Abstract: A cDNA encoding a putative gonadoliberin receptor was cloned from the pituitary of the African catfish. Conceptual translation predicts a protein of 379 amino acids which shows typical characteristics of GTP-binding-protein-coupled receptors. The isolated cDNA was stable expressed in human embryonic kidney (HEK) 293 cells which were used for studies on gonadoliberin-activated second messenger systems (inositol phosphate production; increase in cAMP and/or intracellular Ca2+). The isolated cDNA encoded a functional receptor, designated catfish gonadoliberin receptor (cfGnRH-R), which had an amino acid sequence similarity of 38% with mammalian gonadoliberin receptors. In contrast to its mammalian counterparts which lack an intracellular carboxy-terminal domain, the cfGnRH-R contains an additional 49 amino acid residues. From the two endogenous gonadoliberins in African catfish, chicken gonadoliberin-II had a several hundredfold higher potency than catfish gonadoliberin to activate cfGnRH-R-associated second messenger systems in transfected HEK 293 cells. This is in line with the previously determined higher gonadotropin-release capacity of chicken gonadoliberin-II in catfish. Stimulation of second messenger systems with chicken gonadoliberin-II, but not with catfish gonadoliberin, resulted in a biphasic effect and chicken gonadoliberin-II led to a higher maximum stimulation than catfish gonadoliberin. Challenging cfGnRH-R simultaneously with chicken gonadoliberin-II and catfish gonadoliberin did not lead to additive effects. In contrast, two types of mutual inhibitory effects were recorded. These data indicate that a single cognate cfGnRH-R couples with distinct efficacies to signal transduction systems upon stimulation by the two endogenous gonadoliberins which, in addition, may interact negatively.

Abstract: .– Juvenile channel catfish Ictalurus punctatus (initial weight: 6.8 g/fish) were fed four practical diets containing 0, 250, 500, and 750 units of microbial phytase/kg and a diet containing 1% feed grade dicalcium phosphate (but no microbial phytase) under laboratory conditions for 12 wk. Fish fed the diets containing 250 units of microbial phytase/kg and above consumed more feed, gained more weight, and had a lower feed conversion ratio (FCR) in comparison to fish fed the basal diet containing no microbial phytase. Fish fed the diet containing dicalcium phosphate had intermediate weight gain and feed conversion ratio as compared to fish fed the basal diet and diets containing microbial phytase. Bone ash and phosphorus concentrations were lower for fish fed the basal diet than for fish fed other diets. No differences in weight gain, feed consumption, FCR, bone ash and bone phosphorus were observed among fish fed the diets containing various levels of microbial phytase. Fish fed the diet containing dicalcium phosphate had a lower bone phosphorus concentration than fish fed diets containing microbial phytase. Fecal phosphorus concentrations were lower for fish fed the diets containing microbial phytase than for fish fed the basal diet and the diet containing dicalcium phosphate. Results from the present study indicated that addition of 250 units of microbial phytase/kg to practical diets can effectively improve bioavailability of phytate phosphorus to channel catfish and may possibly eliminate the use of an inorganic phosphorus supplement in channel catfish diets. However, these data must be verified in trials conducted in ponds, prior to recommending removal of supplemental phosphorus from channel catfish diets.

Abstract: These studies demonstrated that intestinal mucosa of the channel catfish contained activities comparable with liver for several phase 2 xenobiotic-metabolizing enzymes, and showed that CYP1A-dependent monooxygenase activities were inducible in intestine but not liver by dietary exposure to low concentrations of the Ah agonist, beta-naphthoflavone (BNF). The diets administered were laboratory-prepared, semisynthetic pellets of known composition, commercial chow, or chow supplemented with BNF at 10 or 100 mg BNF/kg chow. Very low intestinal benzo(a)pyrene hydroxylase [aryl hydrocarbon hydroxylase (AHH)] and ethoxyresorufin O-deethylase (EROD) activities were found in catfish fed the semisynthetic diet. Intestinal EROD and AHH activities were elevated by the commercial chow diet and further induced by supplementation with 10, but not 100, mg BNF/kg diet. In vitro studies showed that catfish EROD and AHH activities were sensitive to inhibition by BNF, with mean IC50 values of 0.078 and 2.2 microM, respectively. Thus, residues of BNF retained in intestinal mucosa may have masked monooxygenase induction in catfish fed the 100 mg BNF/kg diet. Microsomal UDP-glucuronosyltransferase and cytosolic PAPS-sulfotransferase activities with 3-hydroxybenzo(a)pyrene as substrate were largely unaffected by the diets studied, and intestinal activities were similar to hepatic activities. Glutathione S-transferase activity was slightly induced in intestinal, but not hepatic cytosol of catfish treated with BNF at the 10 mg/kg diet level relative to chow controls. Epoxide hydrolase activity with styrene oxide as substrate was not affected by diet in intestinal microsomes.

Abstract: This study was conducted to evaluate the use of low protein diets for channel catfish Ictalurus punctatus raised in earthen ponds at high density. Fingerling channel catfish were stocked into 0.04-ha earthen ponds at a rate 24,700 fish/ha and fed experimental diets daily to satiation from April to October 1995. The five diets contained either 32, 28, 24, 20, or 16% crude protein with digestible energy to protein (DE:P) ratios ranging from 8.9 to 16.2 kcal/ g protein. Weight gain was not different among channel catfish fed diets containing 32, 28, or 24% crude protein. Fish fed diets containing 20% or 16% crude protein gained less weight than fish fed the diets containing 28% or 24% crude protein, but not statistically less than the fish fed the 32% crude protein diet. Feed consumption data followed similar trends as weight gain data. Feed conversion ratio increased linearly as dietary protein decreased, but was not significantly different (multiple range test) for fish fed diets containing either 32% or 28% crude protein. There were no differences in survival and hematocrit of fish fed the different diets. No differences (multiple range test) were observed in dressout percentages for fish fed the various diets, but dressout percentage tended to decrease linearly as dietary protein decreased. Visceral fat and fillet fat increased and fillet protein and moisture decreased linearly as dietary protein decreased. Results from this study indicated that dietary protein concentrations as low as 24% are adequate for maximum weight gain of pond-raised channel catfish fed daily to satiation. Fish fed dietary protein levels below 24% grew relatively well, particularly considering that dietary protein was reduced 40–50% below that typically used in commercial channel catfish feeds. However, dietary protein levels below 24% may increase fattiness to an unacceptable level presumably because of the high digestible energy to protein ratio.

Abstract: Fingerlings of channel catfish Ictalurus punctatus (average initial weight, 1.70 g) were fed a casein-based purified diet supplemented with 0, 0.02, 0.06, 0.20, or 0.40 mg of selenium/ kg from sodium selenite (Na2SeO3), selenomethionine (Se-M), or selenoyeast (Se-Y) for 9 weeks. Subsequently, fish were challenged by immersion with a virulent strain of Edwardsiella ictaluri (105.9 cells/mL), and mortalities were recorded during a 14-d period. Antibody titers of surviving fish were measured, and macrophage chemotactic activity was determined in fish from each treatment. Dietary concentration and source of selenium significantly influenced weight gain and immune responses of the fish. Dietary selenium concentrations for maximum weight gain were 0.20 mg/kg from Se-M and Se-Y and 0.40 mg/kg from Na2SeO3. Dietary selenium concentration for maximum survival from E. ictaluri challenge was 0.20 mg/kg for fish fed Se-M and 0.40 mg/kg for fish fed Se-Y and Na2SeO3. Antibody production generally increased as...

Abstract: Shelf life (onset of sensory spoilage) and potential for toxin production by Clostridium botulinum type E in retail type packages of fresh catfish fillets in high barrier film were investigated under selected atmospheres when stored under refrigeration and temperature-abuse conditions. Shelf life of fillets in all atmospheres decreased with increase of storage temperature from 4°C to 16°C. Trimethylamine content associated with onset of spoilage was different for each storage temperature and atmosphere. Surface pH and K-values were not good indicators of onset of sensory spoilage. Toxin development coincided with sensory spoilage at 16°C storage for fillets packaged in either atmosphere. At 4°C, none of the MA-packaged fillets became toxic, even after 37 days of sensory spoilage.

Abstract: In order to characterize the Major histocompatibility complex (MHC) class II A genes of the channel catfish (Ictalurus punctatus) a cDNA library was screened and PCR was performed. Four different full-length cDNA sequences for MHC class II A genes were obtained from a clonal B cell line derived from an outbred fish. Two different genomic sequences and corresponding cDNAs were obtained from a presumably homozygous gynogenetic catfish. The A genes have five exons and four phase one introns. The first exon encodes the 5′ untranslated region (UTR) and leader peptide; the second and third exons encode the α1 and α2 domains, respectively. The connecting peptide, transmembrane and cytoplasmic domains, as well as part of the 3′ UTR, are encoded by the fourth exon and the rest of the 3′ UTR is encoded by the fifth exon. Southern blot analyses using an exon three probe revealed two to four hybridizing fragments with considerable restriction fragment length polymorphisms evident among randomly selected outbred channel catfish. These findings are consistent with the presence of at least two functional polymorphic MHC class II A gene loci. An unusual aspect of the channel catfish MHC class II α chain is its lack of N-linked glycosylation sites.

Abstract: In fish larvae the costs of rapid growth may be accommodated by a decrease in the rate of protein turnover or by a reduction in the costs of protein synthesis. Protein growth, synthesis and degradation were measured in yolk-sac larvae of Clarias gariepinus and the costs of protein synthesis and protein growth were estimated. Growth rates were over 100% protein weight day-1. Protein synthesis retention efficiency (retained protein per unit of synthesis) was estimated to be 69.6%, a value comparable to that of larger fish. The larvae used 43% of their oxygen consumption for protein synthesis. Nevertheless, protein synthesis costs were close to theoretical minima. Therefore, the high growth rates of catfish yolk-sac larvae seem to be possible through minimisation of the costs of protein synthesis. These low costs are associated with high rates of protein synthesis (138%protein weight day-1), and elevated RNA concentrations (107 µg RNA mg-1protein), which together suggest very high RNA efficiencies (12.9 g protein synthesized g-1RNA day-1).

Abstract: Pituitary gonadotrophs were studied in male African catfish between 1 and 37 wk of age using antisera against the LH subunits for immunohistological and radioimmunological purposes, and cRNA probes for in situ hybridization. Immunoreactive material was already detectable at the earliest age examined. In juveniles, the signal for the common glycoprotein a subunit (GPca) was stronger than that for the LH 15 subunit. Accordingly, an excess of radioimmunoassayable GPa 100 times that of LHI3 was recorded in the pituitary. Using in situ hybridization, the mRNAs were detected 7 (GPa) and 13 (LHP1) wk after hatching. Detection of LHP1 mRNA coincided with a 300-fold increase in the pituitary content of LHP and intact LH, whereas GPa increased only 15-fold. The number of gonadotrophs per pituitary and the amount of LH per gonadotroph also increased strongly. The strong, initial increase in pituitary LH levels was always associated with the presence of spermatocytes. However, in a limited number of cases (3 out of 12 fish), the pituitary LH content was low despite the presence of spermatocytes. The number of gonadotrophs, the staining intensities (reflecting protein and mRNA), and the pituitary LH content kept increasing, although at a reduced rate, until completion of the first wave of spermatogenesis. In view of the excess of GPa over LHP1, we conclude that expression of the two subunits is regulated in part by different mechanisms, and that expression of LHP is rate-limiting for the amount of intact LH. The strong activation of the gonadotrophs shortly after meiosis opens the possibility that a signal of testicular origin stimulates LH expression, in particular its 1 subunit. In the absence of a FSH-like gonadotropin in catfish, we propose that LH covers all functions requiring gonadotropic regulation in the African catfish.

Abstract: The acute toxicity of individual and mixtures of three herbicides (2,4-D, Garlon-3A, and Roundup) and a chemical additive (Syndets surfactant) was evaluated using three species of freshwater organisms (channel catfish, bluegill sunfish, and crawfish). Among the three herbicides, Roundup was more toxic to catfish and bluegill than Garlon-3A and 2,4-D. The order of toxicity in fish (Roundup > Garlon-3A > 2,4-D) was reversed in bioassays with crawfish, indicating a significant difference in interspecies (vertebrate vs invertebrate) biological variability. Adjusted 96 h LC50's were 14.5, 13.0, and 21,632.8 mg/L for Roundup, 109.5, 91.0, and 6,397.5 mg/L for Garlon-3A, and 181.2, 266.3, and 750.1 mg/L for 2,4-D, for catfish, bluegill, and crawfish, respectively. For Syndets surfactant, LC50 values of 1.9 mg/L (bluegill), 2.3 mg/L (catfish), and 15.2 mg/L (crawfish) were recorded, indicating that this chemical additive was much more toxic than the three herbicides. Bioassays with herbicide mixtures resulted in combined toxic effects that were slightly antagonistic and/or additive. Lethal concentrations of herbicide mixtures were found to be lower than recommended field formulations, but it was anticipated that such hazardous amounts would be rarely reached in roadside ditches where the presence of large volumes of water is likely to provide dilutions to levels that may not pose a threat to aquatic life. ©1997 by John Wiley & Sons, Inc. Environ Toxicol Water Qual 12: 237–243, 1997

Abstract: Juvenile African catfish, Clarias gariepinus (Burchell), of mean initial weight 15 g, were fed practical diets containing fresh or rancid oil (1:1 cod liver:corn oil) supplemented with either 20 or 100 mg all-rac-α-tocopheryl acetate per kg dry diet, at 0.03 × body weight per day for 8 weeks. After this time, catfish had grown by at least four times in body weight. Significant (P < 0.05) inter-treatment differences in final body weight were noted. Clarias fed low-tocopherol: oxidized-oil diets performed least well with regard to growth, though elevated dietary vitamin E partially abrogated this effect. Growth of fish fed fresh-oil diets did not benefit from increased dietary α-tocopherol content. Muscle, liver, plasma, heart and spleen all responded significantly (P < 0.05) to dietary vitamin E dose. Inclusion of oxidized oil in catfish diets decreased tissue α-tocopherol concentration. Hepatic α-tocopherol concentration (μg α-tocopherol per g liver) was observed to be lowered by 90% by the rancid oil diets. When fish previously fed fresh-oil diets were switched to oxidized: low-tocopherol diets, hepatic α-tocopherol concentration was significantly (P < 0.05) lowered within 2 weeks. The results highlight the importance of dietary oil quality in modulating tissue α-tocopherol concentrations in African catfish.

Abstract: Oxytetracycline (OTC) residues exceeding 0.1 ppm tolerance level were detected by capillary electrophoresis (CE) in catfish fillets 18 h after oral feeding with 37.5, 75.0, and 150.0 mg OTC/kg in medicated feed for 10 days. The CE migration time of OTC was 10.9 min using a 24 cm × 25 μm capillary under 8 kV constant voltage. The mean OTC recovery rates in spiked catfish were 92.9% over the concentrations of 0.1−25 ppm. Cooking procedures (frying, baking, and smoking at 190 °C) could only reduce but not completely eliminate OTC residues in catfish fillets. Keywords: Oxytetracycline; capillary electrophoresis; catfish; cooking; frying; baking; smoking

Abstract: Channel catfish Ictalurus punctatus fingerlings were fed purified diets supplemented with iron at levels of 0, 20, 60, and 180 mg/kg from iron sulfate (FeS) or 5, 10, 20, 60, and 180 mg/kg from iron methionine (FeM) in triplicate tanks for 8 wk. Fish were then divided into two groups and subjected to different assays to measure disease resistance and individual immune functions. Representative fish from each dietary treatment were challenged by bacterial immersion with virulent Edwardsiella ictaluri, and mortality due to enteric septicemia was recorded. Other fish were immunized with 0.2–mL formalin-killed E. ictaluri and boosted 21 d post-immunization. Antibody response was determined by FAST-ELISA. Chemiluminescent and chemotaxis assays were performed using peritoneal macrophages. Supplementation of the diet with various levels of iron from FeS or FeM did not significantly affect antibody production. Chemotactic migration by macrophages was depressed in iron-deficient fish and a level of 60 mgkg from either FeS or FeM provided the highest chemotactic indexes. A deficiency of dietary iron was found to increase mortality of channel caffish due to enteric septicemia of catfish (ESC). However, more studies should be conducted to better understand the effects of sources and levels of dietary iron on immune responses and disease resistance in channel caffish.

Abstract: As intensively cultured fish usually require high protein feeds, and since feeds are normally the largest variable cost item in commercial production, the profitability of intensive aquaculture is closely related to the world supply and cost of feed protein. Traditionally fish meal has been the major component of all fish feeds. However, its high cost has necessitated a search for alternative protein sources, especially those that are not suitable for human consumption. This study investigated the partial replacing of fish meal with alternative protein sources (tomato waste, soybean meal, brewers yeast) in iso-nitrogenous diets of C. gariepinus. The tomato used consisted of sun-dried pips and skins from ripe tomatoes used in the production of tomato pastes. The soybean consisted of either dehulled, solvent-(hexane) extracted soybean meal (Soy-2) or the same soy meal that had undergone a further extrusion process (Soy-1). The yeast used was a waste product from a local brewery. A final diet consisting of a mixture of the various ingredients was also prepared. Twenty-five catfish (30 to 45 g live mass (LM) were randomly allocated to 24 500 l tanks and four tanks were allocated to each diet. The tanks were then connected to a recirculating system (13 000 l total volume) and each had a flow rate of 7 ± 1 l·min. The water temperature was maintained at 25 ± 1 °C. The total biomass in each tank was measured weekly and the feed adjusted accordingly. The catfish were fed at 5% of total biomass for the first 4 d and 6% for the last 3 d of the week. The experiment was terminated after a 60 d feeding period. A statistical comparison of the final mean mass showed that all the diets differed significantly from each other (p=0.05), with the exception of the yeast and mixture diet and the yeast and Soy-1 diet. The descending ranking order of the mean final body mass (LM ± standard error, g) of the various diets was as follows: fish meal (284.6 ± 5.2), tomato (261.9 ± 5.3), yeast (222.2 ± 5.7), Soy-1 (220.5 ± 5.2), mix (201.4 ± 5.51), and Soy-2 (115.3 ± 5.5). The relatively strong growth experienced by fish receiving the tomato diet could possibly be caused by the high fish meal content of this diet. The poor growth of the Soy-2 diet is attributed to a high urease activity index (1.73). Soy-1 had an index of 0.07. The growth experienced by catfish fed the various protein sources indicates that C. gariepinus are able to utilise alternative protein sources successfully.

Abstract: The cDNAs encoding the glycoprotein hormone α-subunit (GPα) and the gonadotropin IIβ-subunit (GTH IIβ) were cloned from the pituitary gland of the African catfish, Clarias gariepinus. Using RNase protection analysis, we studied the steady-state mRNA levels of GPα as well as GTH IIβ in the pituitary gland of adult male catfish. Castration of adult male catfish resulted in a significant decrease of GTH IIβ mRNA levels, whereas there was no change in the GPα mRNA levels. Treatment of intact males with a single dose of 11-ketotestosterone (11-KT) resulted in dose-dependent increases in mRNA levels of both GPα and GTH IIβ. We conclude that 11-KT, a prominent, non-aromatizable teleost androgen, has a stimulatory effect on the pituitary mRNA levels of GPα and GTH IIβ of adult male fish.

Abstract: This study was conducted to determine if the level of dietary chromic oxide will affect glucose utilization and tissue chromium retention by channel catfish. Purified diets containing graded levels of supplemental chromic oxide (0, 50, 100, 200, 400, 1000, 5000 and 10,000 mg/kg diet) and glucose as the carbohydrate source were fed to channel catfish fingerlings for 10 wk. Another diet containing dextrin as the carbohydrate source and without chromic oxide supplementation was also fed and served as the control diet. Fish fed the dextrin diet had significantly (P < 0.05) greater weight gain, feed efficiency ratio and protein efficiency ratio but lower plasma glucose concentrations than fish fed the glucose diets irrespective of the level of chromic oxide supplementation. The growth performance and postprandial plasma glucose concentrations of channel catfish fed glucose diets supplemented with various chromic oxide levels were not significantly different. No obvious trends were observed in the whole-body composition of fish fed glucose diets containing various chromic oxide levels. Carbohydrate source or the level of dietary chromic oxide did not significantly affect chromium concentrations in the whole-fish carcass. These results suggest that the level of dietary chromic oxide had no significant effect on glucose utilization or chromium retention by channel catfish. It is suggested that chromic oxide is sufficiently inert to be used as an external marker in digestibility studies in channel catfish.

Abstract: The complete amino acid sequence of a basic liver fatty acid-binding protein (L-FABP) from catfish (Rhamdia sapo) was determined. Alignment of sequences shows that it has more similarity to chicken basic L-FABP than to mammalian L-FABP. The phylogenetic analysis suggests that basic L-FABP from catfish, chicken and iguana diverged from the mammalian protein before the fish-tetrapod divergence, thus implying that the two types are encoded by different genes. Supporting this conclusion, a 14-kDa protein, structurally closely related to mammalian L-FABP, was isolated from catfish intestine, indicating the presence of the two genes in the same species. The catfish basic L-FABP binds only one fatty acid/molecule, while mammalian L-FABP bind two. The former has more affinity for trans-parinaric acid than for cis-parinaric acid, in constrat to the latter proteins.