African catfish, Clarias gariepinus (Burchell, 1822): an ideal candidate for biowaste management

Juveniles of African catfish, C. gariepinus were fed with different biowastes procured from various stations viz., slaughter houses, poultry sheds, fish markets, hotel kitchens and ware houses. Maximum growth was obtained in the fishes fed with poultry wastes and minimum in the fishes fed with warehouse waste. Total protein, fat, and dry matter contents were high in poultry and butcher wastes fed fishes. Culture of catfishes in controlled conditions by feeding biowaste is an alternative step to control the prevailing wide spreading culture practices of African catfish, which poses a threat to inland aquatic biodiversity. The present approach is ideal for recycling biowastes to fish protein and to keep our environment clean and hygienic.     

Affinity purification and partial characterization of IgM-like immunoglobulins of African catfish, Clarias gariepinus (Burchell, 1822)

IgM like macroglobulin from bovine serum albumin (BSA)-immunized African catfish C. gariepinus was purified by affinity chromatography and partially characterized. The molecular weight of this macroglobulin was 840 kDa, as estimated by gel filtration chromatography. Purified macroglobulin was analyzed using SDS-PAGE under reducing and non-reducing conditions. The molecular weight (MW) of heavy and light chain was 74.8 kDa and 27.2 kDa respectively, in presence of a reducing agent. In non-reducing SDS-PAGE, a single high MW band was observed representing tetrameric form.     

Trematode metacercariae from the cranial cavity of African catfish Clarias gariepinus (Burchell, 1822) from Lake Tana,Ethiopia

Metacercariae of two species of trematodes from the fam. Diplostomidae from the cranial cavity of the African catfish Clarias gariepinus are described. The metacercaria Tylodelphys grandis n. sp. is described for the first time. Data are presented on the infection rate of catfishes in Lake Tana.     

Sublethal effects of aquatic pollution in Lake Maryût on the African sharptooth catfish, Clarias gariepinus (Burchell, 1822)

Some aspects of the physiology and biochemistry of the African sharptooth catfish, Clarias gariepinus (Burchell, 1822), were studied along with an array of physicochemical characteristics of the water in Lake Maryût, Egypt. Data were compared to those of a reference fish hatchery. At least 11 of the conventional water pollutants (Cd, Cu, Fe, Pb, Mn, Hg, Ni, Zn, turbidity, chemical oxygen demand and ammonia nitrogen) were elevated in the most polluted main basin of the lake. In turn, serologic analysis of the indigenous catfish C. gariepinus pointed at functional impairment of the liver, heart and kidney as reflected by the elevated activities of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, creatine kinase, cholinesterase, glucose and creatinine. Reduced nucleic acid measurements [the ratio RNA/DNA and the relative RNA content (r)] indicated diminished protein synthesis and impaired growth in polluted fish. In some instances, glucose and nucleic acid measures were elevated in favour of fish from moderately polluted basins of the lake rather than in reference fish. Fish seemed to profit from the typical geographical habitat in the lake, regardless of the virtual contamination there, versus reference fish that seemed to suffer congestion stress and food competition in the confined and overcrowded commercial pond.     

A chemical comparison between the golden and normal coloured strains of the African sharptooth catfish, Clarias gariepinus (Burchell 1822)

The skin and muscle chemical comparisons from normal and golden coloured African sharptooth catfish, Clarias gariepinus , of two different size (± 360 and ± 1500 g live mass) groups are reported. The skin of the golden strain is shown to be that of an albino that contains no melanin. Size has a stronger influence than strain on the proximate, fatty acid, amino acid and mineral profiles of both the skin and muscle. For both strains, the larger size class had statistically (P > 0.05) lower muscle moisture and higher total lipid content than the smaller size class. There was no significant difference in the muscle protein content (16.7–17.6% wet mass basis) between and within the strains and size classes. The skin has higher concentrations of glycine, proline and hydroxyproline than the muscle. The major fatty acids in both the skin and muscle were palmitic (> 23%) and oleic (>28%). Of the muscle minerals, potassium was significantly (P > 0.05) higher in the larger size class for both strains. The lack of any tangible difference in the muscle chemical composition of both strains therefore makes the golden catfish strain more attractive for the fresh fish consumer.     

Growth response of African catfish, Clarias gariepinus (Burchell) to varied protein and lipid levels

To study the growth response of African catfish (Clarias gariepinus) to the diets containing two protein (30 and 35%) and two lipid levels (12 and 18%) in a closed recirculatory system for 60 days, fish were fed to satiation twice daily. The experiment was carried out in triplicate groups. Fortnightly sampling of fish and water samples was carried out. The best result in terms of growth was obtained with the diet containing 34.62% protein and 12.12% lipid. The protein to lipid ratio was 18.57 in the diet that gave best percentage weight gain. However best survival, food conversion ratio and protein efficiency ratio were recorded in the diet containing 29.86% protein and 18.08% lipid.     

Gonadotropin-releasing hormone-immunoreactive neuronal structures in the brain and pituitary of the African catfish,Clarias gariepinus (Burchell)

Summary The distribution of gonadotropin-releasing hormone (GnRH) immunoreactivity was studied in the African catfish, Clarias gariepinus, by means of immunofluorescence and immunoperoxidase techniques. Immunoreactive neurons were found throughout the preoptic nucleus (NPO). However, only a portion of the secretory perikarya in the NPO showed a positive reaction by use of an anti-LHRH serum. Numerous immunoreactive fibres were found to enter the pituitary and to terminate in its proximal pars distalis, the site of concentration of the gonadotropic cells. Since GnRH is present in the brain and pituitary of the African catfish, the lack of spontaneous ovulation in captivity is apparently due to an insufficient release of GnRH.     

The seminal vesicle of the African catfish,Clarias gariepinus

Summary The seminal vesicle of the African catfish, Clarias gariepinus, consists of 36–44 fingerlike lobes built up of tubules in which a fluid is secreted containing acid polysaccharides, acid-, neutral- and basic proteins, and phospholipids. In this fluid sperm cells are stored. The seminal vesicle fluid immobilizes the sperm cells. After ejaculation, it prolongs the period of sperm activity. The seminal vesicle fluid is secreted by the epithelium lining the tubules. The tubules in the proximal part of the lobes are predominantly lined by a simple cylindrical and those of the distal part by a simple squamous epithelium. These epithelial cells contain enzymes involved in energy-liberating processes, the enzyme activites being proportional to the height of the cells. Interstitial cells between the tubules have enzyme-histochemical and ultrastructural features indicative of steroid biosynthesis. Similar characteristics are found in testicular interstitial cells. The most rostral seminal vesicle lobes and the most caudal testicular efferent tubules form a network of tubules that opens at the point where the paired parts of the sperm ducts fuse with each other. The tubules of most seminal vesicle lobes, however, form a complex system that fuses with the unpaired part of the sperm duct.     

Two gonadotropin-releasing hormones from African catfish (Clarias gariepinus).

Two forms of gonadotropin-releasing hormone (GnRH) have been purified from brain extracts of the African catfish, Clarias gariepinus, using reverse-phase high performance liquid chromatography (HPLC) and radioimmunoassay (RIA). The amino acid sequences of both forms of African catfish GnRH were determined using Edman degradation after digestion with pyroglutamyl aminopeptidase. In addition, both GnRHs were studied by mass spectrometry. The primary structure of African catfish GnRH I is identical to Thai catfish GnRH I, pGlu-His-Trp-Ser-His-Gly-Leu-Asn-Pro-Gly-NH2, and the primary structure of African catfish GnRH II is identical to the widely distributed and highly conserved chicken GnRH II, pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2.     

Seminoma in hybrid catfish [Clarias batrachus (Linnaeus) female x Clarias gariepinus (Burchell) male

Spontaneous testicular tumors, seminoma, were noticed in four male hybrid catfish (C. batrachus female x C. gariepinus male) after the age of two years. The hybrids showed massive abdominal swelling with catchectic body and free lobulated, encapsulated tumors (> 325 g) within the serosanguinous fluid-filled peritoneal cavities. The tumor cells were large and polyhedral with prominent centrally located nuclei. Other vital organs appeared normal. It seems to be the first report of seminoma in hybrid catfish and possibly of genetic cause.     

Male-specific DNA markers from African catfish (Clarias gariepinus)

We searched for sex-specific DNA sequences in the male and female genomes of African catfish, Clarias gariepinus (Burchell, 1822) by comparative random amplified polymorphic DNA (RAPD) assays performed on pooled DNA samples. Two sex-linked RAPD markers were identified from the male DNA pool and confirmed on individual samples, showing good agreement with phenotypic sex. Both markers were isolated, cloned and characterized. The first marker (CgaY1) was nearly 2.6 kb long, while the length of second one (CgaY2) was 458 bp. Southern blot analysis with a CgaY1 probe showed strong hybridizing fragments only in males and not in females under stringent conditions, indicating the presence of multiple copies of CgaY1 in the male genome. When tested by zoo blot on the genomes of two closely related species from the Clariidae family, CgaY1 hybridized to the DNA of Heterobranchus longifilis and generated a faint male-specific band at low stringency. CgaY2 produced similar hybridization pattern in both sexes of C. gariepinus, C. macrocephalus and H. longifilis. Specific primers were designed to the sequences and the markers were amplified in multiplex PCR reactions together with a control band common to all individuals. This allowed for rapid, molecular sexing of the species on the basis of a simple three band (male) versus one band (female) pattern. According to our knowledge these are the first sex-specific DNA markers isolated from a siluroid fish species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Introduction of the African Catfish Clarias gariepinus (BURCHELL, 1822) into Southern Brazil

We record here the introduction of the African catfish Clarias gariepinus into the Guaraguaçu River basin in Paraná State, Brazil, an area with an extremely rich endemic fish fauna, including many catfishes. C. gariepinus was introduced as escapees from ponds built for recreational angling. These catfishes are very large and hard predators, thus posing serious potential for impact on the native fish fauna. The impact of C. gariepinus needs study with emphasis on finding means for controlling its spread.     

The effects of aromatizable androgens,non-aromatizable androgens,and estrogens on gonadotropin release in castrated African catfish,Clarias gariepinus (Burchell)

Summary To study the feedback mechanism of gonadal hormones on GTH secretion in male African catfish, the effects of castration and steroid replacement on GTH release, pituitary GTH content, and ultrastructural appearance of gonadotropes were investigated.Castration resulted in an increase in plasma GTH levels, a decrease in pituitary GTH content, and a degranulation of many gonadotropes. The aromatizable androgens testosterone and androstenedione were able to abolish the castration-induced increase in plasma GTH. This was accompanied with a restoration of pituitary GTH content and a regranulation of gonadotropes. The non-aromatizable androgens 5-dihydrotestosterone and 11-hydroxyandros tenedione did not have these effects. Replacement with estrone or estradiol resulted in an increase in pituitary GTH, however, without abolishing the elevated plasma GTH levels; ultrastructurally, many gonadotropes showed a welldeveloped granular endoplasmic reticulum together with a regranulation.The results of the present study indicate the significance of androgen aromatization in the feedback mechanism of gonadal steroids on the brain-pituitary axis.     

Effects of feeding on survival, cannibalism, growth and feed conversion of African catfish, Clarias gariepinus (Burchell) in concrete tanks

Daily feeding rates of 0, 2, 4, 6, 8 and 10% of body weight to juvenile (average weight 0.64–65.4 g) catfish, Clarius gariepinus, for 112 days had significant effects on survival, cannibalism, growth and feed conversion ratio (FCR). Survival was significantly higher in fish fed at 6–10% of body weight than those fed at 2–4%. Mortality was mainly caused by cannibalism, being significantly higher in underfed (2–4%) fish than in fish fed at the 6–10% level. A feeding level above 6% did not further reduce cannibalism. The best growth performance was recorded for the fish fed at 8–10% body weight, followed by the fish fed at 4–6%; poorest growth was found for those fed at the 2% level. FCR significantly increased from 2–4% (FCR, 1.14–1.13) to 6, 8 and 10% (FCR, 1.37, 2.18, 2.98, respectively). The results of this study suggest that the optimum feeding rate of juvenile catfish with an average initial weight of about 0.64 g and grown to a size of about 64 g is at 6% body weight per day.     

Dietary influences on product quality in African catfish (Clarias gariepinus)

In this trial a full-sib family of Clarias gariepinus was raised under standard conditions in a warmwater recirculation system. The fish were divided into two experimental groups of 1200 individuals each and were raised in separate tanks. The groups were fed two experimental diets differing in crude protein (group I 40% and group II 52% DM) and crude fat (group I 8% and group II 13% DM). Gross energy was 21.3 and 22.1 MJ/kg. Slaughtering of 100 fish per group (50 males, 50 females) took place after two experimental periods. Besides the significant effect of the diets on body weight and size, a higher degree of corpulence was observed in group II. Tissue and organ percentages were not influenced, except a higher intestinal fat deposition in intensively fed fish. This group also showed a higher carcass weight. More expressed differences between both feeding alternatives were observed in physical and chemical flesh quality criteria. In group I texture of flesh was firm and water-binding-capacity was significantly increased in group II. The appearance of the filet was affected by the diet. Intensively fed catfish showed a tendency to a lighter and more yellowish colour. The chemical composition of the flesh indicated a significant increase of dry matter caused by higher protein and fat contents in this group. A strong influence of sex and fattening age on inner and outer product quality was evident. High fat and protein content of the diet has a certain influence on product quality in African catfish. It can be concluded that there is a clear effect of diet on quantitative criteria with a tendency to higher slaughtering yields in intensively fed catfish.     

Nutritive value of dried lactic acid fermented fish silage and soybean meal in dry diets for juvenile catfish, Clarias gariepinus (Burchell, 1822)

Dry diets containing either fish meal (C-FM) or dried fermented fish silage and soybean meal blend (1:1, ww⁻¹) (C-FS) as the sole protein source, were fed to triplicate groups of juvenile Clarias gariepinus (10.8 ± 0.3 g) at 5% body weight per day for 70 days. Catfish fed the C-FS diet showed reduced (P < 0.05) growth rate, feed conversion, protein efficiency and digestibility. Lower amounts of available amino acids in the C-FS diet resulted in inferior nutritive value for catfish growth than in the C-FM diet. Postprandial changes in plasma amino acids showed similar patterns in both diet treatments, but the maximal mean levels attained for the C-FS diet were correspondingly lower and occurred earlier than with the C-FM diet. There were no effects of feeding C-FS diet on the hepatosomatic index but carcass analysis showed that body protein deposition was lower (P < 0.05). Differences in haematocrit, haemoglobin content and liver histology were demonstrated but were not pathological. Lower digestible energy of C-FS diet also contributed to the poor performance of catfish in this treatment. Results of this study indicate that C. gariepinus cannot metabolize protein from co-dried fish silage as efficiently as fish meal protein when used as the sole dietary protein.     

Effects of in vivo crude human chorionic gonadotropin on ovulation and spawning of the African catfish, Clarias gariepinus Burchell–1822

The effects of increasing dosages of crude human chorionic gonadotropin (cHCG) on ovulation and spawning of Clarias gariepinus Burchell were examined. Four and 5 mg cHCG/100g body weight of fish gave the best response. The activation of the interrenals and stimulation of the ovary are discussed as a possible route of in vivo human chorionic gonadotropin administration on ovulation and spawning in catfish.     

Survival,growth and feed utilization of two clariid catfish (Clarias gariepinus,Burchell 1822 and Heterobranchus bidorsalis,Geoffroy, 1809) and their reciprocal hybrids

An experiment was conducted to determine the survival rate, fertilization rate, growth performance and feed utilization of two African clariid catfish Clarias gariepinus and Heterobranchus bidorsalis and their reciprocal hybrids. Four genetic crosses were made: C. gariepinus♀ × C. gariepinus♂, H. bidorsalis♀ × H. bidorsalis♂, C. gariepinus♀ × H. bidorsalis♂ and H. bidorsalis♀ × C. gariepinus♂. The experiment was divided into two phases: artificial propagation of the fish species using a synthetic hormone and rearing the fry for 14 days, then further rearing the 14‐day‐old fry for an additional 35 days. In the first phase of the experiment, fry survival was estimated in each experimental unit (genetic cross); in the second phase, growth and nutrient utilization were investigated. Results revealed that the highest percentage of fertilization, hatching rate and percentage of survival was in the hybrid (H. bidorsalis♀ × C. gariepinus♂) followed by the purebred H. bidorsalis (H. bidorsalis♀ × H. bidorsalis♂). These three factors were significantly different (P < 0.05) among the genetic crosses. The purebred H. bidorsalis (H. bidorsalis♀ × H. bidorsalis♂) had the highest percentage values of weight gain, specific growth rate and protein efficiency ratio and that these three parameters were significant (P < 0.05) among the four genetic crosses. Based on the results of this study, the purebred H. bidorsalis is recommended for commercial aquacultural practices.     

Temperature-induced changes of early development and yolk utilization in the African catfish Clarias gariepinus

Artificially fertilized eggs and yolk-sac larvae of a freshwater tropical/subtropical fish Clarias gariepinus receiving no external food were incubated at 22, 25 and 28° C until full yolk resorption. Developmental time, size and matter composition (CHNS-O Analyzer and ashing) were assessed at egg fertilization, hatching and yolk resorption; respiration was measured every 4–5 h. The course of acceleration of C. gariepinus embryonic developmental rate with temperature ( Q_{10 dev}) was compared over the temperature range to those of Cyprinus carpio and Oncorhynchus mykiss ; they differed greatly, but were similar when compared on the basis of effective temperatures specific to each fish. Specific growth rates for energy (88, 150 and 183% per day at 22,25 and 28° C, respectively) as well as the conversion efficiencies of egg energy (64, 71 and 68%, respectively) and protein (71, 78 and 76%, respectively) in C. gariepinus larval tissues were higher than those known for the endogenous feeding period of coldwater and temperate fish species. In C. gariepinus at the end of yolk resorption, the carbon percentage and caloric values of dry weight, size (in terms of dry matter, minerals, protein and energy per larva) and transformation efficiencies were lowest at 22° C, highest at 25° C and had slightly decreased at 28° C. A tentative mechanism which leads to the positive or negative response of body size to temperature over the viable temperature range is defined.     

Observations on the breeding habits of Clarias gariepinus (Burchell)

Clarias gariepinus (Burchell) can be stimulated to spawn in aquaria by hormonal treatment and the breeding habits could be observed. After pre-spawning activities such as the raising of dorsal fins and chasing of the female, the male folds around the head of the female and small batches of eggs are laid, followed by some gas bubbles. Eggs are distributed by the female over a wide area. This behaviour agrees with field observations. The final stimulant to spawning under natural conditions is thought to be a substance called petrichor dissolved in flood waters that have run over dry ground.