Vibriosis in channel catfish, Ictalurus punctatus (Rafinesque)

Abstract. An epizootic due to Vibrio anguillarum was observed in channel catfish, Ictalurus punctatus (Rafinesque). Lesions in infected fish included ulceration and petechiae on body surfaces, vent and caudal peduncle. Internally, haemorrhages in liver and kidney were present and the intestinal tract was filled with a clear viscous fluid. Using an isolant recovered during the epizootic, laboratory studies were conducted to determine (a) bacterial dynamics of the agent in blood, kidney and liver and (b) clinical haematologic and biochemical parameters in infected fish. Under conditions of the study, vibrios were apparently sequestered in kidney and liver during initial stages of infection (8–12 h after exposure). Later, bacterial numbers in blood were comparable to those in kidney and liver. Clinical parameters of infected catfish were suggestive of cellular and tissue destruction and renal dysfunction. Based upon data of the present study and those of others, vibriosis appears to be a disease in which the agent is localized in select tissues. Secondary septicaemia may be incidental to factors which compromise host defences.     

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.     

Branchiomyces infection in farm-reared channel catfish, Ictalurus punctatus (Rafinesque)

Four cases (representing outbreaks in four different ponds on three farms) of branchial mycosis caused by Branchiomyces spp. were identified in channel catfish fry during the summer of 1996. Mortalities ranged from a few hundred to several thousand fish per pond. Significant gross and histopathological findings from these four cases were limited to the gills. All fry examined had fungal mycelia that were mainly but not entirely confined to the base of the primary lamellae and the gill arches. These fungal hyphae were intravascular and occluded vessels in the gill tissues. The present paper describes the fungal characteristics and pathology of branchial mycosis caused by Branchiomyces spp. in channel catfish.     

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.     

Detection of channel catfish virus in asymptomatic adult channel catfish,Ictalurus punctatus (Rafinesque)*

Abstract. Two populations of channel catfish were examined for the presence of channel catfish virus (CCV) by use of a nucleic acid probe. In one population of 22 fish with no history of CCV, viral DNA was found in every liver. These fish had previously been examined by a technique involving co-cultivation of their leucocytes with catfish tissue culture cells. The co-cultivation method had identified virus in 10 of these fish. The second fish population consisted of 14 adults that had survived a CCV outbreak in 1980. Of the 14 fish, 11 showed positive indication of CCV DNA. The tissue distribution of the CCV differed from fish to fish. All fish from the first group and one fish from the second group showed some alterations in the DNA banding patterns expected from pure CCV DNA. This might be indicative of modifications in the genomic structure of the CCV DNA when the virus is latent in a fish.     

Nutritional effects of protein source in starter diets for channel catfish (Ictalurus punctatus Rafinesque) in suboptimal water temperature

Intensive tank rearing of channel catfish (Ictalurus punctatus Rafinesque) fry can be successfully accomplished with commonly available ‘salmonid’ starter diets. Ingredient substitution in starter diets is less important from the cost perspective but growth, survival and health of fish are major concerns. Several combinations of fish meals and animal protein substitutes were evaluated in diet formulations for hatchery rearing of catfish fry. Sub‐optimal thermal conditions were used which are characteristic for the north‐central USA where catfish culture is important for stocking purposes and live‐fish markets. A diet formulated on the basis of menhaden fish meal (29.1%), herring fish meal (25.1%) and animal by‐product mixture (16.38%) gave numerically the highest growth rate after 13 weeks of feeding, although growth reductions in fish fed diets exclusively with mehaden meal (77.6%) as protein or substituted with 50% animal by‐product protein were not significant. Instantaneous mortality rates were the highest between weeks 2 and 4 of rearing and increased almost proportionally with the increased fish meal protein substitution. A diet based on menhaden fish meal had the highest concentration of phosphorus and several other essential minerals, but these were not reflected in the mineral composition of the fish body at the termination of feeding. Among activities of digestive enzymes, trypsin was depressed in fish offered diets with 75–100% fish meal protein replacement. A diet superior in terms of fish performance was defined in the present study and it was concluded that the initial feeding can greatly affect physiological status of juvenile channel catfish.     

Histological effects of prolonged sublethal hypoxia on channel catfish Ictalurus punctatus (Rafinesque)

Abstract. A vacuum degassing apparatus was used to subject channel catfish Ictalurus punctatus (Rafinesque) to sublethal hypoxia for 24, 48 or 72 h. Spleen, liver, gills, anterior kidney and posterior kidney from the catfish exhibited histopathological changes that included necrosis, hyperaemia, oedema, haemorrhage, hyperplasia and hypertrophy. Of the organs examined, gills were most affected by the hypoxic conditions. After 5 days of reacclimatization to normoxic conditions, channel catfish continued to exhibit histopathological effects of prolonged hypoxia.     

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.     

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.     

Environmental factors affecting outbreaks of winter saprolegniosis in channel catfish, Ictalurus punctatus (Rafinesque)

Abstract. Previous studies have led to the development of a laboratory model for a disease termed 'winter saprolegniosis', locally referred to as 'winter kill', occurring in channel catfish, Ictalurus punctatus Rafinesque, raised in commercial ponds in the southeastern United States. In the laboratory, the onset of disease was routinely brought about by a combination of two related factors: (1) a rapid drop in water temperature which induces immunosuppression in catfish; and (2) maintenance of low water temperatures (∼10°C), which favour the proliferation of an ubiquitous fungus of the genus Saprolegnia to produce high levels of fungal zoospores (≥5 spores ml⁻¹). In this study, two commercial catfish ponds were monitored for over one year to determine if the above factors occurred in the field and could be correlated with outbreaks of winter saprolegniosis. It was noted that passages of severe cold weather fronts were able to drop pond water temperatures ≥10°C within 24h and that such decreases in water temperature were associated with immunosuppression of the catfish in the ponds. Furthermore, when Saprolegnia sp. zoospore levels were ≥5 spores ml^-1, the immunocompromised catfish exhibited overt signs of winter saprolegniosis. If one of the factors implicated in the induction of disease was missing, fish in the ponds remained healthy. In addition, the onset of disease in the ponds appeared independent of pH and oxygen, total ammonia nitrogen and un-ionized ammonia levels. Collectively, these field results confirm the laboratory-based hypothesis concerning the aetiology of winter saprolegniosis in channel catfish.