distribution of these genetic variants than previously thought. Along with Planorbella trivolvis Say, 1817, this work identifies a second snail species common to catfish aquaculture ponds that releases D. auritus infective to juvenile channel catfish and is the first report of B. havanensis as an intermediate host for D. auritus in North America. [ABSTRACT FROM AUTHOR]

A pond study was initiated to evaluate effects of no feeding, maintenance feeding, and refeeding on production and processing characteristics of market-size hybrid catfish (female Channel CatfishIctalurus punctatus× male Blue CatfishI. furcatus). Fish with an average weight of 644 g were stocked into 20 earthen ponds (0.04 ha) at 14,826 fish/ha at the end of May. They were either not fed (N2), fed once weekly (W2) to satiation for 2 months to simulate a long-term harvest delay, or fed daily (D2) to satiation. After 2 months fish in half the ponds in each of the two feed-restricted treatments were harvested, and all fish in the remaining ponds were fed daily for an additional month. After 2 months N2fish experienced a 14.3% weight loss compared with a weight gain of 6.7% for FW2fish. After 2 months both N2and W2fish had reduced visceral fat and fillet yield compared with fish fed daily, but there were no significant differences in visceral fat percentage and fillet yield between N2and W2fish. At the end of 3 months, there were no significant differences in weight gain, net yield, fillet yield, or visceral fat whether fish were previously not fed or fed once weekly for the first 2 months, but fish fed daily throughout had significantly higher visceral fat and marginally higher fillet yield. Feeding once weekly for 2 months followed by 1-month full feeding resulted in significantly higher feed conversion ratio than fish fed daily for 3 months. Results demonstrate feeding once weekly can generally maintain body weight of hybrid catfish. No feeding or feeding once weekly for 2 months does not affect survival but significantly reduces fillet yield. One month of full feeding following no feeding or maintenance feeding improves fillet yield relative to values before refeeding. Received July 16, 2015; accepted January 21, 2016 Published online June 15, 2016 [ABSTRACT FROM PUBLISHER]

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]

Proliferative gill disease ( PGD) in catfish is caused by the myxozoan Henneguya ictaluri. The complex life cycle requires Dero digitata as the oligochaete host. Efforts to control PGD by eradicating D. digitata have been unsuccessful. Smallmouth buffalo, Ictiobus bubalus, ( SMB) are opportunistic bottom feeders and a putative option for controlling D. digitata. In 2011, 15 ponds (0.4 ha) were stocked with 5000 channel catfish, Ictalurus punctatus; 7 of these 15 ponds were also stocked with 300 SMB fingerlings. There were no differences in benthic invertebrate numbers or water quality variables between ponds with or without SMB. At harvest, there were no differences in percent survival, total weight, or catfish feed conversion ratio. In the second year, 18 ponds (0.4 ha) were stocked with 6000 channel catfish. Half the ponds were also stocked with 300 SMB. Sentinel fish were used to estimate disease severity, and pond water was collected for molecular estimation of H. ictaluri actinospore concentrations. Similar to the first year, there were no differences between treatments in any variable tested, including PGD severity in sentinel fish and parasite concentrations in pond water. Under these study conditions, presence of SMB did not have a measureable effect on PGD incidence, parasite density, or overall catfish production. [ABSTRACT FROM AUTHOR]

Anemia is a widespread hematological disorder in vertebrates. In channel catfish ( Ictalurus punctatus), anemia is a persistent problem in culture environments, however, its causes and physiological impacts are not well understood. To better understand the symptoms and characterize associated biomarkers of anemia, 1-D H and 2-D H J-resolved NMR were used to analyze metabolite changes in healthy and anemic channel catfish kidney and liver tissue. Additionally, standard physiological analytical techniques were used to analyze blood plasma. NMR analyses revealed energy sources such as glucose were depleted and many metabolites associated with anaerobic metabolism or alternative energy pathways such as lactate, creatine, alanine, acetate and myo-inositol had changed. Energy demanding processes were reduced, such as muscle function, as indicated by reductions in taurine and inosine, and protein synthesis. Stress and oxidative stress related metabolites changed, with increases in valine, leucine and isoleucine and decreases in glutathione. Inhibitory neurotransmitters such as 4-aminobutyric acid (GABA) increased, and excitatory neurotransmitters such as glutamine and glutamate generally decreased, although there were tissue-specific differences. Immune function also decreased in anemic fish. Blood analyses revealed decreased respiratory gas transport capabilities through reductions in erythrocytes and hemoglobin-markers. Taken together, these tissues and analytical techniques produced complementary results, and metabolite expression in anemic channel catfish was similar to that observed in other vertebrates exposed to anoxia, severe hypoxia or experiencing oxidative stress from deficiencies in iron homeostasis. [ABSTRACT FROM AUTHOR]

The combination of open facilities, moisture, and warm weather during channel catfish, Ictalurus punctatus, spawning season causes mosquito-infestation problems. A common solution to mosquito problems in hatcheries is to use mosquito repellents applied to exposed skin and clothing. DEET ( N, N-diethyl- m-toluamide) is the active ingredient in most personal insect repellents. We determined the 24-h acute toxicity of DEET to channel catfish fry. The toxicity test consisted of 10 sac fry in three replications of six concentrations (range: 157-478 μL/L) and a control. In addition to toxicity testing, a trial was conducted to determine the amount of active ingredient dispensed from two different applicators: a pump sprayer and an aerosol can. The 24-h lethal concentration ( LC10) was 274 ppm, and the 24-h LC50 was 345 ppm. The concentration required to kill 50% of the organisms was above the 100 ppm threshold to be considered practically non-toxic. The pump sprayer (98.11% active ingredient) dispensed 113.3 ± 0.57 mg (mean ± SEM) active ingredient per pump. The aerosol can (30% active ingredient) dispensed 526.8 ± 6.71 mg (mean ± standard error mean [ SEM]) active ingredient per second. In hatcheries where air movement by fans is not sufficient to control mosquitoes, using insect repellent products containing DEET should be safe. [ABSTRACT FROM AUTHOR]

There are more than 200 species of Henneguya described from fish. Of these, only three life cycles have been determined, identifying the actinospore and myxospore stages from their respective hosts. Two of these life cycles involve the channel catfish ( Ictalurus punctatus) and the freshwater oligochaete Dero digitata. Herein, we molecularly confirm the life cycle of a previously undescribed Henneguya sp. by matching 18S ribosomal RNA (rRNA) gene sequence of the myxospore stage from channel catfish with the previously described actinospore stage ( Aurantiactinomyxon mississippiensis) from D. digitata. Gill tissue from naturally infected channel catfish contained pseudocysts restricted to the apical end of the primary lamellae. Myxospores were morphologically consistent with Henneguya spp. from ictalurid fishes in North America. The spores measured 48.8 ± 4.8 μm (range = 40.7-61.6 μm) in total spore length. The lanceolate spore body was 17.1 ± 1.0 μm (14.4-19.3 μm) in length and 5.0 ± 0.3 μm (4.5-5.5 μm) in width. The two polar capsules were 6.2 ± 0.4 μm (5.8-7.0 μm) long and 5.0 ± 0.3 μm (4.5-5.5 μm) wide. The polar capsule contained eight to nine coils in the polar filament. The two caudal processes were of equal length, measuring 31.0 ± 4.1 μm (22.9-40.6 μm). The 1980-bp 18S rRNA gene sequence obtained from two excised cysts shared 99.4 % similarity (100 % coverage) to the published sequence of A. mississippiensis, an actinospore previously described from D. digitata. The sequence similarity between the myxospore from channel catfish and actinospore from D. digitata suggests that they are conspecific, representing alternate life stages of Henneguya mississippiensis n. sp. [ABSTRACT FROM AUTHOR]

The actinospore diversity of infected Dero digitata was surveyed (May 2011) from a channel catfish ( Ictalurus punctatus) production pond in the Mississippi Delta region for the elucidation of unknown myxozoan life cycles. At present, only 2 myxozoan life cycles have been molecularly confirmed in channel catfish, linking the actinospore stage from an aquatic oligochaete ( D. digitata) and the myxospore stage from the catfish. In this study D. digitata (n = 2,592) were isolated from oligochaetes collected from the bottom sediment of a channel catfish production pond. After 1 wk of daily observation, a total of 6 genetically different actinospore types were observed. The collective groups were classified as 2 aurantiactinomyxons, 2 helioactinomyxons, 1 raabeia, and 1 triactinomyxon. Overall prevalence of myxozoan infections in the isolated oligochaetes was 4.4%. Actinospores were photographed and measured for morphological characterization. Four previously undescribed actinospore types were identified and characterized molecularly and morphologically. Phylogenetic analysis revealed the raabeia and one of the helioactinomyxon (type 1) actinospores were closely related to the group of myxozoans known to parasitize ictalurids in North America. To date, no myxospores have been linked to the newly sequenced actinospores reported in this survey. The morphological and molecular data generated from this study will assist in the identification of myxospore counterparts for these actinospore stages and aid in the elucidation of unknown myxozoan life cycles in closed production systems. [ABSTRACT FROM AUTHOR]

Channel catfish were fed practical corn-soybean meal diets for 10 weeks that contained various weighed amounts of ground, dried field corn contaminated with 20 mg deoxynivalenol ( DON) kg−1. Weighed amounts of DON corn were blended with weighed amounts of ground, clean corn that contained no DON (0 mg kg−1) to yield five diets that had 0, 2.5, 5.0, 7.5 and 10.0 mg DON kg−1 of diet. Results show that catfish fed diets that contained DON for 7 weeks did not experience lower weight gains or poorer feed conversion ratios that were significantly ( P > 0.05) different from control-fed fish. Mortality of catfish during the 21-day post-challenge period indicate that catfish fed diets containing DON-contaminated corn that provided at least 5.0 mg DON kg−1 of diet had significantly ( P < 0.05) lower mortality than catfish fed the control diet or the diet that provided 2.5 mg DON kg−1 of diet. The presence of DON-contaminated corn in the experimental diets did not significantly ( P > 0.05) alter fish body weight gains and appeared to provide a protective effect for channel catfish challenged with the pathogenic bacterium Edwardsiella ictaluri. [ABSTRACT FROM AUTHOR]

Bolbophorus damnificus was recognized as a threat to channel catfish, Ictalurus punctatus, production in Louisiana and Mississippi in 1997 and 1999, respectively. Severe to moderate outbreaks (≥34% prevalence) are correlated to heavy losses, but impact of mild outbreaks with low prevalence (<33%) was unknown. Laboratory and field studies were conducted to evaluate sublethal acute (early stage) and chronic (late stage) trematode infection impacts on catfish production. Fish raised in ponds seeded with ram's horn snails from ponds harboring active B. damnificus outbreaks resulted in infection prevalence ranging from 1.6 to 20.4%. Compared to fish raised in ponds not seeded with infected snails (0% prevalence), fish biomass, number harvested, and total feed fed were significantly lower. These data agree with previous studies where mild infections reduced feed consumption, fish production, and economic returns. Infected fish were collected from ponds and used in a laboratory growth study. Once removed from the infection source, weight gain, growth rate, feed consumption, and feed efficiency were equal to or greater than trematode-free fish. This suggests that although early B. damnificus infection (premetacercarial development) can severely impact production, infection has little impact on performance once metacercarial cysts are fully developed, and the infection source is removed. [ABSTRACT FROM AUTHOR]

Mosquitofish, Gambusia sp., have been spread throughout the world to biologically control mosquitoes. However, the fish has gained a reputation as an invasive species and has been implicated in displacing native aquatic species. Gambusia affinis are native to the southeastern United States and commonly occur in commercial channel catfish, Ictalurus punctatus, production ponds. We investigated effects of mosquitofish presence on zooplankton populations, water quality, disease occurrence, and fish production in experimental ponds. There were no differences between ponds with or without mosquitofish in numbers of calanoid copepods, cyclopoid copepods, total copepods, Bosmina sp., Ceriodaphnia sp., Moina sp., Daphnia sp., or total cladocerans. There were also no differences in copepod and cladoceran sizes. Copepod nauplii were more numerous during the summer months in ponds with mosquitofish. There were no differences in water quality variables (soluble reactive phosphorus, nitrate, nitrite, ammonia, total nitrogen, total phosphorus, pH) or phytoplankton density between ponds stocked with and without mosquitofish. Catfish production and disease occurrence were also similar between ponds with and without mosquitofish. Although mosquitofish may cause problems when stocked outside their native range, there does not appear to be any adverse effects of mosquitofish presence in catfish production ponds. [ABSTRACT FROM AUTHOR]

The article discusses a study which describes clinical signs and gross and histopathological lesions from 2 cases of visceral toxicosis of catfish (VTC) confirmed through catfish bioassay. Market-size channel catfish from 2 different farms showing abnormal swimming behavior and significant mortalities were submitted for study. It indicates that the histopathologic lesions in VTC-affected fish are nonspecific and cannot form the basis of a definitive diagnosis of this disease syndrome.

The article reports on the results of a study on the development of a duplex quantitative real-time polymerase chain reaction (qPCR) assay for differentiating between Bolbophorus damnificus and Bolbophoris type II series cercariae. According to the authors, both trematode species abound in the commercial catfish industry. The study found that the identification of cercaria through duplex real-time qPCR assay was consistent with previous end-point protocols.

This study was conducted to gain a better understanding of the effect of exposure to the myxozoan Henneguya ictaluri (the agent of proliferative gill disease [PGD]) on host physiology by measuring the variation in selected blood characteristics in three differently affected host taxa (channel catfish Ictalurus punctatus, blue catfish I. furcatas, and blue catfish x channel catfish hybrid fingerlings). Forty-five fish of each host taxon were exposed to PGD, mad 10 fish of each host taxon were sampled at 24, 96, and 168 h. Fish were weighed, blood was collected and analyzed for a suite of physiological variables, and wet mount preparations of gill clips were examined grossly for the presence of cartilage breaks. The results of this study are consistent with the current knowledge regarding H. ictaluri infections in blue catfish, channel catfish, and blue catfish x channel catfish hybrids. Chondrocytic lysis was observed in channel catfish and hybrid catfish at 96 and 168 h but was not observed in blue catfish. There was an observed reduction in oxygen partial pressure (pO2) and an increase in carbon dioxide partial pressure (pCO2) at 96 h in the blood of channel catfish and hybrid catfish, but these changes were not exhibited by blue catfish. For all species, pH decreased as lactate concentrations increased. The lack of physiological changes and the absence of H. ictaluri sporozoites and DNA in gill tissue lead us to speculate that H. ictaluri is unable to estabfish infection in blue catfish. Current research investigating the mechanisms of infection and portals of parasite entry into blue catfish, channel catfish, and blue catfish x channel catfish hybrids is underway to better elucidate the defenses employed by blue catfish against H. ictaluri. [ABSTRACT FROM AUTHOR]

The article presents a research on the myxozoan parasite Henneguya ictaluri that caused the proliferative gill disease (PGD) in channel catfish Ictalarus punctatus. It notes that the extensive gill damage was caused by prolonged exposure of channel catfish to the actinospore stage of the parasite, resulting to reduced production and significant mortality in commercial operations. Findings showed that increases in parasite load correlated with percent mortality in sentinel fish, as did increases in mean actinospore concentrations. It is believed that both applications are more rapid than current protocols for assessing the PGD status of a catfish pond and identified actinospore levels that correlate to both high and low risk of fish loss.

The original description of Henneguya adiposa, a myxozoan parasitizing channel catfish Ictalurus punctatus, is supplemented with new data on spore morphology, including photomicrographs and line drawings, as well as 18S small-subunit (SSU) ribosomal DNA (rDNA) sequence. Elongate, translucent, linear plasmodia were situated between the connective tissue bands of the adipose fin. The myxospore possessed an elongate, lanceolate spore body, flattened parallel to the suture line: 17.1 ± 1.6 μm (range 14.7-20.5) in length, 4.1 ± 0.3 μm (range 3.4-4.6) wide in valvular view, and 3.7 ± 0.3 μm (range 3.2-4.0) thick in sutural view. Polar capsules were pyriform and unequal in length, measuring 7.2 ± 0.6 μm (range 5.8-8.3) long and 1.3 ± 0.2 μm (range 0.9-1.9) wide, with at least 8 turns in the polar filament coil. The caudal appendages were 38.0 ± 6.2 μm (range 23.2-48.8) and split posteriorly. The total length of the spore was 55.6 ± 6.5 mm (range 40.7-65.8). Phylogenetic analysis of 18S SSU rDNA sequence data placed this isolate within the Myxobolidae, indicating a close relationship to a group of Henneguya species parasitizing channel catfish in the southeast United States. [ABSTRACT FROM AUTHOR]

Many fish culturists are interested in applying copper sulfate pentahydrate (CSP) to channel catfish, Ictalurus punctatus, nursery ponds as a prophylactic treatment for trematode infection and proliferative gill disease by killing snails and Dero sp., respectively, before stocking fry. However, copper is an algaecide and may adversely affect phytoplankton and zooplankton populations. We evaluated the effects of prophylactic use of copper sulfate in catfish nursery ponds on water quality and phytoplankton and zooplankton populations. In 2006, treatments of 0 mg/L CSP, 3 mg/L CSP (0.77 mg/L Cu), and 6 mg/L CSP (1.54 mg/L Cu) were randomly assigned to 0.04-ha ponds. In 2007, only treatments of 0 and 3 mg/L CSP were randomly assigned to the 16 ponds. Ponds treated with CSP had significantly higher pH and significantly lower total ammonia concentrations. Treatment of both CSP rates increased total algal concentrations but reduced desirable zooplankton groups for catfish culture. CSP has been shown to be effective in reducing snail populations at the rate used in this study. CSP treatment also appears to be beneficial to the algal bloom, shifting the algal population to green algae and increasing total algal biomass within 1 wk after CSP treatment. Although zooplankton populations were adversely affected, populations of important zooplankton to catfish fry began rebounding 6–12 d after CSP treatment. Therefore, if CSP is used to treat catfish fry ponds of similar water composition used in this study, fry should not be stocked for about 2 wk after CSP application to allow time for the desirable zooplankton densities to begin increasing. [ABSTRACT FROM AUTHOR]