Susceptibility of channel catfish, Ictalurus punctatus (Rafinesque), to Edwardsiella ictaluri challenge following copper sulphate exposure

Channel catfish, Ictalurus punctatus (Rafinesque), with or without a preliminary 24 h exposure to 2 mg copper sulphate L(-1), were challenged with 7.5 x 10(6) colony forming units L(-1) of Edwardsiella ictaluri to determine the effect of copper sulphate on disease resistance. Catfish previously exposed to copper sulphate were significantly more resistant to the bacterial challenge than those not exposed. Catfish not exposed to copper sulphate suffered 35.5% mortality while catfish exposed to copper sulphate experienced 14.1% mortality. Copper concentrations were the same in tank waters of both exposed and control fish at the time of challenge, eliminating the possibility that copper in the water may have been toxic to bacteria. Copper concentrations in freeze dried and ground tissues of unexposed, exposed, and purged channel catfish were highest in fish before copper sulphate exposures suggesting that elevated tissue levels of copper were not responsible for the increased resistance to bacterial challenge. Competition for sites of bacterial attachment to gill or epithelial cells may account for the reduction in mortality; although this is not supported by the low copper content of fish tissue after copper exposure.     

Evaluation of a 4‐h static copper sulphate treatment against experimental infection of Flavobacterium columnare in channel catfish (Ictalurus punctatus)

The efficacy of copper sulphate (CuSO₄) against the early stages of an experimental acute infection of Flavobacterium columnare in channel catfish (Ictalurus punctatus) was evaluated. Fish were challenged, by waterborne exposure to F. columnare in an ultra‐low flow‐through water delivery system, and treated with CuSO₄ at 4.2 and 2.1 mg L^?1 at 5.5 h post challenge for 4 h. Bacterial challenged non‐treated fish acted as a positive control and non‐challenged non‐treated fish acted as a negative control. Fish challenged with F. columnare and treated with CuSO₄ at 4.2 and 2.1 mg L^?1 post challenge had mortalities of 6.4% and 18.3%, respectively, compared with the positive control, which had 90.2% mortality. The mortality of challenged fish treated with CuSO₄ at 4.2 and 2.1 mg L^?1 was significantly different from the positive control. There was no significant difference between the mortalities of the 4.2 and 2.1 mg L^?1 treatments. The results suggest that CuSO₄ has clear therapeutic value against columnaris infections.     

Comparative study on the utilization of different methionine sources by channel catfish,Ictalurus punctatus (Rafinesque, 1818)

The study was conducted to examine the effects of different methionine (Met) sources on the growth performance of channel catfish (Ictalurus punctatus). Six diets with isonitrogen and isoenergy were formulated as positive control (PC) diet (0.57% Met), negative control (NC) diet (0.42% Met) without or with the addition of crystalline DL‐Met (CM), Met hydroxy analogue (MHA), Met hydroxy analogue calcium salt (MHA‐Ca) and microcapsulated DL‐Met (MM) to obtain the same Met level as PC diet. After 8 weeks feeding trial, channel catfish (76.0 ± 0.3 g) fed MHA‐Ca and MM diets, but not CM and MHA diets, had higher weight gain, lipid productive value, protein productive value and lower feed conversion ratio than those in NC group (P < 0.05) and showed no differences in these indicators with PC group (P > 0.05). Levels of serum total protein and total free amino acid (TFAA) of all groups peaked at the 4th h, and CM group had lower TFAA level than that in MM group at the 6th h after feeding (P < 0.05). In NC group, the activities of liver aspartate aminotransferase and alanine aminotransferase peaked at the 4 h after feeding, and the peaking time in CM group was advanced to the 2nd hour, while in MHA, MHA‐Ca and MM groups, the peaking times were delayed to the 6th hour after feeding. The above results indicated that the supplementation of MHA‐Ca, MM rather than CM, MHA in diets deficient in methionine could improve the growth of channel catfish.     

Effectiveness of copper sulphate,potassium permanganate and peracetic acid to reduce mortality and infestation of Ichthyobodo necator in channel catfish Ictalurus punctatus (Rafinesque 1818)

Ichthyobodo necator is a single‐celled biflagellate parasite, which in high density can cause significant mortality in young fish. Copper sulphate (CuSO₄), potassium permanganate (KMnO₄) and peracetic acid (PAA) were evaluated for effectiveness against ichthyobodosis. Treatments were: untreated control, 2.1 mg L^?1CuSO₄, 3.0 mg L^?1 KMnO₄, 1.5 mg L^?1 PAA and 3.0 mg L^?1 PAA, and were applied to flow‐through tanks on three consecutive days. The study was designed to simulate the flow‐through systems utilized in the commercial rearing of juvenile channel catfish (Ictalurus punctatus). Mortality was monitored daily to compare survival rate among treatments. Parasite intensity was assessed pre chemical exposure and 20–24 h after the third application to determine effectiveness of the treatment. An assessment was also done 7 days post application to investigate possible reoccurrence. Copper sulphate, KMnO₄ and PAA (3.0 mg L^?1) significantly reduced the infestation rate of I. necator. Copper sulphate significantly improved the survival of I. necator infested channel catfish after three flow‐through applications compared with the untreated control. The 3.0 mg L^?1 PAA resulted in significantly lower survival than the untreated control, the 1.5 mg L^?1 PAA and the KMnO₄ were not statistically different from the untreated control.     

Effects of dietary arginine supplementation on growth,protein optimization and innate immune response of channel catfish Ictalurus punctatus (Rafinesque 1818)

Juvenile channel catfish Ictalurus punctatus were fed casein–gelatin‐based semi‐purified test diets with graded amounts of arginine (ARG, 0.5%, 1%, 2% and 4% of dry diet) for a 6‐week period, to evaluate the effects of dietary ARG supplementation on performance indicators, levels of plasma ARG, ornithine, citrulline, glutamine and glutamate, as well as selected innate immune parameters. Incremental dietary ARG resulted in significant improvements in weight gain, feed efficiency and protein efficiency ratios, protein retention, protein deposition and arginine deposition. Fish fed the 4% ARG diet had significantly higher values for all performance indicators, although these values were not different from those of fish fed the 2% ARG diet with the exception of protein retention, protein deposition and arginine deposition. Conversely, fish fed the 0.5% ARG diet had significantly lower values for all analysed plasma amino acids. Similarly, both phagocyte superoxide anion production and neutrophil respiratory burst were significantly decreased in fish fed the 0.5% ARG diet. These results demonstrate that the indispensability of dietary ARG is not only related to optimized protein utilization for growth but also its supplementation to fish diets may significantly impact several aspects of the immune system, including phagocyte function and thus improve overall fish health.     

Apparent digestibility of alternative plant‐protein feedstuffs for channel catfish,Ictalurus punctatus (Rafinesque)

A study was conducted with channel catfish, Ictalurus puntatus to determine apparent digestibility/availability coefficients of protein, amino acids, lipid and energy for alternative plant‐protein feedstuffs: corn gluten feed, corn germ meal, distillers dried grains with solubles, and canola meal, compared with those for soybean meal. A 32%‐protein, chemically defined diet containing 8% fish meal was used as the reference diet. Test diets consisted of 70:30 ratio of reference diet to test ingredient with chromic oxide (0.75% of the diet) as an inert indicator. Apparent digestibility/availability coefficients of protein, essential amino acids and energy in alternative protein feedstuffs tested were generally lower than those in soybean meal by channel catfish. Apparent digestibility coefficients of protein ranged from 75 to 87% and those of energy ranged from 52 to 59% for alternative feedstuffs. Lysine in alternative feedstuffs was 67–79%, methionine was 69–85% and cystine was 73–82% available to channel catfish. There were no significant differences in lipid ADCs among test feedstuffs (91.9–96.8%). Results from the present study can be useful in formulating cost‐effective catfish feeds using these alternative feedstuffs.     

Acute columnaris infection in channel catfish, Ictalurus punctatus (Rafinesque): efficacy of practical treatments for warmwater aquaculture ponds

Columnaris disease was induced in channel catfish, Ictalurus punctatus (Rafinesque), by bath exposure to four highly virulent isolates of Flavobacterium columnare. In untreated controls, mortality began 20 h after exposure and reached 100% by 48 h. Mortality in channel catfish given antibiotic treatments with oxytetracycline or a combination of sulphadimethoxine and ormetoprim in feed prior to bacterial challenge was zero with all four strains of F. columnare. Diquat (Zeneca Agricultural Products, Wilmington, DE, USA) was the most effective bath treatment; mortality with all four strains was zero. With potassium permanganate, chloramine-T, hydrogen peroxide and copper sulphate, bath treatment efficacy varied significantly among strains (P = 0.0346) and among treatments (P = 0.0033). Bath treatments with chloramine-T and potassium permanganate significantly reduced (P < 0.05) mortality from 100 to 75 and 69%, respectively, but copper sulphate and hydrogen peroxide treatments were not effective. Based on our results, oral antibiotics prevented columnaris disease but, of the bath treatments, only Diquat produced a dramatic reduction in the mortality of acutely infected fish. Diquat is labelled for aquatic use as an herbicide in the USA but in large ponds it is prohibitively expensive.     

Influence of forage fish and dietary lipid supplements on egg quality and fry production in channel catfish (Ictalurus punctatus) × blue catfish (Ictalurus furcatus) hybridization

Hybrid catfish (channel catfish Ictalurus punctatus × blue catfish Ictalurus furcatus) display characteristics that are favourable to aquaculture production. Low hatch percentages are a principal reason this hybrid is not used widely in the catfish industry. This study was conducted to determine whether additional food source rich in lipids may lead to a higher quality egg production. A 10‐week feed trial was conducted in ponds in Auburn, AL. A total of 219 female Kansas Select channel catfish were stocked into nine ponds, 0.04 ha in size. Three dietary treatments were randomly allocated to the ponds. Diet‐1 was a standard 60 g kg^?1 lipid floating catfish feed. Diet‐2 was the same feed supplemented with forage fish at ～28 kg ha^?1. The third diet was the aforementioned catfish feed topcoated with 20 g kg^?1 lipid [10 g kg^?1 menhaden fish oil, 5 g kg^?1 high docosahexaenoic acid (DHA) oil and 5 g kg^?1 high arachidonic acid oil]. Results indicate that brood fish fed the high lipid diet spawned larger egg masses and had larger eggs both in weight and in diameter, with increased complements of fatty acids such as DHA, eicosapentaenoic acid and total n‐3 fatty acids. The neutral and polar lipid fractions are also presented.     

Evidence of hybridization between Yaqui catfish Ictalurus pricei (Rutter, 1896) and channel catfish Ictalurus punctatus (Rafinesque, 1818) in north-west México revealed by analysis of mitochondrial and nuclear genes

1. The Yaqui catfish, Ictalurus pricei, is the only native ictalurid species described from north-west México and south-west USA. It is an endangered species owing to the decline and loss of most of its historical populations, mainly because of competition and hybridization with the non-native channel catfish, Ictalurus punctatus. The Arroyo Cajón Bonito is one of the few remnant populations of Yaqui catfish in the Yaqui River basin, and it is threatened by the presence of channel catfish that escaped from private culture facilities.
2. Phylogenetic analysis of two mitochondrial and two nuclear genes was used to detect evidence of hybridization with channel catfish in a collection of 20 catfish from Arroyo Cajón Bonito. Fourteen putatively pure Yaqui catfishes, five hybrids and one channel catfish were detected.
3. This study further highlights hybridization between channel and Yaqui catfish as the main threat to the remaining Yaqui catfish populations. We recommend urgent evaluation of the remnant populations of native catfish elsewhere and their current conservation status.

     

Logit models for evaluating spawning performance of channel catfish, Ictalurus punctatus (Rafinesque)

Broodstock evaluations are often measured by variables such as spawning success, fecundity, fertilization and hatching rates, usually expressed as percentage values. Outcomes are generally analysed as continuous random variables, assuming that they follow a normal distribution. Ordinary linear regression models (e.g. analysis of variance) as well as χ² analysis are typically applied. However, these models may not be the most appropriate as a number of test criteria may not be met. For example, spawning success outcomes are inherently discrete and non‐negative data and hence their distribution is not likely to be normal. As these models may not be the most appropriate, a case study using logit analysis as an alternative method for the evaluation of this type of data is presented by considering the response as binary data (spawned versus did not spawn). An exact version of logit analysis was performed due to the sparseness of the data. The results demonstrate that appropriate statistical models provide better insight into the cause–effect relationships that exist between control variables and the dependent variable (likelihood of spawning in this case). As would be expected, each strain of fish responded somewhat differently to the test variables. Changing the protein level of the diet from 32% to 42% or increasing the feeding frequency from three to six times per week either did not influence spawning or negatively affected spawning respectively. Additionally, older fish performed better than younger fish and the early spawning period was better than the later spawning period, regardless of strain. These responses, however, were only detected using logit analysis, which is a more sensitive test and would thus be recommended for this type of data.     

Evaluation of diquat against an acute experimental infection of Flavobacterium columnare in channel catfish, Ictalurus punctatus (Rafinesque)

A trial was performed to evaluate the efficacy of diquat (6,7-dihydrodipyrido[1,2-a:2',1'-c]pyrazinediium dibromide) against an acute experimental infection of Flavobacterium columnare in channel catfish, Ictalurus punctatus . Diquat is an Environmental Protection Agency-approved herbicide and has the potential to be legally and practically used against columnaris. Channel catfish were challenged, by cutaneous abrasion, and waterborne exposure to F. columnare and treated once at 22-h post-challenge with 2.5, 5.0, 10.0 and 15 mg L⁻¹ of diquat active ingredient for 6 h. At the conclusion of the trial, 21-day post-challenge, diquat at 5.0, 10.0 and 15 mg L⁻¹ significantly ( P  < 0.05) reduced the mortality of infected fish from 95% in the challenged non-treated fish to 68%, 59% and 49%, respectively. In vitro , the minimum inhibitory concentration (MIC) of 23 isolates of F. columnare was assayed. The majority of the isolates had an MIC value of 5 μg mL⁻¹ (15 of the 23 isolates). Infected fish exhibited acute clinical signs similar to a natural infection. The skin had severe ulcerative necrotizing dermatitis and the muscles had severe necrotizing myositis. The gills had severe multifocal necrotizing branchitis. The results demonstrate that diquat would reduce mortalities caused by an acute columnaris infection.     

Edwardsiella ictaluri bacteraemia elicits shedding of Aeromonas hydrophila complex in latently infected channel catfish, Ictalurus punctatus (Rafinesque)

Edwardsiella ictaluri is a primary bacterial pathogen of channel catfish, Ictalurus punctatus, and the causative agent of enteric septicaemia of catfish . Edwardsiella ictaluri is known to gain entry to the host by infection of the nares, gastrointestinal tract, and gills, and to disseminate to organs via an as yet uncharacterized acute bacteraemia. In this study, fluorescent microscopy showed E. ictaluri on the gill within 5 min of immersion challenge and E. ictaluri could also be isolated from the circulation within 5 min. When removed to clean water, catfish cleared circulating bacteria within 15 min and the blood remained free of E. ictaluri until its reappearance at the 12 h post-infection sampling. However, Aeromonas hydrophila , the aetiological agent of motile aeromonad septicaemia, appeared within the circulation 7 h post-challenge with E. ictaluri and was detected in all fish at 12 h post-infection. Only 20% of fish carried A. hydrophila in the trunk kidney that could be detected by plate culture on Rimler–Shotts agar; however, 100% of challenged and stress-control fish were A. hydrophila complex positive at 24 h post-challenge. These results suggest that although the catfish is capable of clearing its circulation of E. ictaluri , superinfection with latent A. hydrophila may enhance clinical signs of edwardsiellosis. This is the first report of a bacterial superinfection appearing in fish.     

Low-density silver carp Hypophthalmichthys molitrix (Valenciennes) polyculture does not prevent cyanobacterial off-flavours in channel catfish Ictalurus punctatus (Rafinesque)

Silver carp Hypophthalmichthys molitrix (Valenciennes) were co‐cultured with channel catfish Ictalurus punctatus (Rafinesque) in 0.4 ha earthen ponds to determine the impacts of carp grazing on pond phytoplankton communities and cyanobacterial off‐flavours in catfish. Carp were stocked at densities of 0, 75, or 250 fish ha^?1 in seven replicate ponds per treatment. The mean chlorophyll a concentrations (a measure of phytoplankton standing crop) steadily increased in all treatments from about 100 μg L^?1 in April to more than 400 μg L^?1 by mid‐October. Silver carp had no affect (P>0.1) on chlorophyll a concentrations across all sampling dates (April though October) or for sampling dates late in the growing season (August–October) when the prevalence of cyanobacterial off‐flavours among catfish populations is usually greatest. Silver carp did not eliminate odour‐producing cyanobacteria from pond phytoplankton communities: on sampling dates in September and October, three to six ponds in all treatments contained populations of the odour‐producing cyanobacteria Oscillatoria perornata, Anabaena spp., or both. Failure of silver carp to eliminate odour‐producing cyanobacteria resulted in a relatively high incidence in all treatments of ponds with off‐flavoured catfish. On sampling dates in September and October, catfish in three to five ponds in each treatment were tainted with either musty (2‐methylisoborneol) or earthy (geosmin) off‐flavours. The presence of silver carp had no obvious effect on off‐flavour intensity: on each sampling date, at least three ponds in each treatment contained catfish described as distinctly to extremely off‐flavored. Apparently, hypertrophic conditions in catfish ponds overwhelm the effect of silver carp grazing at the low carp densities used in this study.