Effect of natural free gossypol and gossypol‐acetic acid on growth performance and resistance of channel catfish (Ictalurus punctatus) to Edwardsiella ictaluri challenge

A study was conducted to evaluate the effect of free gossypol from glanded‐cottonseed meal (G‐CSM) (natural free gossypol) or gossypol‐acetic acid on growth performance, body composition, haematology, immune response and resistance of channel catfish (Ictalurus punctatus) to Edwardsiella ictaluri challenge. Soya bean meal‐based diets supplemented with 0, 100, 200, 400, and 800 mg kg^?1 free gossypol from G‐CSM or gossypol‐acetic acid were fed to juvenile channel catfish in triplicate aquaria to apparent satiation twice daily for 12 weeks. Neither sources nor levels of dietary gossypol significantly influenced the final weight gain, feed intake, feed efficiency and survival of channel catfish. Similarly, whole‐body proximate composition, haematological parameters (red blood cell, white blood cell counts, haemoglobin and haematocrit), serum protein concentration, macrophage chemotaxis ratio, phagocytic activity and antibody production against E. ictaluri 21‐day postinfection were not significantly affected at either dietary sources or levels of gossypol. Gossypol concentrations of liver were linearly related to dietary level of gossypol but the retention rate varied dependent on sources of the dietary gossypol. At dietary gossypol levels of 400 or 800 mg kg^?1, total gossypol concentrations in liver of fish fed dietary gossypol from G‐CSM were significantly higher than those of fish fed the corresponding levels of gossypol from gossypol‐acetic acid. The (+)‐isomer of gossypol was predominantly retained in liver regardless of dietary sources of gossypol. The ratio of (+) to (?) gossypol isomers in liver decreased with increasing dietary concentrations of gossypol. Serum lysozyme activity of fish fed dietary gossypol levels of 200 mg kg^?1 or higher, either from G‐CSM or gossypol‐acetic acid, was significantly higher than that of the control. At a level of 800 mg kg^?1 diet, gossypol from G‐CSM stimulated significantly higher lysozyme activity than gossypol from gossypol‐acetic acid. Fish fed diets containing 400 mg kg^?1 gossypol or higher from G‐CSM or 800 mg kg^?1 gossypol from gossypol‐acetic acid had significantly increased superoxide anion (O) production. However, neither the sources nor the levels of dietary free gossypol influenced the resistance of juvenile channel catfish to E. ictaluri challenge.     

No apparent differences in intestinal histology of channel catfish (Ictalurus punctatus) fed heat-treated and non-heat-treated raw soybean meal

The histopathologic effects of feeding heat‐treated soybean meal to fingerling channel catfish (Ictalurus punctatus) were studied. Fish were fed one of six diets: a diet containing 450 g kg^?1 commercial soybean meal (CSBM), or diets with the CSBM replaced by non‐heat‐treated raw soybean meal (RSBM0), or RSBM heated at 130 °C for 5 min (RSBM5), 10 min (RSBM10), 20 min (RSBM20) or 40 min (RSBM40). After 10 weeks, tissue samples were taken from the stomach, proximal intestine, distal intestine, liver, pancreas and spleen from fish in each group for histologic examination. Mild necrotic lesions were found in the gastric glands, pancreas and liver of fish in all the groups (treatment and control groups). Hepatic glycogen deposition was also observed in all the groups, and the spleen samples exhibited considerable brownish‐black pigment deposition around the splenic corpuscles and diffuse mild‐to‐moderate congestion in all of the groups. Generally, these histologic effects appeared to be equivocal between all of the groups, and no abnormalities were noted in the proximal or distal intestine. These findings suggest that feeding channel catfish a diet containing 450 g kg^?1 non‐heat‐treated RSBM did not cause severe histologic changes associated with soybean meal anti‐nutritional factors as have been reported in salmonids.     

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.     

Ultrastructural changes associated with carbon tetrachloride hepatotoxicity in channel catfish, Ictalurus punctatus Rafinesque

Abstract. Ultrastructural changes occurring in juvenile channel catfish, Ictalurus punctatus Ratinesque, hepatocytes were examined following exposure to carbon tetrachloride (CCl₄). Juvenile catfish were intraperitoneally injected with a sublethal dose of undiluted CCl₄and controls, used for comparisons, received physiological saline. The rough endoplasmic rcticulum (RER) was slightly dilated by 1 h and was significantly dilated by 4 and 24 h post-CCl₄-exposure. At 4 h, the RER became degranulated, mitochondrial eristae indistinct with electron dense flocculant matrieal deposits, and nuclear membranes indented. Autophagic vacuoles were present in some hepatocytes. Within 48 h post-exposure, the hepatocytes were indistinguishable from control hepatocytes. CCl₄ can induce reversible or irreversible cell damage which appears dose dependent.     

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.     

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.     

Effects of l-lysine supplementation of diets with different protein levels and sources on channel catfish, Ictalurus punctatus (Rafinesque)

Abstract. Semipurified diets containing either 25% or 30% crude protein (CP) from soy isolate (soy) or 30% CP from casein and gelatin (casein) were supplemented with either of two levels of L-lysine HCI (0 or 0·5% of diet) in a 3 × 2 factorial arrangement and fed to fingerling channel catfish, Ictalurus punctatus (Rafinesque), in aquaria for 8 weeks. Factorial analysis of variance indicated a significant ( P < 0·001) positive effect of lysine on weight gain, protein conversion efficiency (PCE) and feed efficiency. Fish fed the soy diet containing 25% CP showed increased weight gain of 24% with lysine supplementation while fish fed soy and casein diets containing 30% CP showed increases of 11 % and 3%, respectively. However, supplementing the 25% CP soy diet with 0–5% L-lysine HCI did not enhance growth performance to the level offish fed the unsupplemented 30% CP soy diet. Significant effects of dietary protein levels and sources on weight gain, PCE, feed efficiency, haematocrit, hepatosomatic index (HSI; % liver weight), intraperitoneal fat (IPF) ratio, dry matter of fillet and whole-body, as well as lipid and protein content of whole-body tissue, were also observed. Fish fed the casein diet containing 30% CP had the greatest weight gain, PCE, feed efficiency, haematocrit and whole-body protein values and lowest IPF ratio and whole-body lipid values compared with those of fish fed the soy diets. Supplemental lysine did not affect body condition indices or proximate composition of whole-body and fillet tissues of fish fed the different protein sources. Therefore, based on this study, dietary protein levels and sources significantly influenced performance characteristics of channel catfish and supplemental lysine was most beneficial at a reduced CP level.     

Glucan administration potentiates immune defence mechanisms of channel catfish, Ictalurus punctatus Rafinesque

Abstract. Intraperitoncal injection of β-l,3 glucan in channel catfish, Ictalurus punctatus Rafinesque, greatly reduces mortality from experimental infection with Edwardsiella ictaluri. Anterior kidney phagocytes from fish receiving glucan had enhanced phagocytic and bactericidal ability. The elevated bactericidal ability of phagocytes was not accompanied by increased production of hydrogen peroxide. Fish injected with glucan responded to subsequent E. ictaluri immunizations with higher serum antibody titres relative to the control catfish. The timing of glucan administration and antigen immunization was also important. These results indicate that β-1,3 glucan potentially could be utilized prophylactically as an immunomodulator in channel catfish.     

Detection of channel catfish virus in channel catfish,Ictalurus punctatus (Rafinesque): use of a nucleic acid probe*

A nucleic acid probe for channel catfish virus (CCV) was constructed using recombinant DNA techniques. This probe consisted of a specific viral DNA fragment generated by digestion of CCV DNA with the restriction enzyme EcoRI. The probe was used to examine DNA isolated from tissues of fish that had been injected with CCV. Viral DNA was detected in some tissues of various injected fish. The sensitivity limit of detection was determined to be one viral DNA per cell.     

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.     

Molecular cloning and sequencing of hemoglobin-β gene of channel catfish, Ictalurus punctatus Rafinesque

The hemoglobin-β gene of channel catfish, Ictalurus punctatus, was cloned and sequenced. Total RNA from head kidneys was isolated, reverse transcribed and amplified. The sequence of the channel catfish hemoglobin-β gene consists of 600 nucleotides. Analysis of the nucleotide sequence reveals one open reading frame and 5′- as well as 3′-untranslated regions. The open reading frame of the sequence potentially encodes 148 amino acids with a calculated molecular mass of 16.3 kDa. The pI and charge at pH 7.0 of the deduced hemoglobin-β protein were 7.28 and 0.47, respectively. Overall, 22 amino acid residues were conserved throughout the sequences, including His64 and His93, the sites for heme-binding. Unlike the counterpart of other common cultured fish such as Salmo salar, Oncorhynchus nerka, Oncorhynchus mykiss, Cyprinus carpio and Ctenopharyngodon idella, the hemoglobin-β of channel catfish did not have cysteine. The amino acid sequence of channel catfish hemoglobin-β shows 84% homology with that of Silurus asotus (both are in the order Siluriformes). However, comparison with those of other fish species shows homology ranging from 53 to 68%. Structural analysis by the 3D-PSSM program displays that channel catfish hemoglobin-β has eight α-helices, A–H.     

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.