Vitamin C deficiency in the catfish Clarias gariepinus

Regardless of the absence of spinal deformities, vitamin C deprivation in adult-sized Clarias gariepinus challenged the physical integrity and survival of fish, inducing changes that greatly resembled those of fingerlings of other species. Vitamin C was presumed to be a dietary facilitator, which when deprived in the diet of C. gariepinus , would obstruct intestinal absorption of iron and/or impair its release from the reticulo-endothelial stores. This impaired erythrocyte synthesis led into anaemia (as indicated by lowered levels of red blood cells, haemoglobin and haematocrit). Leukopenia noted in fish on a scorbutic (lacking vitamin C) diet suggested functional depression of phagocytic engulfment with increased susceptibility to the deteriorating action of pathogenic agents. Changes in histology included hypertrophy, oedematous separation and telangiectasia of gill lamellae. Shrunken glomeruli, sloughed Bowman's capsules and tubular dilation and distortion were also shown. Shrunken hepatocytes and the occurrence of yellowish ceroid pigments were the concrete histopathological signs in liver. Vitamin C is thus suggested as a potent antioxidant that offers protection against oxidative damage to various fish tissues.     

Purification of vitellogenin from the air breathing catfish, Clarias gariepinus

Vitellogenin (Vtg) is a female specific glycophospholipoprotein which can be induced both in male and female with estradiol and xeno-estrogens. The basic theme behind the purification of vitellogenin from the fish is to understand the evolutionary relationship and for the purification and characterization of the Vtg receptor. The male catfish, Clarias gariepinus was administrated with estradiol over a period of time for the synthesis of Vtg and the serum was collected. The Vtg was purified from the serum using a two step chromatographic technique. The serum was passed on to DEAE-ion exchange column and the protein was eluted using a salt gradient. The fractions containing the Vtg were pooled and passed onto a gel permeation chromatography column and the pure protein was obtained. The molecular weight is around 200 kDa on the SDS-PAGE and around 520 kDa on the native gel electrophoresis.     

A simulation model for the metabolism of yolk sac larvae of the African catfish, Clarias gariepinus (Burchell)

Abstract. In fish larvae there is a strong natural selection for high yolk utilization efficiencies and high yolk absorption rates. Larvae with higher absorption and utilization will be larger at the onset of exogenous feeding, leading to higher survival and growth rates in the following stages of development. Modelling can be a powerful tool in clarifying the processes of fish larvae metabolism, providing the model is as explanatory as possible. The present model considers the larvae as a two-compartment system: the yolk sac and the larval body. This system exchanges oxygen, carbon dioxide, water, ammonia and heat with the environment. Yolk is absorbed through the syncytium, digested, and the resulting nutrients are released into the blood circulation. Circulating amino acids and fatty acids are considered to be used first for respiration, and what is left will be used for growth. From the moment that absorbed nutrients do not satisfy the energy needs, embryo tissue starts to be catabolized. Temperature is the only environmental factor which was assumed to affect significantly the metabolic processes. From the comparisons between simulations and experimental data, the simulations would appear to be accurate until complete yolk absorption, losing accuracy afterwards. Simulation outputs suggest that fat is the main energy substrate during yolk absorption, with protein becoming progressively more important, being predominant during starvation. Ideal culture conditions for African catfish yolk sac larvae seem to include: the highest temperature that combines with acceptable mortality rates; selection of broodstck towards obtaining the largest egg size, insofar as viability is not affected; the start of feeding as close as possible to 144 physiological day-degrees.     

Stress in African catfish (Clarias gariepinus) following overland transportation

Of the many stressors in aquaculture, transportation of fish has remained poorly studied. The objective of this study was therefore to assess the effects of a (simulated) commercial transportation on stress physiology of market-size African catfish (Clarias gariepinus). Catfish weighing approximately 1.25 kg were returned to the farm after 3 h of truck-transportation, and stress-related parameters were measured for up to 72 h following return. Recovery from transportation was assessed through blood samples measuring plasma cortisol, glucose and non-esterified fatty acids (NEFA) and gill histology. Also, the number of skin lesions was compared before and after transport. Pre-transport handling and sorting elevated plasma cortisol levels compared to unhandled animals (before fasting). Plasma cortisol levels were further increased due to transportation. In control fish, plasma cortisol levels returned to baseline values within 6 h, whereas it took 48 h to reach baseline values in transported catfish. Plasma glucose and NEFA levels remained stable and were similar across all groups. Transported catfish did not, on average, have more skin lesions than the handling group, but the number of skin lesions had increased compared to unhandled animals. The macroscopic condition of the gills was similar in control, transported and unhandled catfish; however, light microscopy and immunohistochemistry revealed atypical morphology and chloride cell migration normally associated with adverse water conditions. From our data, we conclude that transportation may be considered a strong stressor to catfish that may add to other stressors and thus inflict upon the welfare of the fish.     

Sertoli cell proliferation and FSH signalling in African catfish, Clarias gariepinus

Sertoli cell proliferation occurs mainly during the phase of rapid spermatogonial proliferation, allowing the cyst-forming Sertoli cells to form an increasingly large space for housing the growing germ cell clone. There is no information in fish on the regulation of Sertoli cell proliferation; follicle-stimulating hormone (FSH) stimulates Sertoli cell proliferation in mammals. Increasing or decreasing FSH and FSH receptor expression experimentally in male African catfish was associated with respective changes in Sertoli cell proliferation or testis growth, suggesting that also in fish, one role of FSH may be to regulate Sertoli cell numbers.     

Thyroid hormone modulation of ovarian recrudescence of air-breathing catfish Clarias gariepinus

In the present study, thiourea-induced thyroid hormone depletion and thyroxine (T₄) ‘overdose’ were used as a strategy to understand the influence of thyroid hormones on ovarian recrudescence of juvenile (3-months-old), immature (8-months-old) and adult (1-year-old) air-breathing catfish, Clarias gariepinus. Thiourea-induced thyroid hormone depletion in juvenile catfish impaired ovarian development, but no significant effect was observed in immature catfish and during late stage of ovarian recrudescence of mature catfish. T₄ treatment in females undergoing late stages of ovarian recrudescence induced rapid oocyte growth by promoting its early entry into maturational phase as evident from the presence of more number of vitellogenic and post-vitellogenic follicles, decrease in aromatse immunoreactivity and reduced estradiol–17β levels. Hence, thyroid hormones have an important role to play during early stages of ovarian development and vitellogenesis of catfish and also indicating that thyroid has a stage dependent effect on ovary.     

Thyroxine-induced alterations in the testis and seminal vesicles of air-breathing catfish, Clarias gariepinus

Effect of experimentally induced thyroxine overdose on the testis and seminal vesicles was studied in the air-breathing catfish, Clarias gariepinus during the preparatory and the pre-spawning phase. The present study revealed a marked reduction in testosterone level in serum, testis and seminal vesicles (SV). Histological examination showed a considerable reduction in the number of spermatozoa/spermatids in the seminiferous tubular lumen as well as depletion of fluid in the loculi of SV. SDS-PAGE analysis of SV fluid proteins demonstrated a significant decrease in the level of a ~27 kDa protein in thyroxine treated fishes. Evidences are presented here to indicate that thyroid hormone plays a role in regulating testis and SV function in catfish. T.N. Jacob and J.P. Pandey contributed equally     

Catecholestrogens inhibit dopamine methylation in the gonadotrops of the African catfish,Clarias gariepinus

Isolated gonadotrops of the African catfish,Clarias gariepinus, were incubated with dopamine (DA) and/or catecholestrone and the activity of the enzyme catechol-O-methyltransferase (COMT) was determined by measuring the methylated products. From the apparent Km values for DA and catecholestrone of 0.4–1.3 M and 17.9–25.2 M respectively, it was concluded that catecholestrone is a better substrate for the enzyme COMT, compared to DA. Moreover, the methylation of DA is inhibited by comparatively low concentrations of catecholestrone.     

Steroidogenesis during induced oocyte maturation and ovulation in the African catfish,Clarias gariepinus

Changes in ovarian steroidogenesis accompanying oocyte maturation and ovulation were studied in the African catfish,Clarias gariepinus. Laboratory-reared females with postvitellogenic ovaries were treated with pimozide and LHRH-analogue. The plasma gonadotropin levels were determined by means of a homologous radioimmunoassay, the condition of the ovaries was studied by histological examination of the follicles, and the steroidogenetic capacity of the ovaries was analyzed byin vitro incubation of tissue fragments for 3 h with [³H]-pregnenolone and [³H]androstenedione as precursors. Data were collected at regular intervals between 0 and 16 h after pimozide-LHRH analogue administration.Until 4 h after the beginning of the experiments the plasma gonadotropin levels did not rise above 25 ng/ml, the ovaries remained in the stage of postvitellogenesis, and testosterone was the main end product of steroidogenesis. Four hours later the gonadotropin concentration in the blood had risen to more than 150 ng/ml, and the ovaries had entered the stage of germinal vesicle migration. At the same time steroidogenesis shifted towards the production of 17,20-dihydroxy-4-pregnen-3-one, 5-pregnane-3, 17-diol-20-one, 5-pregnane-3,6,17-triol-20-one, 5-pregnane-3,17,20-triol and 5-pregnane-3,6,17,20-tetrol. During the subsequent stage of germinal vesicle breakdown the plasma gonadotropin level remained high, and the synthesis of the C₂₁-steroids showed a further increase. Simultaneously, the production of some C₁₉-steroid glucuronides was enhanced. The preovulation and especially the postovulation stages were accompanied by a gradual decrease in steroidogenic capacity of the ovaries, even though the plasma gonadotropin level remained high. It is concluded that the prematuration surge of gonadotropin influences the activity of enzymes involved in steroidogenesis, leading to a reduced C_17,20-lyase and to an augmented activity of the enzymes 20-hydroxysteroid dehydrogenase (HSD), 5-reductase, 3-HSD, 6-hydroxylase and UDP-glucuronosyltransferase. During ovulation the activity of all steroidogenic enzymes, including such key enzymes as 3-HSD and 17-hydroxylase, gradually decreases.Not only 17,20-dihydroxy-4-pregnen-3-one, but also the 5-reduced pregnanes may be involved in inducing oocyte maturation and/or ovulation. The very polar triol and tetrol products may function, together with the steroid glucuronides as sex pheromones.A preliminary account of these results was presented at the XIII Conference of European Comparative Endocrinologists, Belgrade, September 7–12, 1986     

Evaluation of full-fat and defatted maggot meals in the feeding of clariid catfish Clarias gariepinus fingerlings

The nutritional implication of processed maggot meals, hydrolysed, defatted, full‐fat, sun‐dried and oven‐dried, in the diets of Clarias gariepinus fingerlings were evaluated. The nutrient density, proximate composition, gross energy and mineral constituents of the maggot meals were determined. Five isonitrogenous and isocaloric diets were formulated to provide 40% crude protein in which fish meal in the reference diet was completely replaced by any of the following processed maggot meals: oven‐dried full‐fat (ODM), sun‐dried full‐fat (SDM), defatted oven‐dried (DODM) and defatted sun‐dried (DSDM) maggot meals respectively. Fish were fed ad libitum in triplicate treatments for 56 days in glass tanks. Biological evaluations of the fish were based on growth performance and nutrient utilization indices. The result of the nutrient composition analysis showed that processing methods of defattening and drying influenced the nutrient density of maggot meal, with crude protein content ranging between 43.30% and 46.70% for full‐fat sun‐dried and hydrolysed/defatted oven‐dried maggot meals respectively. The result showed that growth performance and nutrient utilization of fish fed DODM and DSDM dietary inclusions were not significantly different and similar to fish fed the fish meal‐based diet. However, fish fed the diet containing SDM exhibited lower daily weight gain, protein efficiency ratio and specific growth. Generally, fish performed better when fed diets containing defatted maggot meals than full‐fat maggot meal, and compared favourably with fish fed the fish meal‐based diet.     

Mismatch between patterns of circulating and testicular androgens in African catfish, Clarias gariepinus

11-Ketotestosterone (11-KT) is an important plasma androgen in male African catfish. The quantitatively predominating androgen produced by the testis, however, is 11-hydroxyandrostenedione (OHA). Our working hypothesis to explain this mismatch assumed that OHA is converted to 11-KT at extratesticular sites. First, we examined the in vivo metabolism of [³H]-OHA in mature males after sham-operation or removal of either the testes (TC), the seminal vesicles (SVC), or both (TSVC) by analysing the pattern of circulating [³H]-androgens two hours after intravenous injection of [³H]-OHA. [³H]-OHA was converted to [³H]-11-KT to the same extent in all groups, indicating that neither ablation of testes nor of seminal vesicles, or both attenuates this conversion. We then examined the in vitro metabolism of [³H]-OHA by several types of tissues. Liver and seminal vesicle tissue were found to produce significant amounts of [³H]-11-KT. The conversion capacity in vivo was assessed by injecting TSVC-castrated males with increasing doses of radioinert OHA, followed by the quantification of OHA and 11-KT plasma levels. Saturation of the conversion capacity was not reached but the 11-KT production capacity is at least 80 ng per ml of plasma per hour. Moreover, liver fragments were tested for their OHA to 11-KT conversion capacity in vitro using increasing concentrations of radioinert OHA. The 11-KT producing increased with time and OHA concentration. The production rate was 90 pg 11-KT mg^-1 liver h^-1. Considering the results of the surgical experiments and the fact that the total hepatic mass by far exceeds that of the seminal vesicles, we conclude that the hepatic conversion is of primary relevance in vivo.     

Petroleum – induced free radical toxicity in African catfish (Clarias gariepinus)

The reaction products derived from lipid peroxidation, as well as superoxide dismutase and catalase enzyme activities were measured in tissues of catfish (Clarias gariepinus) exposed to oil in water dispersions of 0%, 0.5%, 1.0% and 1.5% for 0, 7, 14, 21 and 28 days. Lipid peroxidation significantly (P<0.05) increased in various tissues relative to control values after 14, 21, and 28 days of exposure to 1.0% and 1.5% oil in water dispersions. Catalase and superoxide dismutase activities decreased after 7 days of exposure but significantly (P<0.05) increased after 14, 21 and 28 days of exposure to 1.0% and 1.5% oil in water dispersions. The elevated levels of lipid peroxidation, superoxide dismutase and catalase activities in all tissues examined in C. gariepinus could be a reflection of oxidative stress on the fish. These observations seem to implicate that petroleum hydrocarbons act as a mediator in free radical generation. The increase in catalase and superoxide dismutase activities in these tissues could be an adaptive response to protect the fish from petroleum-hydrocarbon-induced free radical toxicity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preliminary studies on the renaturation of denatured catfish (Clarias gariepinus) glutathione transferase

Purified juvenile catfish (Clarias gariepinus) glutathione transferase (cgGST) was denatured in vitro and renatured in the absence and presence of different concentrations of endogenous or xenobiotic model substrates. Protein transitions during unfolding and refolding were monitored by activity measurement as well as changes in protein conformation using UV difference spectra at 230 nm. Gdn-HCl at 0.22 M caused 50 % inactivation of the enzyme and at 1.1 M, the enzyme was completely unfolded. Refolding of cgGST main isozyme was not completely reversible at higher concentrations of Gdn-HCl and is dependent on protein concentration. An enzyme concentration of 30 μg/ml yielded 40 % percentage residual activity in the presence of glutathione (GSH), regardless of the concentration that was present as opposed to 30 % obtained in its absence. The xenobiotic model substrate, lindane, appears to have no effect on the refolding of the enzyme. In summary, our results show that GSH assists in the refolding of cgGST in a concentration-independent manner and may be involved in the same function in vivo whereas the xenobiotic model substrate does not.     

Balance trials with African catfish Clarias gariepinus fed phytase-treated soybean meal-based diets

Balance trials were conducted with African catfish Clarias gariepinus to assess the effect of phytase treatment of soybean meal-based diets on growth, feed utilization and nutrient budgets. Isocaloric (20–22 kJ g⁻¹) and isonitrogenous (47–50% protein) diets were tested. In a first experiment the control diet (58% fish meal and 18% soybean meal) was compared with two diets containing 6% fish meal and 69% soybean meal, and two diets containing 29% fish meal and 41% soybean meal. One of each of these two diets had been pretreated with phytase (1000 units per kg dry diet). In the second experiment, the control diet (6% fish meal and 69% soybean meal, pretreated with 1000 units phytase kg⁻¹ dry diet) was compared with four diets that were similar in composition but supplemented with increasing amounts of phytase (15, 380, 750, 1000 units kg⁻¹ dry diet). Replacement of fish meal by soybean meal in the first experiment led to a depression in growth rate and feed utilization parameters. Results of both experiments clearly indicated a positive effect of phytase treatment, particularly on phosphorus digestibility and retention, and consequently the phosphorus conversion efficiency and the phosphorus budget. No differences in these parameters were found between addition of equal amounts of phytase by pretreatment or supplementation.     

Optimum histidine requirement of fry African catfish, Clarias gariepinus (Burchell)

Dietary histidine requirement of fry African catfish, Clarias gariepinus (2.57 ± 0.02 cm; 0.22 ± 0.03 g) was quantified by feeding casein–gelatin-based isonitrogenous (40% crude protein) and isocaloric (17.90 kJ g⁻¹ gross energy) amino acid test diets with graded levels of histidine (0.25%, 0.30%, 0.35%, 0.40%, 0.45% and 0.50% dry diet) in eighteen 80 L indoor circular aqua-coloured troughs provided with the flow-through system for 12 weeks. Maximum absolute weight gain (2.66), best feed conversion ratio (1.29), highest protein efficiency ratio (1.94), protein retention efficiency (34%) and energy retention efficiency (70.4%) were achieved at 0.40% dietary histidine. Broken-line and non-linear regression models were adopted to assess dietary histidine requirement for C. gariepinus . When analysed using broken-line regression model these parameters were also best at 0.40% dietary histidine corresponding to 1.0% protein, respectively, whereas using second-degree polynomial regression analysis, histidine requirement was obtained at 0.42%, 0.41%, 0.40%, 0.41% and 0.41% of dry diet, corresponding to 1.05%, 1.02%, 1.0%, 1.02% and 1.02% protein respectively. Based on the broken-line and second-degree polynomial regression analyses of the growth and nutrient retention data, optimum histidine requirement of fry C. gariepinus was found to be in the range of 0.40–0.42% dry diet, corresponding to 1.0–1.05% of dietary protein.     

Nicotinic acid supplementation of diets for the African catfish, Clarias gariepinus (Burchell)

Semi-purified diets containing 39% crude protein and 5% lipid were used to identify the qualitative requirement of African cattish, Clarias gariepinus (Burchell), for niacin and to characterize the pathologies associated with a deficiency of this vitamin. After 48 days of feeding, C. gariepinus supplied with the unsupplemented diet had developed severe deficiency symptoms and were subsequently withdrawn from the growth study. Niacin deficiency was characterized by feed refusal, listlessness, weight loss, poor feed utilization and high mortality. The skin overlaying the lateral line of the deficient fish became haemorrhagic and this clinical sign was accompanied by severe anaemia. After 126 days of feeding, fish fed diets containing 17.0 mg niacin kg^?1 had also developed a dermopathy. but without anaemia or high mortality. The feeding of diets containing less than 33.1 mg niacin kg^?1 resulted in suboptimal feed efficiency and poor protein utilisation. Allometric analysis of proximate composition indicated that carcass moisture, protein and ash were influenced by fish size, and not by dietary niacin content. However, significantly more lipid per unit of weight gain was deposited in the carcasses of fish fed the unsupplemented diet than in fish fed diets containing 17.0mgkg^?1. The indicators used in the present study could not be applied to accurately determine a value for niacin requirement. However, until a more accurate assessment is performed, it is recommended that diets for C. gariepinus contain not less than 33.1 mg nicotinic acid kg^?1 feed.     

Characterization of the receptor for gonadotropin-releasing hormone in the pituitary of the African catfish,Clarias gariepinus

Receptors for gonadotropin-releasing hormone (GnRH) were characterized using a radioligand prepared from a superactive analog of salmon GnRH (sGnRH), D-Arg⁶-Pro⁹-sGnRH-NEt (sGnRHa). Binding of¹²⁵I-sGnRHa to catfish pituitary membrane fractions reached equilibrium after 2 h incubation at 4°C. Displacement experiments with several GnRH analogs as well as other peptides, demonstrated the specificity of¹²⁵I-sGnRHa binding. Specific binding was enhanced in the presence of the cation chelator ethylene bis (oxyethylenenitrilo) tetra-acetic acid (EGTA), indicating an inhibitory effect of cations on GnRH-receptor binding. The binding of¹²⁵I-sGnRHa to pituitary membranes was found to be saturable at radioligand concentrations of 5 nM and above. A Scatchard analysis of the saturation data suggested the presence of a single class of high-affinity binding sites (Ka=0.901±0.06×10⁹M^–1, Bmax=1678±150 fmol/mg protein). A comparative study on¹²⁵I-sGnRHa binding to pituitary membrane fractions of male and female catfish, indicated that there were no differences in binding affinity and binding capacity between both sexes. The results demonstrate the presence of specific, saturable GnRH receptors in the African catfish pituitary.     

Acute toxicity of inorganic fertilizers to African catfish, Clarias gariepinus (Teugals)

Abstract. Acute toxicity of Ca(OH)₂, NPK, Na₃PO₄ 12H₂O and NaNO₃ fertilizers on Clarias gariepinus (Teugals) was investigated in glass aquaria. Results showed that Ca(OH)3 was the most toxic of the four fertilizers. Na3PO4.12H2O and NaNO3 were less toxic. The 96-h LC50 for the fertilizers ranged from 33.9 mg/l for Ca(OH)2 to 1258.9 mg/1 for NaNO3. It is concluded that secondary application of these fertilizers in stocked ponds should be avoided.